Photocatalytic Oxidative Denitrogenation of Fuels Using Hydrochar-Hybridized Nano-TiO2 Supported on Lava Particles

Abstract

Photocatalytic oxidation enables efficient removal of nitrogen-containing impurities from fuels under mild reaction conditions and with solar energy. However, it faces challenges such as low light utilization, insufficient carrier separation, and incompatibility between powder catalysts and supporting infrastructure. The current study developed a macroscopic photocatalyst utilizing lava rock-supported hydrochar-hybridized TiO₂ nanoparticles (HC/TiO₂@LPs). The photocatalytic oxidative denitrogenation was evaluated on simulated and actual oil samples, yielding favorable results. This study employed X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy to characterize the physicochemical properties of HC/TiO₂@LPs and used ultraviolet–visible diffuse reflection spectroscopy, photoluminescence, and transient photocurrent response to analyze the optical and photoelectric properties. Under visible-light irradiation, the efficiency of the HC/TiO₂@LPs-H₂O₂ system for removing N-heterocyclic compounds from n-nonane model oil was investigated, and the reaction conditions were optimized. The types and relative contributions of reactive oxygen species (ROS) in the system were identified using electron paramagnetic resonance and radical quenching experiments. The results demonstrate that HC/TiO₂ uniformly coats the surface of lava particles, enhancing both light absorption and photogenerated carrier separation. The reaction system generates ROS, including ^•OH, ^•O₂^–, and ¹O₂, which contribute about 42.1, 33.9, and 24.0%, respectively, to the degradation of quinoline, demonstrating an oxidative process involving the synergistic action of multiple active species. The effectiveness and cycling stability of the macroscopic catalyst loaded with natural porous minerals for actual diesel denitrogenation show the feasibility and practicality of the Vis-HC/TiO₂@LPs-H₂O₂ system in large-scale green petroleum processing.