Mayenite-Type Catalyst for Ammonia Decomposition
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Solution Overview
Problem
Current ammonia decomposition catalysts face challenges in efficiently converting ammonia to hydrogen at high concentrations and low temperatures, with heat-resistant ceramics experiencing decreased catalytic activity at high temperatures and low NH3 conversion rates, especially in high-concentration ammonia environments.
Innovation Solution
A supported metal catalyst using a mayenite-type compound as the base material, containing conduction electrons or hydrogen anions, is employed for ammonia decomposition, which enhances the conversion rate and stability, allowing for efficient ammonia decomposition into hydrogen and nitrogen at relatively low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If heat-resistant ceramics are used as catalyst support for ammonia decomposition, then the catalyst can maintain structural stability at high temperatures, but the catalytic activity decreases at high temperatures and the NH3 conversion rate is low
Solution Approach 1:
The patent uses mayenite-type compound (12CaO·7Al2O3) as a composite catalyst support material that combines the structural stability of ceramics with enhanced catalytic properties. The mayenite structure provides both thermal stability and active sites for ammonia decomposition, resolving the contradiction between structural stability and catalytic activity.
2Temperature
If conventional catalysts are used for ammonia decomposition, then the process can proceed at moderate temperatures, but the NH3 conversion rate is insufficient especially in high-concentration ammonia environments
Solution Approach 1:
The patent modifies the catalyst support parameters by using mayenite-type compound with specific properties (12CaO·7Al2O3 structure, specific surface area 8.5-100 m2/g, pore volume 0.3-1.5 ml/g). These parameter changes enable the catalyst to achieve high NH3 conversion rates at moderate temperatures, particularly in high-concentration ammonia environments.
3Productivity
If expensive rare metals are used as catalyst components, then the catalytic activity and NH3 conversion rate improve, but the production cost increases and the production process becomes complex
Solution Approach 1:
The patent replaces expensive rare metal catalysts with a cost-effective mayenite-type compound (12CaO·7Al2O3) as the catalyst support. This substitution maintains high NH3 conversion rates while significantly reducing production costs and simplifying the manufacturing process, making the catalyst more economically viable for industrial application.
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 a high NH3 conversion rate of up to 2 times that of alumina-supported catalysts, producing high-purity hydrogen with a high conversion rate and extended catalyst life, reducing the need for expensive rare metals and simplifying the production process.
Implementation Method 1
contact decomposition of ammonia gas (NH3) into hydrogen (H2) and nitrogen (N2) at a relatively low temperature
Implementation Method 2
Decomposition reaction of ammonia is volume expansion-type endothermic reaction represented by 2NH3 → 3H2 + N2
Implementation Method 3
A supported metal catalyst using a mayenite-type compound as the base material, containing conduction electrons or hydrogen anions
Implementation Method 4
a rate-controlling step of ammonia decomposition reaction is desorption of nitrogen species adsorbed on a catalyst surface
Data Source
Figure 1
AI summary
[Problem] To provide a metal-supporting catalyst for decomposing ammonia into hydrogen and nitrogen, said catalyst showing a high performance, having a low cost and being advantageous from the viewpoint of resources, and an efficient method for producing hydrogen using the catalyst. [Solution] A hydrogen generation catalyst for catalytically decomposing ammonia gas to generate hydrogen, characterized in that the hydrogen generation catalyst comprises, as a support, a mayenite type compound having oxygen ions enclosed therein or a mayenite type compound having 1015 cm-3 or more of conduction electrons or hydrogen anions enclosed therein, and metal grains for decomposing ammonia are supported on the surface of the support. Hydrogen is produced by continuously supplying 0.1-100 vol% of ammonia gas to a catalyst layer that comprises the aforesaid catalyst, and reacting the same at a reaction pressure of 0.01-1.0 MPa, at a reaction temperature of 300-800°C and at a weight hourly space velocity (WHSV) of 500/mlg-1h-1 or higher.