Silver-Promoted Catalysts for Oxidative Coupling of Methane
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Solution Overview
Problem
Current catalyst systems for oxidative coupling of methane (OCM) face challenges such as high reaction temperatures, catalyst deactivation due to uncontrolled heat excursions, and reduced selectivity of ethylene production due to deep oxidation reactions, which affect the efficiency and stability of the process.
Innovation Solution
Development of silver (Ag) promoted catalyst compositions, including Ag-doped Mn/Na2WO4 and Ag-doped lanthanum (III) and cerium (IV) mixtures, which are used to enhance methane conversion and C2+ hydrocarbon selectivity by reducing the ignition temperature and catalyst bed temperature, thereby minimizing hot spots and deep oxidation reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional catalyst systems are used for OCM, then methane conversion can be achieved, but reaction temperatures become excessively high leading to catalyst deactivation and reduced selectivity
Solution Approach 1:
The patent employs composite catalyst systems combining silver with metal oxides (such as MnOx, La2O3, CeO2, and their combinations) to create a synergistic effect. This composite structure allows the catalyst to achieve high methane conversion at lower temperatures by distributing the catalytic function across multiple components, each contributing specific properties that collectively reduce the required reaction temperature while maintaining productivity
Solution Approach 2:
The invention modifies the catalytic parameters by introducing silver as a promoter that changes the activation energy and reaction pathway of methane oxidation. This parameter change enables the reaction to proceed at lower temperatures by altering the kinetic properties of the catalyst, thereby resolving the contradiction between maintaining high conversion and reducing temperature
2Productivity
If high reaction temperatures are used to maintain catalyst activity, then methane conversion improves, but deep oxidation reactions increase reducing ethylene selectivity
Solution Approach 1:
The composite catalyst system with silver and metal oxides provides selective active sites that favor partial oxidation to ethylene over complete oxidation to CO and CO2. The specific composition and structure of the composite material create a controlled reaction environment that enhances selectivity while maintaining conversion efficiency
Solution Approach 2:
The catalyst design incorporates local quality variations through different metal oxide components and silver distribution, creating zones with different catalytic properties. This allows certain regions to promote methane activation while other regions favor ethylene formation, thereby maintaining high selectivity even at elevated conversion levels
3Productivity
If exothermic reactions are promoted to increase conversion rate, then productivity improves, but uncontrolled heat excursions occur leading to catalyst deactivation
Solution Approach 1:
The composite catalyst structure with silver and metal oxides provides thermal stability and heat distribution properties that prevent localized hot spots. The multiple components work together to moderate the exothermic reaction, distributing heat generation across the catalyst bed and preventing thermal runaways that would lead to deactivation
Solution Approach 2:
The metal oxide components act as intermediaries that moderate the exothermic oxidation reaction. They provide a controlled pathway for oxygen activation and radical formation, preventing direct uncontrolled oxidation that generates excessive heat. This intermediary function stabilizes the reaction while maintaining high conversion rates
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 silver-promoted catalysts improve methane conversion and C2+ hydrocarbon selectivity, increase catalyst stability, and reduce the formation of unwanted carbon monoxide and carbon dioxide, leading to more efficient and selective production of ethylene and other C2+ hydrocarbons.
Implementation Method 1
catalysts are used to overcome the endothermic nature of the C—H bond breakage
Implementation Method 2
CH4 and O2 react exothermically over a catalyst to form C2H4, water (H2O) and heat
Implementation Method 3
CH4 is activated heterogeneously on a catalyst surface, forming methyl free radicals
Implementation Method 4
enhance methane conversion and C2+ hydrocarbon selectivity by reducing the ignition temperature and catalyst bed temperature
Data Source
AI summary
An oxidative coupling of methane (OCM) catalyst composition comprising one or more oxides doped with Ag; wherein one or more oxides comprises a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof; and wherein one or more oxides is not La2O3 alone. A method of making an OCM catalyst composition comprising calcining one or more oxides and/or oxide precursors to form one or more calcined oxides, wherein the one or more oxides comprises a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof, wherein the one or more oxides is not La2O3 alone, and wherein the oxide precursors comprise oxides, nitrates, carbonates, hydroxides, or combinations thereof; doping the one or more calcined oxides with Ag to form the OCM catalyst composition; and thermally treating the OCM catalyst composition.