Patent Application
20130202524
The present invention relates to a zeolitic material having a BEA-type framework structure comprising Cu and/or Fe as non-framework elements and to a process for the production of the material which does not involve the use of an organotemplate. Furthermore, the present invention relates to the use of the zeolitic material having a BEA-type framework structure comprising Cu and/or Fe as non-framework elements in a catalytic process, in particular as a catalyst for selective catalytic reduction (SCR), as well as to a method for the treatment of NOx by selective catalytic reduction (SCR) in which the zeolitic material is employed.
The most prominent and best studied example for a zeolitic material with a BEA-type framework structure is zeolite beta, which is a zeolite containing SiO2 and Al2O3 in its framework. Zeolite beta is considered to be one of the most important nanoporous catalysts with its three-dimensional 12-membered-ring (12MR) pore/channel system and has been widely used in petroleum refining and fine chemical industries. Zeolite beta was first described in U.S. Pat. No. 3,308,069 and involved the use of the tetraethylammonium cation as the structure directing agent. Although numerous alterations and improvements had since then been made to the preparation procedure, including the use of other structure directing agents such as dibenzyl-1,4-diazabicyclo[2,2,2]octane in U.S. Pat. No. 4,554,145 or dibenzylmethylammonium in U.S. Pat. No. 4,642,226, the known processes for its preparation still relied on the use of organic template compounds. In U.S. Pat. No. 5,139,759, for example, it is reported that the absence of an organic template compound in the synthetic procedure of zeolite beta leads to the crystallization of ZSM-5 instead.
Recently, however, it has surprisingly been discovered that zeolite beta and related materials may be prepared in the absence of the organotemplates, which, until then, had always been used as structure directing agents. Thus, in Xiao et al., Chem. Mater. 2008, 20, pp. 4533-4535 and Supporting Information, a process for the synthesis of zeolite beta is shown, in which crystallization of an aluminosilicate gel is conducted using zeolite beta seed crystals. In WO 2010/146156 A the organotemplate-free synthesis of zeolitic materials having the BEA-type framework structure, and, in particular, to the organotemplate-free synthesis of zeolite beta is described. In Majano et al., Chem. Mater. 2009, 21, pp. 4184-4191, on the other hand, Al-rich zeolite beta materials having Si/Al ratios as low as 3.9 are discussed, which may be obtained from reactions employing seeding in the absence of organic templates. Besides the considerable advantage of not having to use costly organotemplates which required subsequent removal from the microporous framework by calcination, the new organotemplate-free synthetic methodologies further allowed for the preparation of Al-rich zeolite beta with unprecedentedly low Si/Al ratios.
In this respect, both synthetic and natural zeolites and their use in promoting certain reactions, including the selective catalytic reduction of nitrogen oxides with ammonia in the presence of oxygen, are well known in the art. More specifically, the reduction of nitrogen oxides with ammonia to form nitrogen and H2O can be catalyzed by metal-promoted zeolites to take place preferentially to the oxidation of ammonia by the oxygen or to the formation of undesirable side products such as N2O, hence the process is often referred to as the “selective” catalytic reduction (“SCR”) of nitrogen oxides. The catalysts employed in the SCR process ideally should be able to retain good catalytic activity over the wide range of temperature conditions of use, for example, 200° C. to 600° C. or higher, under hydrothermal conditions and in the presence of sulfur compounds. High temperature and hydrothermal conditions are often encountered in practice, such as during the regeneration of the catalyzed soot filter, a component necessary for the removal of soot particles in the exhaust gas treatment system.
Amongst others, iron- and copper-promoted zeolite catalysts are notably used for the selective catalytic reduction of nitrogen oxides with ammonia. Thus, as known from U.S. Pat. No. 4,961,917, for example, iron-promoted zeolite beta is an effective commercial catalyst for the selective reduction of nitrogen oxides with ammonia. However, it has been found that under harsh hydrothermal conditions, for example exhibited during the regeneration of a catalyzed soot filter with temperatures locally exceeding 700° C., the activity of many metal-promoted zeolites begins to decline. This decline is often attributed to dealumination of the zeolite and the subsequent loss of metal-containing active centers within the zeolite.
WO 2008/106519, on the other hand, discloses a catalyst comprising a zeolite having the CHA crystal structure and a molar ratio of silica to alumina greater than 15 and an atomic ratio of copper to aluminum exceeding 0.25. The catalyst is prepared via ion-exchange of copper into the NH4+-form of the CHA-type zeolite with copper sulfate or copper acetate. These materials offer improvement in low temperature performance and hydrothermal stability in comparison to iron-promoted zeolite beta. However, Chabazite remains an expensive material due to the cost of the trimethyladamantylammonium hydroxide necessary for its synthesis.
Thus, there is an on-going need to provide cost-effective hydrothermally stable catalysts for SCR applications. Lower cost catalysts are desired which exhibit similar or improved SCR performance and stability compared to the state of the art SCR catalysts. In addition, the catalysts should show high activity over a wide temperature range, wherein especially the low temperatures activity around 200° C. is of utmost importance. Hydrothermal stability at temperatures of 750° C., on the other hand, is equally desired for the reasons mentioned in the foregoing. In this respect, it must be noted that hydrothermal stability is dependent on the specific configuration of the catalyst system utilized in the exhaust treatment. Thus, although raising the amount of Fe or Cu in moles of Fe or Cu per 100 g zeolites provides a higher amount of catalytically active centres and thus a higher activity, high loadings on the other hand lead to poor aging stability resulting in a loss of surface area via deterioration of the zeolite framework during aging.
Thus, although notable progress has been made in the recent past with respect to the synthesis of new zeolitic materials having the BEA-type framework structure, there still remains a considerable need for the provision of new zeolitic materials having improved characteristics. This applies in particular in view of the numerous catalytic applications in which they are currently used, and notably in SCR.
A first aspect of the present invention is directed to a process for the production of a zeolitic material having a BEA-type framework structure comprising YO2 and X2O3. In one or more embodiments, the process comprises the steps of (1) preparing a mixture comprising one or more sources for YO2, one or more sources for X2O3, and seed crystals comprising one or more zeolitic materials having a BEA-type framework structure; (2) crystallizing the mixture obtained in step (1); and (3) subjecting the zeolitic material having a BEA-type framework structure obtained in step (2) to an ion-exchange procedure with Cu and/or Fe. Y is a tetravalent element, and X is a trivalent element. The mixture provided in step (1) and crystallized in step (2) does not contain an organotemplate as structure-directing agent, and the total amount of Cu and/or Fe in the ion-exchanged material obtained in step (3) ranges from 0.1 to 25 wt.-% calculated as Fe2O3 and CuO.
In one or more embodiments, the zeolitic material obtained in step (2) comprises one or more alkalki metals M. M can be selected from the group consisting of Li, Na, K, Cs, and combinations of two of more thereof. In one or more embodiments, Y is selected from the group consisting of Si, Sn, Ti, Zr, Ge, and mixtures of two or more thereof.
In one or more embodiments, the one or more sources for YO2 provided in step (1) comprises one or more silicates. The one or more sources for YO2 can further comprise one or more silicas in addition to the one or more silicates.
In one or more embodiments, the mixture provided in step (1) comprises water glass.
In one or more embodiments, X is selected from the group consisting of Al, B, In, Ga, and a mixture of two or more thereof. The one or more sources for X2O3 can comprise one or more aluminate salts.
In one or more embodiments, the molar ratio YO2:X2O3 of the mixture according to step (1) ranges from 1 to 200. The amount of seed crystals comprised in the mixture according to step (1) can range from 0.1 to 30 wt.-% based on 100 wt.-% of YO2 in the one or more sources for YO2.
In one or more embodiments, the mixture according to step (1) further comprises one or more solvents. The molar ratio H2O:YO2 of the mixture according to step (1) can range from 5 to 100.
In a specific embodiment, the molar ratio M:YO2 in the mixture according to step (1) ranges from 0.05 to 5. The molar ratio YO2:X2O3:M molar ratio in the mixture according to step (1) can range from (1 to 200): 1: (0.5 to 100).
In one or more embodiments, the crystallization in step (2) involves heating of the mixture at a temperature ranging from 80 to 200° C. In a further embodiment, the crystallization in step (2) is conducted under solvothermal conditions. The crystallization in step (2) can involve heating of the mixture for a period ranging from 5 to 200 h.
In one or more embodiments, after step (2) and prior to step (3), the process further comprises one or more of the following steps of: isolating the zeolitic material having a BEA-type framework structure obtained in step (2), and optionally washing the zeolitic material having a BEA-type framework structure obtained in step (2); and/or optionally drying the zeolitic material having a BEA-type framework structure obtained in step (2). The steps (i) and/or (ii) and/or (iii) can be conducted in any order, and one or more of the steps is repeated one or more times.
In one or more embodiments, the ion-exchange of the zeolitic material having a BEA-type framework structure in step (3) comprises one or more of the steps of: (3a) optionally exchanging one or more of the ionic non-framework elements contained in the zeolitic material having a BEA-type framework structure obtained in step (2) against H+ and/or NH4+; and/or (3b) optionally calcining the zeolitic material having a BEA-type framework structure obtained in step (2) or (3a); and/or (3c) exchanging one or more of the ionic non-framework elements contained in the zeolitic material having a BEA-type framework structure obtained in any of steps (2), (3a), or (3b) against Cu and/or Fe.
In one or more embodiments, the zeolitic material having a BEA-type framework structure formed in step (2) comprises zeolite beta. The seed crystals can comprise a zeolitic material having a BEA-type framework structure.
A second aspect of the invention is directed to a zeolitic material having a BEA-type framework structure obtained according to the process of the invention.
A further aspect of the invention is directed to a zeolitic material having a BEA-type framework structure, optionally obtained according to the process of the invention. The zeolitic material has an X-ray diffraction pattern comprising at least the following reflections:
100% relates to the intensity of the maximum peak in the X-ray powder diffraction pattern. The BEA-type framework structure comprises YO2 and X2O3. Y is a tetravalent element, and X is a trivalent element, and the zeolitic material comprises Cu and/or Fe as non-framework elements in a loading ranging from 0.1 to 25 wt.-% calculated as Fe2O3 and CuO.
In one or more embodiments, the YO2:X2O3 molar ratio ranges from 2 to 100 and the molar ratio of Cu:X2O3 ranges from 0.005 to 2. The molar ratio of Fe:X2O3 can range from 0.005 to 2.
In one or more embodiments, Y is selected from the group consisting of Si, Sn, Ti, Zr, Ge, and a mixture of two or more thereof, and X is selected from the group consisting of Al, B, In, Ga, and a mixture of two or more thereof.
A further aspect of the inventions is directed to a method for the treatment of NOx by selective catalytic reduction (SCR). The method comprises (a) providing a catalyst comprising the zeolitic material of the invention; and (b) contacting a gas stream comprising NOx with the catalyst provided in step (a). In one or more embodiments, the gas stream further comprises one or more reducing agents.
In one or more embodiments, the gas stream comprises one or more NOx containing waste gases. In a specific embodiment, the gas stream comprises a NOx containing waste gas stream from an internal combustion engine.
A final aspect of the invention relates to a method of using the zeolitic material of the invention in a catalytic process. The method comprises using the zeolitic material as a catalyst.
Accordingly, provided is an improved zeolitic material and in particular an improved zeolite catalyst. More specifically, the present invention provides a zeolite catalyst displaying higher activities under prolonged conditions of use, in particular with respect to applications in selective catalytic reduction (SCR), i.e. for the conversion of nitrogen oxide with a reducing agent to environmentally inoffensive compounds such as in particular nitrogen and oxygen.
