Highly efficient photo-thermal synergistic catalysis of CO₂ methanation over La_1−xCe_xNiO₃ 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 (La_1−xCe_xNiO₃, x = 0, 0.2, 0.5, 0.8, 1) were synthesized for CO₂ methanation. The La_0.2Ce_0.8NiO₃ exhibited the highest CH₄ formation rate of 258.9 mmol·g⁻¹·h_cat⁻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 (O_v) 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 O_v 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.