Wall Flow Catalyst PM Trapping and NOx Purification
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Solution Overview
Problem
The exhaust gas purifying catalyst of wall flow type used in SCR type purification devices experiences a significant increase in pressure loss due to the accumulation of particulate matter (PM), which reduces the gas flow rate, and the noble metal catalysts used to burn PM also interfere with NOx purification.
Innovation Solution
The catalyst design includes an inlet-side catalyst layer with a reduced pore diameter to trap PM on the surface, preventing it from entering the partition walls, and an outlet-side catalyst layer with a larger SCR catalyst amount to maintain high NOx purification efficiency, ensuring that the PM is trapped on the surface and not inside the partition walls, thereby reducing pressure loss and maintaining NOx purification rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the exhaust gas purifying catalyst of wall flow type is used in the SCR type purification device, then the NOx purification function is improved, but the pressure loss increases due to PM accumulation in the partition walls
Solution Approach 1:
The partition wall is divided into two distinct regions: an inlet-side region with smaller pores that trap PM, and an outlet-side region with larger pores that maintain gas flow. This segmentation allows each region to perform its specific function - PM trapping at the inlet and efficient exhaust gas passage at the outlet - thereby resolving the contradiction between PM filtration and pressure loss prevention
Solution Approach 2:
Different pore sizes are assigned to different regions of the partition wall based on local functional requirements. The inlet-side region has smaller pores optimized for PM trapping, while the outlet-side region has larger pores optimized for maintaining low pressure loss. This local differentiation of properties allows the single partition wall structure to simultaneously achieve both PM accumulation prevention and pressure loss reduction
2Productivity
If noble metal catalysts are used to burn PM, then the PM combustion efficiency is improved, but the NOx purification efficiency deteriorates due to interference with SCR reaction
Solution Approach 1:
The harmful noble metal catalysts that interfere with NOx purification are completely removed from the partition wall structure. Instead, the invention uses the physical trapping mechanism of the porous structure itself to accumulate and burn PM, extracting the PM combustion function from the catalytic material and relying on the structural design and thermal oxidation instead, thereby eliminating the negative interference with SCR reactions
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively suppresses the increase in pressure loss and maintains a high NOx purification rate by trapping PM on the surface and utilizing a larger SCR catalyst amount in the outlet-side layer for efficient NOx purification.
Implementation Method 1
an inlet-side catalyst layer which is formed with a predetermined thickness on the inner side of the partition wall from a surface of the partition wall in contact with an inlet-side cell and is formed with a predetermined length along an extension direction of the partition wall from the vicinity of an end portion on an exhaust gas inflow side, so that an average pore diameter of the partition wall in an inlet-side region is 0.1 μm or more and 10 μm or less
Implementation Method 2
a catalyst layer including an SCR catalyst is formed in the partition walls of the base... the reducing agent adsorbed on the SCR catalyst is reacted with NOx in the exhaust gas by the catalytic action of the SCR catalyst, thereby purifying the NOx in the exhaust gas
Implementation Method 3
the reducing agent adsorbed on the SCR catalyst is reacted with NOx in the exhaust gas by the catalytic action of the SCR catalyst, thereby purifying the NOx in the exhaust gas
Data Source
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AI summary
The exhaust gas purifying catalyst disclosed herein includes a base of a wall flow structure having a porous partition wall 4, an inlet-side catalyst layer 6a which is formed on an inner side of the partition wall from a surface of the partition wall in contact with an inlet-side cell and which is formed along an extension direction from an end portion on the exhaust gas inflow side, and an outlet-side catalyst layer which is formed on the inner side of the partition wall from a surface of the partition wall in contact with an outlet-side cell and which is formed along the extension direction from an end portion on the exhaust gas outflow side. Here, a sum of the lengths of the inlet-side catalyst layer and the outlet-side catalyst layer is larger than the entire length of the partition wall, and a total amount of an SCR catalyst body present in the outlet-side catalyst layer is larger than a total amount of an SCR catalyst body present in the inlet-side catalyst layer.