Thus, it has surprisingly been found that zeolitic materials supporting copper and/or iron, wherein the zeolitic materials have a BEA-type framework structure as may be obtained from organotemplate-free synthesis display an improved performance as a catalyst compared to conventional zeolitic materials having the BEA-type framework structure obtained from organotemplate-mediated synthesis, wherein this improved performance is particularly apparent in the selective catalytic reduction reaction. Even more surprisingly, it has been observed that zeolitic materials having a BEA-type framework structure obtainable from organotemplate-free synthetic procedures may not only display a higher catalytic activity at comparable loadings relative to the known catalysts from the prior art wherein the zeolitic material is obtained from templated synthesis, it has furthermore quite unexpectedly been found that the improved catalytic activity observed for the zeolitic materials obtainable from organotemplate-free synthesis may actually be improved towards higher loadings compared to the general decrease of catalytic activity towards higher loadings observed for the prior art materials. All the more surprisingly, the considerably improved catalytic performance is not only observed at particularly low temperatures, but is furthermore sustained even after severe conditions of use as may for example be simulated by hydrothermal ageing of the materials, in particular when compared to the known catalytic materials of the prior art.
Therefore, the present invention relates to a process for the production of a zeolitic material having a BEA-type framework structure comprising YO2 and X2O3, wherein the process comprises the steps of
According to one or more embodiments, there is no particular restriction as to the number and/or types of zeolitic materials which are obtained in step (2) of the inventive process, provided that they have the BEA framework structure and comprise YO2 and X2O3. Thus, by way of example, the zeolitic material may comprise one or more zeolites having the BEA framework structure which are selected from the group consisting of zeolite beta, [B—Si—O]-BEA, [Ga—Si—O]-BEA, [Ti—Si—O]-BEA, Al-rich beta, CIT-6, tschernichite, and pure silica beta, wherein, in one or more embodiments, the zeolitic material obtained in step (2) comprises zeolite beta, wherein, in specific embodiments, the zeolitic material having a BEA-type framework structure is zeolite beta.
According to the inventive process, at no point does the mixture provided in step (1) and crystallized in step (2) contain more than an impurity of an organic structure directing agent specifically used in the synthesis of zeolitic materials having a BEA-type framework structure, in particular specific tetraalkylammonium salts and/or related organotemplates such as tetraethylammonium and/or dibenzylmethylammonium salts, and dibenzyl-1,4-diazabicyclo[2,2,2]octane. Such an impurity can, for example, be caused by organic structure directing agents still present in seed crystals used in the inventive process. Organotemplates contained in seed crystal material may not, however, participate in the crystallization process since they are trapped within the seed crystal framework and therefore may not act as structure directing agents within the meaning of the present invention.
Furthermore, YO2 and X2O3 are comprised in the BEA-type framework structure as structure building elements, as opposed to non-framework elements which can be present in the pores and cavities formed by the framework structure and typical for zeolitic materials in general.
According to one or more embodiments, a zeolitic material having a BEA-type framework structure is obtained in step (2). The material comprises YO2, wherein Y stands for any conceivable tetravalent element, Y standing for either one or several tetravalent elements. In one or more embodiments, the tetravalent elements include Si, Sn, Ti, Zr, and Ge, and combinations thereof. In a specific embodiment, Y stands for Si, Ti, or Zr, or any combination of the trivalent elements, even more preferably for Si and/or Sn. According to a specific embodiment, Y stands for Si.
Furthermore, according to the process of the present invention YO2 can be provided in step (1) in any conceivable form, provided that a zeolitic material having a BEA-type framework structure comprising YO2 can be crystallized in step (2). In one or more embodiments, YO2 is provided as such and/or as a compound which comprises YO2 as a chemical moiety and/or as a compound which (partly or entirely) is chemically transformed to YO2 during the inventive process. In one or more embodiments, wherein Y stands for Si or for a combination of Si with one or more further tetravalent elements, the source for SiO2 provided in step (1) can be any conceivable source. There can, therefore, be used, for example, all types of silica and silicates, preferably fumed silica, silica hydrosols, reactive amorphous solid silicas, silica gel, silicic acid, water glass, sodium metasilicate hydrate, sesquisilicate or disilicate, colloidal silica, pyrogenic silica, silicic acid esters, tetraalkoxysilanes, or mixtures of two or more of these compounds.
In one or more embodiments, wherein the mixture according to step (1) comprises one or more sources for SiO2, the source comprises one or more compounds selected from the group consisting of silica and silicates, preferably silicates, more preferably alkali metal silicates. Among the alkali metal silicates, the alkali metal is selected from the group consisting of Li, Na, K, Rb, and Cs, wherein more preferably the alkali metal is Na and/or K, and wherein even more preferably the alkali metal is Na. According one or more embodiments, the one or more sources for SiO2 comprised in the mixture provided in step (1) comprises water glass, preferably sodium and/or potassium water glass, and even more preferably sodium water glass. According to the embodiments, the one or more sources for SiO2 comprises sodium and/or potassium silicate, and even more preferably sodium silicate, wherein In specific embodiments of the present invention, the source for SiO2 is sodium silicate.
According to an embodiment, the one or more sources for YO2 comprise one or more further sources for YO2 in addition to one or more silicates, and, in particular, one or more further sources for SiO2 in addition thereto. In this respect, there is no particular restriction as to the one or more additional sources for YO2, and preferably for SiO2, which may be used in addition to one or more silicates, provided that an organotemplate-free zeolitic material having a BEA-type framework structure may be crystallized in step (2). Thus, by way of example, the additional one or more sources for SiO2 may include any one of silica, preferably fumed silica, silica hydrosols, reactive amorphous solid silicas, silica gel, silicic acid, colloidal silica, pyrogenic silica, silicic acid esters, tetraalkoxysilanes, or mixtures of two or more of these compounds. According to one or more embodiment, the one or more additional sources for SiO2 comprises one or more silicas. By way of example, the one or more silicas additionally used may include fumed silica, silica hydrosols, reactive amorphous solid silicas, silica gel, colloidal silica, pyrogenic silica, or mixtures of two or more of these compounds. In specific embodiments, the one or more silicas additionally used include one or more silica hydrosols and/or one or more colloidal silicas, and even more preferably one or more colloidal silicas.
Thus, in one or more embodiments, the one or more sources for YO2 provided in step (1) comprises one or more silicates, preferably one or more alkali metal silicates, wherein the alkali metal is preferably selected from the group consisting of Li, Na, K, Rb, and Cs, wherein more preferably the alkali metal is Na and/or K, and wherein even more preferably the alkali metal is Na. Furthermore, according to the embodiments, the one or more sources for YO2 further comprises one or more silicas in addition to the one or more silicates, preferably one or more silica hydrosols and/or one or more colloidal silicas, and even more preferably one or more colloidal silicas in addition to the one or more silicates. Alternatively or in addition thereto, the one or more silicates provided in step (1) comprise water glass, preferably sodium and/or potassium silicate, and even more preferably sodium silicate.
Furthermore, as regards the zeolitic material having a BEA-type framework structure obtained in step (2) comprising X2O3, X may stand for any conceivable trivalent element, X standing for either one or several trivalent elements. In one or more embodiments, the trivalent elements include Al, B, In, and Ga, and combinations thereof. In specific embodiments, Y stands for Al, B, or In, or any combination of the trivalent elements, even more preferably for Al and/or B. According to a very specific embodiment, X stands for Al.
If, for example, boron is incorporated, for example free boric acid and/or borates and/or boric esters, such as, for example, triethyl borate or trimethyl borate, can be used as starting materials.
Concerning the one or more sources for X2O3 which are provided in step (1), there is no particular restriction as to the X2O3 can be provided in any conceivable form, provided that a zeolitic material having a BEA-type framework structure comprising X2O3 can be crystallized in step (2). In one or more embodiments, X2O3 is provided as such and/or as a compound which comprises X2O3 as a chemical moiety and/or as a compound which (partly or entirely) is chemically transformed to X2O3 during the inventive process.
In one or more embodiment, wherein X stands for Al or for a combination of Al with one or more further trivalent elements, the source for Al2O3 provided in step (1) can be any conceivable source. There can be used, for example, any type of alumina and aluminates, aluminum salts such as, for example, alkali metal aluminates, aluminum alcoholates, such as, for example, aluminum triisopropylate, or hydrated alumina such as, for example, alumina trihydrate, or mixtures thereof. In one or more embodiment, the source for Al2O3 comprises at least one compound selected from the group consisting of alumina and aluminates, preferably aluminates, more preferably alkali metal aluminates. Among the alkali metal aluminates, the at least one source comprises sodium and/or potassium aluminate, more preferably sodium aluminate. In specific embodiments of the present invention, the source for Al2O3 is sodium aluminate.
There is no particular restriction as to the amounts of the one or more sources for YO2 and X2O3 respectively provided in step (1), provided that an organotemplate-free zeolitic material having a BEA-type framework structure comprising both YO2 and X2O3 may be crystallized in step (2). Thus, by way of example, the YO2:X2O3 molar ratio of the mixture according to step (1) may range anywhere from 1 to 200, wherein, in one or more embodiment, the YO2:X2O3 molar ratio of the mixture ranges from 5 to 100, more preferably from 10 to 50, more preferably from 15 to 40, more preferably from 20 to 30, and even more preferably from 23 to 25. According to specific embodiments, the YO2:X2O3 molar ratio of the mixture provided in step (1) is comprised in the range of from 23.5 to 24.
In one or more embodiments, the zeolitic material obtained in step (2) of the inventive process comprises one or more alkali metals M, wherein M is preferably selected from the group consisting of Li, Na, K, Cs, and combinations of two or more thereof. According to specific embodiments, the one or more alkali metals M are selected from the group consisting of Li, Na, K, and combinations of two or more thereof, wherein even more preferably the alkali metal M is Na and/or K, and even more preferably Na. In specific embodiments, the alkali metal is partly or entirely contained in the at least one source for YO2 and/or X2O3 provided in step (1), wherein In one or more embodiments, the alkali metal is entirely contained therein.
In general, the alkali metal M can be contained in the mixture according to step (1) of the inventive process in any conceivable amount, provided that a zeolitic material having a BEA-type framework structure is crystallized in step (2). Thus, by way of example, the M:YO2 molar ratio in the mixture provided in step (1) may range anywhere from 0.05 to 5, wherein preferably the mixture provided in step (1) and crystallized in step (2) displays a M:YO2 molar ratio comprised in the range of from 0.1 to 2, more preferably or from 0.3 to 1, more preferably of from 0.4 to 0.8, more preferably of from 0.45 to 0.7, and even more preferably from 0.5 to 0.65. According to specific embodiments, the M:YO2 molar ratio in the mixture according to step (1) ranges from 0.55 to 0.6
Thus, in general, any conceivable amounts of one or more sources for YO2, of the one or more sources for X2O3, and of the one or more alkali metals M optionally comprised in the mixture provided in step (1) can be used in the inventive process, again provided that an organotemplate-free zeolitic material having a BEA-type framework structure may be crystallized in step (2). Thus, by way of example, the YO2:X2O3:M molar ratios in the mixture according to step (1) may range anywhere from (1 to 200): 1: (0.5 to 100). In one or more embodiment, the YO2:X2O3:M molar ratios displayed by the mixture provided in step (1) and crystallized in step (2) are comprised in the range of from (5 to 100): 1: (5 to 75), more preferably of from (10 to 50): 1: (8 to 50), more preferably of from (15 to 40): 1: (10 to 30), more preferably of from (20 to 30): 1: (11 to 20), and even more preferably of from (23 to 25): 1: (12 to 15). According to specific embodiments, the YO2:X2O3:M molar ratio of the mixture provided in step (1) and crystallized in step (2) is comprised in the range of from (23.5 to 24): 1: (13 to 14).
