Catalysts for gasoline lean burn engines with improved NH₃-formation activity

摘要

Described is a catalyst comprising a substrate and a catalyst coating of two or more layers: (a) a first layer comprising Pd and Rh on the substrate; and (b) a second layer comprising Pt and/or Pd on the first layer; these layers each further comprising: one or more particulate support materials; one or more oxygen storage component (OSC) materials; and one or more nitrogen oxide storage materials comprising one or more elements selected from the group of alkali and/or alkaline earth metals, wherein the total amount of alkali and alkaline earth metals ranges from 0.18 to 2.0 g/in3 calculated as the respective alkali metal oxides M2O and alkaline earth metal oxides MO. Also described is a method for the production of a catalyst, as well as a process for the treatment of a gas stream, in particular of an exhaust gas stream resulting from an internal combustion engine.

主权项

1. A catalyst comprising a substrate and a catalyst coating, the catalyst coating comprising two or more layers, said layers comprising:
(a) a first layer provided on the substrate, said first layer comprising:
(a′) a layer containing Pd; and(a″) a layer containing Rh; and (b) a second layer provided on the first layer, said second layer comprising Pt and Pd; the layers (a′), (a″) and second layers each further comprising:
one or more particulate support materials;one or more oxygen storage component (OSC) materials; andone or more nitrogen oxide storage materials comprising one or more elements selected from the group of alkali metals, alkaline earth metals and combinations thereof, wherein the total amount of alkali and alkaline earth metals comprised in the one or more nitrogen oxide storage materials contained in the catalyst ranges from 0.18 to 2.0 g/in3 calculated as the respective alkali metal oxides M2O and alkaline earth metal oxides MO, wherein the layer (a′) comprises less than 500 ppm of Pt and Rh, wherein the layer (a″) comprises less than 500 ppm of Pt and Pd, and wherein the second layer comprises less than 500 ppm of Rh.