Mixed Oxide Catalyst for Methane Oxidative Coupling
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Solution Overview
Problem
The oxidative coupling of methane (OCM) process faces challenges in achieving high yield and selectivity of ethylene and ethane due to non-selective reactions, thermodynamic stability of methane, and the need for catalysts with both basic and redox properties, which often compromise stability and selectivity.
Innovation Solution
A catalytic material with the formula AaBbCcDdOx, comprising alkaline earth metals, rare earth metals, and transition metals, which creates a synergistic effect to enhance methane conversion and C2+ selectivity, providing a catalyst with balanced basic and redox properties for improved OCM reaction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the catalyst possesses high basic properties to activate methane, then methane conversion is improved, but catalyst stability is reduced
Solution Approach 1:
The patent employs a composite catalyst system comprising multiple metal oxides (e.g., alkaline earth metal oxides like SrO, CaO combined with rare earth metal oxides like CeO2, La2O3) that work synergistically. The composite structure allows the catalyst to achieve high methane conversion through basic properties while the combined materials provide enhanced thermal stability and structural integrity, resolving the contradiction between activity and stability.
Solution Approach 2:
The patent optimizes the stoichiometric ratios of metal oxides in the catalyst formulation and controls calcination temperature parameters to achieve the desired balance. By adjusting the basicity parameters and redox properties through compositional changes, the catalyst achieves high methane conversion while maintaining stability under reaction conditions.
2Reliability
If the catalyst possesses high redox properties to stabilize catalyst performance, then catalyst stability is improved, but C2+ product selectivity is reduced
Solution Approach 1:
The composite catalyst combines metal oxides with complementary properties: rare earth metal oxides (CeO2, La2O3) provide redox functionality and stability, while alkaline earth metal oxides (SrO, CaO) contribute basic properties that enhance C2+ selectivity. This composite approach allows simultaneous achievement of catalyst stability and high selectivity for desired products.
Solution Approach 2:
Different regions or components of the composite catalyst perform specialized functions: certain metal oxide phases provide redox cycling for stability while other phases with higher basicity locally enhance C2+ formation. This functional differentiation within the composite structure resolves the selectivity-stability trade-off.
3Productivity
If non-selective reactions occur on the catalyst surface, then methane activation is achieved, but C2+ product yield is reduced due to formation of CO and CO2
Solution Approach 1:
The catalyst surface acts as an intermediary that facilitates selective methane activation and C2+ formation while suppressing non-selective pathways. The specific metal oxide composition and surface properties mediate the reaction to favor C2+ products over CO and CO2 formation, resolving the selectivity issue while maintaining high methane conversion.
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 catalytic material achieves methane conversion of greater than 15% and C2+ selectivity of greater than 70%, increasing reaction rate and stability, while maintaining catalyst performance over extended periods.
Implementation Method 1
methane (CH4) is activated heterogeneously on the catalyst surface, forming methyl free radicals
Implementation Method 2
The reduced catalyst surface must then be re-oxidized back to its initial state in order for the reaction to continue. In order for re-oxidation to occur, the catalyst needs to possess redox properties
Data Source
AI summary
A mixed oxide catalyst for the oxidative coupling of methane can include a catalyst with the formula AaBbCcDdOx, wherein: element A is selected from alkaline earth metals; elements B and C are selected from rare earth metals, and wherein elements B and C are different rare earth metals; the oxide of at least one of A, B, C, and D has basic properties; the oxide of at least one of A, B, C, and D has redox properties; and elements A, B, C, and D are selected to create a synergistic effect whereby the catalytic material provides a methane conversion of greater than or equal to 15% and a C2+ selectivity of greater than or equal to 70%. Systems and methods can include contacting the catalyst with methane and oxygen and purifying or collecting C2+ products.