Silver-Gallium Composite Oxide for Low-Temperature NOx Storage
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Solution Overview
Problem
Current NOx storage materials are inadequate in terms of NOx storage capacity at low temperatures, and materials using transition metals pose environmental concerns, necessitating a solution that uses inexpensive metals without transition metals to effectively store NOx at temperatures of 200° C. or less.
Innovation Solution
A composite oxide of silver and gallium, potentially with aluminum, is used as an NOx storage material, where the molar ratio of silver to gallium can range from 2:8 to 7:3, and the material is produced by dissolving metal salts in a solvent and baking the solution, forming a delafossite-type composite oxide with high NOx storage capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional exhaust gas purification catalysts are used, then NOx purification is achieved at temperatures of 250°C or more, but NOx generated before sufficient warmup cannot be purified
Solution Approach 1:
The catalyst system is divided into two functional segments: an NOx storage material segment (first catalyst layer) that operates at low temperatures to capture NOx, and a conventional purification catalyst segment (second catalyst layer) that activates at higher temperatures to purify the stored NOx. This segmentation allows each component to operate in its optimal temperature range, resolving the contradiction between low-temperature NOx capture and high-temperature purification effectiveness.
2Quantity of substance
If Ce1-xZrxO2 or Pd-supported materials are used for low-temperature NOx storage, then NOx storage capacity is enhanced, but the materials require noble metals or transition metals which increase cost and environmental concerns
Solution Approach 1:
The invention replaces expensive noble metals (Pt, Pd) and transition metals (Mn, Ce) with inexpensive base metals, specifically copper (Cu) and zinc (Zn), to form the active catalyst component. This substitution dramatically reduces material cost and environmental impact while maintaining sufficient NOx storage capacity through the copper zinc alloy's unique electronic structure and surface properties that enable effective NOx adsorption at low temperatures.
Solution Approach 2:
The invention employs a composite material system consisting of a copper zinc alloy (Cu-Zn) supported on an oxide carrier (such as Al2O3, SiO2, or mixed oxides). This composite structure combines the high NOx storage activity of the copper zinc alloy with the structural stability and surface area of the oxide support, achieving both low-temperature effectiveness and cost-efficiency without requiring noble metals.
3Reliability
If MnOx-CeO2 composite oxide is used, then high NOx storage performance is achieved at 200°C or less, but transition metals are required which have harmful effects
Solution Approach 1:
The invention extracts and eliminates the harmful transition metal components (Mn, Ce) from the catalyst system while retaining the essential function of low-temperature NOx storage. This is achieved by substituting the copper zinc alloy for the transition metal composite, thereby removing the source of harmful effects (transition metal toxicity and environmental persistence) while preserving the low-temperature operational capability through the unique properties of base metals.
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 low temperatures, particularly below 200° C., outperforming conventional materials like Pd-chabazite, with high concentrations of active NOx storage sites, enabling efficient NOx storage and subsequent purification in exhaust gas systems.
Implementation Method 1
NOx is held as a nitrate (nitrite) salt having Ce as the cation
Implementation Method 2
dissolving salts of metals constituting the composite oxide in a solvent
Implementation Method 3
baking the solution
Data Source
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.