2026/01/01 by Bruno R. S. de Paula, Pedro H. Vendramini, Pedro Henrique Vendramini +3
Engineering · Chemical Engineering · Chemistry · #Catalysis and Hydrodesulfurization Studies #Catalysis and Oxidation Reactions #Zeolite Catalysis and Synthesis
paper · doi:10.21577/0103-5053.20260117
Extractive and catalytic oxidative desulfurization (ECODS) has emerged as an attractive alternative to hydrodesulfurization for producing ultra-low-sulfur fuels under mild conditions. Although methyltrioxorhenium (MTO)/H2O2 systems effectively facilitate sulfur removal from aromatic sulfur compounds, the detailed reaction mechanism for S-removal remains largely inferred just from product analysis. Here, we synthesized a charge-tagged thiophene derivative and used it as a mechanistic probe to study the MTO-catalyzed oxidation of thiophene by hydrogen peroxide. Real-time monitoring with electrospray ionization high-resolution mass spectrometry (ESI-HRMS) enabled us to directly intercept and characterize key intermediates formed during the reaction. Sulfoxide and sulfone derivatives, as well as homo- and heterodimeric cycloadducts produced through Diels-Alder reactions, were detected and structurally characterized using accurate-mass measurements and tandem mass spectrometry. Time-resolved analysis showed rapid conversion of oxidized thiophene intermediates into cycloadducts, followed by sulfur extrusion via SO and SO2 eliminations, leading to desulfurized products. Based on the experimentally characterized intermediates, we propose a revised mechanism that extends the mechanism previously reported., now incorporating direct evidence for transient oxidation and cycloaddition species in ECODS systems. These findings deepen our understanding of oxidative desulfurization processes and could support the development of more efficient technologies and catalysts to produce cleaner fuels.