Copper-containing zeolites and their preparation

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the production of catalysts and adsorbents which can be used for the removal of nitrogen oxides from exhaust gases containing the same.
2. Description of the Background
Nitrogen oxides (hereinafter referred to as NO.sub.x) are found in combustion exhaust gases from industrial plants and automobiles and lead to the production of photochemical smog. Methods to prevent the formation of such smog are urgently needed for environmental safety.
At present, both dry and wet methods are known for the removal of NO.sub.x. Using wet methods, the NO.sub.x is contained in exhaust liquids which are quite difficult to treat. Therefore, the wet methods are still not of practical use. Among the dry methods, there are known methods such as non-catalytic reduction, direct catalytic decomposition, selective catalytic reduction, and adsorption. Among these methods, the selective NH.sub.3 catalytic reduction method is already in practical use. However, this process requires NH.sub.3 as a reducing agent, and further requires devices for the recovery or decomposition of unreacted NH.sub.3, thus leading to a more complicated process.
The direct catalytic decomposition of NO.sub.x is the most preferred method, since it entails the simplest process and does not require a reducing agent such as NH.sub.3. Hitherto, a number of investigations have been performed on the direct catalytic decomposition of NO.sub.x. Pt, CuO and Co.sub.3 O.sub.4 are known to exhibit catalytic activity in decomposing NO.sub.x, but the activity remains insufficient due to the poisoning action of the decomposition product oxygen. Thus, these catalysts cannot be used in practice.
Recently, the zeolite (ZSM-5) which contains copper ions and has a specific crystalline structure has been found to act as a decomposition catalyst for NO (Japanese Laid-Open Patent Application No. Sho 60-125250) in the direct catalytic decomposition of NO.sub.x which does not suffer from the poisoning action of moisture and oxygen even if they are present in the gas to be treated. The ZSM-5 containing copper as disclosed in the cited reference is prepared from conventional ZSM-5 by subjecting the same to ion exchange in an aqueous solution of a water-soluble divalent copper salt.
There are a large number of reports regarding ZSM-5containing copper. In Japanese Laid-Open Patent Application No. Sho 54-96500, for example, the ZSM-5 containing copper is prepared from ZSM-5 by repeated ion exchange with an aqueous solution of a watersoluble divalent copper salt. The product is used as a catalytic combustion catalyst.
In Japanese Laid-Open Patent Application No. Sho 57-36015 and U.S. Pat. No. 4,297,328, the ZSM-5 is ion exchanged three times with an aqueous solution of copper(II) chloride at a refluxing temperature to obtain a rate of exchanged copper ions of larger than 160%. The prepared materials are used as a combustion catalyst and as ternary catalyst, respectively.
However, as long as the conventional ion exchange method is employed, the exchange of a large amount of copper is not possible in a single run, instead, several repeated runs of exchange are needed.
ZSM-5 containing copper which evinces activity in the direct catalytic decomposition reaction of NO can be prepared by the process described in the existing literature. However, the ion exchange carried out as described in the literature does not yield a sufficient amount of copper ions in a single run and repeated runs are necessary. Therefore, several repeated procedures of ion exchange are needed to obtain a larger amount of exchanged copper and to attain a high activity for the decomposition of NO.
Thus, a need continues to exist for a process by which nitrogen oxides in exhaust gases can be catalytically decomposed in an efficacious manner. A need also continues to exist for a process by which a catalyst having the above-described properties can be prepared in high yield.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide a process for the production of a copper-containing zeolite catalyst which is advantageously used in the decomposition of nitrogen oxides in gases containing the same.
Further, it is an object of this invention to provide a process for the catalytic decomposition of nitrogen oxides.
These objects and others which will become more apparent in view of the following disclosure are provided, in particular, by a copper-containing zeolite which is produced by subjecting a zeolite having the following lattice spacings (d values) as determined by powder X-ray diffraction to ion exchange with copper ions in an aqueous solution containing a water-soluble copper salt and ammonia.
