SCR Catalyst Monolith with Platinum Trapping Zone
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Solution Overview
Problem
The volatilization of platinum group metals (PGMs) from upstream catalysts, particularly platinum, poses a significant challenge as it contaminates downstream selective catalytic reduction (SCR) catalysts, leading to reduced NOx conversion activity and secondary emissions.
Innovation Solution
A substrate monolith design with a second zone comprising particulate metal oxides such as alumina, silica-alumina, or zirconia is implemented to trap and prevent the migration of platinum group metals, ensuring they do not contaminate the SCR catalyst, thereby maintaining NOx conversion activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If platinum group metals are used in upstream catalysts for oxidation reactions, then catalytic activity for CO and HC oxidation is improved, but platinum volatilizes at high temperatures and contaminates downstream SCR catalyst, reducing NOx conversion activity
Solution Approach 1:
A barrier layer comprising at least one of ceria, zirconia, or mixtures thereof is introduced between the upstream oxidation catalyst and the downstream SCR catalyst. This intermediary barrier layer captures volatilized platinum group metals, preventing them from contaminating the SCR catalyst while allowing exhaust gases to pass through. The barrier layer thus mediates the harmful interaction between the oxidation catalyst and SCR catalyst.
Solution Approach 2:
The harmful function of platinum volatilization is extracted and isolated by placing a dedicated barrier layer between the oxidation catalyst and SCR catalyst. This barrier layer specifically targets and captures volatilized platinum group metals, separating the harmful effect from the beneficial catalytic functions of both upstream and downstream catalysts.
2Productivity
If high temperatures are used in exhaust systems for filter regeneration and oxidation reactions, then combustion efficiency of soot and oxidation of pollutants is improved, but platinum group metals volatilize more readily, increasing contamination risk to SCR catalyst
Solution Approach 1:
The barrier layer acts as a heat-resistant intermediary that can withstand high temperatures during filter regeneration while capturing volatilized platinum. It allows the system to operate at high temperatures for efficient soot combustion and pollutant oxidation without transferring the harmful effect of platinum volatilization to the SCR catalyst.
Solution Approach 2:
The barrier layer is pre-positioned between the oxidation catalyst and SCR catalyst to provide beforehand protection against platinum volatilization. During high-temperature operations, this pre-positioned barrier captures volatilized platinum before it can reach and contaminate the SCR catalyst, cushioning the SCR catalyst against thermal and chemical damage.
3Reliability
If a barrier layer is added between upstream catalyst and SCR catalyst to prevent platinum contamination, then SCR catalyst activity is preserved, but exhaust system complexity and number of components increase
Solution Approach 1:
The barrier layer is merged with either the upstream oxidation catalyst substrate or the downstream SCR catalyst substrate, forming an integrated multi-functional component. This combining approach reduces the total number of separate components in the exhaust system while maintaining the barrier function to protect the SCR catalyst from platinum contamination.
Solution Approach 2:
The barrier layer is designed to perform multiple functions: it serves as a structural support substrate, provides thermal stability during high-temperature operations, captures volatilized platinum group metals, and maintains exhaust flow. This multi-functionality reduces the need for additional dedicated components, simplifying the overall exhaust system structure.
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 reduces the contamination of SCR catalysts by platinum group metals, preserving NOx conversion efficiency and preventing secondary emissions, even at high temperatures.
Implementation Method 1
the second zone (8) comprising at least one particulate metal oxide or a mixture of any two or more thereof for trapping gas phase platinum group metal (PGM)
Data Source
Figure 1~2
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AI summary
A substrate monolith (6) having a length L and comprising a first zone (11) of substantially uniform length defined at one end by a first end of the substrate monolith, which first zone comprising a selective catalytic reduction (SCR) catalyst for reducing oxides of nitrogen with a nitrogenous reductant in exhaust gas emitted from an internal combustion engine and a second zone (8) of substantially uniform length less than L defined at one end by a second end of the substrate monolith, which second zone comprising (a) at least one particulate metal oxide or a mixture of any two or more thereof for trapping gas phase platinum group metal (PGM), which at least one particulate metal oxide does not act as a support for any other catalytic component; or (b) a component capable of trapping and/or alloying with gas phase PGM.