Zoned Vanadium SCR Catalyst for Low-Temperature NOx Conversion
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Solution Overview
Problem
Conventional SCR catalysts struggle to effectively reduce NOx from exhaust gases at low temperatures, as they require sufficient NO2 conversion, which is challenging at cold start and warm-up phases, and also face difficulties in providing adequate ammonia at low temperatures.
Innovation Solution
The development of emissions treatment systems using vanadium-based SCR catalysts with two material zones, where the first zone has a lower vanadium content and the second zone has a higher vanadium content, arranged in a specific order to enhance NOx conversion across a wide temperature range while minimizing N2O selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional SCR catalysts are used, then high-temperature NOx conversion is achieved, but low-temperature NOx conversion is insufficient
Solution Approach 1:
The catalytic device is divided into two distinct material zones with different vanadium contents. The first zone (lower vanadium content) handles low-temperature NOx conversion, while the second zone (higher vanadium content) handles high-temperature NOx conversion. This segmentation allows each zone to be optimized for its specific temperature range, resolving the contradiction between low-temperature and high-temperature performance.
Solution Approach 2:
Different regions of the catalytic device are assigned different vanadium concentrations tailored to their functional requirements. The first zone has lower vanadium content suitable for low-temperature operation, while the second zone has higher vanadium content for high-temperature operation. This local quality differentiation enables simultaneous optimization for both temperature ranges.
2Productivity
If vanadium content is increased to improve low-temperature performance, then low-temperature NOx conversion improves, but high-temperature NOx conversion and selectivity deteriorate
Solution Approach 1:
The catalytic device is divided into two distinct material zones with different vanadium contents. The first zone (lower vanadium content) handles low-temperature NOx conversion, while the second zone (higher vanadium content) handles high-temperature NOx conversion. This segmentation allows each zone to be optimized for its specific temperature range, resolving the contradiction between low-temperature and high-temperature performance.
Solution Approach 2:
Different regions of the catalytic device are assigned different vanadium concentrations tailored to their functional requirements. The first zone has lower vanadium content suitable for low-temperature operation, while the second zone has higher vanadium content for high-temperature operation. This local quality differentiation enables simultaneous optimization for both temperature ranges.
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 system achieves both high low-temperature and high-temperature NOx conversion, while maintaining low N2O selectivity, thereby addressing the limitations of conventional SCR catalysts.
Implementation Method 1
Nitrogen oxides may be converted on an SCR catalyst in the presence of oxygen to nitrogen and water by means of ammonia. 'SCR' stands for 'selective catalytic reduction'.
Implementation Method 2
In NH3—SCR, the NOx molecules are catalytically reduced to N2 using NH3 as reducing agent.
Implementation Method 3
To take advantage of the fast NH3—SCR reaction, an additional catalyst is needed to oxidize part of the NO into NO2.
Implementation Method 4
The ammonia used as reducing agent may be made available by feeding an ammonia precursor compound into the exhaust gas which is thermolyzed and hydrolyzed to form ammonia.
Implementation Method 5
The ammonia used as reducing agent may be made available by feeding an ammonia precursor compound into the exhaust gas which is thermolyzed and hydrolyzed to form ammonia.
Data Source
AI summary
The present invention discloses emissions treatment systems for the removal of NOx from exhaust combustion gases comprising, in the following order, from upstream to downstream: a) means for the injection of ammonia or an ammonia precursor solution into the exhaust gas stream, and b) a catalytic device comprising at least one carrier substrate, a material zone A comprising a first V/TiO2 SCR catalytically active composition SCRfirst which comprises at least one oxide of vanadium supported on titanium dioxide, a material zone B comprising a second V/TiO2 SCR catalytically active composition SCRsecond which comprises at least one oxide of vanadium supported on titanium dioxide, wherein the two material zones are affixed to the at least one carrier substrate in such a way that the exhaust gas first comes into contact with material zone A and then with material zone B, and wherein the ratio Vfirst:Vsecond of the percentages of vanadium contained in the first to the second V/TiO2 SCR catalytically active composition, each calculated as V2O5, is from 0.05 to 0.75. Methods for the removal of NOx emissions from exhaust gases of internal combustion engines are also envisaged.