Exhaust Gas Purification Catalyst with Rare Earth Surface Concentration
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Solution Overview
Problem
Current three-way catalysts (TWCs) used in gasoline engines face challenges with thermal stability and performance deterioration due to precious metal particle aggregation, particularly rhodium oxide formation in high-temperature oxidizing atmospheres, which affects the catalyst's ability to efficiently oxidize CO, reduce NOx, and purify hydrocarbons.
Innovation Solution
A catalyst system comprising a platinum group metal (PGM) component, an inorganic oxide, and a rare earth metal component, where the rare earth metal is concentrated on the surface of the oxide at specific concentrations (1 μmol/m2 to 20 μmol/m2) to suppress PGM particle aggregation, improve dispersion, and enhance thermal durability and purification efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If rhodium is used as the PGM component for NOx reduction, then the catalyst achieves high conversion rates, but the rhodium particles aggregate and transform to rhodium oxide in high-temperature oxidizing atmospheres, causing performance deterioration
Solution Approach 1:
A rare earth metal component (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu) is introduced as an intermediary substance between the rhodium PGM and the oxidizing atmosphere. This rare earth metal forms a protective interaction with rhodium, preventing its oxidation and aggregation while maintaining catalytic activity for NOx reduction.
Solution Approach 2:
The catalyst employs a composite structure combining rhodium PGM with rare earth metal components on an oxide support. This composite material approach allows the system to simultaneously achieve high conversion rates from rhodium while gaining thermal stability and resistance to oxidation from the rare earth metal component.
2Productivity
If the engine operates at stoichiometric conditions (λ=1) to optimize TWC performance, then the catalyst efficiently performs oxidation and reduction reactions, but the engine cannot operate on either side of λ=1 during various stages of the operating cycle
Solution Approach 1:
The catalyst is designed with multi-functional capability through the combination of PGM components (rhodium for reduction, palladium/platinum for oxidation) and rare earth metal components. This universal design enables the single catalyst to efficiently perform both oxidation reactions (CO, HC) and reduction reactions (NOx) across a broader operating window, accommodating engine operation on both sides of stoichiometric conditions.
3Adaptability or versatility
If ceria-based materials are used as oxygen storage components to extend the effective operating window, then the catalyst can handle rich and lean operating conditions, but the precious metal particles still aggregate under high-temperature conditions
Solution Approach 1:
The solution merges multiple functional components into a unified catalyst system: ceria-based oxygen storage components for extending the operating window, combined with rare earth metal components specifically for preventing PGM aggregation. This combination allows the catalyst to simultaneously achieve broad adaptability to different operating conditions and high thermal stability.
Data Source
AI summary
A three-way catalyst article, and its use in an exhaust system for internal combustion engines, is disclosed. The catalyst article for treating exhaust gas comprises: a substrate; and a catalytic region on the substrate; wherein the catalytic region comprises a platinum group metal (PGM) component, an oxide, and a rare earth metal component; wherein the oxide is an inorganic oxide, an oxygen storage component (OSC) material, or a mixture thereof; wherein the rare earth metal component concentration by element on the surface of the oxide per unit specific surface area of the oxide is 1 μmol/m2 to 20 μmol/m2.