Exhaust Gas Catalyst Phosphorus Vanadium Ratio
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Solution Overview
Problem
Conventional NOX-removal catalysts face a tradeoff between maintaining high elemental mercury (Hg) oxidation activity and suppressing sulfur dioxide (SO2) oxidation activity, as increased vanadium content enhances Hg oxidation but also promotes SO2 oxidation, leading to smoke pollution.
Innovation Solution
A catalyst composition containing titanium (Ti), molybdenum (Mo) or tungsten (W), vanadium (V), and phosphorus (P) in specific atomic proportions, where the P/(sum of V and Mo/W) ratio is between 0.5 and 1.5, reduces SO2 oxidation while maintaining high Hg oxidation activity, achieved by reacting V compounds with phosphoric acid or phosphate salts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vanadium content is increased to enhance Hg oxidation activity, then Hg oxidation activity is improved, but SO2 oxidation activity increases leading to smoke pollution
Solution Approach 1:
The invention changes the chemical composition parameters by introducing phosphorus (P) into the catalyst system and optimizing the atomic ratio of P to (V+Mo/W) to be 0.5-1.5. This parameter change selectively suppresses SO2 oxidation activity while preserving Hg oxidation activity, resolving the contradiction between these two functions.
Solution Approach 2:
The invention creates a composite catalyst material containing Ti, Mo/W, V, and P in specific proportions. The composite structure allows the phosphorus component to selectively inhibit SO2 oxidation pathways while maintaining the vanadium-driven Hg oxidation capability, thus resolving the functional contradiction.
2Reliability
If vanadium content is increased to maintain high Hg oxidation activity, then Hg oxidation performance is improved, but SO3 formation increases causing smoke and secondary pollution
Solution Approach 1:
By optimizing the atomic ratio of P/(V+Mo/W) to 0.5-1.5 and controlling the overall composition ratios, the invention changes the catalytic properties to selectively reduce SO3 formation while maintaining Hg oxidation performance at high levels.
Solution Approach 2:
Phosphorus acts as an intermediary substance that selectively interacts with the vanadium oxide species to modify their catalytic behavior. The phosphorus component mediates the interaction between the catalyst and SO2, preventing excessive SO3 formation while allowing Hg oxidation to proceed efficiently.
3Object-generated harmful factors
If a NOX-removal catalyst is designed to achieve low SO2 oxidation, then SO2 oxidation is suppressed, but Hg oxidation activity may be compromised
Solution Approach 1:
The invention optimizes the atomic proportions of Ti (85-97.5%), Mo/W (2-10%), V (0.5-10%), and P (achieving P/(V+Mo/W) ratio of 0.5-1.5) to create a catalyst that simultaneously achieves low SO2 oxidation and high Hg oxidation activity, resolving the trade-off between these two functions.
Solution Approach 2:
The phosphorus addition creates local chemical environments within the catalyst structure that selectively affect SO2 oxidation pathways while leaving Hg oxidation pathways intact. This local modification of catalytic properties allows differential control over the two oxidation reactions.
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 achieves high NOX removal and mercury oxidation performance while significantly reducing SO2 oxidation, meeting the requirement for low SO2 oxidation and high Hg oxidation, thus overcoming the tradeoff limitations of conventional catalysts.
Implementation Method 1
highly volatile metallic mercury (elemental mercury, Hg) is oxidized into a mercury compound
Implementation Method 2
NOX contained in exhaust gas is reduced by NH3
Data Source
AI summary
To overcome the problem of a conventional catalyst and to provide an exhaust gas purifying catalyst that meets the requirement concerning Hg oxidation activity and SO2 oxidation activity; i.e., an exhaust gas purifying catalyst which specifically reduces percent SO2 oxidation, while maintaining percent Hg oxidation at a high level.The invention provides an exhaust gas purifying catalyst which comprises a composition containing oxides of (i) titanium (Ti), (ii) molybdenum (Mo) and/or tungsten (W), (iii) vanadium (V), and (iv) phosphorus (P), wherein the catalyst contains Ti, Mo and/or W, and V in atomic proportions of 85 to 97.5:2 to 10: 0.5 to 10, and has an atomic ratio of P/(sum of V and Mo and/or W) of 0.5 to 1.5, and an exhaust gas purifying method comprising exposing an exhaust gas containing a nitrogen oxide (NOX) and metallic mercury (Hg) to the catalyst in the presence of ammonia as a reducing agent, to thereby perform reduction of NOX contained in the exhaust gas and oxidation of metallic mercury (Hg) contained in the exhaust gas.