Reverse Water-Gas Shift Catalyst for Methane Suppression
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Solution Overview
Problem
The reverse water-gas shift (rWGS) reaction faces challenges such as competing Sabatier and carbon monoxide methanation reactions, especially at lower temperatures, which reduce carbon monoxide yield and lead to carbon deposits on catalysts, limiting catalyst lifetime. Additionally, the use of excess hydrogen to drive the rWGS equilibrium towards carbon monoxide risks hydrogenating carbon monoxide to methane.
Innovation Solution
A supported reverse water-gas shift catalyst comprising a metal oxide support, such as cerium oxide, titanium oxide, or a mixed oxide, combined with metals like manganese, copper, gallium, or zirconium, and optionally platinum, palladium, gold, or nickel. This catalyst is designed to operate within a temperature range of 200-1100 °C, utilizing CO2 from renewable sources like biogas or direct air capture to enhance carbon utilization and reduce greenhouse gas emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the reaction temperature is lowered to favor the endothermic rWGS reaction, then carbon monoxide yield is improved, but the Sabatier reaction and CO methanation are enhanced leading to reduced CO selectivity and increased methane production
Solution Approach 1:
The patent employs a dual-catalyst system where one catalyst promotes the reverse water-gas shift reaction while another catalyst suppresses methanation. This parameter change in catalyst composition allows the system to operate at lower temperatures to favor endothermic rWGS while simultaneously inhibiting exothermic side reactions through the selective catalytic properties of the second catalyst.
Solution Approach 2:
The patent introduces a second catalyst as an intermediary component that mediates between the rWGS reaction and unwanted side reactions. This intermediary catalyst specifically targets and suppresses the Sabatier reaction and CO hydrogenation pathways, allowing the primary rWGS catalyst to operate effectively at lower temperatures without excessive methane formation.
2Quantity of substance
If excess hydrogen is used to drive the rWGS equilibrium toward carbon monoxide, then carbon monoxide production is improved, but hydrogenation of carbon monoxide to methane increases
Solution Approach 1:
The second catalyst acts as an intermediary that selectively interacts with hydrogen and carbon monoxide to prevent their unwanted hydrogenation. By introducing this intermediary catalyst, the system can maintain high hydrogen concentrations necessary for driving rWGS equilibrium toward CO while the intermediary catalyst captures and redirects hydrogen away from CO hydrogenation pathways.
Solution Approach 2:
The patent changes the catalytic parameter by introducing a second catalyst with specific activity for suppressing hydrogenation reactions. This allows the system to operate with excess hydrogen to drive rWGS equilibrium while the modified catalytic environment prevents the stoichiometric hydrogenation of CO to methane that would normally occur.
3Object-generated harmful factors
If the reaction temperature is raised to favor endothermic rWGS and prevent methanation, then carbon monoxide selectivity is improved, but carbon deposits form on the catalyst surface reducing catalyst lifetime
Solution Approach 1:
The patent changes the temperature parameter from extreme high temperatures to moderate temperatures by introducing a dual-catalyst system. This parameter modification allows the system to achieve high CO selectivity without the severe carbon deposition problems that occur at very high temperatures, thereby extending catalyst lifetime while maintaining product selectivity.
Solution Approach 2:
The second catalyst serves as an intermediary that protects the primary rWGS catalyst from carbon deposition. By introducing this protective catalyst component, the system can operate at temperatures that favor rWGS selectivity without suffering from the carbon fouling that would otherwise rapidly deactivate the catalyst.
4Device complexity
If a single catalyst is used for rWGS, then device complexity is reduced, but the ability to suppress competing reactions and extend catalyst lifetime is limited
Solution Approach 1:
The patent creates a composite catalyst system combining two different catalyst materials with complementary functions. One catalyst material promotes rWGS reaction while the other suppresses side reactions and carbon deposition. This composite approach enhances overall system reliability and catalyst lifetime while maintaining reasonable structural simplicity through integrated catalyst formulation.
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 high CO selectivity and low methane selectivity, even at lower temperatures, thereby extending catalyst lifetime and improving the efficiency of the rWGS reaction. The integration of this catalyst with Fischer-Tropsch processes allows for the production of C5+ hydrocarbons, contributing to the development of low-carbon, carbon-neutral, or negative carbon footprint hydrocarbon synthesis processes.
Implementation Method 1
The reverse water-gas shift (rWGS) reaction is an advantageous route to obtain carbon monoxide from carbon dioxide for further chemical processing. The rWGS converts carbon dioxide and hydrogen to carbon monoxide and water
Implementation Method 2
a competing reaction is the Sabatier reaction (Equation (3)), which decreases carbon monoxide yield in favor of methane production
Implementation Method 3
the carbon monoxide product from rWGS can be hydrogenated to methane, as shown in Equation (4). Hydrogenation of carbon monoxide to methane is also an exothermic reaction
Implementation Method 4
These side reactions can form undesirable carbon deposits on the surface of catalysts used to promote rWGS. Examples of these carbon-producing side reactions are shown in Equations (5), (6), and (7)
Data Source
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AI summary
The present disclosure relates generally to reverse water-gas shift processes, integrated Fischer-Tropsch processes, and a supported reverse water-gas shift catalyst for conducting these processes. The catalysts described herein include a support that is a cerium oxide support, a titanium oxide support, aluminum oxide support, zinc oxide support, a zirconium oxide support, or a mixed oxide support comprising a mixture of two or more of cerium oxide, titanium oxide, aluminum oxide, zinc oxide, and zirconium oxide; a metal selected from at least one of manganese, copper, gallium, indium, lanthanum, titanium, niobium, vanadium, and zirconium, present in an amount in the range of 0.5 to 20 wt% of the catalyst, based on the total weight of the catalyst; and optionally, at least one of platinum, palladium, gold, and nickel, present in an amount in the range of 0.05 to 10 wt% of the catalyst, based on the total weight of the catalyst.