Patent Application
20190321804
The present invention relates to a manganese oxide alumina containing composition with high resistance against SOx, to a method for making the composition, and to use of the composition as a catalyst carrier. The composition comprises at least an alumina based support material, manganese oxide, and silica (SiO2).
Lean burn engines, as for example diesel engines, are known to provide high fuel efficiency. The oxygen rich operation conditions in these engines result in prevailing oxidizing conditions in an emission stream. In these engine systems, the main raw emission pollutants are CO, NOx, unburned hydrocarbons and soot particles. Catalyst systems, including various components and precious metals, for dealing with emission control have been developed. Usually a so called Diesel Oxidation Catalyst (DOC) converts CO into CO2 and the unburned hydrocarbons into CO2 and water. Due to the oxygen rich conditions, the conversion of NOx into N2 requires special strategies and dedicated NOx after treatment catalysts, such as a Lean NOx Trap (LNT) or Selective Catalytic Reduction (SCR) catalyst(s). The NOx removal by these catalysts is enhanced by a high NO2 to NO ratio that is obtainable by an effective NO oxidation by the DOC. The NO oxidation performance is also relevant for operating a Continuous Regeneration Trap (CRT) for the removal and combustion of soot particles.
There is a continuous demand for improving the performance and long term stability of the various components of emission control catalyst system. Furthermore a reduction of the precious metal loading of the catalyst system is desirable in order to reduce its cost. This can for example be achieved by incorporating catalytically active and/or promoting metal oxides, as for example manganese oxides, into the catalyst system.
Due to its high redox activity manganese oxide (MnOx) itself shows activity or at least has a beneficial promoting effect in the desired oxidation reactions including CO oxidation, NO oxidation and the oxidation of hydrocarbons or soot.
Therefore, manganese oxide has been reported to be a useful component in automotive emission control catalyst systems, in particular for application in a diesel oxidation catalyst, catalyzed soot filter or selective catalytic reduction catalyst.
It is beneficial to use the manganese oxide in an enhanced dispersion state by utilizing it in tight contact to or supported on a high surface area support material, in particular an alumina based support material, as for example alumina or silica-alumina.
The preparation of manganese oxide containing alumina based support materials and their use especially in automotive emission control catalysts is well known in the art. For example US2015/0165423 A1 teaches the use of a metal oxide support containing manganese as a catalyst support material for platinum group metals in a diesel oxidation catalyst with improved catalytic performance. In addition WO2016/130456 A1 describes the beneficial effects on the NO2 storage/release properties that are attained by incorporating manganese oxide into an oxidation catalyst as passive NOx adsorption component.
Furthermore, manganese oxides and supported manganese oxides are known to be active in the selective catalytic reduction of NOx to N2.
However, some diesel fuel qualities as well as lubricants are showing considerable sulphur levels leading to poisoning effects on the emission control catalyst system. The sulfur compounds contained in fuels are oxidized in the combustion process to form sulfur oxides, SO2 and SO3, further referred to as SOx. In turn these SOx are known to easily react with manganese oxides at the prevailing temperature under operation conditions, resulting in severe deactivation of the catalyst system. The deterioration of manganese oxide functionality is ascribed to its strong adsorption of SOx leading to the formation of surface and bulk manganese-sulfates (M. Tepluchin, Catalysis Today 258 (2015) 498).
Both alumina and silica-alumina supported manganese oxide materials as described in the art adsorb a considerably high amount of SOx, thus leading to significant deactivation by poisoning the manganese oxide functionality.
The object of the present invention is therefore to provide a manganese oxide containing composition applicable in emission control catalysts that is highly stable towards the uptake of SOx.
The inventors of the present application have surprisingly found a composition having amongst other benefits improved resistance against SOx for example when used in Diesel Oxidation Catalyst and (a) method(s) for making such composition.
According to one aspect of the invention there is provided a composition with high stability against SOx comprising:
a support material comprising an alumina based support material and manganese oxide, the content of the manganese oxide in the support material being between 0.1 and 20 wt. % of the total support material calculated as MnO2, the support material further comprising SiO2 and optionally oxides of zirconium, titanium, rare-earth elements or combinations thereof, the SiO2 being either incorporated into the support material or coating the support material or both;
By “incorporated” is meant combining the SiO2 into the support material. By “coating” is meant a surface covering formed over the support material, including the coating of surfaces of inner pore walls.
