Reverse Water-Gas Shift (RWGS) Reaction on Pd/Al₂O₃ Catalyst: The Importance of Interface Studied by a Combination of First-Principles and Microkinetic Modeling

Abstract

CO 2 hydrogenation over oxide-supported metal catalysts proceeds through multiple reaction pathways and yields a variety of products, with product selectivity toward CO and CH 4 being of particular interest. In this work, the reaction mechanisms of CO 2 hydrogenation to CO and CH 4 on Pd/Al 2 O 3 were investigated using density functional theory (DFT) calculations and mean-field microkinetic modeling (MKM). Catalyst models with distinct Pd layer structures (monolayer (Pd 7 /Al 2 O 3 ), bilayer (Pd 11 /Al 2 O 3 ), and trilayer (Pd 13 /Al 2 O 3 )) were developed to investigate the impact of Pd layer configurations on CO 2 adsorption. Results reveal that CO 2 adsorption at the Pd–Al interface is energetically more favorable than on the Pd surface, highlighting the critical role of the metal–support interface in enhancing CO 2 activation. The bilayer Pd 11 /Al 2 O 3 model, which exhibited superior CO 2 activation, was selected for detailed mechanistic studies. Three RWGS pathways (redox, carboxyl, and formate) were studied. CO from the redox pathway desorbs as gaseous CO, while CO formed via the carboxyl and formate pathways remains at the Pd–Al interface, undergoing further hydrogenation to CH 4 . MKM simulations demonstrate temperature-dependent selectivity: CH 4 predominates below 640 K, while CO is favored above 640 K. Degree of selectivity control (DSC) identifies CO desorption from the Pd surface and interfacial O hydrogenation to OH as key steps governing CO selectivity, where reducing their energy barriers enhances CO selectivity. Degree of rate control (DRC) analysis further reveals that HCO dissociation to CH and interfacial O hydrogenation to OH are the rate-limiting steps for CH 4 and CO formation, respectively. These insights provide a foundation for designing efficient catalysts for selective CO 2 hydrogenation.

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