According to the process of the present invention, seed crystals are provided in step (1), wherein the seed crystals comprise a zeolitic material having a BEA-type framework structure. In general, the seed crystals can comprise any zeolitic material having a BEA-type framework structure, provided that a zeolitic material having a BEA-type framework structure is crystallized in step (2). In one or more embodiment, the zeolitic material having a BEA-type framework structure comprised in the seed crystals is a zeolitic material obtained according to the inventive process. In a specific embodiment, the zeolitic material having a BEA-type framework structure comprised in the seed crystals is the same as the zeolitic material having a BEA-type framework structure which is then crystallized in step (2). Particularly preferred are seed crystals comprising zeolite beta, more preferably zeolite beta which has been obtained according to the inventive process. In specific embodiments, the seed crystals are zeolite beta crystals, preferably zeolite beta crystals obtained according to the inventive process.
According to the inventive process, any suitable amount of seed crystals can be provided in the mixture according to step (1), provided that a zeolitic material having a BEA-type framework structure is crystallized in step (2). In general, the amount of seed crystals contained in the mixture according to step (1) ranges from 0.1 to 30 wt.-% based on 100 wt.-% of YO2 in the at least one source for YO2, wherein preferably from 0.5 to 20 wt.-% of seed crystals are provided in the mixture crystallized in step (2). In one or more embodiment, the amount of seed crystals contained in the mixture according to step (1) ranges from 1 to 10 wt.-%, more preferably from 1.5 to 5 wt.-%, and even more preferably from 2 to 4 wt.-%. According to specific embodiments, the amount of seed crystals provided in the mixture according to step (1) ranges from 2.5 to 3.5 wt.-%
In step (1) according to one or more embodiments, the mixture can be prepared by any conceivable means, wherein mixing by agitation is preferred, preferably by means of stirring.
According to one or more embodiments, the mixture according to step (1) of the inventive process further comprises one or more solvents. In this respect, any conceivable solvent may be used in any suitable amount, provided that a zeolitic material having a BEA-type framework structure comprising YO2 and X2O3 can be obtained from crystallization in step (2). Thus, by way of example, the one or more solvents may be chosen from water, organic solvents, and mixtures thereof, preferably from the group consisting of deionized water, alcohols, and mixtures thereof. In one or more embodiments, the solvent is selected from the group consisting of deionized water, methanol, ethanol, propanol, and mixtures thereof. According to specific embodiments of the present invention, only water and preferably only deionized water is contained in the mixture according to step (1) as the solvent.
As regards the amount of the one or more solvents provided in the mixture according to step (1) of the inventive process, again, no particular restriction applies provided that an organotemplate-free zeolitic material having a BEA-type framework structure comprising YO2 and X2O3 may be crystallized in step (2). Thus, by way of example, according to specific embodiments of the present invention wherein the solvent comprises water, the H2O:YO2 molar ratio of the mixture may range anywhere from 5 to 100, wherein, in one or more embodiments, the H2O:YO2 molar ratio is comprised in the range of from 10 to 50, more preferably of from 13 to 30, and even more preferably of from 15 to 20. According to specific embodiments, the H2O:YO2 molar ratio of the mixture provided in step (1) and crystallized in step (2) of the inventive process is comprised in the range of from 17 to 18.
In general, step (2) can be conducted in any conceivable manner, provided that a zeolitic material having a BEA-type framework structure is crystallized from the mixture according to step (1). The mixture can be crystallized in any type of vessel, wherein a means of agitation is employed, preferably by rotation of the vessel and/or stirring, and more preferably by stirring the mixture.
According to one or more embodiments, the mixture is heated during at least a portion of the crystallization process in step (2). In general, the mixture can be heated to any conceivable temperature of crystallization, provided that a zeolitic material having a BEA-type framework structure is crystallized from the mixture. In one or more embodiments, the mixture is heated to a temperature of crystallization ranging from 80 to 200° C., more preferably from 90 to 180° C., more preferably from 100 to 160° C., more preferably from 110 to 140° C., and even more preferably from 115 to 130° C.
The heating in step (2) can be conducted in any conceivable manner suitable for the crystallization of a zeolitic material having a BEA-type framework structure. In general, heating may be conducted at one temperature of crystallization or vary between different temperatures. In one or more embodiments, a heat ramp is used for reaching the temperature of crystallization, wherein the heating rate ranges from 10 to 100° C./h, more preferably from 20 to 70° C./h, more preferably from 25 to 60° C./h, more preferably from 30 to 50° C./h, and even more preferably from 35 to 45° C./h.
In one or more embodiments of the present invention, the mixture according to step (1) is subjected in step (2) to a pressure which is elevated with regard to normal pressure. The term “normal pressure” as used herein relates to a pressure of 101,325 Pa in the ideal case. However, this pressure may vary within boundaries known to the person skilled in the art. By way of example, this pressure can be in the range of from 95,000 to 106,000 or of from 96,000 to 105,000 or of from 97,000 to 104,000 or of from 98,000 to 103,000 or of from 99,000 to 102,000 Pa.
In one or more embodiments, wherein a solvent is present in the mixture according to step (1), heating in step (2) is conducted under solvothermal conditions, meaning that the mixture is crystallized under autogenous pressure of the solvent which is used, for example, by conducting heating in an autoclave or other crystallization vessel suited for generating solvothermal conditions. In specific embodiments, wherein the solvent comprises or consists of water, preferably of deionized water, heating in step (2) is accordingly conducted under hydrothermal conditions.
The apparatus which can be used in the present invention for crystallization is not particularly restricted, provided that the desired parameters for the crystallization process can be realized, in particular with respect to the requiring particular crystallization conditions. In one or more embodiments conducted under solvothermal conditions, any type of autoclave or digestion vessel can be used.
In general, the duration of the crystallization process in step (2) of the inventive process is not particularly limited. In one or more embodiments involving heating of the mixture according to step (1), the crystallization process is conducted for a period ranging from 5 to 200 h, more preferably from 20 to 160 h, more preferably from 60 to 140 h, and even more preferably from 100 to 130 h.
According to one or more embodiments, wherein the mixture is heated in step (2), the heating may be conducted during the entire crystallization process or during only one or more portions thereof, provided that a zeolitic material having the BEA-type framework structure is crystallized. In one or more embodiments, heating is conducted during the entire duration of crystallization.
In general, the process of the present invention can optionally comprise further steps for the work-up and/or further physical and/or chemical transformation of the zeolitic material having a BEA-type framework structure crystallized in step (2) from the mixture provided in step (1). The crystallized material can, for example, be subject to any number and sequence of isolation and/or washing and/or drying procedures, wherein the zeolitic material obtained from crystallization in step (2) is subject to one or more isolation procedures, more preferably to one or more isolation and one or more washing procedures, and even more preferably to one or more isolation, one or more washing, and one or more drying procedures.
As regards preferred embodiments of the present invention wherein the organotemplate-free zeolitic material crystallized in step (2) is subject to one or more isolation procedures, the isolation of the crystallized product can be achieved by any conceivable means. In one or more embodiments, isolation of the crystallized product is achieved by means of filtration, ultrafiltration, diafiltration, centrifugation and/or decantation methods, wherein filtration methods can involve suction and/or pressure filtration steps.
With respect to the one or more optional washing procedures, any conceivable solvent can be used. Washing agents which may be used are, for example, water, alcohols, such as methanol, ethanol or propanol, or mixtures of two or more thereof. Examples of mixtures are mixtures of two or more alcohols, such as methanol and ethanol or methanol and propanol or ethanol and propanol or methanol and ethanol and propanol, or mixtures of water and at least one alcohol, such as water and methanol or water and ethanol or water and propanol or water and methanol and ethanol or water and methanol and propanol or water and ethanol and propanol or water and methanol and ethanol and propanol. Water or a mixture of water and at least one alcohol, preferably water and ethanol, is used in one or more embodiments, deionized water being very particularly preferred as the only washing agent.
In one or more embodiments, the separated zeolitic material is washed until the pH of the washing agent, preferably the washwater, is in the range of from 6 to 8, preferably from 6.5 to 7.5, as determined via a standard glass electrode.
Furthermore, as regards the one or more optional drying steps, in principle, any conceivable means of drying can be used. The drying procedures however, in one or more embodiments, include heating and/or applying vacuum to the zeolitic material having a BEA-type framework structure. In one or more embodiments, the one or more drying steps may involve spray drying, and preferably spray granulation of the zeolitic material crystallized in step (2) of the inventive process.
In embodiments which comprise at least one drying step, the drying temperatures are in the range of from 25° C. to 150° C., preferably of from 60 to 140° C., more preferably of from 70 to 130° C. and even more preferably in the range of from 75 to 125° C. The durations of drying are in the range of from 2 to 60 h, preferably in the range of 6 to 48 hours, and more preferably of from 12 to 24 h.
In general, the optional washing and/or drying procedures comprised in the inventive process can be conducted in any conceivable order and repeated as often as desired.
Thus, according to the inventive process it is preferred that after step (2) and prior to step (3) the process further comprises one or more of the following steps of:
In one or more embodiments, the inventive process comprises at least one step (i) of isolating the zeolitic material crystallized according to step (2), more preferably by filtration thereof. According to one or more embodiments, after the at least one step (i) of isolation, the zeolitic material is subject to at least one step (iii) of drying, wherein the zeolitic material is subject to at least one step (ii) of washing prior to the at least one drying step. In a specific embodiment, the zeolitic material crystallized according to step (2) is subject to at least one step (i) of isolating, followed by at least one step (ii) of washing, followed by at least one step (iii) of drying.
According to a further embodiment of the inventive process, the zeolitic material crystallized in step (2) is directly subject to one or more steps of drying, preferably to one or more steps of spray drying or of spray granulation, wherein the one or more steps of spray drying or spray granulation are performed without isolating or washing the zeolitic material beforehand. Directly subjecting the mixture obtained from step (2) of the inventive process to a spray drying or spray granulation stage has the advantage that isolation and drying is performed in a single stage. Consequently, according to this embodiment of the present invention, a process is provided wherein not only removal of organotemplate compounds is avoided, but also the number of post-synthesis workup steps is minimized, as a result of which the organotemplate-free zeolitic material having a BEA-type framework structure can be obtained from a highly simplified process.
According one or more embodiments, the zeolitic material crystallized in step (2) is subject to one or more ion-exchange procedures, wherein the term “ion-exchange” herein generally refers to non-framework ionic elements and/or molecules contained in the zeolitic material. More specifically, according to one or more embodiments, the zeolitic material crystallized in step (2) is ion-exchanged with either copper or iron, or both copper and iron, wherein the zeolitic material crystallized in step (2) is ion-exchanged with either copper or iron.
As regards the ion-exchange procedure performed in step (3) of the inventive process, there is no particular restriction either regarding the specific impregnation method which is applied, nor with respect to whether the step is repeated and, if yes, the number of times the step is repeated. Thus, by way of example, ion-exchange may be conducted with the aid of a solvent or solvent mixture in which the ion to be exchanged is suitably dissolved. With respect to the type of solvent which may be used, there is again no particular restriction in this respect, provided that the ions to be exchanged, i.e. copper and/or iron and preferably copper or iron, may be solvated therein. Thus, by way of example, the solvent or mixture of solvents which may be used include water and alcohols, and in particular short chain alcohols selected among C1-C4, and preferably C1-C3 alcohols, in particular methanol, ethanol or propanol, including mixtures of two or more thereof. Examples of mixtures are mixtures of two or more alcohols, such as methanol and ethanol or methanol and propanol or ethanol and propanol or methanol and ethanol and propanol, or mixtures of water and at least one alcohol such as water and methanol or water and ethanol or water and propanol or water and methanol and ethanol or water and methanol and propanol or water and ethanol and propanol or water and methanol and ethanol and propanol. According to one or more embodiments, however, water or a mixture of water and one or more alcohols is preferred, wherein a mixture of water and ethanol is further preferred, deionized water being particularly preferred as the solvent for the one or more ion-exchange procedures conducted in step (3).
