Preparation and characterization of sulfated TiO2 with rhodium modification used in esterification reaction and decomposition of methyl orange

Abstract

A unique Rh/TiO2 solid acid catalyst modified with H2SO4 was synthesized and evaluated in the esterification reaction of propylene glycol methyl ether and decomposition of methyl orange (MO) in aqueous phase under halogen lamp irradiation. For this purpose, rhodium (Rh) nanoparticles were loaded on SO42−/TiO2via the photo-deposition method. It was found that SO42−/Rh–TiO2 exhibited stronger catalytic activity than SO42−/TiO2. The new catalysts were characterized by X-ray powder diffraction (XRD), Brunauer–Emmett–Teller (BET), Transmission electron microscopy (TEM) and high-resolution (HRTEM), X-ray photoelectron spectroscopy (XPS) and Fourier Transform infrared spectroscopy (FTIR). Results from XRD and BET show that SO42−/Rh–TiO2 has higher specific surface area and smaller pore size than SO42−/TiO2. The distribution of loaded Rh was found to be uniform with a particle size of 2–4nm. Data from XPS reveal that Rh primarily exists as Rh0 and Rh3+ in Rh–TiO2 and SO42−/Rh–TiO2. These valence forms of Rh likely contribute to the enhanced catalytic activity. Furthermore, FT-IR spectra of the catalysts show an abundance of surface hydroxyl groups, which help the formation of hydroxyl radicals and the enhancement of surface acid density. The results show that more acid sites are formed on the sulfated Rh–TiO2, and these acidic sites are largely responsible for improving the catalytic performance. This superior SO42−/Rh–TiO2 catalyst has potential applications in reactions requiring efficient acid catalysts, including esterification reactions and waste water treatment.