Unveiling the origin of alkali metal promotion in CO2 methanation over Ru/ZrO2

Alkali metals are used as promoters in a broad range of catalytic reactions involving supported metal catalysts, and the origin of their promotional effects has become one of the fundamental questions in heterogeneous catalysis. However, a thorough understanding of the promotional mechanism is still unclear. Combining experiments and theory, the effects of alkali metals on the reactivity of CO2 methanation reaction over Ru/ZrO2, a crucial reaction for CO2 utilization is explored. The conventionally assumed electron enrichment of Ru is not the decisive factor for the promotion. Rather, Na promotion facilitate the adsorption and dissociation of CO on the local interfacial Ru sites of Ru/ZrO2, which is the key step of CO2 methanation process. The feasible dissociation of CO on the alkali metal promoted Ru/ZrO2 originates from the enhanced electron back-donation from the interfacial Ru sites, which leads to more than an order of magnitude increase in CO2 conversion activity.