catalyst with argon dilution

The use of non-thermal plasma-mediated catalysis has emerged as a viable strategy in recent years for enhancing the reactivity of CO₂ hydrogenation to C₁ intermediates (e.g. CO, methanol, methane), which form the building blocks for clean fuels and chemical synthesis using renewable hydrogen and electricity. However, considerable uncertainty remains pertaining to the coupling and synergistic effects of plasma catalysis. In this work, numerical modeling of CO₂ hydrogenation over a Co/Al₂O₃ catalyst at atmospheric pressure under varying temperatures and gas compositions (including argon as a carrier gas) is performed. This work will specifically address the research question on the optimal argon fraction that favors both optimal plasma power coupling and CO₂/H₂ reactivity. First, a reduced microkinetic mechanism is presented that describes a wide array of gas-phase plasma processes including the excitation, dissociation, and ionization of CO₂, H₂, and argon species, excited species quenching, charge transfer reactions, charged species recombination, and electron attachment and detachment. The gas-phase kinetics mechanism is coupled with a surface kinetics mechanism that describes various pathways by which CO₂ conversion and hydrocarbon (HC) formation occur over a Co/Al₂O₃ catalyst with and without the presence of non-thermal plasma. Molecular scale simulations are performed to calculate sticking probabilities of the dominant gas-phase species, which are used to evaluate the surface reaction rate coefficients in the microkinetics model. These mechanisms are then incorporated into a massively-parallel open-source plasma fluid solver, and multidimensional simulations of a propagating streamer interacting with a catalytic surface are performed. The temperature of the gas and the argon dilution are varied from 300-500 K and 0-90%, respectively, to explore how these parameters impact CO₂ conversion and HC formation. It is found that elevated temperatures and increased argon dilution enhance catalyst reactivity up to a point, indicating the existence of an optimal set of parameters for catalytic activity. Lastly, detailed insight is given into which surface reaction pathways play a dominant role in HC formation over the Co/Al₂O₃ catalyst.