The above definition encompasses the following alternatives:
If present the oxides of zirconium, titanium, rare-earth elements or combinations thereof form part of what is referred to as the support material and of what it is referred to as the alumina based support material. The alumina based support material does not contain manganese oxide. The support material contains manganese oxide and silica, either as part of the alumina based support material, separately added or both.
The composition according to the first embodiment comprises a support material comprising an alumina based support material and manganese oxide, the content of the manganese oxide in the support material being between 0.1 and 20 wt. % of the total support material calculated as MnO2, the support material further comprising SiO2, wherein where the SiO2 is incorporated into the support material, the SiO2 content is greater than 5 wt % relative to the alumina based support material.
According to a second embodiment the composition comprises a support material comprising an alumina based support material and manganese oxide, the content of the manganese oxide in the support material being between 0.1 and 20 wt. % of the total support material, calculated as MnO2, the support material further comprising SiO2 and oxides of zirconium, titanium, rare-earth elements or combinations thereof, wherein where the SiO2 is incorporated into the support material, the SiO2 content is at least 5 wt % relative to the alumina based support material.
According to a third embodiment the composition comprises a support material comprising an alumina based support material and manganese oxide, the content of the manganese oxide in the support material being between 0.1 and 20 wt. % of the total support material calculated as MnO2, the support material comprising oxides of zirconium, titanium, rare-earth elements or combinations thereof, the support material being coated with SiO2, wherein where the SiO2 coats the support material the SiO2 coating makes up at least 0.2 wt. % relative to the alumina based support material.
According to a fourth embodiment the composition comprises a support material comprising an alumina based support material and manganese oxide, the content of the manganese oxide in the support material being between 0.1 and 20 wt. % of the total support material calculated as MnO2, the support material being coated with SiO2, wherein where the SiO2 coats the support material the SiO2 coating makes up at least 0.2 wt. % relative to the alumina based support material.
The composition may be used in a catalyst system for emission control.
At least 75 wt. % of the support material, more preferably at least 80 wt. % of the support material consists of the alumina based support material.
The alumina based support material is either alumina, silica-alumina, or a mixture thereof, preferably alumina. The support material preferably includes oxides of zirconium, preferably ZrO2.
Typically, the BET surface area of the alumina based support material is above 50 m2/g and more preferably above 100 m2/g. The term BET surface area refers to the Brunauer-Emmett-Teller method for the determination of specific surface area by N2 adsorption. Independent thereof the BET surface area of the support material is typically above 50 m2/g and more preferably above 100 m2/g. Independent thereof the pore volume of the alumina based support material is preferably between 0.1 ml/g and 1.5 ml/g. Independent thereof the pore volume of the support material is preferably between 0.1 ml/g and 1.5 ml/g. The pore volume is measured by N2 adsorption as per known standard practice, in particular according to DIN 66134.
The alumina based support material has no or very little amounts of sodium impurities. In particular the alumina based support material comprises less than 500 ppm Na2O, more preferably less than 100 ppm Na2O. Independent thereof the support material typically comprises less than 500 ppm Na2O, more preferably less than 100 ppm Na2O.
The manganese oxide content is preferably between 1 and 10 wt. %, calculated as MnO2, of the support material. The manganese oxide may exist in its various oxidation states either in bulk form or surface forms, or as discrete manganese oxide forms.
The manganese oxide is preferably derived by thermal decomposition of soluble manganese salts selected from acetate, nitrate, sulfate; preferably acetate. These manganese salts decompose during a calcination step to form a manganese oxide, and solutions of the soluble manganese salts are further referred to as manganese oxide salt solutions.
The support material is either coated with SiO2 or the SiO2 is incorporated into the support material. By “incorporated” is meant combining the SiO2 into the support material. By “coating” is meant a surface covering formed over the support material, including the coating of surfaces of inner pore walls.
Where the alumina based support material is silica-alumina, there is a specific amount of SiO2 incorporated into the silica-alumina support material or an additional amount of SiO2 used to coat the silica-alumina support material.
