Enhanced CO2-to-CH4 conversion via grain boundary oxidation effect in CuAg systems

Abstract

The authentic active sites of oxide-derived copper (OD-Cu), namely grain boundaries (GBs) and oxidized Cu^δ+ species, is still debatable, and their role in governing CH₄ conversion remains unclear. Herein, this study answers these questions using bimetallic catalysts by novel electro-shock strategy with controllable GBs for the oxidization of Cu^δ+ species by modulating Ag loading. The Ag enrichment at the GBs facilitates the bonding of oxygen with the uncoordinated Cu atoms, resulting in GB oxidation effect. The obtained CH₄ selectivity is twice that of GBs or nanoalloy effect. The enhanced performance is attributed to the stable Cu^δ+ species and unique electron transfer mechanism from GB oxidation structure. Operando attenuated-total-reflection Fourier-transform-infrared-spectroscopy unveils the reaction pathway of CO₂-to-CH₄ and the sluggish reversible quenching processes of intermediates. Theoretical calculations indicate that the weak *CO adsorption on GB oxidation structure facilitates *CO hydrogenation, promoting CO₂-to-CH₄ conversion.