Molybdenum Chalcogenides for Photo-Oxidative Desulfurization of Liquid Fuels Under Ambient Conditions: Process Optimization, Kinetics, and Recyclability Studies

In this article, we report on the catalytic photochemical oxidative desulfurization studies carried out on hydrocarbon-based liquid fuels, with molybdenum chalcogenides as catalyst. Our aim was to understand the synergistic effect of different chalcogenide elements present within the same molybdate compound towards the desulfurization process. Thus, in the present study, the desulfurization activity of hetero-chalcogenide molybdate anions, viz. the dioxo-dithio-molybdate, -(MoO2S2)(2-), and the monoxo-trithio-molybdate, -(MoOS3)(2-), respectively; have been compared with that of the homo-chalcogenide molybdate anions, i.e., the tetraoxo-molybdate, -(MoO4)(2-), and the tetrathio-molybdate, -(MoS4)(2-), respectively. The catalysts were extensively characterized in the solid-state by different analytical techniques such as powder X-ray diffraction (P-XRD), infrared (IR) and optical (UV-Vis) spectroscopy, imaging and elemental analysis with SEM-EDX, surface area analysis and thermal stability studies. The desirable band gap observed in the visible region for all four materials, makes them ideally suited towards their exploration as photocatalysts for oxidative-desulfurization of liquid fuels. The photo-oxidative desulfurization studies have thus been performed on a multicomponent sulfur system consisting of thiophene, benzothiophene (BT) and dibenzothiophene (DBT) in a mixture of aliphatic and aromatic hydrocarbons, and their reactions monitored using gas chromatography-flame photometric detector. The as synthesized disubstituted chalcogenide, -(MoO2S2)(2-) anion, shows significantly high desulfurization activity followed by the -(MoOS3)(2-) anion, with the -(MoO4)(2-) and -(MoS4)(2-) anions showing lower catalytic activity. The catalytic reactions were observed to follow pseudo-first order kinetic model. Additionally, the catalysts demonstrated remarkable recyclability and reusability across a minimum of four consecutives recycle runs.

Automated summary

This study reports on the catalytic photochemical oxidative desulfurization of hydrocarbon-based liquid fuels using molybdenum chalcogenides as catalysts. The research aims to understand the synergistic effect of different chalcogenide elements in the same molybdate compound on the desulfurization process. The results show that the dioxo-dithio-molybdate and monoxo-trithio-molybdate have higher desulfurization activity compared to the homo-chalcogenide molybdate compounds. The catalysts exhibit desirable band gaps in the visible region, making them suitable for photocatalytic oxidative desulfurization of liquid fuels. The catalytic reactions follow a pseudo-first order kinetic model and demonstrate remarkable recyclability.