Preferably the silica-alumina is obtainable by mixing an aluminium compound with a silicic acid compound in an aqueous medium, and subsequently drying or calcining the product obtained. The aluminium component used is a C2- to C20-aluminium alkoxide hydrolyzed with water and preferably purified by means of ion exchangers. Prior, during or after the hydrolyzation silicic acid, preferably orthosilicic acid, preferably purified by means of ion exchangers, is added to the aluminium compound respectively the hydrolyzed aluminium compound. The method is described in detail in U.S. Pat. No. 5,045,519 A.
Where the SiO2 is incorporated into the support material without oxides of zirconium, titanium, rare earth elements or combinations thereof, the support material preferably comprises a SiO2 content of at least 10 wt %, preferably between 10 wt % and 40 wt %, most preferably between 10 wt % and 25 wt %, each relative to the alumina based support material.
Where the support material includes, oxides of zirconium, titanium, rare earth elements or combinations thereof, particularly ZrO2, then at least 5% wt. and preferably up to 40 wt %, more preferably at least 5 wt % and up to 25 wt % of SiO2 and at least 5% wt. to 40 wt %, preferably 5 wt % to 25 wt % of oxides of zirconium, titanium, rare earth elements or combinations thereof, preferably ZrO2, is incorporated into the support material, each relative to the aluminium based support material.
Where the SiO2 coats the support material, the SiO2 coating is preferably 0.2 to 5 wt. %, most preferably 0.2 to 1 wt. % relative to the alumina based support material as determined by the amount of SiO2 solution which is added to the support material.
According to a second aspect of the invention there is provided a method to prepare a composition with high stability against SOx, the method comprising with the steps ii) to iv) in any order):
Step iv) may also be applied as part of the manufacturing step of the alumina based support material provided in step i), if the alumina based support material is a silica-alumina (e.g. for steps iv) b) and iv) c)).
Preferably the method is carried out in the following order of steps i), ii) iii) and then iv).
According to a first embodiment of the method, the method includes providing an alumina based support material; adding oxides of zirconium, titanium, rare-earth elements or combinations thereof to the alumina based support material; impregnating the alumina based support material with a manganese oxide salt solution to form (at least after calcination) a manganese oxide impregnated support material; and coating the manganese oxide impregnated support material with a SiO2 solution to form (at least after calcination) a SiO2 coating around the manganese oxide impregnated support material, the SiO2 coating forming at least 0.2 wt. % of the impregnated manganese oxide support material.
According to an alternative method of the first embodiment of the method (if no oxides of zirconium, titanium, rare-earth elements or combinations thereof are incorporated), the method includes providing an alumina based support material; impregnating the alumina based support material with a manganese oxide salt solution to form (at least after calcination) a manganese oxide impregnated support material; and coating the manganese oxide impregnated support material with a SiO2 solution to form a SiO2 coating around the manganese oxide impregnated support material, the SiO2 coating forming at least 0.2 wt. % relative to the alumina based support material.
According to a second embodiment of the method (if no oxides of zirconium, titanium, rare-earth elements or combinations thereof are incorporated), the method includes providing an alumina based support material; impregnating the alumina based support material with a manganese oxide salt solution to form a manganese oxide impregnated support material; and adding SiO2 into the alumina based support material wherein the content of SiO2 is greater than 5 wt % of the support material.
According to a third embodiment of the method, the method includes providing an alumina based support material; adding oxides of zirconium, titanium, rare-earth elements or combinations thereof to the alumina based support material; impregnating the alumina based support material with a manganese oxide salt solution to form a manganese oxide impregnated support material; and adding SiO2 to the alumina based support material, wherein the content of SiO2 is at least 5 wt % of the support material.
This method includes adding the oxide or a solution of the oxide of zirconium, cerium, titanium or rare earth elements to an aluminium compound and then calcining. Preferably oxides of zirconium, more preferably ZrO2 are incorporated into the support material.
The alumina based support material is preferably alumina, silica-alumina, or a mixture thereof and most preferably alumina.
Different types of impregnation techniques can be used for impregnation. These comprise for example incipient wetness impregnation, equilibrium deposition filtration, or wetness impregnation.
