Ag-Pd Alloy Catalyst for Exhaust Purification
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Solution Overview
Problem
Conventional exhaust gas purification catalysts, particularly those using platinum group elements like Pd, suffer from reduced oxidation activity due to poisoning by hydrocarbons, leading to decreased performance and lower fuel economy when attempting to suppress oxidation through reductive atmosphere operations.
Innovation Solution
A catalyst comprising an alloy of silver (Ag) and Pd supported on a carrier, where the Ag prevents Pd poisoning and maintains its active state, enhancing the synergistic exhaust gas purification effect, with a preferred molar ratio of Pd:Ag ranging from 99.9:0.1 to 10:90, and a method involving the synthesis of reduced metal microparticles with a protective substance for uniform dispersion and support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Pd-based catalyst is used for exhaust gas purification, then oxidation activity is improved, but Pd poisoning by HC occurs leading to performance degradation
Solution Approach 1:
The patent introduces Ag as an intermediary substance that mediates between Pd and HC. Ag has high affinity for HC and acts as a protective layer, preventing HC from directly poisoning Pd while maintaining Pd's oxidation activity for CO removal.
Solution Approach 2:
The patent creates a composite catalyst system combining Pd and Ag in specific ratios (Pd:Ag = 9:1 to 1:9). This composite structure leverages the complementary properties of both metals: Pd for CO oxidation and Ag for HC resistance, achieving synergistic effect that resolves the poisoning problem.
2Reliability
If reductive atmosphere operations are used to suppress oxidation, then oxidation activity is reduced, but fuel economy deteriorates
Solution Approach 1:
The patent changes the chemical composition parameter of the catalyst by incorporating Ag, which fundamentally alters the catalyst's behavior. This allows the catalyst to maintain high oxidation activity without requiring reductive atmosphere operations, thus avoiding fuel economy penalties.
3Reliability
If Ag content in alloy is increased to prevent Pd poisoning, then protection effect is improved, but cost and complexity increase
Solution Approach 1:
The patent applies partial action by using only 10-90 mol% Ag content, which is sufficient to provide protection against Pd poisoning without excessive Ag addition. This optimal range achieves the necessary protection effect while minimizing alloy complexity and cost.
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 Ag-Pd alloy catalyst maintains high purification efficiency for CO and HC, offering superior oxidation activity and preventing Pd poisoning, thus improving catalytic performance and fuel economy compared to traditional Pd-based catalysts.
Implementation Method 1
an exhaust gas purification catalyst whose main component is a platinum group element such as platinum, rhodium or palladium (Pd) supported on a metal oxide such as alumina
Implementation Method 2
JP-A-2009-011951 discloses in working examples the results for simulation of the adsorption energy on a titanium dioxide (TiO2) carrier of a Pd—Au alloy
Data Source
AI summary
An exhaust gas purification catalyst for removing CO or HC, which contains a carrier and an alloy of palladium and silver supported on this carrier.