Gradient SCR-Coated Particle Filter for High-Temperature Selectivity
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Solution Overview
Problem
Existing wall flow filters coated with SCR catalysts have low selectivity in the SCR reaction, particularly at high temperatures, leading to undesirable ammonia oxidation.
Innovation Solution
A particle filter with a wall flow filter coated on the inner surfaces of its porous walls with a gradient of SCR-active material, where the side facing the exhaust gas has higher selectivity than the side facing the inner surfaces, utilizing small-pore zeolites exchanged with copper or iron, and a specific layer configuration to optimize the SCR reaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SCR catalyst is coated on the inner surfaces of the porous walls, then SCR activity is improved, but selectivity in the SCR reaction deteriorates at high temperatures
Solution Approach 1:
The patent applies different SCR catalyst compositions at different locations within the porous wall structure. The outer surface contains catalyst with lower selectivity to ammonia oxidation, while the inner surfaces contain catalyst with higher selectivity. This spatial differentiation of catalyst properties allows the system to maintain high SCR activity while minimizing harmful ammonia oxidation, as the inner high-selectivity catalyst processes ammonia that has diffused into the pores away from the exhaust gas atmosphere.
Solution Approach 2:
The patent transitions from a single-layer surface coating to a multi-layer porous wall structure with catalyst distributed throughout the pore network. By utilizing the third dimension (depth into the porous wall), the invention creates distinct functional zones: an outer layer for initial SCR conversion and an inner layer for selective ammonia processing. This dimensional approach allows simultaneous optimization of both SCR activity and selectivity that cannot be achieved with uniform surface coating alone.
2Reliability
If required quantity of SCR-active material is applied onto the porous walls, then SCR performance is improved, but back pressure of the filter increases
Solution Approach 1:
The patent utilizes the porous structure of the wall flow filter walls as the substrate for catalyst support. By impregnating or coating the porous walls with SCR-active material, the catalyst is distributed throughout the pore network rather than forming a dense surface layer. This approach provides high SCR performance through extensive catalyst surface area while maintaining low back pressure, as the porous structure preserves gas permeability and does not create significant flow resistance.
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
The particle filter achieves improved selectivity in the SCR reaction, reducing nitrogen oxides to nitrogen and water efficiently, even at high temperatures, while minimizing ammonia oxidation, and effectively removes particles from exhaust gases.
Implementation Method 1
the nitrogen oxides to be removed from the exhaust gas are converted to nitrogen and water using ammonia
Implementation Method 2
The particles are retained when the exhaust gas passes through the wall
Implementation Method 3
the side of the coating facing the exhaust gas has a higher selectivity in the SCR reaction than the side of the coating facing the inner surfaces of the pores
Data Source
AI summary
The invention relates to a particle filter, which comprises a wall flow filter and SCR-active material, wherein the wall flow filter comprises ducts which extend in parallel between the first and the second end of the wall flow filter and which are alternately closed in a gas-tight manner either at the first or the second end and which are separated by porous walls, the pores of which have inner surfaces, and the SCR-active material is located in the form of a coating on the inner surfaces of the pores of the porous walls, characterized in that the coating has a gradient, such that the side of the coating facing the exhaust gas has a higher selectivity in the SCR reaction than the side of the coating that faces the inner surfaces of the pores. The SCR-active material is preferably a small-pore zeolite, which has a maximum ring size of eight tetrahedral atoms and is exchanged with copper and/or iron.