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

A unique Rh/TiO 2 solid acid catalyst modified with H 2 SO 4 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 SO 4 2   − /TiO 2 via the photo-deposition method. It was found that SO 4 2   − /Rh–TiO 2 exhibited stronger catalytic activity than SO 4 2   − /TiO 2 . 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 SO 4 2   − /Rh–TiO 2 has higher specific surface area and smaller pore size than SO 4 2   − /TiO 2 . The distribution of loaded Rh was found to be uniform with a particle size of 2–4   nm. Data from XPS reveal that Rh primarily exists as Rh 0 and Rh 3   + in Rh–TiO 2 and SO 4 2   − /Rh–TiO 2 . 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–TiO 2 , and these acidic sites are largely responsible for improving the catalytic performance. This superior SO 4 2   − /Rh–TiO 2 catalyst has potential applications in reactions requiring efficient acid catalysts, including esterification reactions and waste water treatment.