______________________________________lattice spacing relative(d value) strength______________________________________11.1 .+-. 0.3 strong10.0 .+-. 0.3 strong7.4 .+-. 0.2 weak7.1 .+-. 0.2 weak6.3 .+-. 0.2 weak6.04 .+-. 0.2 weak5.56 .+-. 0.1 weak5.01 .+-. 0.1 weak4.60 .+-. 0.08 weak4.25 .+-. 0.08 weak3.85 .+-. 0.07 very strong3.71 .+-. 0.05 strong3.04 .+-. 0.03 weak2.99 .+-. 0.02 weak2.94 .+-. 0.02 weak______________________________________

BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 illustrate the time variation of the rate of conversion of NO in Examples 6 and 10, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to the production of catalysts which are used to remove nitrogen oxides from gases containing the same which are released from industrial plants and automobiles, for example. Also, this invention provides a process for producing catalysts for the direct catalytic decomposition of NO.sub.x as well as a method of use therefor.
The catalyst of the present invention is prepared from a basic material zeolite having the following lattice spacings (d values) as shown in Table 1. The basic material zeolite may be prepared by any known method without restriction.
TABLE 1______________________________________Latticespacing Relative(d value) strength______________________________________11.1 .+-. 0.3 strong10.0 .+-. 0.3 strong7.4 .+-. 0.2 weak7.1 .+-. 0.2 weak6.3 .+-. 0.2 weak6.04 .+-. 0.2 weak5.56 .+-. 0.1 weak5.01 .+-. 0.1 weak4.60 .+-. 0.08 weak4.25 .+-. 0.08 weak3.85 .+-. 0.07 very strong3.71 .+-. 0.05 strong3.04 .+-. 0.03 weak2.99 .+-. 0.02 weak2.94 .+-. 0.02 weak______________________________________
Preferably, the ratio in moles of SiO.sub.2 to Al.sub.2 O.sub.3 of the zeolite to be used in this invention is 15 to 300, more preferably 20 to 200. The basic material zeolite having the lattice spacings (d values) as indicated in Table 1 has almost no activity in decomposing NO.sub.x, if it is used without further treatment.
The copper-containing zeolite of the present invention can be prepared from the zeolite having the lattice spacings (d values) as indicated in Table 1 either by exchanging cations in the zeolite with copper ions in an aqueous solution containing a water-soluble copper salt and ammonia, or by supplying ammonia gas to be adsorbed on zeolites on which cations have been exchanged with copper ions.
Any copper salt may be used so long as it is a water-soluble salt. Salts applicable are, for example, the sulfate, chloride, acetate, nitrate and other salts of copper. Ammonia may be applied in the form of ammonia water, hydrous ammonia compounds, and aqueous solutions containing dissolved ammonia. The ammonia may be added in any amount, but preferably in such a amount that the pH of a slurry containing the zeolite is in the range from 4 to 12. When the pH is less than 4, the exchange of ions hardly occurs because of the low speed of ion exchange. When the pH exceeds 12, impure copper is deposited and therefore the activity of the catalyst in decomposing NO.sub.x is lowered. The concentration of copper ions in the aqueous solution may be set as needed according to the required rate of exchanged copper ions of the zeolite.
The copper ions in the form of Cu.sup.+, Cu.sup.2+, CuOH.sup.+, and [Cu(NH.sub.3).sub.4 ].sup.2+ exchange with cations on the zeolite. A part of the zeolite is also turned into the NH.sub.4 -type due to the presence of a large excess of NH.sub.3 molecules.
In the above method of preparation, a rate of exchanged copper ions greater than 100% and a NH.sub.3 content of more than 0.2 molecule per unit Cu atom can be achieved with the product obtained by a single exchange procedure.
The product produced by ion exchange is washed with water and dried, to obtain the present copper-containing zeolite catalyst.
The copper content of the copper-containing zeolite is preferably larger than 0.03%, more preferably larger than 1% by weight. In general, the larger the copper content of the copper-containing zeolite is, the greater is the decomposition activity for NO.sub.x.
