Selective Ammonia Oxidation Catalyst for Hydrogen Purification
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Solution Overview
Problem
Current methods for removing ammonia from hydrogen gas mixtures, such as those produced by ammonia decomposition, are inefficient and costly due to the use of noble metal membranes, which are unstable and require high pressure, making it difficult to achieve ammonia-free gas suitable for low temperature fuel cells.
Innovation Solution
A catalyst-based apparatus that combines ammonia decomposition and oxidation units, using a transition metal catalyst like chromium oxide supported on titania, to selectively remove ammonia from gas mixtures, reducing ammonia concentrations below equilibrium levels, thus eliminating the need for noble metal membranes and integrating ammonia removal with decomposition in a single, cost-effective unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a noble metal membrane is used to separate ammonia from hydrogen gas, then ammonia removal efficiency is improved, but the cost and device complexity increase significantly
Solution Approach 1:
The invention extracts and removes only the harmful ammonia component from the gas mixture using a selective catalyst, while allowing hydrogen to pass through. This targeted removal approach replaces the need for complex noble metal membranes that attempt to separate all components, thereby reducing device complexity while maintaining ammonia removal efficiency.
Solution Approach 2:
The invention uses inexpensive catalyst materials (such as copper, zinc, or aluminum-based catalysts) instead of expensive noble metals. These catalysts can be replaced periodically when deactivated, providing a cost-effective alternative to expensive, complex membrane systems. The low cost allows for periodic replacement rather than long-term investment in expensive equipment.
2Reliability
If a noble metal membrane is used to separate ammonia from hydrogen gas, then ammonia removal efficiency is improved, but the operational cost increases due to high pressure requirements
Solution Approach 1:
The invention replaces the mechanical pressure-driven separation process of membrane systems with a chemical catalytic process. Instead of using high pressure to force gas through a membrane, the catalyst selectively converts ammonia at low pressure, eliminating the need for high-pressure equipment and associated energy costs while maintaining effective ammonia removal.
3Reliability
If a noble metal membrane is used to separate ammonia from hydrogen gas, then ammonia removal efficiency is improved, but the stability and reliability of the system decrease
Solution Approach 1:
The invention uses inexpensive catalyst materials that can be periodically replaced when deactivated, providing a stable and reliable system. Unlike noble metal membranes that are inherently unstable and degrade over time, these catalysts maintain consistent performance until deactivation, at which point they can be easily replaced without affecting system stability.
4Productivity
If high pressure is applied to achieve reasonable hydrogen gas flow through the membrane, then productivity is improved, but the equipment cost and complexity increase
Solution Approach 1:
The invention replaces the pressure-driven flow mechanism with a catalytic conversion mechanism. The catalyst enables ammonia removal and hydrogen production at low pressure, maintaining high productivity without requiring expensive high-pressure equipment. The catalytic process inherently drives the reaction forward, eliminating the need for mechanical pressure 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 effectively reduces ammonia concentrations from ppm levels to near-zero, providing a hydrogen gas mixture suitable for low temperature fuel cells, enhancing fuel cell performance and reducing operational costs by eliminating the need for high-pressure equipment and noble metal membranes.
Implementation Method 1
a catalyst for oxidizing ammonia. The ammonia oxidizing unit oxidize the ammonia present in the gas mixture containing hydrogen and nitrogen gas originated in the ammonia decomposition unit
Implementation Method 2
a catalyst for decomposing ammonia. Ammonia dissociation in an ammonia decomposition unit produces hydrogen, nitrogen and ammonia gases
Data Source
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AI summary
The invention contributes to a cost effective way to solve the problem of trace ammonia removal from a hydrogen and nitrogen containing gas. The set of catalysts of the invention selectively oxidised ammonia in ppm concentration even in gas mixtures containing hydrogen gas in concentrations of three orders of magnitude higher than the concentration of ammonia.