Stable small-pore zeolites
The present invention provides crystalline aluminosilicate zeolites having a maximum pore size of eight tetrahedral atoms, wherein the zeolite has a total proton content of less than 2 mmol per gram. The zeolite may comprise 0.1 to 10 wt.-% of at least one transition metal, calculated as the respective oxide and based on the total weight of the zeolite. It may furthermore comprise at least one alkali or alkaline earth metal in a concentration of 0 to 2 wt.-%, calculated as the respective metal and based on the total weight of the zeolite. The zeolites may be used for the removal of NOx from automotive combustion exhaust gases.
1. A crystalline aluminosilicate zeolite having a maximum pore size of eight tetrahedral atoms, wherein the zeolite has a total proton content of less than 2 mmol per gram, and wherein the zeolite framework type material is chosen from AEI, CHA, LEV, ETL, ESV, and DDR.
2. The crystalline aluminosilicate zeolite according to claim 1 , wherein the SAR is between 5 and 50.
3. The crystalline aluminosilicate zeolite according to claim 1 , wherein the zeolite comprises at least one transition metal in a concentration of 0.1 to 10 wt.-%, calculated as the respective oxides and based on the total weight of the zeolite.
4. The crystalline aluminosilicate zeolite according to claim 3 , wherein the at least one transition metal is chosen from copper, iron, and mixtures thereof.
5. The crystalline aluminosilicate zeolite according to claim 3 , wherein the at least one transition metal is introduced into the zeolite during the synthesis of said zeolite by an organic structure-directing agent comprising said at least one transition metal.
6. The crystalline aluminosilicate zeolite according to claim 1 , wherein the zeolite comprises at least one alkali and/or alkaline earth metal in a concentration of 0 to 2 wt.-%, calculated as the respective metals and based on the total weight of the zeolite.
7. The crystalline aluminosilicate zeolite according to claim 6 , wherein the at least one alkali or alkaline earth metal is selected from sodium, potassium, and mixtures thereof.
8. The crystalline aluminosilicate zeolite according to claim 1 , wherein the transition metal to aluminium atomic ratio is in the range of between 0.003 to 0.5.
9. The crystalline aluminosilicate zeolite according to claim 1 , wherein the mean crystal size is between 0.3 to 7 μm.
10. The crystalline aluminosilicate zeolite according to claim 1 , wherein the zeolite is present in the form of a washcoat on a carrier substrate.
11. A process for the removal of NOx from automotive combustion exhaust gases wherein a zeolite according to claim 1 is used as the SCR catalytically active material for the conversion of NOx.
12. A catalysed substrate monolith comprising an SCR catalytically active material for the conversion of NOx for use in treating automotive combustion exhaust gases, wherein said SCR catalytically active material for the conversion of NOx is a zeolite according to claim 1 .
13. A catalysed substrate monolith according to claim 12 , wherein the zeolite is present in the form of a washcoat on a carrier substrate.
14. The catalysed substrate monolith according to claim 13 , wherein the carrier substrate is a flow-through substrate or a wall-flow filter.
15. A catalysed substrate monolith according to claim 12 , wherein the catalysed substrate monolith is an extruded catalysed substrate monolith.
16. An exhaust gas purification system comprising a particulate filter coated with an SCR catalyst, wherein the SCR catalytically active material is a crystalline aluminosilicate zeolite according to claim 1 .
17. An exhaust gas purification system comprising a PNA catalyst, wherein the PNA catalytically active material comprises a crystalline aluminosilicate zeolite according to claim 1 and at least one platinum group metal selected from ruthenium, rhodium, palladium, osmium, iridium, platinum, and mixtures thereof.
18. An exhaust gas purification system according to claim 17 , wherein the platinum group metal is palladium, and the palladium is present in a concentration of 0.5 to 5 wt.-%, calculated as Pd and based on the total weight of the zeolite.
19. An exhaust gas purification system comprising an ASC catalyst, wherein the ASC catalytically active material comprises a crystalline aluminosilicate zeolite according to claim 1 and at least one platinum group metal selected from ruthenium, rhodium, palladium, osmium, iridium, platinum, and mixtures thereof.
20. An exhaust gas purification system according to claim 19 , wherein the platinum group metal is platinum, and the platinum is added in the form of a precursor salt to a washcoat slurry and applied to the carrier monolith, and the platinum is present in a concentration of 0.1 to 1 wt.-%, calculated as Pt and based on the total weight of the washcoat loading.