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

• FeK/CuAl 2 O 4 was systematically restructured by exsolution engineering. • Exsolved Cu, oxygen vacancy in CuAl 2 O 4 and Fe 3 O 4 interplayed synergistically. • In-situ DRIFTS analysis revealed cascade mechanism activated by hydrogen spillover. • Optimized FeK/CuAl 2 O 4 controlled hydrocarbon chain growth in CO 2 hydrogenation. The direct hydrogenation of CO 2 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 CuAl 2 O 4 catalysts have been widely studied for CO 2 hydrogenation, the mechanistic role of hydrogen spillover across dynamic Cu–Fe and associated oxygen vacancies has remained elusive. Here, the structure of FeK/CuAl 2 O 4 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 CO 2 as carbonate species on oxygen vacancies created by Cu exsolution in CuAl 2 O 4 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 Fe 5 C 2 formed by the facilitated Fe carburization at the exsolved Cu–Fe 3 O 4 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 CO 2 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 CO 2 hydrogenation catalysts.