Studies on the Selection of a Catalyst-Oxidant System for the Energy-Efficient Desulfurization and Denitrogenation of Fuel Oil at Mild Operating Conditions

This study reports the selection of an ideal catalyst-oxidant system for the energy-efficient catalytic oxidative desulfurization (CODS) of dibenzothiophene (DBT) and denitrogenation (CODN) of pyridine over Mn-Co-Mo/Al2O3 and acid-functionalized 1-butyl-3-methyl imidazolium chloride ([Bmim]Cl/ZnCl2) ionic liquid (IL) catalysts using H2O2 and NaClO as oxidants. The NaClO-catalyst system realized 100% CODS/CODN activity within 15 min at 25 degrees C at comparatively low activation energies of 4.9 and 5.4 kJ/mol for DBT and pyridine, respectively, under optimal conditions of oxidant-to-sulfur ratio of 4, oxidant-to-nitrogen ratio of 8, ionic liquid-to-oil ratio of 1.5/5, and 0.1 g of Mn-Co-Mo/Al2O3 catalyst for 15 mL of model fuel. Both catalytic activity and kinetics results revealed a NaClO-catalyst system with greater efficiency and lesser energy requirements than a H2O2-catalyst system, and hence the former realized enhanced CODS and CODN than the latter. Furthermore, the Mn-Co-Mo/Al2O3 catalyst favored CODS, while [Bmim]Cl/ZnCl2 possessed greater affinity for the CODN process, owing to the stronger nucleophilic interaction of the cationic species in IL toward hindered nitrogen compounds. Further justification for the CODS and CODN activities and textural characterization of the fresh and spent catalysts were provided by PXRD, XPS, SEM, EDX elemental mapping, and BET surface area characterizations. Based on the results, this study is potentially viable owing to its environmental greenness, enhancement in the calorific value of the final fuel, and genially benignant application in energy consumption via mild operating conditions and hence can be envisaged as a practicable alternative approach in industrial processing of fuel oils.