Catalytic oxidative desulfurization of 4,6-dimethyl dibenzothiophene by phosphotungstic acid loaded on Al₂O₃, V₂O₅, and ZrO₂ oxides

This work reports the synthesis, characterization, and catalytic testing of ZrO₂, V₂O₅, and Al₂O₃ that have been loaded with two amounts of phosphotungstic acid for the catalytic oxidative desulfurization of 4,6-dimethyl dibenzothiophene as a reaction test model to reduce the sulfur content in diesel. The catalysts were synthesized through the impregnation of individual oxides with a solution of the heteropolyacid to 3% and 3.5% mol with respect to the metal in each oxide. The materials were characterized by x-ray diffraction, infrared and Raman spectroscopy, nitrogen adsorption–desorption technique, scanning electron microscopy, and x-ray photoelectron spectroscopy. The acidity of the catalysts was determined by potentiometry by titration of the catalysts with pyridine. The reaction test is considered a viable alternative, because it is performed at ambient temperature and pressure. This reaction can be conducted in the liquid–liquid, liquid–solid, or triphasic phase using oxidants and catalysts. In this study, dimethyl dibenzothiophene was used as the sulfur species in diesel and as the molecule for evaluating catalyst activity. Acetonitrile was the solvent, and hydrogen peroxide was the oxidizing agent. Al₂O₃-based catalysts had the highest surface area and acidity among all catalysts. Catalytic activity was affected by the type of support and the heteropolyacid content. As the level of heteropolyacid increased, the catalytic activity rose. Other factors that influenced catalytic activity were the catalyst's surface area, acidity, and morphology. The catalytic activity improved when the acidity and surface area in the catalysts increased. For V₂O₅, empty spaces were observed, favoring adsorption of the reactants.