Dual-Layer SCR Catalyst for NOx Reduction
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Solution Overview
Problem
Vanadium SCR catalysts face a challenge in achieving simultaneous high low-temperature activity and high-temperature selectivity, with improvements in one aspect often leading to deficits in the other, which is critical for effectively reducing nitrogen oxides in exhaust gases from lean-burn internal combustion engines.
Innovation Solution
A dual-layer SCR catalyst system comprising layers A and B, where layer A contains vanadium pentoxide, tungsten trioxide, and optional silicon dioxide, and layer B contains vanadium pentoxide, tungsten trioxide, and silicon dioxide, with specific weight percentage ratios and oxidic forms optimized for enhanced activity and selectivity across varying temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the vanadium content is increased to improve low-temperature activity, then the low-temperature nitrogen oxide conversion is enhanced, but the high-temperature selectivity deteriorates
Solution Approach 1:
The catalyst is divided into two distinct layers: Layer A (front layer) with higher vanadium content optimized for low-temperature activity, and Layer B (rear layer) with lower vanadium content and higher tungsten/silicon content optimized for high-temperature selectivity. This segmentation allows each layer to specialize in different temperature ranges, resolving the contradiction between low-temperature activity and high-temperature selectivity.
Solution Approach 2:
Different regions of the catalyst have different compositions tailored to local requirements. The front layer has higher vanadium concentration for low-temperature effectiveness, while the rear layer has lower vanadium and higher tungsten/silicon for high-temperature selectivity. This local quality differentiation enables the catalyst to perform optimally across the entire temperature range.
2Reliability
If the catalyst composition is optimized for high-temperature selectivity, then the high-temperature nitrogen oxide conversion is improved, but the low-temperature activity deteriorates
Solution Approach 1:
The catalyst is divided into two distinct layers: Layer A (front layer) with higher vanadium content optimized for low-temperature activity, and Layer B (rear layer) with lower vanadium content and higher tungsten/silicon content optimized for high-temperature selectivity. This segmentation allows each layer to specialize in different temperature ranges, resolving the contradiction between low-temperature activity and high-temperature selectivity.
3Device complexity
If a single-layer catalyst design is used to simplify the structure, then the manufacturing complexity is reduced, but the performance across varying temperatures deteriorates
Solution Approach 1:
The catalyst is divided into two distinct layers: Layer A (front layer) with higher vanadium content optimized for low-temperature activity, and Layer B (rear layer) with lower vanadium content and higher tungsten/silicon content optimized for high-temperature selectivity. This segmentation allows each layer to specialize in different temperature ranges, resolving the contradiction between low-temperature activity and high-temperature selectivity.
Solution Approach 2:
The catalyst uses a composite structure with two layers having different material compositions. Layer A contains higher vanadium oxide content for low-temperature activity, while Layer B contains lower vanadium oxide and higher tungsten oxide and silicon dioxide for high-temperature selectivity. This composite material approach enables the catalyst to achieve broad temperature range 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 dual-layer catalyst system achieves improved nitrogen oxide conversion rates at both low and high temperatures, addressing the limitations of previous vanadium SCR catalysts by maintaining high selectivity and activity across a broader temperature range.
Implementation Method 1
A dual-layer SCR catalyst system comprising layers A and B, where layer A contains vanadium pentoxide, tungsten trioxide, and optional silicon dioxide, and layer B contains vanadium pentoxide, tungsten trioxide, and silicon dioxide
Implementation Method 2
carbon monoxide (CO), gaseous hydrocarbons (HC) and, if applicable, organic agglomerates adhering to the soot particles (so-called "Volatile Organic Fraction" VOF) can be oxidatively removed using oxidation catalysts
Data Source
AI summary
The invention relates to a catalyst comprising at least two catalytically active layers, A and B, wherein A contains a carrier oxide and components A1 and A2, and B contains a carrier oxide and components B1, B2, and B3, wherein A1, A2, and B1 to B3 are defined as disclosed in claim 1. The proportion of component A1 in layer A is thereby greater than the proportion of component B1 in layer B, wherein the proportion of layer A with respect to the total weight of layers A and B, is greater than the proportion of layer B. The invention further relates to a method for reducing nitrogen oxides in exhaust gases of lean-burn internal combustion engines and to an exhaust gas cleaning system.