Characterization of a coal fly ash–silica composite as a potential catalyst for hydrogenation

Abstract

 The steady energy demand across the continent, population growth, and increasing consumption of petroleum-based fuels driven by commercialization, urbanization, industrialization, and technological advancement have intensified the search for sustainable alternative energy sources. Hydrogenation-Derived Renewable Diesel (HDRD), also known as green diesel, is a promising renewable fuel capable of reducing environmental degradation and providing compatibility with compression ignition (CI) engines with little or no modification. This study investigated the potential of silica oxide (SiO₂)-reinforced fly ash (FA) as a heterogeneous catalyst for HDRD production from used cooking oil. Fly ash sourced from Eskom Holdings SOC Limited, South Africa, was processed, sieved, and calcined before characterization. A 60:40 FA/SiO₂ catalyst ratio was employed to enhance active metal oxides, surface area, thermal stability, and hydroprocessing performance. Physicochemical characterization using Fourier Transform Infrared Spectroscopy (FTIR), Brunauer–Emmett– Teller (BET), X-ray Diffraction (XRD), and thermal analysis confirmed improvements in surface area, pore structure, and pore volume, increasing from 0.8621 to 41.2551 m²/g, 0.5920 to 45.2757 m²/g, and 0.0042 to 0.1544 cm³/g, respectively. The synergistic catalyst exhibited desirable hydrogenation properties and moderate cracking capability, demonstrating strong potential for sustainable HDRD production and waste valorization.