Oxidative Desulfurization of Model Fuel Using Ni or Mo-based Catalysts Supported on Bio-synthesized γ-Al<sub>2</sub>O<sub>3</sub>; Optimization of Synthesis Parameters

In this study, γ-Al₂O₃ was synthesized via a green sol–gel route using four bio-templates (Pistacia Atlantica gum, glucose, gelatine, and gond katira gum) and applied as support for Ni- and Mo-based oxidative desulfurization (ODS) catalysts. XRD analysis confirmed the selective formation of high-purity γ-Al₂O₃ in all bio-templated samples, while gelatine-assisted alumina exhibited enhanced crystallinity. BET measurements revealed significantly increased surface areas (up to 190 m² g⁻¹) compared to non-templated alumina, and TEM analysis demonstrated uniform nanoparticles below 5 nm. Following metal deposition, FESEM and TEM analyses showed that ultrasound-assisted impregnation effectively reduced agglomeration and improved NiO dispersion over the mesoporous support. This structural refinement was further supported by BET results, which indicated improved accessible surface area in ultrasonically prepared catalysts compared with conventionally impregnated samples. The NiO/γ-Al₂O₃ catalyst prepared under ultrasound achieved 80% DBT conversion, outperforming conventionally impregnated NiO (76%), Mo-based catalyst (65%), and bare alumina (40%), highlighting the critical role of metal–support interaction and dispersion. A central composite design (CCD) approach was employed to optimize five synthesis and operational parameters (sol pH, calcination temperature, gelatine content, NiO loading, and oxidant-to-sulfur ratio). Under optimized conditions (pH 8.7, 685 °C calcination temperature, 3.65 wt.% gelatine, 16.86 wt.% NiO, O/S = 16.41), DBT conversion reached 98.11%, representing a substantial enhancement over the non-optimized ultrasonically prepared catalyst (80%). The optimized catalyst maintained high stability over seven consecutive cycles, with conversion decreasing only from 97.4% to 86.3%, and recovered to 91.5% after regeneration.