The alumina based support material is preferably impregnated with a manganese oxide salt solution by incipient wetness impregnation. The content of the manganese oxide in the support material is between 0.1 and 20 wt. % of the total support material calculated as MnO2, preferably between 1 and 10 wt. %, calculated as MnO2, of the support material.
The calcining of the final composition to obtain the support material may be carried out at a temperature between 100 and 1000° C., preferably 500 to 900° C., each for at least ½ hour. The method of the invention may include a further step of calcining, namely calcining the manganese oxide impregnated support material at a temperature of between 100 and 1000° C., preferably 500 to 900° C., each for at least ½ hour to form a calcined manganese oxide impregnated support material.
The manganese oxide impregnated support material or calcined manganese oxide impregnated support material is either coated with a SiO2 solution or a SiO2 solution is incorporated into the alumina based support material.
The term SiO2 solution as used herein refers to a solution containing a suitable compound that is able to form SiO2 during a subsequent drying or calcination step. Examples of such SiO2 sources are silicic acid, in particular orthosilicic acid obtained from water glass by ion exchange.
When coating is selected, the either calcined or non-calcined manganese oxide impregnated support material is then coated with a SiO2 solution. The SiO2 solution is preferably a silicic acid. Coating refers to a surface covering including the surface of inner pore walls of the manganese oxide impregnated support material.
The amount of SiO2 coating is preferably 0.2 to 5 wt. %, most preferably 0.2-1 wt. % relative to the alumina based support material, as each determined by the amount of SiO2 in the SiO2 solution which is added to the support material and calculated as SiO2.
In particular, the coating is achieved by incipient wetness impregnation, where the volume of the SiO2 impregnation solution is nearly equal to the pore volume of the manganese oxide impregnated support material. This method is known to lead to uniform distribution of the SiO2 throughout the pore system of the manganese oxide impregnated support material.
The coated calcined or non-calcined manganese oxide impregnated support is then subjected to a further thermal treatment step at a temperature above 100° C. for at least 0.5 hours after the SiO2 is added, preferably at 500-900° C. for at least 0.5 hours.
Where the SiO2 is incorporated into the alumina based support material without oxides of zirconium, titanium, rare earth elements or combinations thereof, the support material preferably comprises a SiO2 content of at least between 10 wt % and 40 wt %, most preferably between 10 wt % and 25 wt %.
Where the support material includes oxides of zirconium, titanium, rare earth elements or combinations thereof, then at least 5% wt. and preferably up to 40 wt %, more preferably at least 5 wt % and up to 25 wt % of SiO2 and at least 5 wt % to up to 40 wt %, preferably greater than 5 wt % up to 25 wt. % of oxides of zirconium, titanium, rare earth elements or combinations thereof is/are incorporated relative to the alumina based support material. Where the support material includes oxides of zirconium then at least 5% wt. and preferably up to 40 wt %, more preferably at least 5 wt % and up to 25 wt % of SiO2 and at least 5 wt % to up to 40 wt %, preferably greater than 5 wt % up to 25 wt. % of ZrO2 is incorporated relative to the alumina based support material.
The SiO2 may be incorporated into the support material by adding silicic acid to an aluminium compound that is formed by hydrolysis of aluminium alkoxides. When ZrO2 is further incorporated into the support material, a compound that forms ZrO2 after a calcination step, preferably Zr-Acetate is added as an aqueous solution (solution of the oxide of zirconium) to an aluminium compound/water/silicic acid mixture that is formed by the hydrolysis. The respective mixture obtained is subsequently dried, preferably by spray drying and calcined at a temperature above 500° C. for at least an hour.
The support may contain other metal oxides such as alkaline earth metal oxides in particular magnesium oxide or barium oxide.
It is shown that the SOx uptake capacity of the compositions of the present invention is significantly reduced when compared to state-of-the art manganese oxide containing compositions. This effect can clearly be ascribed to the inclusion of SiO2 into the catalyst composition.
