Theoretical assessments of CO2 activation and hydrogenation pathways on transition-metal surfaces

Abstract

Carbon dioxide (CO2) hydrogenation on transition-metal active sites offers a promising carbon utilization route toward mitigating greenhouse gas emissions. C1 products are often formed in parallel during CO2 hydrogenation, prompting investigations into the intrinsic properties of transition metals that drive activity and product selectivity. In this work, close-packed surfaces of a selection of transition-metal catalysts (Ni, Co, Rh, Ru, Pd, and Pt) were studied with density functional theory (DFT) calculations to understand their fundamental reactivities for CO2 transformation reactions. Results indicate that CO2 conversion proceeds through CO* formation and hydrogenation to form C1 products (* denotes an adsorbed species). Ni, Co, Rh, and Ru favor CO/CH4 formation, while Pd and Pt favor CO/CH3OH formation. The ability of a metal to dissociate C-O bonds drives selectivity between CH4 and CH3OH, while competition between CO* desorption and surface hydrogenation describes CO selectivities. The C-O bond dissociation steps often impose the highest barrier along CH4 formation reaction profiles, suggesting their kinetic relevance for CH4 formation rates. The provided DFT-derived data sets detail a comprehensive reaction network of elementary steps relevant to C1 chemistries, ultimately offering a benchmark for insights into design strategies for materials that exploit transition-metal active sites in carbon capture or utilization processes.