The present copper-containing zeolite catalysts also exhibit high activities as a reductive denitration catalyst for NO.sub.x.
The ratio in moles of SiO.sub.2 to Al.sub.2 O.sub.3 of copper-containing zeolite is substantially the same as that of the original zeolite. Also the crystalline structure of the copper-containing zeolite remains unchanged through the ion exchange treatment and therefore can be characterized by the lattice spacings (d values) indicated in Table 1.
The NH.sub.3 content of the copper-containing zeolite catalyst was determined by the neutralization titration for the analysis of ammonia ("Handbook for Analytical Chemistry", 1971, Maruzen, Tokyo). The procedure used is as follows. First, a solution of NaOH is added to a sample of the catalyst, then NH.sub.3 is liberated by distillation and absorbed in a known excess of a standard solution of acid where the excess of acid is determined by back titration with a standard solution of NaOH.
At present, it is not clear why the copper-containing zeolites prepared according to the present invention exhibit such a high activity in the catalytic decomposition of NO.sub.x, however it is thought that the ammonia molecules captured on the zeolite together with copper ions are liberated in the pretreatment stage of the catalytic decomposition reaction of NO.sub.x, and partially reduce the Cu.sup.2+ into Cu.sup.+ which forms an active site for the catalytic decomposition reaction of NO.sub.x. The facility of the oxidation-reduction process, Cu.sup.+ .revreaction.Cu.sup.2+, is perhaps decisive in maintaining the high activity.
Japanese Laid-Open Patent Application Nos. Sho 54-96500 and Sho 57-36015 disclose that copper, after ion exchange treatment, exists in the form of CuOH.sup.+ and can be changed to Cu.sup.+ at temperatures approximately above 300.degree. C. However, the copper-containing ZSM-5 prepared according to the method of these references exhibit a much lower activity for decompositing NO.sub.x than the copper-containing zeolite catalysts of the present invention.
The copper-containing zeolite catalysts of the present invention may have a higher activity due to the presence of Cu.sup.+ which is formed when the ammonia molecules coordinating to copper ions are liberated in the pretreatment stage. This Cu.sup.+ may be considered to be different in the degree of reduction from the Cu.sup.+ formed via CuOH.sup.+, thus leading to the difference in the activity for decomposing NO.sub.x.
In short, the copper-containing zeolite catalysts prepared by the method of the present invention having a specific crystalline structure are highly active even at low temperatures as a result of the compound effect of structural stability and thermal resistance. The present catalysts are, moreover, free from the influence of oxygen and moisture, and are also stationarily stable.
In the decomposition reaction using the copper-containing zeolite catalysts, time of contact of the gases to be treated with the catalysts is not particularly restricted. In accordance with the components and the concentration of gas to be treated, the best ratio values for moles of SiO.sub.2 to Al.sub.2 O.sub.3 and the rate of exchanged copper ions can be selected. In the combined use of these factors, the temperature of the reaction and time of contact of the gas with the catalyst can be set so that the decomposition activity together with other characteristics of the catalyst can be exhibited to the highest degree.
The temperature at which the copper-containing zeolite catalysts are used as a decomposition catalyst for NO.sub.x is in the range from 200.degree. to 1,000.degree. C., preferably from 300.degree. to 700.degree. C.
The copper-containing zeolite catalysts prepared in the present invention can be used as a catalyst and also as an adsorbent in petroleum chemistry, the purification of petroleum and the prevention of environmental pollution. Among the above applications, these catalysts particularly exhibit excellent activity in decomposing NO.sub.x, when they are used as a catalyst for decomposing and removing NO.sub.x from a gas containing the same.
The copper-containing zeolite catalysts of the present invention may also be supplied in the form of moldings which are shaped using such binders as clay minerals.
In another aspect of this invention, a zeolite molding which is shaped beforehand is submitted to exchange with copper ions in an aqueous solution containing a water-soluble copper salt and ammonia. The dimensions of the moldings are not particularly restricted.
