A novel strategy for dramatically improving catalytic performance for light-driven thermocatalytic CO2 reduction with CH4 on Ru/MgO: the CO2 molecular fencing effect promoted by photoactivation

Abstract

The catalytic dry reforming of CH₄ (DRM, CO₂ + CH₄ = 2H₂ + 2CO) is merely driven by sunlight and has provided an effective strategy for addressing the two global issues of CO₂ emission reduction and energy shortage. Challenges faced by the strategy, such as prone catalyst deactivation due to thermodynamically more favorable coking side reactions, high fuel production rate and light-to-fuel efficiency (η) being achieved only with high solar light intensity so far, need to be addressed urgently. Herein, we have synthesized a nanocomposite with Ru nanoparticles (NPs) with a high dispersion of 94.8% supported on MgO (Ru/MgO). By light-driven thermocatalytic DRM on Ru/MgO under concentrated UV-vis-IR illumination with relatively low light intensity (73.2 kW m⁻²), high production rates of H₂ (r_H2, 43.51 mmol g⁻¹ min⁻¹) and CO (r_CO, 59.31 mmol g⁻¹ min⁻¹) and a large η of 19.4% have been achieved, and coking is completely prohibited. In striking contrast, a referenced catalyst of Ru NPs supported on SiO₂ (Ru/SiO₂) showed much lower r_H2, r_CO and η with obvious coking. This significantly improved light-driven thermocatalytic performance arises from the effect induced by a fence of strongly adsorbed CO₂ molecules on MgO around Ru NPs at the Ru/MgO interface, which participate in the oxidation of C* species (formed by CH₄ dissociation on Ru NPs) as a rate-decisive step of DRM, thus significantly enhancing catalytic activity and prohibiting C* species being polymerized to coke. The CO₂ molecular fencing effect is dramatically promoted by novel photoactivation in which light not only facilitates DRM on Ru NPs but also dramatically facilitates the oxidation of C* species (formed on Ru NPs) by the strongly adsorbed CO₂ on MgO at the Ru/MgO interface.