Mechanistic elucidation of cascade CO2 hydrogenation enabled by Cu–Fe interfaces and oxygen vacancies

Abstract

The direct hydrogenation of CO₂ using green hydrogen offers a sustainable route to produce carbon-neutral liquid hydrocarbons, emerging as a viable alternative to conventional naphtha cracking. Although Fe-based CuAl₂O₄ catalysts have been widely studied for CO₂ hydrogenation, the mechanistic role of hydrogen spillover across dynamic Cu–Fe and associated oxygen vacancies has remained elusive. Here, the structure of FeK/CuAl₂O₄ catalysts was systematically tailored by controlling the reduction temperature to elucidate the exsolution-driven restructuration of pristine catalyst structure and its influences on the catalytic performance. We investigated the reaction process using in-situ DRIFTS analysis, from which we for the first time observed a cascade mechanism activated by hydrogen spillover, revealing various elementary reaction steps: (i) preferential adsorption of CO₂ as carbonate species on oxygen vacancies created by Cu exsolution in CuAl₂O₄ lattice, (ii) effective formate-mediated reverse water–gas shift (RWGS) reaction via the hydrogen spillover from exsolved Cu, (iii) promoted Fischer–Tropsch synthesis (FTS) reaction on Fe₅C₂ formed by the facilitated Fe carburization at the exsolved Cu–Fe₃O₄ interfaces, (iv) rapid desorption of hydrocarbons produced via controlled carbon chain growth. This cooperative interaction enabled the selective production of C_5–11 hydrocarbons, achieving the highest C_5–11 productivity of 290.7 mL g_cat^–1 h^–1, surpassing our previous work at a CO₂ conversion of 36.4%. These findings establish a quantitative structure–performance–mechanism relationship and offer design principles for selectivity control toward desired hydrocarbon ranges in multifunctional CO₂ hydrogenation catalysts.