The zeolite moldings as the basic material of the catalysts of this invention are required to exhibit the lattice spacings (d values) indicated in Table 1, but may be prepared by any known method without restriction. The zeolites are granulated using clay as a binder. For example, kaolin, attapulgite, montmorillonite, bentonite, allophane, and sepiolite may be used. Five to thirty parts of these binders are used to 100 parts of zeolite. Otherwise, moldings called binderless moldings, may be prepared directly from the zeolite, itself, without using any binder.
The present invention will now be further illustrated by reference to the following Examples which are provided solely for the purpose of illustration and are not intended to be limitative
EXAMPLE 1
Synthesis of zeolite
Into an overflow type reaction tank of a 2 liter net capacity which is under agitation, aqueous solutions of sodium silicate (SiO.sub.2 ; 153.4 g/1, Na.sub.2 O; 49.9 g/1, Al.sub.2 O.sub.3 ; 0.8 g/1) and aluminum sulfate together with sulfuric acid (Al.sub.2 O.sub.3 ; 38.4 g/1, H.sub.2 SO.sub.4 ; 275.4 g/1) were supplied continuously at a speed of 3.2 1/hr and 0.1 1/hr, respectively. The temperature of the reaction was 30.degree. to 32.degree. C. and the pH of the slurry was 6.4 to 6.6.Solid matter was separated with a centrifuge from the slurry produced, thoroughly washed with water, to obtain a homogeneous and amorphous aluminosilicate compound in fine particles (Na.sub.2 O; 1.72 wt %, Al.sub.2 O.sub.3 ; 2.58 wt %, SiO.sub.2 ; 39.3 wt %, H.sub.2 O; 56.4 wt %). This homogeneous compound (2840 g) and an aqueous solution of NaOH (1.39 wt %, 5160 g) were placed in an autoclave of a 10 liter capacity and the solid matter was allowed to be crystallized at 160.degree. C. under agitation for 72 hrs. The product obtained was separated, washed with water and dried, to obtain zeolite TSZ-821 which is used as a basic material for preparing the copper-containing zeolite catalyst. Chemical analysis revealed the composition to have a molar ratio of oxides on an anhydride basis:
1.05 Na.sub.2 O.multidot.Al.sub.2 O.sub.3 .multidot.23.3 SiO.sub.2
In addition, d values estimated by powder X-ray diffraction patterns were essentially identical with those indicated in Table 1.
Next, using the same procedure as that for the synthesis of TSZ-821, fine particles of homogeneous amorphous compounds of aluminosilicate of different SiO.sub.2 and Al.sub.2 O.sub.3 content were prepared, allowed to crystallize by heating in an aqueous solution of sodium hydroxide under agitation, to obtain zeolites TSZ-841 and TSZ-851 which are basic materials for the preparation of the copper-containing zeolite catalysts. These may be represented by the following formulae in molar ratios of oxides on an anhydride basis:
TSZ-841: 1.41 Na.sub.2 O.multidot.Al.sub.2 O.sub.3 .multidot.40.4 SiO.sub.2
TSZ-851: 1.05 Na.sub.2 O.multidot.Al.sub.2 O.sub.3 .multidot.49.0 SiO.sub.2
The d values of these zeolites determined by the powder X-ray diffraction patterns were essentially identical with those in Table 1.
EXAMPLE 2
Preparation of copper-containing zeolite
TSZ-821 obtained in Example 1 was taken in an amount of 10 g, mixed with a 0.1 mol/1 aqueous solution of copper acetate so as to make the number of copper atoms equal to the number of Al atoms in the zeolite. The mixture was stirred at room temperature, mixed with a 2.5% aqueous NH.sub.3 solution, to make the pH of the slurry 6.0. Then, the slurry was agitated for 12 hrs. at room temperature. The solid matter was separated, thoroughly washed with water, dried at 100.degree. C. for 10 hrs. The copper-containing zeolite catalyst thus obtained was designated as TSZ-821-A. The rate of exchanged copper ions of the copper-containing zeolite catalyst as determined by chemical analysis is indicated in Table 2, where divalent copper was assumed to indicate the rate of exchanged copper ions. In addition, ammonia existing in the copper-containing zeolite catalyst was determined by the neutralization titration, of which result expressed in moles per unit atom of Cu is also found in Table 2.
