Extruded honeycomb catalyst

Abstract

An extruded honeycomb catalyst for nitrogen oxide reduction according to the selective catalytic reduction (SCR) method in exhaust gases from motor vehicles includes an extruded active carrier in honeycomb form having a first SCR catalytically active component and with a plurality of channels through which the exhaust gas flows during operation, and a washcoat coating having a second SCR catalytically active component being applied to the extruded body, wherein the first SCR catalytically active component and the second SCR catalytically active component are each independently one of: (i) vanadium catalyst with vanadium as catalytically active component; (ii) mixed-oxide catalyst with one or more oxides, in particular those of transition metals or lanthanides as catalytically active component; and (iii) an Fe- or a Cu-zeolite catalyst.

1 . Extruded honeycomb catalyst for nitrogen oxide reduction according to the selective catalytic reduction (SCR) method in exhaust gases from motor vehicles, comprising an extruded active carrier in honeycomb form comprising a first SCR catalytically active component and with a plurality of channels through which the exhaust gas flows during operation, and a washcoat coating comprising a second SCR catalytically active component being applied to the extruded body, wherein the first SCR catalytically active component and the second SCR catalytically active component are each independently selected from the group consisting of:
 (i) vanadium catalyst with vanadium as catalytically active component;   (ii) mixed-oxide catalyst with one or more oxides, in particular those of transition metals or lanthanides as catalytically active component; and   (iii) an Fe- or a Cu-zeolite catalyst.   
     
     
         2 . Honeycomb catalyst according to  claim 1 , wherein in the extruded catalyst carrier the
 vanadium catalyst has, as active main components, vanadium oxide, titanium oxide, tungsten oxide in a proportion by volume of 10 to 85%   the mixed oxide catalyst contains as main components mixed oxides in particular of lanthanides or of transition metals, in particular cerium oxide, zirconium oxide and tungsten oxide in a proportion by volume of 10 to 85% and is free from zeolites and from vanadium   the metal zeolite catalyst contains an Fe-zeolite or a Cu-zeolite in a proportion by volume of 10 to 70%,   
       and wherein the rest is formed in each case by catalytically inactive components such as binders, fillers as required and, when the active components are reduced, a component which is neutral with respect to the extrusion process. 
     
     
         3 . Honeycomb catalyst according to  claim 1 , wherein the proportion of active components in the extruded carrier is reduced by comparison with a conventional uncoated extruded honeycomb catalyst and lies in particular in the range between 10 and 60 vol. %, preferably in the range between 10 and 40 vol. %. 
     
     
         4 . Honeycomb catalyst according to  claim 1 , wherein the reduced proportion of the catalytically active component by comparison with a conventional uncoated honeycomb catalyst is replaced by a component which is neutral with respect to the extrusion process, in particular clay. 
     
     
         5 . Honeycomb catalyst according to  claim 1 , wherein the proportion of the neutral component lies in the range of 10 to 70 vol. %, in particular in the range of 20-50 vol. %. 
     
     
         6 . Honeycomb catalyst according to  claim 1 , wherein the washcoat coating, at least in a frontal area—in relation to a direction of flow of the exhaust gas during operation—is free from noble metals. 
     
     
         7 . Honeycomb catalyst according to  claim 1 , wherein the carrier has a rear area—in relation to a direction of flow of the exhaust gas during operation—on which there is preferably a noble metal coating to prevent ammonia slip. 
     
     
         8 . Honeycomb catalyst according to  claim 7 , wherein the washcoat coating extends over the entire length of the carrier and also covers the noble metal coating, in particular in the rear area. 
     
     
         9 . Honeycomb catalyst according to  claim 1 , wherein the washcoat coating and in particular also the carrier have a high porosity, in particular a BET surface area in the range of about 40-80 m 2 /g. 
     
     
         10 . Honeycomb catalyst according to  claim 1 , wherein the layer thickness of the washcoat coating lies in the range of 30 to 100 jam, in particular in the range of about 40-60 μm. 
     
     
         11 . Honeycomb catalyst according to  claim 1 , wherein the honeycomb structure has webs and the web width is reduced by comparison with a conventional uncoated extruded honeycomb catalyst and in particular lies in the range of about 150-220 μm. 
     
     
         12 . Honeycomb catalyst according to  claim 1 , wherein the extruded catalyst carrier is a mixed oxide catalyst and the washcoat coating is a metal-zeolite catalyst, in particular an Fe- or a Cu-catalyst. 
     
     
         13 . Honeycomb catalyst according to  claim 1 , wherein the extruded catalyst carrier is a mixed oxide catalyst and the washcoat coating is a vanadium catalyst. 
     
     
         14 . Honeycomb catalyst according to  claim 1 , wherein the extruded catalyst carrier is an Fe-zeolite catalyst and the washcoat coating is a Cu-zeolite catalyst. 
     
     
         15 . Honeycomb catalyst according to  claim 1 , wherein the extruded catalyst carrier is a Cu-zeolite catalyst and the washcoat coating is an Fe-zeolite catalyst. 
     
     
         16 . Honeycomb catalyst according to  claim 1 , wherein the extruded catalyst carrier is an Fe-zeolite catalyst and the washcoat coating is a vanadium catalyst. 
     
     
         17 . Honeycomb catalyst according to  claim 1 , wherein the extruded catalyst carrier and the washcoat coating are formed from the same catalyst, in particular each being in the form of an Fe-zeolite catalyst. 
     
     
         18 . Honeycomb catalyst according to  claim 1 , wherein the extruded catalyst carrier and the washcoat coating are formed from the same catalyst, in particular each being in the form of a Cu-zeolite catalyst. 
     
     
         19 . Honeycomb catalyst according to  claim 1 , wherein the extruded catalyst carrier and the washcoat coating are formed from the same catalyst, in particular each being in the form of a vanadium catalyst. 
     
     
         20 . Honeycomb catalyst according to  claim 1 , wherein the extruded catalyst carrier and the washcoat coating are formed from the same catalyst, in particular each being in the form of a mixed-oxide catalyst with one or more oxides, in particular those of transition metals or lanthanides as catalytically active component. 
     
     
         21 . Honeycomb catalyst according to  claim 1 , wherein the carrier is a vanadium catalyst and the washcoat coating is an Fe-zeolite catalyst. 
     
     
         22 . A set of variously embodied extruded honeycomb catalysts according to  claim 1 , wherein all the honeycomb catalysts in the set have an identical carrier. 
     
     
         23 . Method for producing a set of variously embodied extruded honeycomb catalysts according to  claim 1 , wherein identically-embodied carriers are provided and coated with different washcoats. 
     
     
         24 . An exhaust system for a vehicular lean burn internal combustion engine comprising an extruded honeycomb catalyst according to  claim 1  disposed in a flow conduit thereof. 
     
     
         25 . An exhaust system according to  claim 24 , comprising means for injecting a nitrogenous reductant or a precursor thereof into the exhaust gas upstream of the extruded honeycomb catalyst. 
     
     
         26 . A lean burn internal combustion engine comprising an exhaust system according to  claim 24  comprising a catalyst for generating NH 3  in situ in exhaust gas upstream of the extruded honeycomb catalyst and control means for changing an exhaust gas composition to a composition which promotes in situ NH 3  on the catalyst for generating NH 3  in situ. 
     
     
         27 . A lean burn internal combustion engine according to  claim 26 , wherein the catalyst for generating NH 3  in situ in exhaust gas upstream of the extruded honeycomb catalyst is a diesel oxidation catalyst or a NO x  absorber catalyst. 
     
     
         28 . A vehicle comprising an exhaust system according to  claim 24 .