Catalyst binders for filter substrates
Provided is a catalyst washcoat comprising (i) a molecular sieve loaded with about 1 to about 10 weight percent of at least non-aluminum promoter metal (wherein the promoter metal weight percent is based on the weight of the molecular sieve); and (ii) about 1 to about 30 weight percent of a binder having a d90 particle size of less than 10 microns (wherein the binder weight percent is based on the total weight of the washcoat). In another aspect of the invention, the catalyst washcoat is applied to a wall-flow filter to form a catalyst article. In another aspect of the invention the catalyst article is part of an exhaust gas treatment system. And in yet another aspect of the invention, provided is a method for treating exhaust gas using the catalyst article.
1. A catalytic article:
a. a honeycomb wall-flow filter having porous walls;
b. a catalyst washcoat disposed on and/or within at least a portion of the porous walls,
wherein the catalyst washcoat comprises (i) a molecular sieve having about 1 to about 10 weight percent of at least one non-aluminum promoter metal, based on the total weight of the molecular sieve; and (ii) about 1 to about 30 weight percent of a binder having a d90 particle size of less than 10 microns, based on the total weight of the washcoat,
wherein said molecular sieve is an aluminosilicate having a framework selected from the group consisting of CHA, AEI, AFX, AFT, ERI, LEV, or KFI and said at least one non-aluminum promoter metal is selected from the group consisting of Cu, Fe, V, Ce, Pt, Pd, Ru, Rh, and Ni, wherein the promoter is useful for catalytically reducing undesirables in the automotive exhaust gas, and
the particle size distribution of the binder has a variance about the mean of one or less.
2. The catalyst article of claim 1 , wherein the d90 particle size is less than 5 microns.
3. The catalyst article of claim 1 , wherein the d90 particle size is greater than 1 micron.
4. The catalyst article of claim 1 , wherein the binder is selected from the group consisting alumina, silica, ceria, titania, zirconia, or combinations of two or more of these.
5. The catalyst article of claim 1 , wherein the binder is alumina.
6. The catalyst article of claim 5 , wherein the alumina is selected from gamma-alumina and theta alumina.
7. The catalyst article of claim 1 , wherein the honeycomb wall-flow filter is a ceramic monolith.
8. The catalyst article of claim 1 , wherein the filter is constructed of aluminum titanate, cordierite, silicon carbide, silicon nitride, zirconia, mullite, alumina-silica-magnesia, zirconium silicate, ceramic fiber composite, wherein the filter is passivated or unpassivated.
9. The catalyst article of claim 1 , wherein the molecular sieve has a silica-to-alumina ratio (SAR) of about 10 to about 50.
10. The catalyst article of claim 9 , wherein the framework is AEI.
11. The catalyst article of claim 10 , wherein the SAR is about 10 to about 20.
12. The catalyst article of claim 1 , wherein the promoter metal is Cu, Fe or Pd.
13. The catalyst article of claim 1 , wherein the binder has:
(a) a mean crystalline size of about 5 to 150 nm and/or
(b) a mean disperse particle size of about 15 microns to about 500 nm, and/or
(c) a mean dispersed particle size with a relative standard deviation of not more than 50%.