TABLE 2______________________________________Copper- Rate of Cucontaining exchanged content NH.sub.3zeolite copper (%) (wt %) (NH.sub.2 /Cu)______________________________________TSZ-821-A 124 6.37 0.51______________________________________
EXAMPLE 3
Preparation of copper-containing zeolite catalyst
The TSZ-821 obtained in Example 1 was taken in the amount of 10 g and an aqueous 0.1 mol/1 solution of copper acetate was added so that the number of copper atoms is 0.34 times as many as that of Al atoms in the zeolite. The mixture was stirred at room temperature and mixed with a 2.5% aqueous solution of NH.sub.3 to afford a pH of 10.5 in the resulting slurry. Then agitation was continued at room temperature until the required rate of exchanged copper ions is attained in the zeolite. Solid matter formed was separated, thoroughly washed with water, and dried at 100.degree. C. for 10 hrs. The copper-containing zeolite obtained was named TSZ-821-B. The rate of exchanged copper ions of the copper-containing zeolite catalyst as determined by chemical analysis is shown in Table 3. Divalent copper was assumed on the exchange in determining the rate of exchanged copper ions.
Ammonia existing in the copper-containing zeolite catalyst was determined by the neutralization titration, of which result expressed in moles per unit atom of Cu is also found in Table 3.
Example 4
Preparation of copper-containing zeolite catalyst
The TSZ-821, TSZ-841and TSZ-851 obtained in Example 1 were taken each in the amount of 10 g and an aqueous 0.1 mol/1 solution of copper acetate was added to each so that the number of copper atoms are equal to that of Al atoms in each zeolite. The mixtures were stirred at room temperature and mixed with a 2.5% aqueous solution of NH.sub.3 to afford a pH of 10.5 in the resulting slurry. Then agitation was continued at room temperature until the required rate of exchanged copper ions was attained in the zeolite. Solid matter was separated, thoroughly washed with water, and dried at 100.degree. C. for 10 hrs. The copper-containing zeolites obtained were named TSZ-821-C, TSZ-841-D, and TSZ-851-E, respectively. The rates of exchanged copper ions of the copper-containing zeolites determined by chemical analysis are shown in Table 3. Divalent copper was assumed on exchange in determining the rate of exchanged copper ions.
Ammonia existing in the copper-containing zeolite catalysts was determined by the neutralization titration, of which result expressed in moles per unit atom of Cu is also found in Table 3.
TABLE 3______________________________________Copper- Rate of Cucontaining exchanged content NH.sub.3zeolite copper (%) (wt %) (NH.sub.3 /Cu)______________________________________TSZ-821-B 66 3.43 0.82TSZ-821-C 123 6.12 0.83TSZ-841-D 121 3.61 0.78TSZ-851-E 127 3.29 0.69______________________________________
EXAMPLE 5
Test of the decomposition activity for NO of copper-containing zeolite catalyst
The copper-containing zeolite catalysts prepared in Examples 2, 3 and 4 were press-molded and broken into uniform particles of 42 to 80 mesh. A normal pressure flow-type fixed bed reaction tube was packed with 1 g of each catalyst. Prior to the reaction, the copper-containing zeolite catalysts were pretreated by elevating the temperature to 500.degree. C. at a speed of 5.degree. C./min in a stream of helium and maintaining the temperature for 2 hrs. Helium gas which contained NO in a concentration of 5000 ppm was forced to flow through the packing layer of the copper-containing zeolite catalysts at a flow rate of 15 cc/min to allow reaction. In 50 min of reaction at selected temperatures, the rate of conversion of NO was determined. Results are shown in Table 4.
