Enhanced Photocatalytic Performance toward CO2 Hydrogenation over Nanosized TiO2-Loaded Pd under UV Irradiation

A series of Pd/TiO2 photocatalysts were synthesized by a simple glucose reduction method, and their photocatalysis properties were evaluated in an array of CO2 hydrogenations. The samples were characterized by XRD, SEM, TEM, EDX, EDX mapping, UV-vis DRS, Raman spectroscopy, PL spectroscopy, XPS, and N-2 adsorption. In terms of product yields (in micromoles per gram of Catalyst), a 1.0 wt % Pd/TiO2 catalyst (CH4, 355.62; CO, 46.35; C2H6, 39.69) was found to be superior to pristine TiO2 (CH4, 42.65; CO, 4.73; C2H6, 2.7) and other composites under UV irradiation for 3 h, possibly because of a synergistic effect between the palladium nanoparticles and the TiO2 support. The palladium nanoparticles on the surface of TiO2 substantially accelerated electron transfer and acted as active sites for the adsorption and activation of CO2 molecules, to promote CO2 hydrogenation. During the photocatalytic CO2 hydrogenation, dissociated hydrogen reacts with CO2- activated on the Pd/TiO2 photocatalyst to form a new Pd-C surface species that is stable during the reaction and further transforms to generate methane. A detailed mechanism of photocatalytic CO2 hydrogenation is discussed to account for the performance of the Pd/TiO2 photocataryst in the reaction.