A Co-nanoparticle/layered TiO2–TiN composite for selective photothermocatalytic reduction of CO2 to CH4

Abstract

Photothermocatalytic carbon dioxide (CO₂) reduction into value-added chemicals is one of the promising methods for solar-to-chemical energy conversion. However, the improvement of catalytic activity and product selectivity remain a challenge in view of practical applications. Herein, we report a facile “two-step” approach – nitrogen treatment of Ti₃C₂ MXene (TC) and loading of Co nanoparticles – to synthesize a Co-nanoparticle/layered TiO₂–TiN composite as an efficient photothermocatalyst for selective reduction of CO₂ to methane (CH₄). The optimal 35Co/TiO₂–TiN catalyst exhibits a 62.8% CO₂ conversion ratio with a CH₄ evolution rate of 45.5 mmol g_cat⁻¹ h⁻¹ and 99.3% selectivity under 300 W xenon lamp irradiation for 60 min. In contrast, the Co/Ti₃C₂ catalyst shows a high selectivity toward CO production. The synergistic effect of increased light absorption capacity, reactive sites, CO₂ adsorption/activation ability, and desorption energy barrier of the CO* intermediate by the loaded Co nanoparticles and the formation of Ti–N–O bonds could account for the significantly enhanced photothermocatalytic performance of 35Co/TiO₂–TiN for selective CO₂ reduction into CH₄. Our work demonstrates that metal nanoparticle loading and formation of Ti–N–O bonds can be integrated into the strategy in developing a photothermocatalyst for efficient CO₂ reduction with controlled product selectivity.