TABLE 4__________________________________________________________________________Copper- TSZ-821-A TSZ-821-B TSZ-821-C TSZ-841-D TSZ-851-Econtaining Rate of conversion Rate of conversion Rate of conversion Rate of conversion Rate of conversionzeolite of NO (%) of NO (%) of NO (%) of NO (%) of NO (%)__________________________________________________________________________400 97.3 94.0 97.2 94.1 95.8500 100 100 100 100 80.5600 100 100 100 100 60.3__________________________________________________________________________
EXAMPLE 6
Stability of activity of the copper-containing zeolite catalyst
Sustaining ability of the copper-containing zeolite catalyst TSZ-821-C (rate of exchanged copper ions of 123%) to decompose NO was determined. The same apparatus and the same method as in Example 5 were employed and the temperature for reaction 500.degree. C. was selected. Time variation of the rate of conversion is shown in FIG. 1.
COMPARISON EXAMPLE 1
Preparation of zeolite for comparison
The TSZ-821 obtained in Example 1 was taken in the amount of 10 g, mixed with an aqueous 0.1 mol/1 solution of copper acetate so that number of copper atoms is equal to that of Al atoms on the zeolite and stirred for 12 hrs. at room temperature. Solid matter was separated from the slurry, washed with water and dried at 100.degree. C. for 10 hrs. The obtained zeolite for comparison was named TSZ-821-F. The rates of exchanged copper ions on the catalysts for comparison which was determined by chemical analysis is shown in Table 5.
COMPARISON EXAMPLE 2
Preparation of zeolite for comparison
The TSZ-821 obtained in Example 1 was taken in the amount of 10 g, mixed with an aqueous 0.1 mol/1 solution of copper acetate so that number of copper atoms is equal to that of Al atoms in the zeolite, and stirred for 12 hrs. at room temperature. Solid matter was separated from the slurry and washed with water. After repeating the procedure two times, the solid was dried at 100.degree. C. for 10 hrs.
The obtained zeolite for comparison was named TSZ-821-G. The rate of exchanged copper ions on the catalysts for comparison, determined by chemical analysis, is found in Table 5.
COMPARISON EXAMPLE 3
Preparation of zeolite for comparison
The TSZ-821 obtained in Example 1 was taken in the amount of 10 g, mixed with an aqueous 0.1 mol/1 solution of copper(II) chloride so that number of copper atoms is equal to that of Al atoms in the zeolite, and stirred for 12 hrs. at room temperature. Solid matter was separated from the slurry, washed with water and dried at 100.degree. C. for 10 hrs. The obtained zeolite for comparison was named TSZ-821-H. The rates of exchanged copper ions on the catalyst for comparison determined by chemical analysis is shown in Table 5.
COMPARISON EXAMPLE 4
Preparation of zeolite for comparison
The TSZ-821 obtained in Example 1 was taken in the amount of 10g, mixed with an aqueous 0.1 mol/1 solution of copper(II) chloride so that number of copper atoms is equal to that of Al atoms on the zeolite, and stirred for 12 hrs. at room temperature. Solid matter was separated from the slurry and washed with water. After additional 2 time repetition of the procedure, the solid was dried at 100.degree. C. for 10 hrs.
The obtained zeolite for comparison was named TSZ-821-I. The rate of exchanged copper ions on the catalysts for comparison, determined by chemical analysis, is also found in Table 5.
TABLE 5______________________________________Zeolite for Rate of exchanged Copper contentcomparison copper ion (%) (wt %)______________________________________TSZ-821-F 88 4.43TSZ-821-G 103 5.26TSZ-821-H 88 4.50TSZ-821-I 104 5.33______________________________________
COMPARISON EXAMPLE 5
Test of activity for decomposing NO of zeolite for comparison
The rate of conversion of NO was determined according to the method in Example 5 with the zeolites for comparison prepared in Comparison Examples 1, 2, 3 and 4. Results are shown in Table 6.
