Method for producing metal exchanged zeolites by solid-state ion exchange at low temperatures

Abstract

Method for the preparation of a metal-exchanged zeolites or mixtures of metal-exchanged zeolites, such as Cu-SSZ-13, Cu-ZSM-5, Cu-beta, or Fe-beta, comprising the steps of providing a dry mixture of a) one or more microporous zeotype materials that exhibit ion exchange capacity and b) one or more metal compounds; heating the mixture in a gaseous atmosphere containing ammonia to a temperature lower than 300? C. for a time sufficient to initiate and perform a solid state ion exchange of ions of the metal compound and ions of the zeolite material; and obtaining the metal-exchanged zeolite material.

Claims

1. Method for the preparation of a metal-exchanged zeolite material or mixtures of metal-exchanged zeolites materials comprising the steps of providing a dry mixture containing a) one or more zeolites starting materials that exhibit ion exchange capacity and b) one or more metal compounds; heating the mixture in a gaseous atmosphere containing ammonia at a temperature of between 150? C. and 250? C. to perform a solid state ion exchange of ions of the metal compound and ions of the one or more zeolites; and obtaining the metal-exchanged zeolite material or the mixture of metal-exchanged zeolite materials, wherein the metal compound is Cu (I) oxide.

2. Method according to claim 1, wherein the one or more zeolite starting materials have the framework code of AEI, AFX, CHA, KFI, LTA, IMF, ITH, MEL, MFI, SZR, TUN, *BEA, BEC, FAU, FER, MOR, LEV.

3. Method according to claim 1, wherein the one or more zeolite starting materials are selected from the group consisting of ZSM-5, zeolite Y, beta zeolite, SSZ-13, SSZ-39, SSZ-62, and Chabazite.

4. Method according to claim 1, wherein the one or more zeolite starting materials are in the H.sup.+ or NH.sub.4.sup.+ form.

5. Method according to claim 1, wherein the one or more zeolite starting materials contain an organic structure directing agent.

6. Method according to claim 1, wherein the one or more metal compounds are selected from the group of metal oxides, metal nitrates and phosphates, sulfates, oxalates, acetates or combinations thereof.

7. Method according to claim 1, wherein the content of ammonia in the atmosphere is between 1 and 5000 vol. ppm.

8. Method according to claim 1, wherein the content of oxygen in the atmosphere is 10% or lower.

9. Method according to claim 1, wherein the content of water in the atmosphere is 5 vol. % water or less.

10. Method according to claim 1, wherein the mixture of one or more zeolites starting materials that exhibit ion exchange capacity and one or more metal compounds is heated in the gaseous atmosphere containing ammonia at a temperature of between 150? C. and 250? C.

11. A metal-exchanged zeolite or mixtures of metal-exchanged zeolites obtained by a method according to claim 1.

12. A method for the removal of nitrogen oxides from exhaust gas by selective catalytic reduction with a reductant, comprising contacting the exhaust gas with a catalyst comprising a metal-exchanged zeolite or mixtures of metal-exchanged zeolites obtained by a method according to claim 1.

13. A method according to claim 12, wherein the reductant is ammonia or a precursor thereof.

14. A method according to claim 12, wherein the reductant comprises hydrocarbons.

Description

EXAMPLE 1

(1) This example shows that an active catalyst for SCR is obtained by the method of the invention. A catalyst was prepared by mixing CuO and H-ZSM-5 zeolite to a content of 12.5 wt % CuO. A sample of the catalyst was put in a quartz-U tube reactor, and heated to 250? C. for 10 h in a gas atmosphere containing 500 ppm NH.sub.3 in nitrogen. After heating, the catalyst was cooled down to 200? C. and exposed to a gas mixture of 500 ppm NO, 533 ppm NH.sub.3, 5% H.sub.2O, 10% O.sub.2 in N.sub.2, and the conversion of NO was measured at a space velocity of 2700 Nl/g cat h, as a record for the material's SCR activity.

(2) The conversion of NO measured after a treatment of a mixture of CuO and H-ZSM-5 in NH.sub.3 at 250? C. is 36.0%. For comparison, the NOx conversion, measured under the same conditions, over the untreated mixture of CuO and H-ZSM-5 is 1.4%, which indicates that the presence of gaseous NH.sub.3 is essential for producing active catalysts for SCR below 300? C.

EXAMPLE 2

(3) This example shows that it is advantageous to avoid the presence of oxygen and water under the exposure to ammonia. A catalyst sample was prepared as described in Example 1. A sample of the catalyst was put in a quartz-U tube reactor, and heated to 250? C. for 10 h in a gas atmosphere containing 500 ppm NH.sub.3, and also containing 10% oxygen or both 10% oxygen and 5% water. After heating, the catalyst was cooled down to 200? C. and exposed to a gas mixture of 500 ppm NO, 533 ppm NH.sub.3, 5% H.sub.2O, 10% O.sub.2 in N.sub.2, and the conversion of NO was measured at a space velocity of 2700 Nl/g cat h, as a record for the material's SCR activity.

(4) In the case the mixture of CuO and H-ZSM-5 was treated in a gas atmosphere containing NH.sub.3 and O.sub.2, the conversion was 10.6%; in the case the treatment gas atmosphere contained both O.sub.2 and H.sub.2O, the conversion was 2.0%.

EXAMPLE 3

(5) This example shows that an active catalyst for SCR can be prepared below 300? C. by the method of the invention using Cu.sub.2O. A dry mixture of 10 wt. % Cu.sub.2O and a H-ZSM-5 zeolite was prepared by grinding in a mortar. A sample of this mixture was placed in a quartz U-tube reactor, and heated to a predetermined temperature between 100 and 250? C. in nitrogen. After reaching the desired temperature, 500 ppm NH.sub.3 was added to the gas stream for 5 hours. After this treatment the catalytic activity of the resulting material was determined by cooling to 160? C. in nitrogen, and exposing the powder mixture to a gas atmosphere consisting of 500 ppm NO, 533 ppm NH.sub.3, 5% H.sub.2O, 10% O.sub.2 in N.sub.2, and the NOx conversion was measured at a space velocity of 2700 Nl/g cat h, as a record for the material's SCR activity. Then, the reaction temperature was increased to 180 and 200? C. and at each temperature the NOx conversion was determined under the same conditions.

(6) The NOx conversion in the SCR reaction over the metal exchanged zeolite prepared at 100, 150, 200 and 250? C. respectively in 500 ppm NH.sub.3 is given in Table 1.

(7) TABLE-US-00001 TABLE 1 NOx conversion over Cu.sub.2O + H-ZSM-5 mixtures after treatment in NH.sub.3 for 5 h at various temperatures Pretreatment NOx conv. @ NOx conv. @ NOx conv. @ temperature 160? C. (%) 180? C. (%) 200? C. (%) 100 0.8 1.9 6.8 150 1.9 3.9 10.9 200 4.3 6.9 14.7 250 12.6 27.7 58.6