Patent DE-502007001275-D1 (DE)
Inventor: DOERING ANDREAS
IPC: B01D53/94
Filed: 2007-06-05
Abstract: The device for the reduction of nitrogen oxides in the exhaust gas of combustion engines with the help of ammonia and/or reducing agents, comprises a first catalyst element (5) with selective catalytic reduction (SCR) activity and a downstream second catalyst element (6) with honeycomb-shaped cross-section. The downstream catalyst element forms individual flow channels having a zone with SCR-activity and a zone with ammonia-oxidation activity in an alternating manner along the flow direction. An oxidation catalyst (4) and a hydrolysis catalyst (3) are arranged upstream to the device. The device for the reduction of nitrogen oxides in the exhaust gas of combustion engines with the help of ammonia and/or reducing agents, comprises a first catalyst element (5) with selective catalytic reduction (SCR) activity and a downstream second catalyst element (6) with honeycomb-shaped cross-section. The downstream catalyst element forms individual flow channels having a zone with SCR-activity and a zone with ammonia-oxidation activity in an alternating manner along the flow direction. An oxidation catalyst (4) for the oxidation of nitric oxide to nitrogen dioxide and a hydrolysis catalyst (3) for better conversion of the reducing agent in ammonia are arranged upstream to the device. The ammonia is supplied to the exhaust gas flow and/or the reducing agents are added to the exhaust gas flow. The reducing agent releases ammonia in the exhaust gas flow. The flow channels are designed parallel or at an angle to one another. A fluid exchange takes place between two adjacent flow channels by perforations and/or flow baffles in the walls of the flow channels. Active components are embedded in a matrix of zeolites. The zeolites are the type of ZSM-5 and/or OSI and/or EPI and/or AEN and/or MFI and/or FAU and/or BEA. The second catalyst element is a multi-layered catalyst, and a bulk catalyst that is manufactured by extrusion. The different active zones are produced in the flow channels during the extrusion process. The second catalyst element and the layers are bulk catalyst layers or are coated with the catalyst material. The coating is applied on the metal, ceramic carrier, glass, ceramic and/or silicate mats. The first catalyst element and the second catalyst element are placed on a common carrier and/or designed as a single component. The catalyst elements are composed of unit layers that form a catalyst body. The catalyst material that has the ammonia oxidation-activity of the second catalyst element varies in its chemical composition along the direction of flow of the exhaust gas. The oxidation catalyst and the hydrolysis catalyst are arranged parallel to one another in the exhaust gas flow and the supply of the reducing agent takes place immediately before the hydrolysis catalyst. The zones of the catalyst with varying activity are produced by impregnation of a catalyst layer that is applied on the carrier or of a bulk catalyst. Each of the metal foils and/or mats is coated before it is rolled up or stacked one above the other to a honeycomb-shaped structure by spraying and/or paint coating and/or dipping using a metal foil carrier, a glass, ceramic and/or silicate mats.