CO2 methanation mechanism on Ru4/Cr2O3 and factors for selective hydrogenation on supported metal catalysts: A DFT study

Abstract

Unraveling reaction mechanisms and identifying the drivers of selectivity remain grand challenges in heterogeneous catalysis. Here, density functional theory calculations were performed to investigate CO₂ methanation on an oxygen-deficient Cr₂O₃ (012)-supported Ru₄ cluster (Ru₄/Cr₂O₃–O_v) and to decode the origin of product selectivity across M₄/Cr₂O₃–O_v (M = Ru, Ni, Pt) surfaces. CO₂ adsorbs at bridge Ru sites and is readily activated, while H₂ dissociates spontaneously on Ru sites. The CO* pathway that CO₂* → CO* → HCO* → CH₂O* → CH₂* → CH₄, is the most favorable route, with the dissociation of CO₂* and deoxygenation of CH₂O* acting as rate-determining steps with energy barriers of approximately 1.0 eV. Comparative analysis shows that the oxygen adsorption energy on M₄/Cr₂O₃–O_v dictates CO₂ hydrogenation selectivity. Moreover, a smaller work function of metal strengthens O* binding and thereby promotes CH₄ selectivity. Conversely, a bigger work function weakens O* adsorption and favors CO formation. These findings establish the work function of metals as an intrinsic, experimentally accessible descriptor for tuning CO₂ hydrogenation selectivity, guiding the rational design of supported metal catalysts.