As regards the amount of the one or more solvents used in the ion-exchange procedure according to step (3), there is again no particular restriction according to the inventive process, provided that copper and/or iron may be effectively exchanged as non-framework elements in the zeolitic material obtained in step (2). Thus, by way of example, an excess of solvent or solvent mixture may be used in the ion-exchange procedure according to step (3) wherein solvated copper and/or iron may enter the porous system of the zeolitic material obtained in step (2) and, in counterpart, ions contained in the zeolitic material against which iron and/or copper is exchanged are suitably solvated in the solvent or solvent mixture and accordingly allowed to exit the porous system of the zeolitic material. Alternatively, however, ion-exchange may be achieved with a volume of solvent or a solvent mixture which slightly exceeds or approximately corresponds to or is slightly inferior to the porous volume of the zeolitic material such that copper and/or iron solvatized in the solvent or solvent mixture enters the porous system of the zeolitic material by capillary action according to an insipient wetness impregnation technique. In particular, according to specific embodiments which employ the ion-exchange technique, the ion-exchange process directly takes place within the porous system of the zeolitic material obtained in step (2) without any ions necessarily leaving the zeolitic material via excess solvent. According to one or more embodiments, however, the ion-exchange procedure in step (3) is conducted with an excess of solvent or solvent mixture, wherein, by way of example, a liquid to solid weight ratio ranging anywhere from 0.1 to 20 may be used. According to the embodiments of the present invention, however, it is preferred that the liquid to solid weight ratio being the weight ratio of the solvent or solvent mixture to the zeolitic material obtained in step (2), is comprised in the range of from 1 to 15, more preferably of from 2 to 12, more preferably of from 3 to 10, more preferably of from 4 to 9, and even more preferably of from 5 to 8. According to specific embodiments of the present invention, the liquid to solid weight ratio employed in the ion-exchange procedure of step (3) is comprised in the range of from 6 to 7.
According to one or more embodiments, the total amount of copper and/or iron which is ion-exchanged into the material obtained in step (3) is comprised in the range of from 0.1 to 25 wt.-% calculated as Fe2O3 and CuO, respectively. Consequently, the type of ion-exchange procedure employed in step (3) is suitably chosen, in particular also with respect to the type and/or amount of solvent or solvent mixture preferably used therein, and repeated one or more times if necessary for achieving a loading of copper and/or iron in the ion-exchanged material which is comprised by the aforementioned inventive range. According to one or more embodiments it is however preferred that the total amount of copper and/or iron in the ion-exchanged material obtained in step (3) is comprised in the range of from 0.5 to 20 wt.-%, more preferably of from 1 to 15 wt.-%, more preferably of from 2 to 10 wt.-%, more preferably of from 2.5 to 8 wt.-%, more preferably of from 3 to 7 wt.-%, more preferably of from 3.5 to 6.5 wt.-%, and even more preferably of from 4 to 6 wt.-%. According to specific embodiments of the invention, the total amount of copper and/or iron is comprised in the range of from 4.5 to 5.5 wt.-%.
According to one or more embodiments, the zeolitic material crystallized in step (2) is ion-exchanged in step (3) either with iron or with copper. According to the embodiments wherein the zeolitic material is ion-exchanged in step (3) with iron alone, there is no particular restriction as to the amount of iron in the ion-exchange material obtained in step (3) provided that the total amount thereof is comprised in the range of from 0.1 to 25 wt.-% calculated as Fe2O3. According to specific embodiments, however, the total amount of iron is comprised in the range of from 0.5 to 20 wt.-%, more preferably of from 1 to 15 wt.-%, more preferably of from 2 to 10 wt.-%, more preferably of from 3 to 7 wt.-%, and even more preferably of from 3.2 to 5.5. According to specific embodiments thereof, the total amount of iron which is ion-exchanged in step (3) is comprised in the range of from 3.3 to 5.4 wt.-% calculated as Fe2O3.
According to one or more embodiments wherein the zeolitic material obtained from step (2) of the inventive process is ion-exchanged with copper alone in step (3), there is, again, no particular restriction as to the total amount of copper contained in the ion-exchange material provided that the total amount of copper is comprised in the range of from 0.1 to 25 wt.-% calculated as CuO. According to specific embodiments, however, the total amount of copper in the ion-exchange material obtained in step (3) is comprised in the range of from 0.5 to 20 wt.-%, more preferably of from 1 to 15 wt.-%, more preferably of from 2 to 10 wt.-%, more preferably of from 3 to 8 wt.-%, more preferably of from 4 to 6.5 wt.-%.
According to specific embodiments thereof, the total amount of copper in the ion-exchange material obtained in step (3) is comprised in the range of from 4.5 to 6 wt.-% calculated as CuO.
As discussed in the foregoing, the surprising technical effects of the present invention are particularly pronounced at high loadings of copper and/or iron in the zeolitic material obtained from step (3) of the inventive process. Consequently, in specific embodiments, the total amount of copper and/or iron in the ion-exchange material obtained in step (3) is comprised in the range of from 3 to 25 wt.-% calculated as Fe2O3 and CuO, respectively. In one or more embodiments, the total amount of copper and/or iron is comprised in the range of from 3.5 to 20 wt.-%, preferably of from 4 to 15 wt.-%, more preferably of from 4.4 to 10 wt.-%, more preferably of from 4.6 to 9 wt.-%, more preferably of from 4.8 to 7 wt.-%, and even more preferably of from 5 to 6.5 wt.-%. According to yet further embodiments thereof, the total amount of copper and/or iron in the ion-exchange material obtained in step (3) ranges from 5.2 to 6 wt.-% calculated as Fe2O3 and CuO, respectively.
Among the aforementioned specific embodiments displaying particularly high loadings of copper and/or iron it is again preferred that the ion-exchange zeolitic material obtained in step (3) has been ion-exchanged with either copper or iron. According to those specific embodiments which have been ion-exchanged with copper alone, it is preferred that the total amount of copper in the ion-exchanged material calculated as CuO is comprised in the range of from 3.5 to 25 wt.-%, more preferably of from 4 to 20 wt.-%, more preferably of from 4.5 to 15 wt.-%, more preferably of from 5 to 12 wt.-%, more preferably of from 5.2 to 9 wt.-%, more preferably of from 5.4 to 7 wt.-%, more preferably of from 5.6 to 6.5 wt.-%. According to yet further embodiments thereof, the total amount of copper in the ion-exchanged material obtained in step (3) is comprised in the range of from 5.8 to 6 wt.-% based on CuO. On the other hand, according to alternative embodiments, and wherein the zeolitic material has been ion-exchanged with iron alone in step (3) of the inventive process, the total amount of iron contained therein calculated as Fe2O3 is comprised in the range of from 3 to 25 wt.-%, preferably of from 3.5 to 20 wt.-%, more preferably of from 4 to 15 wt.-%, more preferably of from 4.4 to 10 wt.-%, more preferably of from 4.6 to 8 wt.-%, more preferably of from 4.8 to 6 wt.-%, more preferably of from 5 to 5.7 wt.-%. According to specific embodiments, the total amount of iron in the ion-exchanged material obtained in step (3) calculated as Fe2O3 is comprised in the range of from 5.2 to 5.4 wt.-%.
As regards the one or more copper and iron compounds which may be used in the inventive process for ion-exchange in step (3), no particular restriction applies provided that the zeolitic material obtained in step (2) may be ion-exchanged therewith to afford an ion-exchanged zeolitic material wherein the total amount of copper and/or iron therein is comprised in the range of from 0.1 to 25 wt.-% calculated as Fe2O3 and CuO, respectively. Thus, as concerns the one or more iron compounds which may be employed in step (3) of the inventive process, any suitable iron compound or mixture of iron compounds may be used, wherein Fe2+ and/or Fe3+-ion containing compounds are preferably used, Fe2+-containing compounds being most preferably used. Furthermore, as concerns the one or more copper compounds which may be employed in step (3) of the inventive process, any suitable copper compound or mixture of copper compounds may be used, wherein Cu2+ and/or Cu+-ion containing compounds are preferably used, Cu2+-containing compounds being most preferably used. According to one or more embodiments wherein a solvent or solvent mixture is employed in the ion-exchange step (3), the solubility of the one or more copper and/or iron compounds in the solvent or solvent mixture which is used is preferably such, that the concentration of copper and/or iron in the solvent or solvent mixture is suitable for obtaining a zeolitic material having a loading with copper and/or iron according to particular and/or preferred embodiments of the present invention, wherein it is preferred that the loading of the zeolitic material having a BEA-type framework structure as obtained from step (2) is achieved after five or less ion-exchange procedures when using such a solution, preferably after four or less, more preferably after three or less, more preferably after two or three, and even more preferably after only one ion-exchange procedure using such a solution.
Thus, by way of example, any suitable iron(II) and/or iron(III) compound, preferably any iron(II) compound, may be employed such as one or more iron(II) and/or iron(III) salts, and more preferably one or more iron(II) salts, selected from the group consisting of iron halides, preferably iron chloride and/or iron bromide, more preferably iron chloride, iron perchlorate, iron sulfite, iron sulfate, iron hydrogensulfate, iron nitrite, iron nitrate, iron dihydrogenphosphate, iron hydrogenphosphate, iron carbonate, iron hydrogencarbonate, iron acetate, iron citrate, iron malonate, iron oxalate, iron tartrate, and mixtures of two or more thereof. In one or more embodiments, the one or more iron compounds used for ion-exchange in step (3) is selected from the group consisting of iron chloride and/or iron bromide, preferably iron chloride, iron perchlorate, iron sulfate, iron nitrate, iron acetate, and mixtures of two or more thereof, wherein the one or more iron compound is an iron(II) compound. According to specific embodiments of the present invention, iron used for ion-exchange in step (3) comprises iron sulfate, preferably iron(II) sulfate, wherein even more preferably iron(II) sulfate is used as the iron compound in step (3).
As regards the copper compound which may be used for ion-exchange in step (3) again any suitable copper(I) and/or copper(II) compound may be used, wherein preferably a copper(II) compound is used which is preferably a copper(II) salt. Thus, by way of example, one or more copper(II) salts may be used which are selected from the group consisting of copper(II) halides, preferably copper(II) chloride and/or copper(II) bromide, more preferably copper(II) chloride, copper(II) perchlorate, copper(II) sulfite, copper(II) hydrogensulfate, copper(II) sulfate, copper(II) nitrite, copper(II) nitrate, copper(II) dihydrogenphosphate, copper(II) hydrogenphosphate, copper(II) phosphate, copper(II) hydrogencarbonate, copper(II) carbonate, copper(II) acetate, copper(II) citrate, copper(II) malonate, copper(II) oxalate, copper(II) tartrate, and mixtures of two or more thereof, wherein more preferably the copper(II) salt is selected from the group consisting of copper(II) chloride and/or copper(II) bromide, preferably copper(II) chloride, copper(II) sulfate, copper(II) nitrate, copper(II) acetate, and mixtures of two or more thereof. According to specific embodiments of the present invention, copper used for ion-exchange in step (3) of the inventive process comprises copper(II) acetate, wherein more preferably the copper compound used for ion-exchange is copper(II) acetate.
