Tuning electron back-donation to switch reaction pathway in CO₂ hydrogenation.

Abstract

CO₂ hydrogenation over earth-abundant Ni catalysts is attractive for CO-based fuel synthesis, but Ni intrinsically favors methanation. Here we show that ordered Ni₃Sn₂ intermetallics tune Ni-CO electron back-donation and switch CO₂ hydrogenation from CH₄ formation to the reverse water-gas shift reaction. Atomic-resolution microscopy and X-ray absorption spectroscopy reveal disruption of extended Ni-Ni ensembles by Sn, while spectroscopy and theoretical calculations show that Ni-Sn d-p hybridization downshifts the Ni 3d band and weakens Ni→CO 2π* back-donation. The Ni₃Sn₂ catalyst achieves CO₂ conversion approaching thermodynamic equilibrium with nearly 100% CO selectivity and remains stable for 300 h. In situ infrared spectroscopy, steady-state isotopic transient kinetic analysis and theoretical calculations indicate that H-assisted CO₂ activation, spectator-like formate species and facile CO desorption underpin the CO-selective pathway. Similar behavior over Ni-Ga and Ni-In catalysts suggests a general back-donation strategy for redirecting Ni-based CO₂ hydrogenation.