Significant improvement in activity, durability, and light-to-fuel efficiency of Ni nanoparticles by La2O3 cluster modification for photothermocatalytic CO2 reduction

A novel nanocomposite of La2O3 cluster modified Ni nanoparticles loaded on mesoporous silica (Ni-La2O3/SiO2) was synthesized. Under focused UV-vis-IR irradiation, Ni-La2O3/SiO2 exhibits high production rates of CO (r(CO)) and H-2 (r(H2)) (42.90 and 38.11 mmol min(-1) g(-1)) for photothermocatalytic CO2 reduction by CH4 (CRM). A high light-to-fuel efficiency (eta) of 20.3 % is achieved. Ni-La2O3/SiO2 also exhibits excellent photothermocatalytic durability. Its photothermocatalytic activity almost remains unchanged after reacted for 90 h. It is found for the first time that the photothermocatalytic activity, durability, and eta value of Ni nanoparticles are substantially promoted by the La2O3 cluster modification. The results of TG-MS, TEM, XRD, isotope labelling experiment using (CH4)-C-12 and (CO2)-C-12-O-18 as reactants, and Raman show that oxygen of La2O3 clusters in Ni-La2O3/SiO2 takes part in oxidization of carbon species formed by CH4 dissociation. This causes a substantial reduction in carbon deposition rate, thus promoting the catalytic activity and durability. It is found that the focused irradiation substantially decreases the apparent activation energy of CRM on Ni-La2O3/SiO2, thus promoting the catalytic activity. The new photoactivation also restrain CO disproportionation as major side-reaction of carbon deposition, thus decreasing the rate of carbon deposition.