Catalyst for oxidising ammonia

Abstract

A catalyst for oxidising ammonia comprises a selective catalytic reduction (SCR) catalyst and a composite heterogeneous extruded honeycomb having longitudinally extending parallel channels, which channels being defined in part by channel walls having a total longitudinal length, wherein the channel walls comprise a pore structure including a periodic arrangement of porous cells embedded in an inorganic matrix component, at least some of which porous cells are defined at least in part by an active interface layer of a catalytically active material comprising a precious metal supported on particles of a support material.

The invention claimed is: 
     
       1. A catalyst article for oxidizing ammonia, the catalyst article comprising a selective catalytic reduction (SCR) catalyst and a composite heterogeneous extruded honeycomb having longitudinally extending parallel channels, which channels being defined in part by channel walls having a total longitudinal length, wherein the channel walls comprise a cellular ceramic and open pore structure including a periodic arrangement of porous cells, each porous cell defined by a cell wall comprising a catalytically active interface layer, with adjacent catalytically active interface layers being joined to one another to form the cellular ceramic and open-pore structure, wherein the cellular ceramic and open-pore structure is embedded in an inorganic matrix component, wherein
 at least some of which porous cells are defined at least in part by a cell wall comprising a catalytically active interface layer of a catalytically active material comprising a precious metal supported on particles of a support material, and 
 wherein the inorganic matrix material component is at least substantially free of the catalytically active material of the catalytically active interface layers. 
 
     
     
       2. The catalyst article of  claim 1 , wherein the porous cells in the periodic arrangement are interconnected by windows between cells, which windows defining macropores. 
     
     
       3. The catalyst article of  claim 1 , wherein the porous cells in the periodic arrangement are substantially not interconnected by windows between cells. 
     
     
       4. The catalyst article of  claim 1 , wherein the support material for supporting the precious metal comprises ceria, titania, a crystalline molecular sieve, alumina, zirconia, a mixed oxide of ceria and zirconia or a mixture of any two or more thereof. 
     
     
       5. The catalyst article of  claim 1 , wherein the supported precious metal is a platinum group metal, gold or silver. 
     
     
       6. The catalyst article of  claim 5 , wherein the platinum group metal is platinum, palladium, or both platinum and palladium. 
     
     
       7. The catalyst article of  claim 1 , further comprising an wherein the SCR catalyst provided in a washcoat coated on at least part of a total length of the channel walls. 
     
     
       8. The catalyst article of  claim 1 , wherein the composite heterogeneous extruded honeycomb comprises a population of the porous cells embedded in the matrix, wherein the catalytically active interface layer comprise a mixture of an the SCR catalyst and precious metal supported on a the support material. 
     
     
       9. The catalyst article of  claim 1 , wherein the porous cells embedded in the inorganic matrix comprises
 (a) a first fraction of porous cells, wherein the catalytically active interface layer is a precious metal supported on a the support material, the support material comprising ceramically bonded particles of the support material joined to one another via sinter bridges; and 
 (b) a second fraction of porous cells wherein the catalytically active interface layer comprises an the SCR catalyst. 
 
     
     
       10. The catalyst article of  claim 1 , wherein the SCR catalyst is a crystalline molecular sieve supporting a base metal promoter or vanadium compound supported on a the support material comprising titanium. 
     
     
       11. The catalyst article of  claim 10 , wherein the crystalline molecular sieve is an aluminosilicate zeolite and the supported base metal promoter is copper, iron or both copper and iron. 
     
     
       12. The catalyst article of  claim 11 , wherein the aluminosilicate zeolite has the MFI, BEA, CHA, AEI, FAU, AFX or ERI framework structure. 
     
     
       13. The catalyst article of  claim 1 , wherein the inorganic matrix component comprises an alumina phase, a silicate phase, an inorganic fibre phase or a combination of any two or more thereof. 
     
     
       14. The catalyst article of  claim 13 , wherein the silicate phase comprises a pillared clay and/or a diatomaceous earth. 
     
     
       15. The catalyst article of  claim 1 , wherein the inorganic matrix component comprises 5 to 50% by weight of the catalyst. 
     
     
       16. The catalyst article of  claim 1 , wherein the extruded honeycomb is in the form of a flow-through monolith. 
     
     
       17. The catalyst article of  claim 1 , wherein the extruded honeycomb is in the form of a wall-flow filter. 
     
     
       18. The catalyst article of  claim 1 , wherein the porosity of the composite heterogeneous extruded honeycomb is from 40 to 80%. 
     
     
       19. An exhaust system for an electrical power station or an internal combustion engine, which system comprising an inlet end and an outlet end, the catalyst article of  claim 1 , and a device for introducing ammonia or a precursor of ammonia into an exhaust gas flowing in the exhaust system in the direction of the inlet end from the outlet end, wherein a the catalyst article for oxidizing ammonia of  claim 1  is located downstream of the device for introducing ammonia or a precursor of ammonia into an exhaust gas flowing in the exhaust system. 
     
     
       20. The exhaust system of  claim 19 , further comprising a substrate monolith comprising an a further SCR catalyst disposed between the device for introducing ammonia or a precursor of ammonia into an exhaust gas flowing in the exhaust system and the catalyst article for oxidizing ammonia. 
     
     
       21. A vehicle comprising an internal combustion engine and an exhaust system of  claim 19 . 
     
     
       22. The catalyst article of  claim 1 , wherein the catalytically active interface layer is substantially free of the inorganic matrix material component. 
     
     
       23. The catalyst article of  claim 1 , wherein the inorganic matrix material component is at least substantially free of any catalytically active material layer. 
     
     
       24. The catalyst article of  claim 1 , wherein the inorganic matrix material component comprises a second catalytically active material that is different than the catalytically active material in the the catalytically active material layer.