Catalysts, Systems and Methods Utilizing Non-Zeolitic Metal-Containing Molecular Sieves Having the CHA Crystal Structure

Abstract

Catalysts comprising metal-loaded non-zeolitic molecular sieves having the CHA crystal structure, including Cu-SAPO-34, methods for preparing such catalysts, and systems and methods for treating exhaust gas incorporating such catalysts are disclosed. The catalysts can be used to remove nitrogen oxides from a gaseous medium across a broad temperature range and exhibit hydrothermal stability at high reaction temperatures.

1 . A catalyst comprising:
 a Cu-loaded non-zeolitic molecular sieve having the CHA crystal structure having a Cu loading so that the catalyst is effective to selectively reduce nitrogen oxides with ammonia in the presence of oxygen in an exhaust gas stream at 200° C. when the catalyst has been deposited on a honeycomb substrate having a cell density of 400 cpsi at a loading between 2 and 2.5 g/in 3  and tested at a space velocity of 80,000 hr −1  where the feed stream comprises a mixture of 10% O 2 , 5% H 2 O, 500 ppm NO and 500 ppm NH 3  to provide at least 80% NOx conversion.   
   
   
       2 . The catalyst of  claim 1 , wherein the non-zeolitic molecular sieve comprises Cu-SAPO-34 and the catalyst is effective to provide at least about 85% NOx conversion in the exhaust gas stream at 200° C. 
   
   
       3 . The catalyst of  claim 2 , wherein the catalyst is effective to provide at least about 90% NOx conversion in the exhaust gas stream at 200° C. 
   
   
       4 . The catalyst of  claim 1 , wherein the Cu-SAPO-34 material, upon hydrothermal aging in 10% steam at 850° C. and 6 hours, retains at least 85% on a percentage basis of the NOx conversion at 200° C. 
   
   
       5 . The catalyst of  claim 2 , wherein the Cu-SAPO-34 material, upon hydrothermal aging in 10% steam at 900° C. and 1 hour, retains at least 90% of the NOx conversion on a percentage basis at 200° C. 
   
   
       6 . The catalyst of  claim 3 , wherein the Cu-SAPO-34 material, upon hydrothermal aging in 10% steam at 900° C. and 1 hour, retains at least 95% of the NOx conversion on a percentage basis at 200° C. 
   
   
       7 . The catalyst of  claim 2 , wherein the catalyst is effective to reduce NOx so that that ratio of NOx to N 2 O in the gas stream after passing through the catalyst is greater than 2.5 
   
   
       8 . The catalyst of  claim 2 , wherein the catalyst is effective to reduce NOx so that that ratio of NOx to N 2 O in the gas stream after passing through the catalyst is greater than 5. 
   
   
       9 . The catalyst of  claim 2 , wherein the catalyst is effective to make less than 10 ppm N 2 O over the temperature range of 200° C. to 450° C. 
   
   
       10 . The catalyst of  claim 2 , wherein the catalyst is effective to make less than 5 ppm N 2 O over the temperature range of 200° C. to 450° C. 
   
   
       11 . The catalyst of  claim 2 , wherein the Cu-SAPO-34 contains a secondary metal. 
   
   
       12 . The catalyst of  claim 11 , wherein the secondary metal comprises zirconium. 
   
   
       13 . The catalyst of  claim 2 , the Cu-SAPO-34 contains in the range of about 2 weight percent and 4 weight percent Cu. 
   
   
       14 . A catalyst composite, wherein the catalyst of  claim 2  is deposited on a honeycomb substrate as a washcoat at a loading in the range of about 0.5 g/in 3  and 3.5 g/in 3 . 
   
   
       15 . The catalyst composite of  claim 14 , wherein the honeycomb substrate comprises a wall flow substrate. 
   
   
       16 . The catalyst composite of  claim 14 , wherein the honeycomb substrate comprises a flow through substrate. 
   
   
       17 . The catalyst composite of  claim 16 , wherein at least a portion of the flow through substrate is coated with a washcoat containing Pt and a metal-loaded non-zeolitic molecular sieve to oxidize ammonia in the exhaust gas stream. 
   
   
       18 . The catalyst composite of  claim 15 , wherein at least a portion of the wall flow substrate is coated with a washcoat containing Pt and a metal-loaded non-zeolitic molecular sieve to oxidize ammonia in the exhaust gas stream. 
   
   
       19 . An exhaust gas treatment system comprising an oxidation catalyst and the catalyst composite of  claim 15 . 
   
   
       20 . An exhaust gas treatment system comprising an oxidation catalyst and the catalyst composite of  claim 16 . 
   
