NOx Removal Catalyst Production via ZrO2-TiO2 Composite Support
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional NOx removal catalysts using ammonia as a reducing agent are ineffective at high temperatures due to the oxidation of ammonia, leading to poor NOx removal performance, especially in exhaust gases from fossil-fuel power plants and gas turbines operating above 500°C, where the catalyst's catalytic activity is limited by the mechanical strength of the support and the tungsten component.
Innovation Solution
A method involving the calcination of a mixture of ZrO2 and TiO2 to create a composite oxide support with a desired ratio of ZrO2, followed by supporting tungsten oxide and calcination at a higher temperature, which maintains the adhesion of tungsten oxide and enhances catalytic activity, while allowing sulfate ions to remain on the support to suppress ammonia decomposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If tungsten is supported on titanium oxide support optimized for mechanical strength, then the catalyst structure is stable, but the catalytic activity is limited and NOx removal reaction cannot proceed efficiently
Solution Approach 1:
The patent uses a composite oxide support made of ZrO2 and TiO2 instead of pure TiO2. The ZrO2 component provides mechanical strength while TiO2 provides catalytic activity. This composite structure resolves the contradiction by combining materials with complementary properties - ZrO2 for structural stability and TiO2 for catalytic function, enabling both high mechanical strength and high catalytic activity simultaneously.
Solution Approach 2:
The patent creates solid acid sites with specific properties in specific regions of the catalyst. By controlling the ratio of ZrO2 to TiO2 and the distribution of tungsten oxide, the patent creates localized areas with different functions: some regions provide mechanical strength (ZrO2-rich areas) while others provide catalytic activity (TiO2-rich areas with solid acid sites). This local differentiation resolves the contradiction between structural stability and catalytic efficiency.
2Productivity
If ammonia is used as reducing agent at high temperature (450°C or more), then NOx removal reaction proceeds, but oxidation reaction of NH3 also proceeds causing NH3 to be not utilized effectively
Solution Approach 1:
The patent changes the chemical environment parameters by introducing solid acid sites on the catalyst surface. These solid acid sites modify the reaction pathway and reduce the activation energy for the desired NOx reduction reaction, allowing it to proceed selectively at high temperatures without promoting the competing ammonia oxidation reaction. This parameter change (chemical environment modification) resolves the contradiction by enabling selective catalysis.
Solution Approach 2:
The solid acid sites act as intermediaries that facilitate the desired reaction. These sites provide alternative reaction pathways where ammonia can reduce NOx without directly oxidizing. The solid acid sites mediate the interaction between ammonia and NOx, enabling the reduction reaction to proceed preferentially even at high temperatures where oxidation would normally dominate.
3Adaptability or versatility
If the catalyst is designed for high temperature operation (500°C or above), then it can handle gas turbine exhaust, but conventional catalysts show deterioration in NOx removal performance
Solution Approach 1:
The ZrO2-TiO2 composite support maintains structural integrity at high temperatures due to ZrO2's thermal stability, while TiO2 maintains catalytic activity. This composite structure allows the catalyst to operate reliably at 500°C and above, resolving the contradiction between temperature adaptability and performance reliability.
Solution Approach 2:
The patent creates localized solid acid sites with specific chemical properties that remain stable at high temperatures. These sites are distributed throughout the catalyst structure, providing consistent catalytic activity across the entire catalyst bed even under high-temperature conditions. This local quality control ensures reliable NOx removal performance across a wide temperature range.
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 method produces a NOx removal catalyst with improved solid acid sites and catalytic activity, maintaining high NOx removal performance even at temperatures above 500°C, with tungsten oxide supported in five molecular layers or fewer, ensuring effective NOx reduction and reducing ammonia decomposition.
Implementation Method 1
making a control to provide solid acid sites at a desired ratio
Implementation Method 2
supporting tungsten oxide on the composite oxide support followed by calcination at 650±15° C. to obtain a powder catalyst
Implementation Method 3
calcining a mixture comprising ZrO2 and TiO2 with a ZrO2 content ration of 15% by weight to 55% by weight at 500±15° C.
Data Source
AI summary
Provided is a method for producing a NOx removal catalyst for high-temperature exhaust gas, comprising: calcining a mixture comprising ZrO2 and TiO2 with a ZrO2 content ratio of 15% by weight to 55% by weight at 500±15° C. to obtain a composite oxide support; and supporting tungsten oxide on the composite oxide support, followed by calcination at 650±15° C. to obtain a powder catalyst.