Oxidative Desulphurization of Thiophene in Model Diesel over Copper-Promoted Nickel Oxide Supported on Silica

Abstract

Stringent environmental regulations and the demand for ultra-low-sulfur fuels have increased interest in oxidative desulfurization (ODS), which operates under mild conditions and efficiently oxidizes refractory sulfur compounds.  This study aimed to synthesize and optimize silica-supported nickel oxide and copper-promoted nickel oxide catalysts for the ODS of model diesel fuel.  Nominal 2.1 wt% Ni/SiO₂ and 0.23 wt% Cu-promoted Ni/SiO₂ catalysts (Cu/Ni-SiO₂) were prepared by incipient wetness impregnation, dried at 80 °C, and calcined at 600 °C for 5 h.  The catalysts were characterized by FTIR, XRD, and EDX spectroscopy.  Model diesel (containing 100 ppm thiophene) was oxidized with H₂O₂ and extracted using Dimethylformamide solvent.  The conversion of thiophene into extractable sulfone form was determined by UV/Visible Spectrometer at 380 λ max using an external calibration curve (R² = 0.9497).  The process optimization employed a 17-run Box–Behnken design.  Experiments were performed in triplicate.  Preliminary experiments showed that the Cu-promoted catalyst calcined at 600 °C achieved 75% sulfur removal, outperforming the monometallic catalyst (Ni-SiO₂).  Analysis of variance indicated that the quadratic response surface model was statistically significant (F = 105.35, p < 0.05) with a non-significant lack of fit (p = 0.28), confirming its adequacy for process optimization.  The optimized conditions were 52.5 °C, 60 min, and an oxidant-to-sulfur molar ratio of 1.0, under which a maximum sulfur removal of 92.0% was achieved.  Cu-promoted Ni/SiO₂ is a promising catalyst for the oxidative desulfurization of model diesel under mild conditions.