The invention will now be described with reference to the following non-limiting examples and Figures, where:
SOx Tolerance Test
The SOx tolerance was determined by measuring the SOx uptake capacity of the composition. Ca. 80 mg of the material were placed in a tubular quartz microreactor and were heated at a constant rate (10° C./min) under N2 (total flow 0.5 l/min) until 300° C. Adsorption experiments were conducted under isothermal condition at 300° C. in O2/SO2/N2 gas mixture (10% O2 v/v+200 ppm SO2, balance N2; total flow 0.5 l/min), up to saturation of the sample. Then the temperature was cooled down to 100° C. and the gas mixture was changed to N2 (total Flow 0.5 l/min) until SO2 Concentration signal went back to zero. The outlet gas composition (i.e. SO2) was measured by using FT-IR gas analyzers (MultiGas 2030, MKS).
A state-of-the-art Mn oxide impregnated support material was prepared by impregnating a commercially available alumina having a BET surface area of 150 m2/g and a pore volume of 0.8 ml/g (measured by N2 adsorption) with manganese acetate solution by incipient wetness impregnation yielding a total loading of 5% MnO2 relative to the manganese oxide impregnated support material followed by a calcination at 550° C. for 3 h.
The Mn oxide impregnated support material as prepared in Comparative Example 1 was impregnated with an aqueous solution of silicic acid under incipient wetness impregnation conditions. Subsequently the material was calcined at 550° C. for 3 h. The final amount of coated SiO2 was 1 wt. % based on the total Mn oxide impregnated support material.
A state-of-the-art Mn oxide impregnated support material was prepared by impregnating a commercially available silica-alumina containing 5 wt. % SiO2 and having a BET surface area of 180 m2/g and a pore volume of 0.7 ml/g (measured by N2 adsorption) with manganese acetate solution by incipient wetness yielding a total loading of 5% MnO2 relative to the manganese oxide impregnated support material followed by a calcination at 550° C. for 3 h.
The Mn oxide impregnated support material as prepared in Comparative Example 2 was impregnated with an aqueous solution of silicic acid under incipient wetness impregnation conditions. Subsequently the material was calcined at 550° C. for 3 h. The final amount of coated SiO2 was 0.2 wt. % based on the total Mn oxide impregnated support material.
The material was prepared as in Example 2 but the amount of SiO2 coating was 0.5 wt. % based on the total composition.
The material was prepared as in Example 2 but the amount of SiO2 coating was 1 wt. % based on the total composition.
The results of the Examples and Comparative Examples are included in Table 1. From Table 1 it is clear that the uptake of SOx is greatly reduced by the present invention when compared to the Comparative Examples.
A silica-alumina containing 10 wt. % SiO2 and having a BET surface area of 250 m2/g was prepared by adding silicic acid to an aluminium compound that was formed by the hydrolysis of an aluminium alkoxide, followed by spray drying and a subsequent calcination at 900° C. for 3 h. The silica-alumina was impregnated with manganese acetate solution by incipient wetness impregnation yielding a total loading of 5% MnO2 relative to the manganese oxide impregnated support material followed by calcination at 550° C. for 3 h.
The material was prepared as in Example 5 but the amount of SiO2 added to the aluminium compound was adjusted to obtain a silica-alumina containing 25 wt. % SiO2 with a BET surface area of 321 m2/g and a pore volume of 1.07 ml/g after calcination at 1000° C. for 3 h.
An aqueous solution of Zr Acetate was added to a mixture of silicic acid and an aluminium compound that was formed by the hydrolysis of an aluminium alkoxide and the mixture was spray dried and calcined at 900° C. for 3 h to obtain a ZrO2 containing silica-alumina based support material having a BET surface area of 156 m2/g and a pore volume of 0.8 ml/g (measured by N2 adsorption). The percentage of ZrO2 added and SiO2 added is each 5% (relative to the alumina based support material). The alumina based support material was further impregnated with a manganese acetate solution by incipient wetness impregnation yielding a total loading of 5% MnO2 relative to the manganese oxide impregnated support material followed by calcination at 550° C. for 3 h.
The results of the experiments are included in Tables 2 and 3 hereunder:
Again, from the Tables it is clear that the uptake of SOx is greatly reduced by the present invention when compared to the Comparative Examples.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17152530.6 | Jan 2017 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/051289 | 1/19/2018 | WO | 00 |