TABLE 6__________________________________________________________________________ TSZ-821-F TSZ-821-G TSZ-821-H TSZ-821-IZeolite for Rate of conversion Rate of conversion Rate of conversion Rate of conversioncomparison of NO (%) of NO (%) of NO (%) of NO (%)__________________________________________________________________________400 60.0 70.0 61.5 65.0500 55.2 67.5 58.0 59.8600 38.8 52.3 39.0 47.0__________________________________________________________________________
COMPARISON EXAMPLE 6
Preparation of zeolite for comparison
The TSZ-821, TSZ-841 and TSZ-851 obtained in Example 1 were taken in the amount of 10 g each, mixed with an aqueous 0.1 mol/1 solution of copper acetate so that number of copper atoms is equal to that of Al atoms on the zeolites, and stirred for 12 hrs. at room temperature. Solid matter was separated from the slurry and washed with water. This procedure was repeated 3 times and the product was dried at 100.degree. C. for 10 hrs. The obtained zeolites for comparison were named TSZ-821-J, TSZ-841-K and TSZ-851-L, respectively. The rates of exchanged copper ions on the catalysts for comparison which were determined by chemical analysis are shown in Table 7.
TABLE 7______________________________________Zeolite for Rate of exchanged Copper contentcomparison copper ion (%) (wt %)______________________________________TSZ-821-J 112 5.67TSZ-841-K 108 3.31TSZ-851-L 118 3.16______________________________________
COMPARISON EXAMPLE 7
Test of activity for decomposing NO of zeolites for comparison
The rate of conversion of NO was estimated with the zeolites for comparison prepared in Comparison Example 6, according to the method in Example 5. Results are found in Table 8.
TABLE 8______________________________________ TSZ-841-K TSZ-821-K TSZ-851-L Rate of Rate of Rate ofZeolite for conversion conversion conversioncomparison of NO (%) of NO (%) of NO (%)______________________________________400 70.8 37.9 31.0500 69.0 39.3 27.0600 54.9 28.8 17.0______________________________________
COMPARISON EXAMPLE 8
Preparation of zeolite for comparison
The TSZ-821 obtained in Example 1 was taken in the amount of 10 g, mixed with an aqueous 0.10 mol/1 solution of copper(II) chloride. The mixture was stirred for 3 hrs. at a refluxing temperature. Solid matter was separated and washed. After repeating the procedure three times, the product was dried at 100.degree. C. for 10 hrs. The zeolite for comparison thus obtained was named TSZ-821-M. The rate of exchanged copper ions as determined by chemical analysis is shown in Table 9.
TABLE 9______________________________________Zeolite for Rate of exchanged Copper contentcomparison copper ion (%) (wt %)______________________________________TSZ-821-M 167 6.38______________________________________
COMPARISON EXAMPLE 9
Test of activity of decomposing NO of zeolite for comparison
The rate of conversion of NO was estimated by the method described in Example 5 with the zeolite for comparison prepared in Comparison Example 8. Results are shown in Table 10.
TABLE 10______________________________________ TSZ-821-M Rate ofZeolite for comparison conversion of NO______________________________________400 76.8500 70.5600 62.0______________________________________
EXAMPLE 7
Production of zeolite molding
With 100 parts of zeolite prepared in Example 1, 20 parts of bole clay was mixed and thoroughly kneaded with a kneader. The starting mixture thus prepared was formed in cylinders of 1.5 mm diameter with an extrusion molder and the cylindrical moldings were dried at 100.degree. C. for 10 hrs. Baking the above products at 650.degree. C. for 1 hr gave zeolite moldings. Their chemical composition can be expressed by molar ratios of oxides on an anhydride basis as follows:
TSZ-821 molding: 0.78 Na.sub.2 O.multidot.Al.sub.2 O.sub.3 .multidot.16.4 SiO.sub.2
The d values of the TSZ-821 molding as determined by the powder X-ray diffraction pattern were essentially identical with those in Table 1.
