Exhaust gas purification catalyst
An object of the present disclosure is to provide an exhaust gas purification catalyst demonstrating superior storage of NOx contained in exhaust gas. The exhaust gas purification catalyst of the present disclosure has a substrate, a first catalyst layer containing a catalytic metal for NOx reduction and a NOx storage material and formed on the substrate, and a second catalyst layer containing a catalytic metal for NOx oxidation and formed on the first catalyst layer. In the exhaust gas purification catalyst of the present disclosure, the value obtained by dividing the volume of all large pores having a pore volume of 1000 μm 3 or more by the total volume of all medium pores of having a pore volume of 10 μm 3 to 1000 μm 3 in the second catalyst layer is 2.44 or less.
1. An exhaust gas purification catalyst comprising:
a substrate,
a first catalyst layer containing a catalytic metal for NOx reduction and an NOx storage material and formed on the substrate, and
a second catalyst layer containing a catalytic metal for NOx oxidation and formed on the first catalyst layer;
wherein a volume percentage of all pores in the second catalyst layer is 2.82% by volume to 8.30% by volume, the % by volume being obtained by dividing a total volume of all pores in the second catalyst layer per unit volume by the unit volume, and the unit volume being a total volume of a three-dimensional image; and
wherein a value obtained by dividing a total volume of all large pores having a pore volume of 1000 μm 3 or more by a total volume of all medium pores having a pore volume of more than 10 μm 3 to less than 1000 μm 3 is 2.44 or less in the second catalyst layer.
2. The exhaust gas purification catalyst according to claim 1 , wherein the catalytic metal for NOx reduction contains Rh.
3. The exhaust gas purification catalyst according to claim 1 , wherein the catalytic metal for NOx oxidation contains Pt and/or Pd.
4. The exhaust gas purification catalyst according to claim 2 , wherein the catalytic metal for NOx oxidation contains Pt and/or Pd.
5. A method for purifying exhaust gas, comprising:
contacting exhaust gas containing NO with the exhaust gas purification catalyst according to claim 1 , to oxidize NO to NO 2 and store the NO 2 in a lean atmosphere, and
purifying the stored NO 2 by reducing the stored NO 2 in a stoichiometric atmosphere or rich atmosphere.
6. A method for purifying exhaust gas, comprising:
contacting exhaust gas containing NO with the exhaust gas purification catalyst according to claim 2 , to oxidize NO to NO 2 and store the NO 2 in a lean atmosphere, and
purifying the stored NO 2 by reducing the stored NO 2 in a stoichiometric atmosphere or rich atmosphere.
7. A method for purifying exhaust gas, comprising:
contacting exhaust gas containing NO with the exhaust gas purification catalyst according to claim 3 , to oxidize NO to NO 2 and store the NO 2 in a lean atmosphere, and
purifying the stored NO 2 by reducing the stored NO 2 in a stoichiometric atmosphere or rich atmosphere.
8. A method for purifying exhaust gas, comprising:
contacting exhaust gas containing NO with the exhaust gas purification catalyst according to claim 4 , to oxidize NO to NO 2 and store the NO 2 in a lean atmosphere, and
purifying the stored NO 2 by reducing the stored NO 2 in a stoichiometric atmosphere or rich atmosphere.