Flame-Made Surface-Substituted Copper–Ceria as an Excellent Reverse Water–Gas Shift Reaction Catalyst via Three Reaction Pathways

The limited mechanistic understanding and ambiguous structure-performance relationships have hindered the optimization of Cu-based catalysts for the reverse water-gas shift (rWGS) reaction. Here, we report a flame spray pyrolysis (FSP)-derived Cu-CeO₂ catalyst featuring highly dispersed, surface-substituted Cu⁺ species (Cu_yCe_1-yO_2-x) anchored on a defect-rich ceria matrix. This catalyst demonstrates excellent stability and outstanding rWGS activity at 600 °C, achieving a CO production rate of 8094 mmol/g_cat./h, surpassing the conventional Cu-CeO₂ catalyst and other reported rWGS catalysts. In situ spectroscopic analyses, supported by DFT calculations, reveal three parallel reaction pathways in which carboxylate- and formate-mediated routes proceed at distinct active sites. A clear structure-activity correlation is established across Cu⁺, Cu⁰, and ceria defect sites in the FSP-derived catalysts. Notably, a previously underexplored carboxylate-mediated pathway, facilitated on the surface-substituted Cu⁺ structure, is identified as the dominant route, featuring a significantly lower apparent activation energy (20-30 kJ/mol) compared to the classical formate pathway.