Simultaneous Photoactivation of Copper and Ti-Doped CeO_2−x Enables Optimal Acceleration of the RWGS Reaction

Abstract

Light-assisted catalysis is a promising approach for accelerating the thermally driven catalytic reverse water gas shift (RWGS) reaction, which converts CO₂ and H₂ into valuable CO. In this work, pure CeO₂ nanorods and titanium-modified CeO₂ nanorods were functionalized with 1–30 wt.% of copper. The catalyst containing 3 wt.% of copper (3Cu–CeTiO₂) was the most active for the light-assisted RWGS reaction. Illuminating the 3Cu–CeTiO₂ catalyst with 770 mW cm⁻² of visible light resulted in a CO rate, which was up to 57 times higher than that under purely thermal conditions at identical catalyst temperature. Catalyst illumination with wavelengths shorter than 450 nm triggers simultaneous photoexcitation of the Ti-doped CeO_2−x support and Cu nanoparticles. This accelerates the RWGS reaction approximately twofold more, compared to excitation of the copper phase alone. Copper is responsible for H₂ dissociation, the Cu–O_v–Ce interface active sites enable the catalytic reaction, and titanium doping diminishes emissive recombination, making photoexcitation more efficient. Furthermore, the E_a for CO formation decreased drastically from 92 to 26 kJ mol⁻¹ during the light-assisted reaction, revealing a change of the reaction mechanism and lowered energetics of the rate-determining step. Our kinetic analysis and operando DRIFTS analysis suggest that hydrogen species chemisorb more strongly under illumination, and the most abundant surface species (carbonates and formates) hydrogenate and dissociate faster, resulting in accelerated CO formation.

Keywords

CO₂ hydrogenation Cu/CeO₂ catalyst / in situ spectroscopy / light-assisted catalysis / reaction mechanism

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