As outlined in the forgoing, the ion-exchange step (3) may comprise one or more ion-exchange procedures. According to one or more embodiments, the zeolitic material obtained in step (2) of the inventive process is first ion-exchanged with H+ and/or ammonium, preferably with H+, prior to one or more ion-exchange procedures with copper and/or iron. According to one or more embodiments, the zeolitic material obtained in step (2) of the inventive process may also be subject to a step of calcination prior to ion-exchange with copper and/or iron in step (3). According to the optional embodiments, wherein the zeolitic material obtained in step (2) is calcined, the calcination may be conducted at any suitable temperature for any conceivable duration provided that the resulting material may be ion-exchanged with copper and/or iron for obtaining an ion-exchanged material wherein the loading with copper and/or iron is comprised in the range of from 0.1 to 25 wt.-% calculated as Fe2O3 and CuO, respectively. Thus, by way of example, the calcination temperature may range anywhere from 250 to 700° C., wherein the calcination temperature is preferably comprised in the range of from 300 to 600° C., more preferably of from 350 to 550° C., and even more preferably of from 400 to 500° C. According to specific embodiments of the present invention including a calcination step prior to ion-exchange, the zeolitic material obtained in step (2) is calcined at a temperature comprised in the range of from 430 to 470° C. prior to ion-exchange with copper and/or iron. Furthermore, as regards the duration of the calcination procedure optionally used prior to ion-exchange in step (3), the calcination may be conducted for a period ranging anywhere from 0.5 to 24 h, wherein the duration of the calcination ranges from 1 to 18 h, preferably from 2 to 12 h, more preferably from 3 to 10 h, and even more preferably from 3.5 to 8 h. According to specific embodiments, the calcination procedure performed to ion-exchange with copper and/or iron is performed for a duration of from 4 to 6 hours.
Thus, according to specific embodiments, the zeolitic material obtained in step (2) of the inventive process may be optionally ion-exchanged with H+ and/or NH4+, preferably with H+, and/or preferably and optionally calcined prior to ion-exchange with copper and/or iron in step (3). According to one or more embodiments of the present invention, the zeolitic material obtained in step (2) is first ion-exchanged with H+ prior to ion-exchange with copper and/or iron in step (3). In this respect, any conceivable ion-exchange procedure such as for example the treatment of the zeolitic material with an acid such as with an acidic medium and in particular with an acidic solution may be employed for achieving the exchange of ionic non-framework elements contained in the zeolitic material obtained in step (2) against H. According to one or more embodiments the ion-exchange of non-framework elements against H+ is achieved by first ion-exchanging one or more of the ionic non-framework elements contained in the zeolitic material against ammonium such as by means of contacting the zeolitic material with ammonium-containing solution, after which the zeolitic material which has been ion-exchanged with ammonium is calcined. According to the embodiments, the ammonium exchange procedure followed by the calcination procedure is repeated one or more times, and preferably repeated twice, thus affording the H-form of the zeolitic material obtained in step (2) of the inventive process.
Therefore, embodiments of the present invention are directed to wherein the ion-exchange of the zeolitic material having a BEA-type framework structure in step (3) comprises one or more of the steps of:
Thus, as mentioned above, it has surprisingly been found that a zeolitic material may be provided according to the inventive process displaying unexpected and improved properties, in particular with respect to the catalytic activity thereof. More specifically, it has surprisingly been found that according to the inventive process a zeolitic material having a BEA-type framework structure which is ion-exchanged with copper and/or iron may be provided which displays an unexpectedly high activity in selective catalytic reduction applications, in particular at high loadings of Cu and/or Fe.
Therefore, aspects of the present invention also relate to a zeolitic material having a BEA-type framework structure which is obtainable and/or obtained according to specific embodiments of the inventive process as defined in the present application. As used herein, the term “obtainable” refers to any zeolitic material having a BEA-type framework structure which is either obtained by the process according to one or more embodiments or by any conceivable process which leads to a zeolitic material having a BEA-type framework structure as is obtainable according to the inventive process.
The present invention, however, also relates to a zeolitic material per se, the zeolitic material having a BEA-type framework structure having an X-ray diffraction pattern comprising at least the following reflections:
wherein 100% relates to the intensity of the maximum peak in the X-ray powder diffraction pattern,
wherein the BEA-type framework structure comprises YO2 and X2O3,
wherein Y is a tetravalent element, and X is a trivalent element, and
wherein the zeolitic material comprises Cu and/or Fe as non-framework elements in a loading ranging from 0.1 to 25 wt.-% calculated as Fe2O3 and CuO, preferably from 0.5 to 20 wt.-%, more preferably from 1 to 15 wt.-%, more preferably from 2 to 10 wt.-%, more preferably from 2.5 to 8 wt.-%, more preferably from 3 to 7 wt.-%, more preferably from 3.5 to 6.5 wt.-%, more preferably from 4 to 6 wt.-%, and even more preferably from 4.5 to 5.5 wt.-%.
In one or more embodiments, the zeolitic material having a BEA-type framework structure has an X-ray diffraction pattern comprising at least the following reflections:
wherein 100% relates to the intensity of the maximum peak in the X-ray diffraction.
In one or more embodiments, the inventive zeolitic material having a BEA-type framework structure displaying a powder diffraction pattern is a zeolitic material which is either obtained by the process according to one or more embodiments or by any conceivable process which leads to a zeolitic material having a BEA-type framework structure as may be obtained, i.e. as is obtainable according to the inventive process.
According to one or more embodiments, in the zeolitic material having a BEA-type framework structure, Y stands for any conceivable tetravalent element, Y standing for either one or several tetravalent elements. In one or more embodiments, the tetravalent elements include Si, Sn, Ti, Zr, and Ge, and combinations thereof. In one or more embodiments, Y stands for Si, Ti, or Zr, or any combination of the trivalent elements, even more preferably for Si and/or Sn. According to one or more embodiments, it is particularly preferred that Y stands for Si.
Furthermore, as regards X2O3 further comprised in the framework of the zeolitic material having a BEA structure further, X may stand for any conceivable trivalent element, X standing for either one or several trivalent elements. In one or more embodiments, the trivalent elements include Al, B, In, and Ga, and combinations thereof. In one or more embodiments, Y stands for Al, B, or In, or any combination of the trivalent elements, even more preferably for Al and/or B. According to one or more embodiments, X stands for Al.
According to one or more embodiments, there is no particular restriction as to the YO2:X2O3 molar ratio displayed by the inventive zeolitic material having a BEA-type framework structure. Thus, in principle, the inventive zeolitic material may have any conceivable YO2:X2O3 molar ratio. Accordingly, by way of example, the zeolitic material having a BEA-type framework structure may have an YO2:X2O3 molar ratio comprised in the range of anywhere from 2 to 100, wherein, the YO2:X2O3 molar ratio is comprised in the range of from 4 to 70, more preferably from 5 to 50, more preferably from 6 to 30, more preferably from 7 to 20, more preferably from 8 to 15, and even more preferably from 9 to 13. According to specific embodiments, the inventive zeolitic material having a BEA-type framework structure has a YO2:X2O3 molar ratio comprised in the range of from 10 to 11.
Regarding copper and/or iron comprised as non-framework elements in the inventive zeolitic material having a BEA-type framework structure, the present invention includes embodiments wherein both copper and iron are contained as non-framework elements in the zeolitic material, as well embodiments wherein substantially either copper or iron alone is comprised therein as non-framework element. As used herein, the term “substantially” is employed with respect to the zeolitic material only containing either copper or iron as non-framework element indicates that the other element is not contained in any substantial amount in the zeolitic material among the non-framework elements. Thus, embodiments of the present invention substantially only comprising copper as non-framework element in the zeolitic material having a BEA-type framework structure indicates that any iron contained in the material as non-framework element is contained therein in an amount of 0.1 wt.-% or less based on 100 wt.-% of YO2 contained in the framework of the zeolitic material, wherein in one or more embodiments, the zeolitic material according to the embodiments contains 0.05 wt.-% or less of iron as non-framework element based on 100 wt.-% of YO2, more preferably 0.001 wt.-% or less, more preferably 0.0005 wt.-% or less, and even more preferably 0.0001 wt.-% or less thereof. Thus, if at all present in the zeolitic material, such amounts of iron in the specific embodiments of the inventive zeolitic material only comprising copper as non-framework element may also be denoted as “impurities” or “trace amounts” of iron within the meaning of the present invention. Same applies accordingly with respect to alternatively preferred embodiments only comprising iron as non-framework element in the zeolitic material having a BEA-type framework structure. Thus, more specifically embodiments of the present invention substantially only comprising iron as non-framework element in the zeolitic material having a BEA-type framework structure indicates that any copper contained in the material as non-framework element is contained therein in an amount of 0.1 wt.-% or less based on 100 wt.-% of YO2 contained in the framework of the zeolitic material, wherein In one or more embodiments, the zeolitic material according to the embodiments contains 0.05 wt.-% or less of copper as non-framework element based on 100 wt.-% of YO2, more preferably 0.001 wt.-% or less, more preferably 0.0005 wt.-% or less, and even more preferably 0.0001 wt.-% or less thereof. Thus, again, if at all present in the zeolitic material, such amounts of copper in the specific embodiments of the inventive zeolitic material only comprising iron as non-framework element may accordingly also be denoted as “impurities” or “trace amounts” of copper within the meaning of the present invention.
Therefore, according to one or more embodiments, only iron or copper is comprised in the zeolitic material having a BEA-type framework structure.
Regarding specific embodiments of the present invention wherein the zeolitic material having a BEA-type framework structure contains iron as a non-framework element, as well as with respect to specific embodiments wherein the zeolitic material only comprises iron as non-framework element, there is no particular restriction as to the Fe:X2O3 molar ratio of the zeolitic material, provided that the total loading of iron and copper as non-framework elements calculated as Fe2O3 and CuO is comprised in the range of from 0.1 to 25 wt.-%. Thus, by way of example, the Fe:X2O3 molar ratio of the zeolitic material may range anywhere from 0.005 to 2, wherein preferably the Fe:X2O3 molar ratio is comprised in the range of from 0.01 to 1, more preferably of from 0.05 to 0.7, more preferably of from 0.09 to 0.5, more preferably of from 0.11 to 0.4, more preferably of from 0.13 to 0.35, and even more preferably of from 0.15 to 0.3. According to specific embodiments of the present invention, the Fe:X2O3 molar ratio of the zeolitic material ranges from 0.16 to 0.26.
Alternatively, concerning specific embodiments of the present invention wherein the zeolitic material having a BEA-type framework structure contains copper as a non-framework element, as well as with respect to specific embodiments wherein the zeolitic material only comprises copper as non-framework element, there is again no particular restriction as to the Cu:X2O3 molar ratio of the zeolitic material, provided that the total loading of copper and iron as non-framework elements respectively calculated as Fe2O3 and CuO is comprised in the range of from 0.1 to 25 wt.-%. Thus, by way of example, the Cu:X2O3 molar ratio of the zeolitic material may range anywhere from 0.005 to 2, wherein preferably the Cu:X2O3 molar ratio is comprised in the range of from 0.01 to 1, more preferably of from 0.05 to 0.7, more preferably of from 0.1 to 0.5, more preferably of from 0.15 to 0.4, more preferably of from 0.18 to 0.35, and even more preferably of from 0.2 to 0.3. According to specific embodiments of the present invention, the Cu:X2O3 molar ratio of the zeolitic material ranges from 0.22 to 0.28.
Depending on the specific needs of its application, the inventive material according to specific embodiments of the present application can be employed as such, like in the form of a powder, a spray powder or a spray granulate obtained from above-described separation techniques, e.g. decantation, filtration, centrifugation, or spraying.
In many industrial applications, it is often desired on the part of the user not to employ the zeolitic material as powder or sprayed material, i.e. the zeolitic material obtained by the separation of the material from its mother liquor, optionally including washing and drying, and subsequent calcination, but a zeolitic material which is further processed to give moldings. Such moldings are required particularly in many industrial processes, e.g. in many processes wherein the zeolitic material is employed as catalyst or adsorbent.
