Catalyst for reducing ammonia emissions
The present invention relates to a composition comprising platinum supported on titanium oxide, the platinum particles having an average particle diameter of 50-200 nm. The composition has a surprisingly low light-off temperature for the ammonia oxidation and a high selectivity for oxidation to N2.
1 . Composition comprising platinum in the form of platinum particles supported on metal oxide A, characterized in that the platinum particles have an average particle diameter of 50-200 nm, wherein metal oxide A is titanium oxide.
2 . Composition according to claim 1 , characterized in that the platinum particles have an average particle diameter of 80-120 nm.
3 . Composition according to claim 1 , characterized in that the composition contains no further precious metal other than platinum.
4 . Composition according to claim 1 , characterized in that the titanium oxide comprises the crystalline phases anatase and rutile, and the anatase to rutile ratio is greater than 9:1.
5 . Composition according to claim 1 , characterized in that the platinum loading is 0.5-20% by weight based on the metal oxide A.
6 . Composition according to claim 1 , characterized in that the platinum loading is 3-8% by weight based on the metal oxide A.
7 . Composition according to claim 1 , characterized in that the metal oxide A contains silicon oxide, wherein the proportion of silicon oxide in the metal oxide A is 1 to 10% by weight.
8 . Composition, characterized in that it comprises a composition according to claim 1 and metal oxide B, wherein metal oxide B equals metal oxide A.
9 . Method for producing a composition according to claim 1 , characterized in that the platinum is deposited from a solution on the metal oxide A and the composition is subjected to a thermal treatment at 700° C. to 900° C. after drying.
10 . Catalyst comprising a composition according to claim 1 , characterized in that the composition is applied to a carrier substrate of length L.
11 . Catalyst according to claim 10 , characterized in that the composition is applied to a carrier substrate over at least 80% of the entire length L.
12 . Catalyst according to claim 10 , characterized in that the composition is applied to a carrier substrate over a length of 10% to 80% of the carrier substrate length L.
13 . Catalyst according to claim 10 , characterized in that the composition is applied to a carrier substrate together with another catalytically active composition that is active for SCR reaction.
14 . Catalyst according to claim 10 , characterized in that the composition and another catalytically active composition are arranged in different zones and/or layers.
15 . Catalyst according to claim 10 , characterized in that the carrier substrate is a ceramic or metallic substrate.
16 . Catalyst according to claim 10 , characterized in that the carrier substrate is a flowthrough substrate.
17 . Catalyst according to claim 16 , characterized in that the flowthrough substrate is a corrugated substrate.
18 . Catalyst according to claim 10 , characterized in that the carrier substrate is a filter substrate.
19 . Catalyst system, characterized in that it comprises a catalyst according to the invention in accordance with claim 10 .
20 . Method for reducing nitrogen oxides in exhaust gases of lean-burn internal combustion engines, wherein the exhaust gas is passed over an exhaust gas system that comprises a catalyst for the selective reduction of nitrogen oxides (SCR) and an ammonia slip catalyst (ASC) downstream of the exhaust gas stream, characterized in that the ASC is a catalyst according to the invention in accordance with claim 10 .
21 . Method according to claim 20 , characterized in that the SCR catalyst is a vanadium oxide-based catalyst or a zeolite-based catalyst of the Fe-zeolite or Cu-zeolite type.