Silver-Gallium Composite Oxide for Low-Temperature NOx Storage
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Solution Overview
Problem
Current NOx storage materials are inadequate in low-temperature regions, particularly below 200°C, and often rely on transition metals, which pose environmental concerns, necessitating a material that uses inexpensive metals without transition metals for effective NOx storage.
Innovation Solution
A composite oxide of silver and gallium, potentially with aluminum, forming a delafossite-type structure, is used for NOx storage, with a molar ratio of silver to gallium between 3:7 and 7:3, and silver to (gallium+aluminum) between 2:8 and 7:3, achieving high NOx storage capacity at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional exhaust gas purification catalysts are used, then NOx purification is effective at temperatures of 250°C or more, but NOx purification is insufficient at low temperatures below 200°C
Solution Approach 1:
The catalyst is divided into two functional segments: an NOx storage section containing silver-gallium composite oxide for low-temperature NOx storage, and an NOx purification section containing conventional catalyst materials for high-temperature NOx conversion. This segmentation allows each segment to operate optimally in its designated temperature range, resolving the contradiction between low-temperature storage effectiveness and high-temperature purification performance.
2Reliability
If transition metals like manganese are used in composite oxides, then NOx storage performance improves at low temperatures, but harmful environmental effects are introduced
Solution Approach 1:
The invention replaces persistent transition metal compounds with a silver-gallium composite oxide system that uses silver in a controlled, non-toxic form. The silver-gallium composite oxide achieves comparable NOx storage capacity without the environmental persistence and toxicity concerns associated with transition metals like manganese, effectively substituting a harmful material with a safer alternative that maintains performance.
3Reliability
If Pd-chabazite is used for NOx storage, then low-temperature NOx adsorption properties are enhanced, but material cost and complexity increase
Solution Approach 1:
The invention uses a composite oxide material consisting of silver and gallium in specific molar ratios (3:7 to 7:3) to achieve low-temperature NOx storage. This composite oxide approach simplifies the material structure compared to Pd-chabazite while maintaining effective NOx adsorption capacity at low temperatures, reducing both material 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 silver-gallium composite oxide exhibits superior NOx storage capacity at temperatures of 200°C or less, outperforming conventional materials like Pd-chabazite, with a concentration of 1.7 mmol/g or more, effectively storing NOx without the use of transition metals.
Implementation Method 1
desorption of surface oxygen accompanied by reduction of Ce cation participates in oxidation of NOx, and NOx is held as a nitrate (nitrite) salt having Ce as the cation
Implementation Method 2
desorption of surface oxygen accompanied by reduction of Ce cation participates in oxidation of NOx
Implementation Method 3
a material obtained by ion exchanging Pd on to a zeolite compound such as chabazite exhibits high NOx adsorption properties
Data Source
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AI summary
An object of the present disclosure is to provide an NOX storage material having sufficient NOX storage capacity even in a low temperature region and a production method thereof. An NOX storage material including a composite oxide of silver and gallium. The composite oxide of silver and gallium is preferably a delafossite-type composite oxide. The composite oxide is produced by dissolving a silver salt and a gallium salt in a solvent and baking the solution, wherein the molar ratio of silver:gallium is preferably from 2:8 to 7:3.