SCR Catalyst Composition for Low-Temperature NOx Conversion
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Solution Overview
Problem
Current SCR catalysts are ineffective in reducing NOx emissions from lean burn engine exhaust gases, especially at low temperatures and under transient lean/rich conditions, and lack sufficient high-temperature thermal stability, which is critical for meeting stringent emission regulations.
Innovation Solution
The development of advanced SCR catalyst compositions comprising a porous refractory metal oxide support coated with platinum group metals and base metal oxides, combined with zeolites promoted with specific metals, which are applied in specific weight ratios and configurations on substrates to enhance NOx conversion across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional SCR catalysts (zeolites ion-exchanged with iron or copper) are used, then NOx reduction is achieved at temperatures above 200°C, but they are ineffective at low temperatures and lack high-temperature thermal stability
Solution Approach 1:
The patent combines two distinct catalyst components: (1) molecular sieve material (zeolite) ion-exchanged with iron or copper for SCR activity, and (2) precious metal component (platinum group metal) on refractory oxide support for high-temperature stability and low-temperature activity. This composite structure allows the catalyst to maintain effectiveness across a wide temperature range from low temperatures up to high temperatures, resolving the contradiction between low-temperature effectiveness and high-temperature stability.
2Object-generated harmful factors
If zeolite-based SCR catalysts are used for lean burn gasoline engines, then NOx reduction is achieved, but thermal stability at high temperatures under transient lean/rich conditions is insufficient
Solution Approach 1:
The patent creates a composite catalyst system where the precious metal component (platinum group metal) on refractory oxide support provides high-temperature thermal stability and resistance to transient lean/rich conditions, while the zeolite component continues to provide NOx reduction activity. This composite structure resolves the contradiction by combining materials with complementary stability and activity properties.
Solution Approach 2:
The patent modifies the catalyst composition parameters by introducing platinum group metals (such as platinum, palladium, or rhodium) at specific loadings (e.g., 0.1-5.0 wt% of the total catalyst weight) on refractory oxide supports. This parameter change enhances thermal stability and maintains catalytic activity under transient conditions, allowing the catalyst to withstand high temperatures and varying air-fuel ratios without degradation.
3Productivity
If standard Cu-chabazite catalysts are used, then some NOx conversion is achieved, but conversion efficiency is insufficient particularly at low temperatures
Solution Approach 1:
The patent combines Cu-chabazite zeolite with a precious metal component on refractory oxide support. The precious metal component (such as platinum or palladium) exhibits high catalytic activity at low temperatures for NOx reduction, complementing the Cu-chabazite's activity at higher temperatures. This composite structure resolves the contradiction by providing effective NOx conversion across the entire temperature spectrum, particularly enhancing low-temperature performance.
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 proposed catalyst compositions significantly increase NOx conversion, particularly at low temperatures, compared to standard Cu-chabazite reference catalysts, and maintain effectiveness even after aging, thereby meeting stringent emission standards.
Implementation Method 1
Oxidation catalysts comprising a precious metal, such as platinum group metals (PGM), dispersed on a refractory metal oxide support, such as alumina, are known for use in treating the exhaust of diesel engines in order to convert both HC and CO gaseous pollutants by catalyzing the oxidation of these pollutants to carbon dioxide and water.
Implementation Method 2
In addition to the conversion of gaseous HC and CO emissions, oxidation catalysts that contain PGM promote the oxidation of NO to NO2.
Implementation Method 3
The SCR process uses catalytic reduction of nitrogen oxides with a reductant (e.g., ammonia) in the presence of atmospheric oxygen, resulting in the formation predominantly of nitrogen and steam: 4NO+4NH3+O2→4N2+6H2O
Data Source
AI summary
A selective catalytic reduction (SCR) catalyst composition effective in the abatement of nitrogen oxides (NOx) is provided. The SCR catalyst composition significantly increases the conversion of NOx relative to a Cu-chabazite reference catalyst composition at any temperature, and especially at low temperatures. A catalyst article, an exhaust gas treatment system, and a method of treating an exhaust gas stream, each including the SCR catalyst composition of the invention, are also provided. The SCR catalyst composition is particularly useful for treatment of exhaust from a lean-burn engine.