Accordingly, the present invention also relates to a molding comprising the zeolitic material of the present invention having a BEA-type framework structure.
In general, the powder or sprayed material can be shaped without any other compounds, e.g. by suitable compacting, to obtain moldings of a desired geometry, e.g. tablets, cylinders, spheres, or the like.
In one or more embodiments, the powder or sprayed material is admixed with or coated by a suitable refractory binder. In general, suitable binders are all compounds which impart adhesion and/or cohesion between the zeolitic material particles to be bonded which goes beyond the physisorption which may be present without a binder. Examples of such binders are metal oxides, such as, for example, SiO2, Al2O3, TiO2, ZrO2 or MgO or clays, or mixtures of two or more of these compounds. Naturally occurring clays which can be employed include the montmorillonite and kaolin family, which families include the subbentonites, and the kaolins commonly known as Dixie, McNamee, Georgia and Florida clays or others in which the main mineral constituent is halloysite, kaolinite, dickite, nacrite, or anauxite. Such clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemical modification. In addition, the zeolitic material according to one or more embodiments can be composited with a porous matrix material such as silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia and silica-titania as well as ternary compositions such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia and silica-magnesia-zirconia.
Also in one or more embodiments, the powder or the sprayed material, optionally after admixing or coating by a suitable refractory binder as described above, is formed into a slurry, for example with water, which is deposited upon a suitable refractory carrier. The slurry may also comprise other compounds such as, e.g., stabilizers, defoamers, promotors, or the like. Typically, the carrier comprises a member, often referred to as a “honeycomb” carrier, comprising one or more refractory bodies having a plurality of fine, parallel gas flow passages extending therethrough. Such carriers are well known in the art and may be made of any suitable material such as cordierite or the like.
In general, the zeolitic material according to any of the specific embodiments as described in the present application can be used as molecular sieve, adsorbent, catalyst, catalyst support or binder thereof. Especially preferred is the use as catalyst. For example, the zeolitic material can be used as molecular sieve to dry gases or liquids, for selective molecular separation, e.g. for the separation of hydrocarbons or amides; as ion exchanger; as chemical carrier; as adsorbent, in particular as adsorbent for the separation of hydrocarbons or amides; or as a catalyst. In one or more embodiments, the zeolitic material according to one or more embodiments is used as a catalyst.
According to a specific embodiment, the zeolitic material according to any of the specific embodiments as described in the present application is used in a catalytic process, preferably as a catalyst and/or catalyst support, and more preferably as a catalyst. In general, the zeolitic material of the invention can be used as a catalyst and/or catalyst support in any conceivable catalytic process, wherein processes involving the conversion of at least one organic compound is preferred, more preferably of organic compounds comprising at least one carbon-carbon and/or carbon-oxygen and/or carbon-nitrogen bond, more preferably of organic compounds comprising at least one carbon-carbon and/or carbon-oxygen bond, and even more preferably of organic compounds comprising at least one carbon-carbon bond. In specific embodiments, the zeolitic material is used as a catalyst and/or catalyst support in a fluid catalytic cracking (FCC) process. According to a further embodiment of the present invention, the zeolitic material of the invention is preferably used in a catalytic process involving the conversion of at least one compound comprising at least one nitrogen-oxygen bond.
Thus, according to one or more embodiments, the zeolitic material having a BEA-type framework structure is preferably used for the oxidation of NH3, in particular for the oxidation of NH3 slip in diesel systems; for the decomposition of N2O; for soot oxidation; for emission control in Advanced Emission Systems such as Homogeneous Charge Compression Ignition (HCCI) engines; as additive in fluid catalytic cracking (FCC) processes; as catalyst in organic conversion reactions; or as catalyst in “stationary source” processes. Therefore, the present invention also relates to a method of oxidizing NH3, in particular of oxidizing NH3 slip in diesel systems, by contacting a stream containing NH3 with a catalyst containing the zeolitic material having a BEA-type framework structure according to one or more embodiments under suitable oxidizing conditions; to a method of decomposing of N2O by contacting a stream containing N2O with a catalyst containing the zeolitic material having a BEA-type framework structure according to one or more embodiments under suitable decomposition conditions; to a method of controlling emissions in Advanced Emission Systems such as Homogeneous Charge Compression Ignition (HCCI) engines by contacting an emission stream with a catalyst containing the zeolitic material having a BEA-type framework structure according to one or more embodiments under suitable conditions; to a fluid catalytic cracking FCC process wherein the zeolitic material having a BEA-type framework structure according to one or more embodiments is employed as additive; to a method of converting an organic compound by contacting the compound with a catalyst containing the zeolitic material having a BEA-type framework structure according to one or more embodiments under suitable conversion conditions; to a “stationary source” process wherein a catalyst is employed containing the zeolitic material having a BEA-type framework structure according to one or more embodiments.
According to a specific embodiment of the present invention, however, the zeolitic material according to any of the specific embodiments as described in the present application is used as a catalyst and/or catalyst support, preferably as a catalyst in a selective catalytic reduction (SCR) process for the selective reduction of nitrogen oxides NOx.
Consequently, the present invention also relates to the use of a zeolitic material according to any of the specific embodiments as described in the present application in a catalytic process, preferably as a catalyst, more preferably in selective catalytic reduction (SCR), wherein the zeolitic material is preferably used in the treatment of industrial or automotive exhaust gas, preferably in the treatment of automotive exhaust gas.
Accordingly, the present invention also relates to a method for selectively reducing nitrogen oxides NOx by contacting a gas stream containing NOx with a catalyst containing the zeolitic material having a BEA-type framework structure according to any of the specific embodiments as described in the present application, in particular under suitable reducing conditions. As used herein, the terms “nitrogen oxides” and “NOX” designate nitrogen monoxide (NO), nitrogen dioxide (NO2), and/or mixtures thereof, and preferably designate a mixture of NO and NO2.
Therefore, the one or more embodiments further relates to a method for the treatment of NOx by selective catalytic reduction (SCR) comprising:
According to the use of the inventive catalyst and/or to the inventive method for the treatment of NOx, there is no particular restriction as to the way or form in which the inventive catalyst is used or in which the inventive catalyst is provided in step (a) of the inventive method, provided that is may be used as a catalyst and, more specifically, provided that it is suited for the treatment of NOx by SCR in the inventive method. Thus, by way of example, when preparing specific catalytic compositions or compositions for different purposes, it is conceivable to blend the zeolitic material according to one or more embodiments having a BEA-type framework structure with at least one other catalytically active material or a material being active with respect to the intended purpose. It is also possible to blend at least two different inventive materials which may differ in the YO2:X2O3 ratio, preferably in the SiO2:Al2O3 ratio, and/or in the presence or absence of a further metal such as a transition metal and/or in the specific amounts of a further metal such as a transition metal, in addition to iron and/or copper contained in the inventive zeolitic material, more preferably in addition to either iron or copper contained in the inventive zeolitic material. It is also possible to blend at least two different inventive materials with at least one other catalytically active material or a material being active with respect to the intended purpose.
The catalysts of the present invention may also be provided in the form of extrudates, pellets, tablets or particles of any other suitable shape, for use as a packed bed of particulate catalyst, or as shaped pieces such as plates, saddles, tubes, or the like.
Also, the catalyst may be disposed on a substrate. The substrate may be any of those materials typically used for preparing catalysts, and will usually comprise a ceramic or metal honeycomb structure. Any suitable substrate may be employed, such as a monolithic substrate of the type having fine, parallel gas flow passages extending therethrough from an inlet or an outlet face of the substrate, such that passages are open to fluid flow therethrough (referred to as honeycomb flow through substrates). The passages, which are essentially straight paths from their fluid inlet to their fluid outlet, are defined by walls on which the catalytic material is disposed as a washcoat so that the gases flowing through the passages contact the catalytic material. The flow passages of the monolithic substrate are thin-walled channels, which can be of any suitable cross-sectional shape and size such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, etc. Such structures may contain from about 60 to about 400 or more gas inlet openings (i.e., cells) per square inch (2.54 cm×2.54 cm) of cross section.
The substrate can also be a wall-flow filter substrate, where the channels are alternately blocked, allowing a gaseous stream entering the channels from one direction (inlet direction), to flow through the channel walls and exit from the channels from the other direction (outlet direction). The catalyst composition can be coated on the flow through or wall-flow filter. If a wall flow substrate is utilized, the resulting system will be able to remove particulate matter along with gaseous pollutants. The wall-flow filter substrate can be made from materials commonly known in the art, such as cordierite, aluminum titanate or silicon carbide. It will be understood that the loading of the catalytic composition on a wall flow substrate will depend on substrate properties such as porosity and wall thickness, and typically will be lower than loading on a flow through substrate.
The ceramic substrate may be made of any suitable refractory material, e.g., cordierite, cordierite-alumina, silicon nitride, zircon mullite, spodumene, alumina-silica magnesia, zircon silicate, sillimanite, a magnesium silicate, zircon, petalite, alpha-alumina, an aluminosilicate, and the like.
The substrates useful for the catalysts of embodiments of the present invention may also be metallic in nature and be composed of one or more metals or metal alloys. The metallic substrates may be employed in various shapes such as corrugated sheet or monolithic form. Suitable metallic supports include the heat resistant metals and metal alloys such as titanium and stainless steel as well as other alloys in which iron is a substantial or major component. Such alloys may contain one or more of nickel, chromium and/or aluminum, and the total amount of these metals may advantageously comprise at least 15 wt. % of the alloy, e.g., 10-25 wt. % of chromium, 3-8 wt. % of aluminum and up to 20 wt. % of nickel. The alloys may also contain small or trace amounts of one or more other metals such as manganese, copper, vanadium, titanium, and the like. The surface or the metal substrates may be oxidized at high temperatures, e.g., 1000° C. and higher, to improve the resistance to corrosion of the alloys by forming an oxide layer on the surfaces of the substrates. Such high temperature-induced oxidation may enhance the adherence of the refractory metal oxide support and catalytically promoting metal components to the substrate.
In alternative embodiments, zeolitic material according to one or more embodiments having a BEA-type framework structure may be deposited on an open cell foam substrate. Such substrates are well known in the art, and are typically formed of refractory ceramic or metallic materials.
In one or more embodiments, the zeolitic material according to any of the specific embodiments as described in the present application is used as a molded catalyst, still more preferably as a molded catalyst wherein the zeolitic material is deposited on a suitable refractory carrier, still more preferably on a “honeycomb” carrier, for the selective reduction of nitrogen oxides NOx according to the preferred use of the inventive material or as the catalyst comprising a zeolitic material according to step (a) of the inventive method for the treatment of NOx by selective catalytic reduction.
As regards the contacting of the gas stream with the catalyst comprising a zeolitic material having a BEA-type framework structure according to specific embodiments as described in the present application, there is no particular restriction as to the mode or the conditions in which the contacting takes place, provided that it is suited for engaging the SCR reaction between the catalyst and the gas stream containing NOx in step (b) of the inventive method. According to one or more embodiments of the present invention, the contacting takes place at an elevated temperature compared to ambient temperature, more preferably at a temperature comprised in the range of anywhere from 150 to 700° C., wherein the temperature of contacting is more preferably comprised in the range of from 200 to 650° C., more preferably of from 250 to 600° C., more preferably of from 300 to 550° C., more preferably of from 350 to 525° C., and even more preferably of from 400 to 500° C. According to specific embodiments of the inventive method, the temperature of contacting in step (b) is comprised in the range of from 425 to 475° C.
