Advanced catalytic CO2 hydrogenation on Ni/ZrO2 with light induced oxygen vacancy formation in photothermal conditions at medium-low temperatures

Abstract

Selective CH₄ formation from CO₂ hydrogenation is an appealing yet challenging sunlight-driven or thermal-driven process due to low solar energy utilization efficiency or high energy input. Herein, we report an enhanced catalytic CO₂ hydrogenation in photothermal conditions on Ni/ZrO₂ catalysts, which provided higher performance than “dark” thermal catalysis at medium-low temperatures (≤350 °C). With the assistance of sunlight, CO₂ conversion and CH₄ selectivity were achieved to 82% and 100% at 350 °C over 3 wt% Ni/ZrO₂ catalyst, which maintained excellent activity and stability for 48 h during the catalyst durability test. The experiment and catalyst characterization results revealed that the illumination stimulated the photothermal effect of Ni and promoted dissociation of H₂, conducive to the formation of oxygen vacancies in ZrO₂. The existing oxygen vacancies provided strong alkaline adsorption of O²⁻ species on the CO₂ surface and enhanced the interaction between the metal and support, which was beneficial to CO₂ activation. The raised Ni doping amount would increase the catalytic active sites and thermal accumulation centers, resulting in the dramatic increase of CO₂ conversion at low temperatures (≤300 °C), while reducing along with the elevated temperature due to switched reaction state and deposited carbon on the catalysts. Additionally, density functional theory (DFT) calculations confirmed the experimental observation, showing that the oxygen vacancies on ZrO₂ facilitate both CO₂ adsorption and hydrogen spillover to further enhance CO₂ hydrogenation.