   
       21 . The catalyst of  claim 2 , wherein the Cu-SAPO-34 material is combined with a metal containing zeolitic SCR catalyst. 
   
   
       22 . The catalyst of  claim 3 , wherein the Cu-SAPO-34 material is combined with a metal containing zeolitic SCR catalyst. 
   
   
       23 . A process for the reduction of oxides of nitrogen contained in a gas stream in the presence of oxygen comprising contacting the gas stream with a Cu-loaded non-zeolitic molecular sieve having the CHA crystal structure and having a Cu loading so that the catalyst is effective to selectively reduce nitrogen oxides with ammonia in the presence of oxygen in an exhaust gas stream at 200° C. when the catalyst has been deposited on a honeycomb substrate having a cell density of 400 cpsi at a loading between about 2 and 2.5 g/in 3  and tested at a space velocity of 80,000 hr −1  where the feed stream comprise a mixture of 10% O 2 , 5% H 2 O, 500 ppm NO and 500 ppm NH 3  to provide at least 80% NOx conversion. 
   
   
       24 . An emission treatment system for treatment of an exhaust stream comprising NOx and particulate matter, the emission treatment system comprising: an oxidation catalyst and a Cu-loaded non-zeolitic molecular sieve having a Cu loading so that the catalyst is effective to selectively reduce nitrogen oxides with ammonia in the presence of oxygen in an exhaust gas stream at 200° C. when the catalyst has been deposited on a honeycomb substrate having a cell density of 400 cpsi at target a loading between about 2 and 2.5 g/in 3  and tested at a space velocity of 80,000 hr −1  where the feed stream is a mixture of 10% O 2 , 5% H 2 O, 500 ppm NO and 500 ppm NH 3  to provide at least 80% NOx conversion. 
   
   
       25 . A process for synthesizing Cu-SAPO-34 comprising:
 mixing a neutral, nitrogen-containing organic template, an alumina source, a silica source and a phosphorous source in a gel mixture;   heating the gel to less than about 200° C. for at least about 12 hours to form crystalline SAPO-34;   filtering and washing the crystalline SAPO-34;   calcining the crystalline SAPO-34; and   ion exchanging the crystalline SAPO-34 with a copper salt to provide Cu-SAPO-34.   
   
   
       26 . The process of  claim 25 , wherein the template comprises morpholine and the heating temperature is less than about 185° C. and the heating time is at least about 24 hours. 
   
   
       27 . The process of  claim 26 , wherein the copper salt comprises copper acetate. 
   
   
       28 . The process of  claim 25 , wherein after ion exchanging the crystalline SAPO-34 with a copper salt to provide Cu-SAPO-34, Cu-SAPO-34 is washed to provide a filtrate having a conductivity less than about 600 μScm −1 . 
   
   
       29 . The process of  claim 25 , wherein the Cu-SAPO-34 is washed to provide a filtrate having a conductivity less than about 400 μScm −1 . 
   
   
       30 . The process of  claim 25 , wherein the Cu-SAPO-34 is washed to provide a filtrate having a conductivity less than about 200 μScm −1  and less than about 200 μScm −1 , 
   
   
       31 . The process of  claim 28 , further comprising calcining the washed Cu-SAPO-34 material at a temperature less than about 600° C. 
   
   
       32 . The process of  claim 25 , wherein the crystalline material has a crystal size having 90% of the crystals less than 20 microns. 
   
   
       33 . The process of  claim 25 , wherein the crystalline material has a crystal size having 90% of the crystals less than 15 microns. 
   
   
       34 . A catalyst made by the method of  claim 25  having a Cu loading so that the catalyst is effective to selectively reduce nitrogen oxides with ammonia in the presence of oxygen in an exhaust gas stream at 200° C. when the catalyst has been deposited on a honeycomb substrate having a cell density of 400 cpsi at target a loading between about 2 and 2.5 g/in 3  and tested at a space velocity of 80,000 hr −1  where the feed stream comprise a mixture of 10% O 2 , 5% H 2 O, 500 ppm NO and 500 ppm NH 3  to provide at least 80% NOx conversion. 
   
   
       35 . A catalyst composite, wherein the catalyst of  claim 25  is deposited on a honeycomb substrate as a washcoat at a loading in the range of about 0.5 g/in 3  and 3.5 g/in 3 . 
   
   
       36 . The catalyst of  claim 35 , wherein the honeycomb substrate comprises a wall flow substrate. 
   
   
       37 . The catalyst of  claim 35 , wherein the honeycomb substrate comprises a flow through substrate.