EXAMPLE 8
Preparation of copper-containing zeolite molding
The molding of TSZ-821 produced in Example 7 was taken in the amount of 10 g and immersed in an aqueous 0.1 mol/1 solution of copper acetate so that the number of copper atoms is equal to that of Al atoms on the zeolite. The mixture was stirred at room temperature, and mixed with an aqueous 2.5% solution of NH.sub.3 so as to make the pH of the slurry 10.5.
Then stirring continued at room temperature for 12 hrs. Solid matter was separated, thoroughly washed with water, and dried at 100.degree. C. for 10 hr. The copper ion content of the copper-containing zeolite molding (designated as TSZ-821-molding-A) as determined by chemical analysis is shown in Table 11.
TABLE 11______________________________________Copper-containing Copper contentzeolite molding (wt %)______________________________________TSZ-821-molding-A 5.17______________________________________
EXAMPLE 9
Test of activity for decomposing NO of the copper-containing zeolite molding
The copper-containing zeolite molding(TSZ-821-molding-A) prepared in Example 8 was grounded in a mortar to obtain particles of 42 to 80 mesh. Then a normal pressure flow-type fixed bed reaction tube was packed with 1 g of the particles. Prior to the reaction, the copper-containing zeolite molding was heated up to 500.degree. C. with an elevation speed at 5.degree. C./min and the final temperature was maintained for 2 hrs. with passage of helium gas. A helium gas containing 5000 ppm of NO was passed through the layer packed with the copper-containing zeolite molding at a speed of 15 cc/min to allow reaction. In 50 min of the reaction, the rate of conversion of NO was estimated at each temperature of reaction. Results are found in Table 12.
TABLE 12______________________________________Copper-containing TSZ-821-molding-Azeolite molding Conversion rateReaction Temperature (.degree.C.) of NO (%)______________________________________400 100500 100600 100______________________________________
EXAMPLE 10
Stability of activity of the copper-containing zeolite molding
The sustained ability of the present catalysts for decomposing NO was tested using TSZ-821-molding-A containing copper. The same apparatus and the same method as in Example 9 were employed and the reaction was carried out at 500.degree. C. Time variation of the rate of conversion is shown in FIG. 2.
COMPARISON EXAMPLE 10
Preparation of zeolite for comparison
The TSZ-821 molding obtained in Example 7 was taken in the amount of 10 g and mixed with an aqueous 0.1 mol/1 solution of copper(II) chloride so that the number of copper atoms is equal to that of Al atoms in the zeolite, and the mixture was stirred at room temperature. Solid matter was separated from the slurry and washed. After repeating the procedure three times, the solid was dried at 1200.degree. C. for 10 hrs. Copper content of the zeolite for comparison (designated as TSZ-821-molding-B) obtained by the chemical analysis is shown in Table 13.
TABLE 13______________________________________Zeolite for comparison Copper content (wt %)______________________________________TSZ-821-molding-B 5.46______________________________________
COMPARISON EXAMPLE 11
Test of activity for decomposing NO for zeolite for comparison
The rate of conversion of NO was determined with the zeolite for comparison (TSZ-821-molding-B) prepared in Comparison Example 10 by the method in Example 9. Results are found in Table 14.
TABLE 14______________________________________Zeolite for comparison TSZ-821-molding-BReaction Rate of conversionTemperature of NO (%)______________________________________400 44.8500 21.2600 9.5______________________________________
Having now fully described the present invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made to the above descriptions while remaining within the spirit and scope of the present invention.

Number	Date	Country
62-251614	Oct 1987	JPX
62-251615	Oct 1987	JPX
62-251616	Oct 1987	JPX

Number	Name	Date
3755540	Rosback	Aug 1973
4125483	Downing et al.	Nov 1978
4297328	Ritscher et al.	Oct 1981
4837398	Chang et al.	Jun 1989
4962075	Green et al.	Oct 1990

Number	Date	Country
93477	Nov 1983	EPX
107384	May 1984	EPX
136789	Apr 1985	EPX

Copper-containing zeolites and their preparation

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