Highly efficient photo-thermal synergistic catalysis of CO2 methanation over La1−xCexNiO3 perovskite-catalyst

Solar-driven photo-thermal catalytic CO2 methanation reaction is a promising technology to alleviate the problems posed by greenhouse gases emissions. However, designing advanced photo-thermal catalysts remains a research challenge for CO2 methanation reaction. In this work, a series of ABO3 (A = lanthanide, B = transition metal) perovskite catalysts with Ce-substituted LaNiO3 (La1−xCexNiO3, x = 0, 0.2, 0.5, 0.8, 1) were synthesized for CO2 methanation. The La0.2Ce0.8NiO3 exhibited the highest CH4 formation rate of 258.9 mmol·g−1·hcat−1, CO2 conversion of 55.4% and 97.2% CH4 selectivity at 300 °C with the light intensity of 2.9 W·cm−2. Then the catalysts were thoroughly analyzed by physicochemical structure and optical properties characterizations. The partial substitution of the A-site provided more active sites for the adsorption and activation of CO2/H2. The sources of the active sites were considered to be the oxygen vacancies (Ov) created by lattice distortions due to different species of ions (La3+, Ce4+, Ce3+) and exsolved Ni0 by H2 reduction. The catalysts have excellent light absorption absorbance and low electron–hole (e−/h+) recombination rate, which greatly contribute to the excellent performance in photo-thermal synergistic catalysis (PTC) CO2 methanation. The results of in situ irradiated electron paramagnetic resonance spectrometer (ISI-EPR) and ISI-X-ray photoelectron spectroscopy (XPS) indicated that the aggregation of unpaired electrons near the defects and Ni metal (from La and Ce ions to Ov and Ni0) accelerated adsorption and activation of CO2/H2. At last, the catalyst properties and structure were correlated with the proposed reaction mechanism from the in situ diffuse reflection infrared Fourier transform spectrum (DRIFTS) measurements. The in situ precipitation of the B-site enhanced the dispersion of Ni, while its enriched photoelectrons upon illumination further promote hydrogen dissociation. More H* spillover accelerated the rate-determining step (RDS) of HCOO* hydrogenation. This work provides the theoretical basis for the development of catalysts and industrial application.