According to alternative embodiments of the inventive method, the contacting at least partly takes place under so-called “cold-start” conditions as are, for example, typically encountered in the treatment of automotive exhaust gas. In particular, within the meaning of the present invention, the contacting of a gas stream comprising NOx under “cold-start” conditions implies that the contacting takes place at lower temperatures than required for the optimal activity of the inventive catalyst according to any of the specific embodiments described in the present application which is used for SCR in the inventive method. According to one or more embodiments, it is however preferred that “cold-start” conditions refer to the conditions and in particular to the temperature typically encountered in automotive applications during the first phase directly following the ignition of the combustion engine, and in particular when the combustion engine has not been in operation for a certain period, such that the temperature of the exhaust gas upon contact with the catalyst and/or the temperature of the catalyst itself which is employed in the inventive method is and/or are below the temperature required for optimal activity of the catalyst. Within the meaning of the present invention, the “temperature of optimal activity of the catalyst” refers in particular to the lowest temperature at which the catalyst, depending on the particular composition and temperature of the gas stream contacting the catalyst in the inventive method as well as the further parameters including the pressure and time of contact of the gas stream containing NOx with the catalyst, displays the maximum activity with respect to the treatment of NOx in the SCR process.
Thus, in general, according to the specific embodiments, the temperature of “cold-start” conditions is any temperature below the temperature of optimal activity of the catalyst employed, wherein the temperature is comprised in the range of from 50 to 500° C. below the temperature of optimal catalyst activity, preferably of from 100 to 400° C. below, more preferably 150 to 350° C. below, more preferably 200 to 300° C. below, and even more preferably or from 225 to 275° C. below the temperature of optimal activity of the catalyst employed in the inventive method. Therefore, according to an alternative embodiment, depending on the specific catalyst according to specific embodiments of the present invention which is used in the inventive method, as well as on the specific composition of the gas stream comprising NOx and the conditions of contacting used therein, the temperature of contacting in step (b) is comprised in the range of from 50 to 500° C., wherein preferably the temperature of contacting is comprised in the range of from 90 to 400° C., more preferably of from 120 to 300° C., more preferably of from 150 to 250° C., and even more preferably of from 180 to 220° C.
Concerning the gas stream comprising NOx which is contacted with the catalyst in step (b), there is no particular restriction as to the further component which may be contained therein, provided that the treatment of NOx by SCR in step (b) is possible. According to one or more embodiments, the gas stream further comprises one or more reducing agents, and more preferably one or more reducing agents which are active in the SCR process when simultaneously contacted with both the catalyst and NOx contained in the gas stream. In general, any suitable reducing agent may be employed, wherein, in one or more embodiments, the reducing agent comprises urea and/or ammonia. In particular, the selective reduction of nitrogen oxides wherein the zeolitic material according to the inventive method is employed as catalytically active material is preferably carried out in the presence ammonia or urea. While ammonia is the reducing agent of choice for stationary power plants, urea is the reducing agent of choice for mobile SCR systems. Typically, the SCR system is integrated in the engine and vehicle design and, also typically, contains the following main components: SCR catalyst containing the zeolitic material according to one or more embodiments; a urea storage tank; a urea pump; a urea dosing system; a urea injector/nozzle; and a respective control unit.
Thus, according to one or more embodiments, the gas stream further comprises one or more reducing agents, the one or more reducing agents preferably comprising urea and/or ammonia, preferably ammonia.
Therefore, the present invention also relates to a method for selectively reducing nitrogen oxides NO in a selective catalytic reduction (SCR) process, wherein a gaseous stream containing nitrogen oxides NOx, preferably further comprising one or more reducing agents, is contacted with the zeolitic material according to any of the specific embodiments as described in the present application, preferably in the form of a molded catalyst, still more preferably as a molded catalyst wherein the zeolitic material is deposited on a suitable refractory carrier, still more preferably on a “honeycomb” carrier. As regards the one or more reducing agents which are used in the inventive SCR process, there is no particular restriction as to the compounds which may be used, wherein preferably the one or more reducing agents comprise ammonia and/or urea, wherein even more preferably the reducing agent preferably further comprised in the gaseous stream is ammonia and/or urea.
The nitrogen oxides which are reduced using a catalyst containing the zeolitic material according to any of the specific embodiments as described may be obtained from any process, in particular as a waste gas stream. Among others, waste gas streams as obtained in processes for producing adipic acid, nitric acid, hydroxylamine derivatives, caprolactame, glyoxal, methyl-glyoxal, glyoxylic acid or in processes for burning nitrogeneous materials may be mentioned.
Thus, according to one or more embodiments, the gas stream comprises one or more NO containing waste gases, preferably one or more NO containing waste gases from one or more industrial processes, wherein more preferably the NO containing waste gas stream comprises one or more waste gas streams obtained in processes for producing adipic acid, nitric acid, hydroxylamine derivatives, caprolactame, glyoxal, methyl-glyoxal, glyoxylic acid or in processes for burning nitrogeneous materials, including mixtures of waste gas streams from two or more of the processes.
Alternatively, however, is the use of a catalyst containing the zeolitic material according to any of the specific embodiments as described for removal of nitrogen oxides NOx from exhaust gases of internal combustion engines, in particular diesel engines or lean-burn gasoline engines, which operate at combustion conditions with air in excess of that required for stoichiometric combustion, i.e., under lean conditions. In particular, as used herein, the term “lean conditions” refer to conditions in which the ratio of air to fuel in the combustion mixtures supplied to such engines is maintained considerably above the stoichiometric ratio so that the resulting exhaust gases are “lean”, i.e., the exhaust gases are relatively high in oxygen content. More specifically, lean-burn engines operate at an air to fuel ratio exceeding Lambda=1.0, preferably exceeding Lamda=1.2, and even more preferably exceeding Lambda=1.5.
Thus, according to further embodiments, the gas stream comprises a NOx containing waste gas stream from an internal combustion engine, preferably from an internal combustion engine which operates under lean-burn conditions, and more preferably from a lean-burn gasoline engine or from a diesel engine.
The present invention includes the following embodiments, wherein these include the specific combinations of embodiments as indicated by the respective interdependencies defined therein:
NOx containing waste gases, preferably one or more NOx containing waste gases from one or more industrial processes, wherein more preferably the NOx containing waste gas stream comprises one or more waste gas streams obtained in processes for producing adipic acid, nitric acid, hydroxylamine derivatives, caprolactame, glyoxal, methyl-glyoxal, glyoxylic acid or in processes for burning nitrogeneous materials, including mixtures of waste gas streams from two or more of the processes.
The data from 29Si MAS NMR contained in the present examples was obtained using a Bruker-Biospin AVANCE400 attached with solid 7 mm MAS-NMR probe using a transmitter frequency of 79.48 MHz, a sample spinning ratio of 5000 rpm. The data was acquired in a 1H-decoupled mode with a transmitter frequency of 400.13 MHz, and a pulse width of 12 μsec for the decoupled nucleus. The specific measuring conditions employed in the 29Si solid state NMR experiment included a sweep-width of 39,682 Hz, an acquisition time of 0.051 sec, a delay time of 7 sec, and a pulse width of 4.5 μsec. The samples were respectively measured at 300 K. The program used for data acquisition was hpdec, using line broadening factor of 10 Hz, wherein the number of scans was 480 times.
335.1 g of NaAlO2 was dissolved in 7,314 g of H2O while stirring, followed by addition of 74.5 g of zeolite beta seeds (Product-Nr. CP814C from Zeolyst International which was converted to the H-form by calcination at 450° C. for 5 h, wherein a heat ramp of 1° C./min was used for attaining the calcination temperature). The mixture was placed in a 20 L autoclave and 7,340 g sodium waterglass solution (26 wt.-% SiO2 and 8 wt.-% Na2O) and 1,436 g Ludox AS40 was added, affording an aluminosilicate gel with a molar ratio of 1.00 SiO2:0.0421 Al2O3:0.285 Na2O:17.48 H2O. The reaction mixture was heated in 3 h to a temperature of 120° C. using a constant heat ramp, wherein the temperature was then maintained 117 h for crystallization. After having let the reaction mixture cool to room temperature, the solid was separated by filtration, repeatedly washed with deionized water and then dried at 120° C. for 16 h affording 1,337 g of a white crystalline product.
Chemical analysis showed the material to have an SiO2:Al2O3 molar ratio of 9.93. The sodium content calculated as Na2O was found to be 7.33 wt % on basis of the calcined material.
100.0 g of the sodium form of the crystalline product as obtained from Example 1 was added to a solution of 142.2 g ammonium nitrate dissolved in 657.8 g of deionized water at 80° C. and the slurry was stirred at 300 rpm for 6 h at 80° C. The solid was then filtered hot (without additional cooling) over a Buechner funnel with suitable filter paper. The filter cake then was washed with deionized water until the conductivity of the wash water was below 200 μS cm−1. The filter cake was then dried for 16 h at 120° C.
This procedure was repeated twice, thus affording an ion-exchanged crystalline product in its ammonium form. Chemical analysis showed this material to have an SiO2:Al2O3 molar ratio of 10.4.
The ion-exchanged zeolitic material obtained from Example 2 was calcined at 450° C. for 5 h to afford the H-form thereof. Chemical analysis showed this material to have an SiO2:Al2O3 molar ratio of 9.91. The sodium content of the calcined material calculated as Na2O was found to be 0.09 wt %.
The procedure of Example 2 was repeated, wherein the ion-exchange procedure was only repeated once. The resulting ion-exchanged zeolitic material was accordingly calcined at 450° C. for 5 h to afford the H-form thereof. Chemical analysis showed this material to have an SiO2:Al2O3 molar ratio of 10.4. The sodium content of the calcined material calculated as Na2O was found to be 0.80 wt %.
Iron-exchanged samples were prepared according to Examples A to F as indicated in Table 1 below. For this purpose, an iron sulfate solution was prepared by dissolving iron(II) sulfate heptahydrate in deionized water, wherein the iron concentration was set as indicated in Table 1 for the respective samples. The respective solutions were heated to 80° C. and the respective zeolite beta starting material was added under stirring in an amount for achieving a weight ratio of the solution to the solid of 6.5, and the temperature of 80° C. was maintained for 2 h. More specifically, as regards the zeolitic starting materials, for Examples A and B the zeolitic material from Example 3 was employed as the starting material, whereas for Example C the zeolitic material from Example 4 was used. For Comparative Examples D and E, on the other hand, a commercially available zeolite beta from Zeolyst (CP814C) was employed for iron-exchange. Comparative Example F is a commercially available iron-exchanged zeolite Beta (Product-Nr. SE08252—finished SCR-grade—obtained from Seneca)
The respective slurry was then filtered hot (without additional cooling) over a Buechner funnel with a suitable filter paper. The filter cake was washed with deionized water until the conductivity of the wash water was below 200 μS cm−1. The filter cake was then dried for 16 h at 120° C. Table 1 respectively indicates the Fe2O3 and Na2O loadings of all resulting products in wt.-%. Based on the further values from chemical analysis, the molar ratios of SiO2: Al2O3, Fe:Al, and Fe:H were then respectively calculated, as indicated in Table 1.
Copper-exchanged samples were prepared according to Examples G to N as indicated in Table 2 below. For this purpose, a copper acetate solution was prepared by dissolving copper(II) acetate monohydrate in deionized water, wherein the copper concentration was set as indicated in Table 2 for the respective samples. The respective solutions were heated to 60° C. and the respective zeolite beta starting material was added under stirring in an amount for achieving a weight ratio of the solution to the solid of 6.5, and the temperature of 60° C. was maintained for 2 h. More specifically, as regards the zeolite beta starting materials, for Examples G, H, and J, the zeolitic material as obtained from Example 2 was employed as the starting material, whereas for Example K, the zeolitic material as obtained from Example 3 was used. For Comparative Examples L, M, and N, a commercially available zeolite beta from Zeolyst (CP814C) was employed for ion-exchange with copper.
