Multi-Oxide SCR Catalyst Composition for Low-Temperature Stability
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Solution Overview
Problem
Existing vanadium-based SCR catalysts struggle to achieve simultaneous good low-temperature activity and thermal stability, as well as consistent performance in both fresh and aged states, due to the trade-off between these properties in prior art compositions.
Innovation Solution
A catalyst composition comprising specific weight percentages of vanadium, tungsten, antimony, and titanium oxides, with optional zirconium, optimized to provide enhanced low-temperature activity and high-temperature selectivity, along with improved thermal stability in both fresh and aged states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional vanadium-based SCR catalyst compositions are used, then nitrogen oxide conversion is achieved, but low-temperature activity and thermal stability cannot be simultaneously optimized
Solution Approach 1:
The patent applies parameter changes by precisely controlling the weight percentages of multiple oxide components: vanadium oxide (2.0-4.0 wt.-%), tungsten oxide (2.5-7.2 wt.-%), antimony oxide (0.6-3.4 wt.-%), and titanium oxide (84.6-94.9 wt.-%). This multi-parameter optimization enables the catalyst to achieve both low-temperature activity and thermal stability simultaneously, resolving the traditional trade-off between these properties.
Solution Approach 2:
The patent employs composite materials by formulating a multi-oxide catalyst system comprising vanadium oxide, tungsten oxide, antimony oxide, and titanium oxide in specific proportions. This composite structure combines the advantages of each oxide: vanadium for catalytic activity, tungsten for thermal stability, antimony for promotion effects, and titanium as a stable support, thereby achieving both low-temperature performance and high-temperature resistance.
2Reliability
If conventional vanadium-based SCR catalyst compositions are used, then nitrogen oxide conversion is achieved, but consistent performance in fresh and aged states cannot be maintained
Solution Approach 1:
The patent applies beforehand cushioning by incorporating tungsten oxide (2.5-7.2 wt.-%) and antimony oxide (0.6-3.4 wt.-%) into the catalyst composition before aging occurs. These components act as protective elements that pre-establish thermal stability and resistance to degradation, cushioning the catalyst against performance loss during aging and maintaining consistent activity from fresh to aged states.
Solution Approach 2:
The multi-oxide composite structure provides consistent performance across the catalyst lifecycle. The synergistic combination of vanadium oxide (catalytic activity), tungsten oxide (thermal stability), antimony oxide (promotion and stability), and titanium oxide (structural support) ensures that the catalyst maintains its performance characteristics whether in the fresh or aged state, eliminating the variability seen in conventional single-oxide systems.
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 catalyst composition demonstrates superior performance across varying temperatures and ages, maintaining effective nitrogen oxide conversion rates and selectivity, addressing the limitations of prior vanadium-based catalysts.
Implementation Method 1
The selective catalytic reduction (SCR) takes place in the presence of an SCR catalyst according to the reaction schemes below: 4NO+4NH3+O2→4N2+6H2O
Implementation Method 2
the nitrogen oxides to be removed from the exhaust gas are converted to nitrogen and water using ammonia
Implementation Method 3
Mixed oxides, for example, which are based in particular on titanium dioxide and/or oxides of vanadium such as vanadium pentoxide, and which can contain other oxides, such as those of silicon, molybdenum, manganese, tungsten, and others, can be used as SCR catalysts
Data Source
AI summary
The present invention disclose catalyst compositions for the selective catalytic reduction of nitrogen oxides, consisting of at least one oxide of vanadium in an amount of 2.0 to 4.0 wt.-%, calculated as V2O5 and based on the total weight of the catalyst composition, at least one oxide of tungsten in an amount of 2.5 to 7.2 wt.-%, calculated as WO3 and based on the total weight of the catalyst composition, at least one oxide of antimony in an amount of 0.6 to 3.4 wt.-%, calculated as Sb2O5 and based on the total weight of the catalyst composition, at least one oxide of zirconium in an amount of 0 to 1.0 wt.-%, calculated as ZrO2 and based on the total weight of the catalyst, and at least one oxide of titanium in an amount of 84.6 to 94.9 wt.-% calculated as TiO2 and based on the total weight of the catalyst, wherein the weight ratio of the oxides of vanadium, tungsten, antimony, titanium and optionally zirconium, calculated as V2O5, WO3, Sb2O5, TiO2 and optionally ZrC2, respectively, add up to 100 wt.-%. Furthermore, SCR catalytic articles are disclosed wherein an SCR catalyst composition according to the invention is affixed in the form of a coating. Suitable catalyst carriers are corrugated substrates and cordierite monoliths. The SCR catalytic articles can be used in a method for the reduction of nitrogen oxides in exhaust gases of lean-burn internal combustion engines, and they can furthermore be comprised in an exhaust gas purification system for the treatment of diesel exhaust gas.