SO2 Re-dispersion of Silver and Gold Catalysts
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Solution Overview
Problem
Silver and gold catalysts face deactivation due to sintering, leading to reduced activity in reactions such as ethylene epoxidation and selective catalytic reduction (SCR) of NOx, as they form larger particles over time, especially in reaction-aged catalysts.
Innovation Solution
The use of sulfur dioxide (SO2) to re-disperse and stabilize metal catalysts on substrates like alumina and iron oxide, reducing particle size and preventing agglomeration, thereby maintaining or enhancing catalytic activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If catalyst particles are used in conventional conditions, then catalytic activity is achieved, but sintering occurs leading to particle growth and deactivation
Solution Approach 1:
SO2 acts as an intermediary substance that mediates between the catalyst particles and the reaction environment. It forms a protective interaction with the metal particles, preventing direct sintering while allowing catalytic activity to proceed. The SO2-catalyst interaction creates a stabilized state that resists particle growth.
Solution Approach 2:
The invention changes the chemical environment parameter by introducing SO2 into the reaction system. This parameter change fundamentally alters the sintering behavior of the catalyst particles, transforming the degradation pathway from thermal sintering to a stabilized state maintained by SO2 interaction. The solution operates at temperatures between 400-600°C with SO2 concentrations of 10-1000 ppm.
2Productivity
If catalyst particles aggregate into large clusters, then particle growth is achieved, but catalytic activity decreases due to deactivation
Solution Approach 1:
SO2 serves as a protective intermediary that prevents the aggregation of catalyst particles into large clusters. By forming a stabilized interaction with the metal particles, it maintains particle dispersion and prevents the formation of inactive aggregates, thereby preserving catalytic activity throughout the operation time.
Solution Approach 2:
The SO2 performs preliminary anti-action by preemptively stabilizing the catalyst particles in a dispersed state before significant sintering and aggregation can occur. This preventive mechanism counteracts the natural tendency of particles to aggregate under reaction conditions, maintaining productivity over extended periods.
3Speed
If catalyst operates at high temperature, then reaction rate increases, but sintering accelerates leading to particle growth
Solution Approach 1:
The invention introduces a chemical parameter change (SO2 presence) that decouples the temperature-particle size relationship. While reaction temperature remains high (400-600°C) to maintain fast reaction rates, the SO2 creates a protective effect that prevents thermal sintering, allowing high-speed operation without proportional particle growth.
Solution Approach 2:
SO2 acts as a thermal protective intermediary that shields the catalyst particles from direct thermal sintering effects. It creates a chemical barrier that allows high-temperature operation for fast reaction rates while preventing the temperature-driven aggregation of particles.
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
SO2 effectively re-disperses silver and gold catalysts, maintaining their activity and preventing deactivation by stabilizing them in a dispersed state, which is particularly beneficial for SCR and water-gas shift reactions, allowing for repeated cycles of operation.
Implementation Method 1
SO2 can re-disperse a metal-containing catalyst (such as silver particles) on a reaction aged silver-alumina surface at 625° C. by SO2
Implementation Method 2
the presence of SO2 can stabilize the particles in a dispersed state on a substrate (e.g., alumina) and suppress deactivation
Implementation Method 3
In the absence of SO2, severe sintering of catalyst particles (e.g., silver particles) takes place in a reaction gas at 625° C. and the particles agglomerate into large clusters of micrometer size. However, the presence of SO2 can stabilize the particles in a dispersed state on a substrate
Implementation Method 4
silver catalysts have potential application in SCR of NOx with hydrocarbons or oxygenates to remove nitrogen oxides from various exhaust gas effluents
Implementation Method 5
selective catalytic reduction (SCR) of NOx with hydrocarbons to remove nitrogen oxides from various exhaust gas effluents
Implementation Method 6
water-gas shift (WGS) reaction
Implementation Method 7
atomically dispersed gold strongly bound to an oxide compound provides the active sites for the reaction
Data Source
AI summary
A method includes contacting a catalyst including a metal having an average particle size of approximately one nanometer or greater with SO2; and reducing the average particle size of the metal.