Selective photothermal CO2 reduction to CO, CH4, alkanes, alkenes over bimetallic alloy catalysts derived from layered double hydroxide nanosheets

Photothermal catalytic reduction of CO2 with H2 as the reducing agent holds great promise for the conversion of combustion-derived CO2 into hydrocarbon fuels and other valuable commodity chemicals. Whilst a number of promising photothermal catalysts have been developed for CO2 reduction, reaction mechanisms remain elusive, and the factors controlling product selectivity are unclear. In this work, three distinct transition metal alloy nanoparticle catalysts, each supported by amorphous alumina, were fabricated by hydrogen reduction of CoFeAl-layered double hydroxide (CoFeAl-LDH), NiFeAl-LDH and NiCoAl-LDH nanosheet precursors at 650 °C. By using the different alloy nanoparticles (CoFe, NiFe or NiCo) and tuning the reaction parameters including temperature and gas flow rate during photothermal CO2 reduction with H2, different product distributions (CH4, CO, light olefins, paraffins) were obtained, with the distribution depending strongly on the alloy catalyst composition. A reaction pathway for CO2 reduction consisting of multiple steps was discovered and confirmed by in-situ diffuse reflectance infrared Fourier transform spectroscopy studies and a series of control catalytic experiments. Findings provide valuable new insights about the reaction mechanism of photothermal catalytic CO2 reduction to hydrocarbon products over metal catalysts and the factors regulating product selectivity.