A Co-Nanoparticle/Layered TiO2-TiN Composite for Selective Photothermocatalytic Reduction of CO2 to CH4

Photothermocatalytic carbon dioxide (CO2) reduction into value-added chemicals is one of the promising methods for solar-to-chemical energy conversion. However, it remains a challenge in the improvement of catalytic activity and product selectivity 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 (Co/TiO2-TiN) composite as an efficient photothermocatalyst for selective reduction of CO2 to methane (CH4). In contrast to the Co/Ti3C2 catalyst that shows a high CO selectivity, the optimal 35Co/TiO2-TiN catalyst exhibits a CH4 evolution rate of 45.5 mmol gcat−1 h−1 with 99.3 % selectivity under a 300 W Xe lamp irradiation. The synergistic effect of increased light absorption capacity, reactive sites, CO2 adsorption/activation ability, and desorption energy barrier of CO* intermediate by the loaded Co nanoparticles and the formation of Ti−N−O bonds accounts 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.