Photocatalytic oxidative desulfurization of dibenzothiophene by C/TiO2@MCM-41 nanoparticles under visible light and mild conditions

Abstract

Today, due to the environmental pressures on the sulfur content of gasoline and fuel cell applications, refineries need a very deep desulfurization process to reach the ultra-low sulfur diesel (ULSD, 1 ppm). In this research, dibenzothiophene (DBT) in n-octane solution (as a diesel fuel model) was completely converted into biphenyl by visible light irradiation in the presence of C/TiO₂@MCM-41 (CTM-41) as a photocatalyst under mild conditions. For the first time, the conversion was carried out through oxidation in one phase without using oxidant. For synthesizing CTM-41, tetra-butylorthotitanate was used as a precursor of Ti. Carbon species were identified in CTM-41 by X-ray photoelectron spectroscopy and UV-Vis spectroscopy. The self-doped carbon in CTM-41 was attributed to the tetra-butylorthotitanate used as a precursor of Ti. In the synthesis process, there was no carbon precursor addition. The formation of two types of carbon (carbonate species and coke-like structure in lattice of TiO₂) is responsible for the visible photocatalytic activity of the catalyst. The samples were characterized by X-ray diffraction, FTIR and UV-Vis spectroscopy. The specific surface areas of the prepared catalysts determined by the nitrogen adsorption–desorption isotherm at 77 K were 922.42 m² g⁻¹ and 767.54 m² g⁻¹. The GC-MS analysis confirmed the conversion of DBT to biphenyl. Based on the experimental results, the hole and hydroxyl radical as reactive species in the proposed mechanism played the key roles in the photocatalytic desulfurization process.