Rhodium-Phosphorus Catalyst Layers for Low-Temperature NOx Purification
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Solution Overview
Problem
Conventional exhaust gas purification catalysts, particularly those used in internal combustion engines, exhibit inadequate NOx purifying performance at low to medium temperatures.
Innovation Solution
The catalyst layer contains rhodium, phosphorus, and a rare earth element other than cerium, with specific mass ratios of these elements, supported on a substrate, enhancing NOx purifying performance at low to medium temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional noble metal catalysts (Pt, Pd, Rh) are used for exhaust gas purification, then harmful components (HC, CO, NOx) can be purified, but NOx purifying performance at low to medium temperatures is insufficient
Solution Approach 1:
The invention changes the chemical composition parameters of the catalyst layer by incorporating phosphorus and rare earth elements (other than cerium) in specific mass ratios. The phosphorus content is controlled at 0.03-0.30 mass% and rare earth element content at 0.06-0.60 mass% relative to rhodium mass, which modifies the catalytic properties to enhance NOx purification at low to medium temperatures while maintaining high-temperature performance
Solution Approach 2:
The invention creates a composite catalyst layer by combining rhodium, phosphorus, and rare earth elements (such as neodymium, praseodymium, or terbium) with oxygen storage components like CeO2-ZrO2 complex oxide. This composite structure synergistically improves NOx purification performance across a wide temperature range, particularly enhancing low to medium temperature activity while maintaining thermal stability
2Object-affected harmful factors
If GPF is installed to collect PM, then PM discharge is reduced, but space for installing exhaust gas purification catalyst is limited
Solution Approach 1:
The invention merges the PM collection function (GPF) and the exhaust gas purification catalyst function into a single integrated device. The catalyst layer containing rhodium, phosphorus, and rare earth elements is directly formed on the GPF substrate, allowing simultaneous PM filtration and harmful component purification in one component, thereby saving installation space while maintaining both functions
Solution Approach 2:
The integrated catalyst-GPF system performs multiple functions: PM collection through the wall-flow substrate structure, NOx purification through rhodium and phosphorus-rare earth combinations, HC and CO oxidation through noble metals, and oxygen storage through CeO2-ZrO2 complex oxide. This multi-functional design eliminates the need for separate catalyst and GPF installations
Data Source
AI summary
An object of the present invention is to provide an exhaust gas purification catalyst having improved exhaust gas (e.g., NOx) purifying performance at low to medium temperature. In order to achieve the object, the present invention provides an exhaust gas purification catalyst including: a substrate; and a catalyst layer formed on the substrate, wherein the catalyst layer contains rhodium element, phosphorus element and a rare earth element other than cerium element, wherein a ratio of a mass of the phosphorus element contained in the catalyst layer to the mass of the rhodium element contained in the catalyst layer is from 1 to 10, and wherein a ratio of a mass of the rare earth element other than cerium element in terms of an oxide thereof contained in the catalyst layer to the mass of the rhodium element contained in the catalyst layer is from 1 to 5.