Exhaust System Guard Bed Traps Volatilized PGMs
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Solution Overview
Problem
Existing exhaust systems for vehicular lean-burn internal combustion engines face challenges with the volatilization of platinum group metals (PGMs) from upstream catalysts, particularly at high temperatures, which can contaminate downstream SCR catalysts and reduce NOx conversion efficiency.
Innovation Solution
An exhaust system arrangement featuring a first substrate monolith with a SCR catalyst, a second substrate monolith with a PGM-containing catalytic washcoat, and a third substrate monolith with materials like stabilised alumina, zirconia, or ceria-zirconia mixed oxides, and catalysts such as copper, silver, or gold, positioned between the first and second monoliths to trap volatilized PGMs, preventing contamination of the SCR catalyst.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a PGM-containing catalyst is placed upstream of the SCR catalyst to treat exhaust gases, then the catalytic conversion of CO and HC is improved, but the PGM volatilizes at high temperatures and contaminates the downstream SCR catalyst, reducing NOx conversion efficiency
Solution Approach 1:
A guard bed comprising metal oxide particles (alumina, zirconia, ceria, or mixed oxides) is positioned between the upstream PGM-containing catalyst and the downstream SCR catalyst. This intermediary guard bed traps volatilized PGMs through adsorption and physical entrapment in its porous structure, preventing them from reaching and poisoning the SCR catalyst, while allowing exhaust gases to pass through for continued catalytic treatment.
2Use of energy by moving object
If the exhaust system operates at high temperatures to improve combustion efficiency, then the catalytic activity is enhanced, but PGM volatilization increases and contaminates the SCR catalyst
Solution Approach 1:
The guard bed utilizes the volatilized PGMs, which would otherwise be harmful contaminants, by trapping them through adsorption onto metal oxide surfaces and physical entrapment in the porous structure. This converts the harmful volatilization phenomenon into a manageable process where PGMs are captured and retained in the guard bed, preventing their migration to the SCR catalyst while allowing the exhaust system to operate at high temperatures for optimal combustion efficiency.
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 configuration effectively reduces the migration of PGMs from upstream catalysts to downstream SCR catalysts, maintaining NOx conversion efficiency and preventing poisoning of the SCR catalyst, even under extreme temperature conditions.
Implementation Method 1
comprising at least one material for trapping volatilised platinum group metal (PGM)
Implementation Method 2
a metal oxide selected from the group consisting of optionally stabilised alumina, optionally stabilised zirconia, an optionally stabilised ceria-zirconia mixed oxide
Implementation Method 3
which at least one third substrate monolith is disposed between said first substrate monolith and said at least one second substrate monolith
Data Source
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AI summary
An exhaust system (10) for a vehicular lean-bum internal combustion engine comprises: . (a) a first substrate monolith (6) comprising a SCR catalyst; . (b) at least one second substrate monolith (4) comprising a catalytic washcoat coating comprising at least one platinum group metal (PGM) disposed upstream of the first substrate monolith; and . (c) a third substrate monolith (2) disposed between the first sub strate monolith and the or each second substrate monolith, wherein at least one PGM on the or each second substrate monolith (4) is liable to volatilise when the or each second substrate monolith (4) is exposed to relatively extreme conditions including relativehigh temperatures, and wherein the third substrate monolith (2) comprises a washcoat comprising at least one material for trapping volatilised PGM.