Preparation and photocatalytic properties of Cu, N co-doped TiO₂ nanotubes for glycerol reforming to syngas

Cu, N co-doped TiO2 nanotubes (Cu/N-TNT) were prepared by alkaline hydrothermal-ion exchange method, and the photocatalytic properties for glycerol reforming to syngas (H-2 and CO) were studied. The results show that Cu/N-TNT catalyst has tubular structures with abundant oxygen vacancies (O-V). N forms the impurity energy level by substituting the partial O in the form of Ti-N. Cu is doped into the crystal lattice gap and surface of the catalyst in the form of Cu2+. Cu, N co-doping promotes the effective surface charge separation on the TiO2, and improves the photocatalytic activity and selectivity for glycerol reforming to syngas. CO and H-2 yields were 7.3 and 8.5 mmol center dot g(-1) on Cu/N-TNT catalyst doped with 0.15% Cu, which were 9.1 and 70.8 times those on the original TiO2. The molar ratio of H-2/CO was increased from 0.52 to 1.18, and the molar ratio of CO/CO2 was raised from 0.21 to 0.42 after 8 h of UV irradiation. N and O-V on Cu/N-TNT surface provide the active sites for the decarbonylation of aldehydes and dehydration of formic acid to produce CO. Cu acts as the shallow potential traps to inhibit the electron-hole recombination. Photogenerated holes (h(+)) play vital roles on the syngas generation during the photocatalytic reforming of glycerol, and excessive hydroxyl radical (center dot OH) and superoxide radical (center dot O-2(-)) favor the deep oxidation of glycerol and decrease the selectivity of CO.