Copper CHA Zeolite Catalysts
Zeolite catalysts and systems and methods for preparing and using zeolite catalysts having the CHA crystal structure are disclosed. The catalysts can be used to remove nitrogen oxides from a gaseous medium across a broad temperature range and exhibit hydrothermal stable at high reaction temperatures. The zeolite catalysts include a zeolite carrier having a silica to alumina ratio from about 15:1 to about 256:1 and a copper to alumina ratio from about 0.25:1 to about 1:1.
1 . A catalyst article comprising a honeycomb wall-flow filter substrate having an SCR catalyst composition coated on the wall flow filter comprising a CuCHA zeolite catalyst having a mole ratio of silica to alumina greater than about 15 and an atomic ratio of copper to aluminum exceeding about 0.25, the SCR catalyst favoring reduction of nitrogen oxides and an ammonia oxidation catalyst coated on the wall flow filter, the ammonia oxidation catalyst favoring the oxidation of ammonia and comprising a CuCHA zeolite catalyst having a mole ratio of silica to alumina greater than about 15 and an atomic ratio of copper to aluminum exceeding about 0.25.
2 . The catalyst article of claim 1 , wherein the ammonia oxidation catalyst comprises a platinum group metal component.
3 . The catalyst article of claim 2 , wherein the platinum group metal component comprises Pt.
4 . The catalyst article of claim 3 , wherein the platinum content is between 0.02% and 1.0% by weight of the catalyst, and the platinum loading is from about 0.5 to about 5 g/in 3 .
5 . The catalyst article of claim 3 , wherein at least a portion of the wall-flow filter substrate is coated with Pt and CuCHA adapted to oxidize ammonia in the exhaust gas stream.
6 . The catalyst article of claim 1 , wherein the ammonia oxidation catalyst comprises SSZ-13 with at least a portion of a platinum group metal component on the washcoat.
7 . The catalyst article of claim 1 , wherein the wherein the wall flow filter substrate comprises a ceramic.
8 . The catalyst article of claim 7 , wherein the ceramic comprises cordierite.
9 . The catalyst article of claim 8 , wherein the ceramic comprises silicon nitride.
10 . A staged catalyst with a first catalyst zone comprising a first SCR catalyst on a filter and a second downstream catalyst zone comprising a second SCR catalyst on a substrate, wherein the first SCR catalyst is sufficient to handle high temperature selective catalytic reduction and the second catalyst zone sufficient to handle lower temperature selective catalytic reduction.
11 . The staged catalyst of claim 10 , wherein the first SCR catalyst comprises a CuCHA zeolite catalyst having a mole ratio of silica to alumina greater than about 15 and an atomic ratio of copper to aluminum exceeding about 0.25.
12 . The staged catalyst of claim 11 , wherein the second SCR catalyst comprises a CuCHA zeolite catalyst having a mole ratio of silica to alumina greater than about 15 and an atomic ratio of copper to aluminum exceeding about 0.25.
13 . The staged catalyst of claim 10 , wherein the second catalyst zone comprises a platinum group metal.
14 . The staged catalyst of claim 10 , wherein the zones are on a single substrate.
15 . The staged catalyst of claim 10 , wherein the zones are on a separate honeycomb substrate.
16 . The staged catalyst of claim 13 , wherein the platinum group metal comprises Pt.
17 . The staged catalyst of claim 16 , wherein the platinum content is between 0.02% and 1.0% by weight of the second SCR catalyst, and the platinum loading is from about 0.5 to about 5 g/in 3 .