Catalyst device

Abstract

A catalyst device has a wall flow-type substrate. The substrate is formed of a porous base material. An SCR catalyst for reduction of NOx is supported in pores in the interior of the base material. The surface of the base material on a diesel engine side is coated with a trapping layer that traps PM in an exhaust gas. The surface of the substrate on a side opposite to the diesel engine side is coated with an oxidation catalyst layer that is formed of an oxidation catalyst.

1 . A catalyst device that purifies an exhaust gas discharged by an internal combustion engine, comprising:
 a porous base material that supports, in the interior thereof, an SCR catalyst that reduces NOx in the exhaust gas;   a trapping layer that traps PM in the exhaust gas and is coated on a surface of the base material on the internal combustion engine side; and   an oxidation catalyst layer that contains an oxidation catalyst and is coated on a surface of the base material on a side opposite to the internal combustion engine side.   
     
     
         2 . The catalyst device according to  claim 1 , wherein porosity of the base material is greater than porosity of the trapping layer, and porosity of the oxidation catalyst layer is equal to or greater than the porosity of the base material,
 an average pore size of the base material is greater than an average pore size of the trapping layer, and an average pore size of the oxidation catalyst layer is equal to or greater than the average pore size of the base material, and   thickness of the base material is greater than both thickness of the trapping layer and thickness of the oxidation catalyst layer.   
     
     
         3 . The catalyst device according to  claim 1 , wherein porosity of the base material and porosity of the oxidation catalyst layer range from 55% to 70%, and porosity of the trapping layer ranges from 20% to less than 55%. 
     
     
         4 . The catalyst device according to  claim 1 , wherein an average pore size of the base material and an average pore size of the oxidation catalyst layer range from 15 μm to 100 μm, and an average pore size of the trapping layer ranges from 6 μm to less than 15 μm. 
     
     
         5 . The catalyst device according to  claim 1 , wherein thickness of the base material ranges from 200 μm to 400 μm, thickness of the trapping layer ranges from 10 μm to less than 200 μm, and thickness of the oxidation catalyst layer ranges from 0.1 μm to less than 200 μm. 
     
     
         6 . The catalyst device according to  claim 1 , wherein the oxidation catalyst layer further contains a second SCR catalyst. 
     
     
         7 . The catalyst device according to  claim 1 , wherein the trapping layer contains a hydrolysis catalyst that hydrolyzes a reductant that is added to the catalyst device in order for NOx to be reduced by the SCR catalyst.