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. Nickel catalysts usually turn carbon dioxide into methane, limiting carbon monoxide production. Forming intermetallic compound Ni3Sn2 weakens carbon monoxide binding over nickel, delivering stable, nearly complete selectivity for carbon monoxide.