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The localized plasmon resonance (LSPR) is recognized as an effective way to convert incident light energy and significantly boost the catalytic reaction. However, a comprehensive understanding of the plasmon-thermo coupling mechanism is still lacking. To address this knowledge gap, we investigate reaction pathway and plasmonic enhancement mechanism of the photo-thermo coupled catalytic reverse water gas shift (RWGS) reactions over Au/γ-Al 2 O 3. The results indicate that both formate and carboxyl pathways contribute to the overall reaction. The m-formate pathway is suggested as the main reaction mechanism at low reaction temperature over small Au NPs. Spectro-kinetics and theoretical calculation analyses indicate that the plasmonic energy preferentially transfers to HCOO* via a combination of hot electron and resonance energy transfer mechanisms. The plasmonic energy facilitates the dehydration of HCOO* to CO, which is the rate-determining step (RDS) of the overall RWGS reaction. [Display omitted] • Plasmon enhances the CO 2 hydrogenation rate by ∼211.8 % over Au/Al 2 O 3. • m-HCOO* is demonstrated as the main reaction intermediate over small-size Au/Al 2 O 3. • br-HCOO* is proven as a reaction intermediate contributing to CO production. • Plasmon preferentially enhances the br-HCOO* pathway via promoting its dehydration. • Both "hot" electrons and resonance energy transfer are the promoting mechanisms. [ABSTRACT FROM AUTHOR]

SYNOPSIS: Coupling photo- and thermo- catalytic CO 2 hydrogenation is a promising way to convert CO 2 with higher sustainability. Herein, the redox pathway is demonstrated as the main reaction pathway for CO 2 hydrogenation at 200 °C over Au/TiO 2. The plasmonic enhancement mechanism is proven to be the facilitated oxygen vacancy generation. [Display omitted] • Plasmon enhances the CO production rate by ∼ 318 % at 200 °C over Au/TiO 2. • Redox mechanism is proven as the main pathway for CO 2 hydrogenation to CO. • DRIFTS analyses prove the spontaneous dissociation of CO 2 at V O site of Au/TiO 2. • Inverse H/D kinetic isotope effects suggest the V O creation is the RDS. • Plasmon-thermo coupling mechanism is the hot-electrons enhanced V O creation. Using solar energy to promote the thermocatalytic CO 2 conversion is a promising way to reduce the energy consumption and increase the sustainability. Au/TiO 2 is known for its good catalytic activity in both thermo- and photo- catalytic CO 2 conversion, however both the reaction mechanisms in dark and in photo-thermo coupled reaction condition remain unclear. In this work, the operando isotope-labelled spectroscopic and computational analyses are combined to clarify these mechanisms. The redox mechanism that CO 2 direct dissociation at the oxygen vacancy (V O) is found as the main reaction pathway of CO 2 hydrogenation over Au/TiO 2. The plasmonic enhancement mechanism is proven to be the hot electrons facilitated V O generation at interface. The clear understandings of reaction pathway and plasmonic enhancement mechanism are helpful for the future design of photo-thermal CO 2 conversion catalysts. [ABSTRACT FROM AUTHOR]