Ce-Based Mixed Oxide Catalyst for NOx Reduction
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Solution Overview
Problem
Current catalyst systems for NOx abatement from diesel vehicle exhaust and coal-fired power plant flue gas face challenges such as narrow operation temperature range, poor activity at low temperatures, susceptibility to reaction space velocity, and the use of toxic vanadium, limiting their effectiveness and environmental safety.
Innovation Solution
A cerium-based mixed oxide catalyst, comprising cerium and transition metals like tungsten, molybdenum, and iron, which forms a solid solution of oxides with different valence states, is developed using methods like homogenous precipitation, sol-gel, citric acid complexing, and hydrothermal synthesis, allowing for effective NOx reduction without carriers and resistant to sulfur and water poisoning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional catalyst systems are used for NOx abatement, then NOx removal function is achieved, but operation temperature range is narrow and low-temperature activity is poor
Solution Approach 1:
The patent uses composite materials by combining cerium oxide with transition metal oxides (tungsten, molybdenum, or iron) to create a mixed oxide catalyst. This composite structure synergistically improves both the low-temperature activity and the broad temperature range performance, resolving the contradiction between temperature adaptability and catalytic activity.
Solution Approach 2:
The patent changes the chemical composition parameters of the catalyst by incorporating multiple metal oxides with different valence states (Ce4+, W6+, Mo6+, Fe3+). This parameter modification enables the catalyst to maintain high activity across a broader temperature range, particularly improving low-temperature performance while maintaining reliability at higher temperatures.
2Reliability
If vanadium-based catalysts are used for NOx reduction, then catalytic activity is achieved, but environmental safety deteriorates due to toxicity
Solution Approach 1:
The patent extracts and removes the toxic vanadium component from the catalyst system while retaining the desired catalytic functionality. By replacing vanadium with non-toxic transition metals (tungsten, molybdenum, or iron) combined with cerium oxide, the catalyst maintains high NOx reduction activity while eliminating environmental and health hazards associated with vanadium toxicity.
3Area of stationary object
If catalysts with carriers are used to increase surface area, then specific surface area increases, but device volume and space requirements increase
Solution Approach 1:
The patent utilizes porous materials by creating a mixed oxide catalyst with inherent porous structure through solid solution formation. This porous architecture provides high specific surface area for catalytic reactions without requiring additional carrier materials, thus maintaining high surface area while minimizing catalyst volume and space requirements.
4Reliability
If conventional catalysts are used, then NOx conversion is achieved, but resistance to sulfur poisoning is insufficient
Solution Approach 1:
The patent employs composite materials combining cerium oxide with sulfur-resistant transition metal oxides (particularly tungsten and molybdenum). This composite structure provides synergistic effects where the transition metal oxides confer sulfur poisoning resistance while cerium oxide maintains high NOx conversion efficiency, thus improving both reliability and sulfur resistance simultaneously.
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 cerium-based mixed oxide catalyst exhibits broad operation temperature range, high NOx conversion efficiency, excellent N2 selectivity, and resistance to high space velocities and sulfur poisoning, reducing environmental hazards and operational costs.
Implementation Method 1
a cerium-based mixed oxide catalyst for catalytic abatement of nitrogen oxides
Implementation Method 2
homogenous precipitation method
Implementation Method 3
sol-gel
Implementation Method 4
citric acid complexing
Implementation Method 5
hydrothermal synthesis
Data Source
AI summary
Disclosed is a Ce-based composite oxide catalyst for selective catalytic reducing nitrogen oxides with ammonia, which comprises Ce oxide and at least one oxide of transition metal except Ce. The Ce-based composite oxide catalyst is prepared by a simple method which uses non-toxic and harmless raw materials, and it has the following advantages: high catalytic activity, and excellent selectivity for generating nitrogen etc. The catalyst can be applied in catalytic cleaning plant for nitrogen oxides from mobile and stationary sources.