Oxidative desulfurisation (ODS) is a promising alternative technology for producing sulfur-free fuel compared to conventional hydrodesulfurisation technology, as the ODS reaction can be performed under moderate operating conditions. This study focuses on investigating the performance of oxidation desulfurisation of Iraqi gas oil using a novel catalyst. High-entropy oxides (HEO) catalysts are prepared by mechanochemical mixing of cobalt, chromium, iron, titanium, and nickel chlorides using a nanoball mill. The HEO catalyst was characterised by X-ray diffraction (XRD), Energy Dispersive Spectroscopy (EDS) , and Fourier Transform Infrared Spectroscopy (FTIR). Scanning Electron Microscopy (SEM) was used to investigate the prepared catalyst morphology. Characterisation findings indicate that the prepared catalysts are in the nano to semi-micron range, with different shapes and varying active functional groups. The gasoil ODS performance was investigated by using ozone as the oxidant agent and the impact of catalyst amount (0.5-1 g), temperature (150-200 °C), and the oxidation time (30-60 minutes) on catalytic desulfurisation performance. A Box-Behnken experimental design (BBD) was used to design the experiments. The removal efficiency ranged between 85% and 99%, with an optimum sulfur removal efficiency of 98% achieved at 0.59 g, 200 °C, and 60 minutes for catalyst dosage, reaction temperature, and oxidation time, respectively.

A kinetics study shows that the reaction obeys a pseudo 1st order reaction and has a relatively low activation energy (22.033 kJ/mol) due to the presence of a catalyst. Thermodynamically, the reaction is non-spontaneous, as indicated by its positive Gibbs free energy (ΔG), and the reaction rate increases with temperature.