| 简介 |
FIELD : chemistry.
SUBSTANCE : invention relates to a NOx trap, i.e. NOx adsorber catalyst, which is a part of exhaust gas aftertreatment systems for internal combustion engines. The catalyst comprises a honeycombed substrate monolith. The first layer substrate comprises components comprising at least one platinum group metal, at least one NOx storage material and bulk ceria or a bulk cerium-containing mixed oxide deposited uniformly in a first layer and a dispersion of rare earth oxides. The first layer has a first, upstream, zone and a second, downstream zone. The loading of the dispersion of rare earth oxide in the first, upstream, zone, g/l, is in the range 0-30% of the loading of the dispersion of the rare earth oxide in the second, downstream, zone. The first, upstream, zone has increased activity relative to a second, downstream zone for oxidising hydrocarbons and carbon monoxide. And a second, downstream, zone has increased activity to generate heat during a desulphation event, relative to the first, upstream, zone.
EFFECT : improved NOx reduction at lower temperatures, offering the ability to release trapped sulphur more efficiently and/or with a less demanding desulphation event.
14 cl, 2 dwg, 1 tbl, 3 ex |
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