Indium-doped TiO2 nanoparticles for photocatalytic CO2 reduction with H2O vapors to CH4

Abstract

Indium (In)-doped titanium dioxide (TiO2) nanoparticles were synthesized using a controlled sol-gel method. The structures and properties of the catalysts were characterized by XRD, FE-SEM, TEM, XPS, BET, UV-vis and PL spectroscopy. Indium, present over the TiO2 in metal state, inhibited crystal growth and produced anatase phase of mesoporous TiO2 nanoparticles. Doping In in TiO2 also increased the surface area and enlarged the band gap. The photocatalytic activities of In-doped TiO2 nanoparticles were considerably improved for CO2 reduction with H2O vapors in a cell type photoreactor. CO was observed as the main product over TiO2, but doping In in TiO2 remarkably increased the CH4 yield. CH4 production rate over 10wt.% In-doped TiO 2 was 7.9-fold higher than the bare TiO2 at 100°C and CO2/H2O ratio of 1.43. In addition, C1-3 higher hydrocarbons namely C2H4, C2H6, C3H6 and C3H8 were detected in the product mixture. The enhanced photoactivity in mesoporous In-doped TiO2 nanoparticles can be attributed to interfacial transfer of photogenerated charges, which led to effective charge separation and inhibited recombination of photogenerated electron-hole (e-/h+) pairs. Langmuir-Hinshelwood model, developed to investigate reaction rate parameters, fitted well with the experimental data