Laser-induced photocatalytic reduction of CO2 into methanol over perovskite LaMnO3

Perovskite oxides offer efficient photocatalytic properties for CO2 reduction to methanol. In this study, LaMnO3+δ nanocrystals were fabricated by the solgel combustion method. The structural properties including lattice constants, occupancies, Mn–O lengths, and Mn–O–Mn angle were studied by Rietveld refinement. Jahn–Teller distortion and O-2p and Mn-3d hybridization have been investigated using the structural parameters and lattice dynamics characterized by Fourier-transform far-infrared spectroscopy. The electron transitions near the lower edge of conduction band were studied by diffuse reflectance spectroscopy. LaMnO3+δ exhibited laser-induced photocatalytic activity for reductive conversion of CO2 to methanol under both visible (532 nm) and infrared (1064 nm) irradiation. The methanol yield as a function of irradiation time was investigated by the gas chromatographic analysis. After 20 min of irradiation at 532 nm, the methanol yield showed the highest value (970 μmol), while the methanol started to degrade with further irradiation time. The recycling stability test from the repeatedly used LaMnO3+δ sample showed the high stability of the catalyst. The authors demonstrated that in addition to the appropriate bandgap energy, the length of eg↑ in the conduction band plays a significant role in the photocatalytic properties of the perovskites with Jahn–Teller distortion under visible and infrared irradiations.