Systems utilizing non-zeolitic metal-containing molecular sieves having the CHA crystal structure
View Patent ↗Systems for treating exhaust gas incorporating catalysts comprising metal-loaded non-zeolitic molecular sieves having the CHA crystal structure, including Cu-SAPO-34, and methods for preparing 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. An emission treatment system for treatment of an exhaust gas stream comprising NOx and particulate matter, the emission treatment system comprising:
a SCR catalyst substrate containing a catalyst comprising a Cu-loaded non-zeolitic molecular sieve having a CHA crystal structure; and
an ammonia injector or an ammonia-precursor injector positioned upstream of the SCR catalyst substrate for injecting ammonia or an ammonia-precursor, wherein the catalyst is effective to promote the reaction of ammonia with nitrogen oxides to form nitrogen and H 2 O selectively.
2. The emission treatment system of claim 1 , wherein the Cu-loaded non-zeolitic molecular sieve having a CHA crystal structure comprises Cu-SAPO-34.
3. The emission treatment system of claim 2 , wherein the Cu-SAPO-34 contains a secondary metal.
4. The emission treatment system of claim 3 , wherein the secondary metal comprises zirconium.
5. The emission treatment system of claim 2 , wherein the Cu-SAPO-34 contains in the range of about 2 wt-% to 4 wt-% Cu.
6. The emission treatment system of claim 1 , wherein the Cu-loaded non-zeolitic molecular sieve having a CHA crystal structure is combined with a metal containing zeolite SCR catalyst selected from Beta zeolite, zeolite Y, and ZSM-5.
7. The emission treatment system of claim 6 , wherein the Cu-loaded non-zeolitic molecular sieve having a CHA crystal structure comprises Cu-SAPO-34.
8. The emission treatment system of claim 1 , wherein the system comprises an ammonia-precursor injector including mixing station to mix air with aqueous urea and a valve.
9. The emission treatment system of claim 8 , further comprising:
a mixing station for mixing the aqueous urea with air; and
a valve for metering precise amounts of aqueous urea.
10. The emission treatment system of claim 1 , further comprising a second substrate interposed between the ammonia injector or ammonia-precursor injector and the SCR catalyst substrate.
11. The emission treatment system of claim 10 , wherein the second substrate is coated with a SCR catalyst composition.
12. The emission treatment system of claim 10 , wherein the second substrate is selected from a honeycomb flow through substrate, an open cell foam substrate, or a honeycomb wall flow substrate.
13. The emission treatment system of claim 1 , further comprising an oxidation catalyst upstream of the ammonia injector or ammonia-precursor injector.
14. An emission treatment system for treatment of an exhaust gas stream comprising NOx and particulate matter, the emission treatment system comprising:
a SCR catalyst substrate containing a catalyst comprising a Cu-loaded non-zeolitic molecular sieve having a CHA crystal structure and 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 low temperature; and
an ammonia injector or an ammonia-precursor injector positioned upstream of the SCR catalyst substrate for injecting ammonia or an ammonia-precursor, wherein the catalyst is effective to promote the reaction of ammonia with nitrogen oxides to form nitrogen and H 2 O selectively.