The respective slurry was then filtered hot (without additional cooling) over a Buechner funnel with a suitable filter paper. The filter cake then was washed with deionized water until the conductivity of the wash water was below 200 μS cm−1. The filter cake was then dried for 16 h at 120° C. Table 2 respectively indicates the CuO and Na2O loadings of all resulting products in wt.-%. Based on the further values from chemical analysis, the molar ratios of SiO2: Al2O3, Cu:Al, and Cu:H were then respectively calculated, as indicated in Table 2.
The powder was first prepared as an extrudate before testing. 18 g water was added to 20 g dried powder in a Stephan-Werke GmbH mixer (Model No.: OZDe042/4s) at a mixing rat of 80 rpm. The slurry way mixed 10 minutes to afford a homogeneous mixture. Then 0.5 g of polyethylenoxide (PEO) were added and mixed 2 minutes until homogeneous. 2.5 wt % PEO was added to the mixture as a binder. Then 2 g of water were added slowly and the paste was mixed for about 5 minutes to homogenize. This paste then was pressed in a hand-made press with an extruding hole of 2 mm diameter and 10 cm length. The resulting extrudates were dried at 120° C. for 5 hours and calcined at 540° C. for 5 hours. The extrudate was then sized into pellets and sieved to separate a pellet size ranging from 0.5 to 1 mm. This size fraction was used for testing in the reactor. The sieves used were obtained from the company Retsch (500 μm sieve S/N 04025277) and a 1 mm sieve (S/B 04009529) both having a diameter of 200 mm and height of 25 mm). The resultant catalysts are referred to as “fresh” thus indicating that they have not been subject to hydrothermal aging.
The aging reactor consisted of a 1 mm thick steel tube (grade 1.4841 from Buhlmann Group) with diameters of 500 mm height and 18 mm internal diameter. A nickel mantle based furnace was used to heat the reactor to the target reaction temperature which was monitored by an internal thermocouple at the location of the sample. The steam was prepared by heating controlled amounts of water at 150° C. through a steel pre-steamer before mixing with the remaining gases in a static mixer. The gases together with the steam were then passed through a pre-heater to enable the target temperature. The extrudates formed as described in Example 7 were hydrothermally aged in a tube furnace in a gas flow containing 10 vol.-% H2O, 10 vol.-% O2, balance N2 at a space velocity of 11,2501 h−1 for 24 hours at 750° C.
In the following, the examples of the catalyst are designated in the same fashion as in Table 1 and 2 relative to the zeolitic material contained therein, respectively. Thus, Catalyst Example A as designated in Tables 3 and 4 below indicates that it has been prepared with the iron-exchange sample from Example A as described in Example 5 and Table 1, respectively. Accordingly, Catalyst Example G as designated in tables 4 and 6 refers to the catalyst which has been prepared with the copper-exchanged zeolitic material of Example G as described in Example 6 and Table 2, respectively. Table 3 reports the surface area data and Table 5 reports the catalytic data for iron-exchanged catalyst samples A to F. Table 4 reports the surface area data and Table 6 reports the catalytic data for copper-exchanged catalyst samples G to N.
The aged catalysts samples obtained from Example 8 were evaluated for selective catalytic reduction (SCR) of NOx activity using the following reactor set up: The reactor consisted of a 1 mm thick steel tube (grade 1.4541 from Buhlmann Group) with diameters of 500 mm height and 18 mm internal diameter. A copper mantle based furnace was used to heat the reactor to the target reaction temperature which was monitored by an internal thermocouple at the location of the sample.
5 ml of a sample was respectively loaded into the reactor and secured with a plug of silica wool at each end of the sample. The sample height is controlled by filling the empty reactor volume with an inert silica based material (Ceramtek AG—product #1.080001.01.00.00; 0.5 to 1 mm-45 g at the bottom and 108 g at the top of the sample).
An inlet gas mixture was formed containing 500 ppm NO, 500 ppm NH3, 10 vol.-% O2, 5 vol.-% steam and balance He. The steam was prepared by heating controlled amounts of water at 150° C. through a steel pre-steamer (grade 1.4541 from Buhlmann, dimensions were 6 mm internal diameter and 900 mm length) before mixing with the remaining gases in a static mixer. This gas mixture then passed through a pre-heater set at 250° C. and static mixer before entering the SCR reactor described in the previous paragraph.
The NO-conversion or “DeNOx” activity was measured under steady state conditions by measuring the NOx, NH3 and N2O concentrations at the outlet using a FTIR spectrometer. Samples were tested at reaction temperatures of 200, 300 and 450° C. at a volume-based gas hourly space velocity of 80,000 h−1. NO conversion was then calculated as (NO outlet concentration (ppm)/NO inlet concentration (ppm))*100. N2O make was also recorded as concentration in ppm. The results obtained for the inventive Catalyst Example A-C and G-K as well as for the Comparative Catalyst Examples D-F and L-N are shown in Tables 5 and 6, respectively, for the respective catalyst sample in their “fresh” state as obtained from Example 7, as well as in their “aged” state as obtained from Example 8.
In
In
All the more surprisingly, however, it is observed that compared to the activity of the comparative catalyst examples, the inventive catalyst examples display an increase in catalytic activity with higher loadings of the zeolitic material with copper, a tendency which is particularly apparent at lower conversion temperatures. Thus, as may be taken from the results displayed in
100.0 g sodium form of the crystalline product from Example 1 was added to a solution of 100.0 g ammonium nitrate dissolved in 898.8 g of distilled water and heated to 80° C. The slurry was stirred at 300 rpm for 2 h at 80° C. The solid was then filtered using a filter press. The filter cake then was washed with distilled water (room temperature wash water) until the conductivity of the wash water was below 100 μS cm−1. The filter cake was then dried for 16 h at 120° C. This procedure was repeated once, affording ion exchanged crystalline product BEA in its ammonium form. Chemical analysis showed this material to have 10.6 SiO2:Al2O3 and 0.07 wt % of Na2O on a calcined basis.
An iron sulfate solution was prepared by dissolving 130.8 g iron sulfate heptahydrate (APPLICHEM) in 519.5 g of distilled water. This solution was heated to 80° C. and under stirring 100 g of NH4-Beta from Example 10 was added. The temperature of 80° C. was maintained for 2 h. The slurry was then filtered over a Buechner funnel with appropriate filter paper. The filter cake was washed with distilled water (room temperature wash water) until the conductivity of the wash water was below 200 μS cm−1. The filter cake was then dried for 16 h at 120° C. Calcination at 500° C. for 5 h (heating ramp 1° C./min) gave iron exchanged Fe-Beta with Fe2O3 content found at 4.94 wt % and Na2O content at 0.01 wt % on calcined basis via elemental analysis. The SiO2:Al2O3 ratio was 10.5.
Based on the data in Table 7, the Si:Al ratio of the zeolite framework was determined according to the procedure outlined in J. Klinowski et al. in J. Chem. Soc., Faraday Trans. 2 1982, 78, pp. 1025-1050 (see in particular formula on page 1034). In particular, this is possible based on the assignment of the individual Si-species detected in function of the number of neighboring Al-atoms to which they are bound via bridging with oxygen. Thus, as may be taken from Table 7, Peak No. 3 is attributed to a Si-species bound to 2 Al-species via oxygen and Peak No. 2 to a Si-species bound to 1 Al-species via oxygen, whereas the remaining peaks are attributed to Si-species not (directly) bound to Al via (one) oxygen bridge, but rather only bound to further Si via oxygen. Based on the 29Si MAS NMR-data in Table 7, the Si:Al ratio in the zeolite framework of the sample obtained from Example 11 is calculated to 8.0.
For comparison, a commercial sample of zeolite beta ion-exchanged with iron was measured in the 29Si MAS NMR experiment, the spectrum of which is displayed in
As for the iron-exchanged sample of Example 11, the Si:Al ratio of the zeolite framework of the commercial sample was determined according to the 29Si MAS NMR-data in Table 8, the Si:Al ratio in the zeolite framework of the sample being calculated to 25.9.
For investigating the behavior of the iron-exchanged zeolite beta of Example 11 under aging conditions, a sample thereof was subject to an ageing procedure. To this effect, 2 g of the sample were transferred onto a ceramic plate (dimensions: Length: 60×Width: 35×Depth: 5 [mm]) which was then played in an electric furnace (Model: OXK-600X electric furnace, made by KYOEI ELECTRIC KILNS CO., LTD). The furnace was then heated to 150° C., and a gas stream of air containing 10 vol.-% H2O was fed into the furnace at a gas hourly space velocity of 10 h−1. The furnace was then heated to 650° C. at a heating rate of 10° C./h and kept at that temperature for 100 h. The furnace was then subsequently cooled down and the gas stream with 10 vol.-% H2O was interrupted and replaced with a gas stream of dry air until the sample had cooled down to room temperature.
After aging, the sample was again investigated by 29Si MAS NMR, the results of which are displayed in
As for Example 11, the Si:Al ratio of the zeolite framework of the aged sample of Example 12 was determined according to the data in Table 8, the Si:Al ratio in the zeolite framework of the sample being calculated from 29Si MAS NMR to 39.6.
For comparison, the commercial sample of zeolite beta ion-exchanged with iron was also subject to the aging procedure, and subsequently measured in the 29Si MAS NMR experiment, the spectrum of which is displayed in
The Si:Al ratio of the zeolite framework of the aged commercial sample was also determined according to the data in Table 10, the Si:Al ratio in the zeolite framework of the sample being calculated from 29Si MAS NMR to 61.6.
Thus, as may be taken from the results obtained for the aged samples, based on the Si:Al ratios obtained from 29Si MAS NMR for the fresh and aged samples, the iron-exchanged zeolite beta is dealuminated to an extent by the aging procedure of Example 12, such that the Si:Al ratio obtained considerably increases from an initial value of 8 to a value of 40, which would correspond to about 80% of the initial aluminum being removed from the framework. The commercial sample, on the other hand, displays an increase in the Si:Al ratio obtained from 29Si MAS NMR from initially 26 to a value of 62 after the dealumination procedure. This would correspond to about 58% of the initial aluminum being removed from the framework structure. Thus, considering that judging from the Si:Al ratios obtained from 29Si MAS NMR, more than 3 times as much Al was contained in the inventive sample according to Example 11 prior to aging, the extent of dealuminaton observed in the iron-exchanged zeolite beta is considerably greater than observed for the commercial iron-exchanged zeolite beta.
For investigating the effect of aging on the catalytic activity of the iron-exchanged zeolite beta according to one or more embodiments, the DeNOx-activity of the aged sample of Example 12 was determined at 200° C. and 500° C., and compared to the activity measured for the aged commercial sample at these temperatures. The results of the NOx-conversion experiments for the respective samples is displayed in
The results from the catalytic testing performed with these materials are, however, highly unexpected considering the considerable degree of dealumination which the sample of Example 12 has suffered compared to the commercial sample. In particular, although it may well have been expected that the superior catalytic activity displayed by the catalyst samples according to one or more embodiments compared to comparative examples after having been exposed to an aging procedure would be the result of a higher stability of the framework structure when exposed to the aging conditions, the present data from 29Si MAS NMR actually indicate that quite to the contrary the Al-rich framework of the inventive materials are prone to considerable dealumination under aging conditions. These highly unexpected findings only further demonstrate the unique characteristics and properties of the inventive materials which strongly contrast to the materials known in the art, not only in view of their physical characteristics but also based on their chemical traits and properties which may not be compared to those of conventional catalytic materials
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/CN2012/070899 | Feb 2012 | CN | national |
This application claims priority under 35 U.S.C. §365(c) to PCT application PCT/CN2012/070899, filed on Feb. 6, 2012, which is incorporated herein by reference in its entirety.
