Abstract
The requirement for ultra-low-sulfur diesel (ULSD) quality necessitates the use of heterogeneous catalysts with high oxidative desulfurization (ODS) activity, which are also robust and inexpensive to produce. In this work, we describe a new type of molybdenum-functionalized biochar catalyst (MoPSBC) prepared from pistachio shell (PS) agricultural waste via impregnation followed by carbothermal reduction, providing a novel means of simultaneously valorizing agricultural waste and preparing well-dispersed monoclinic MoO(2) nanoparticles with a well-developed carbon framework, as evidenced by SEM analysis. Physicochemical characterization using XRD, FTIR spectroscopy, SEM-EDX, and DSC revealed that 10 wt% Mo is the optimal loading, maximizing active-site availability while maintaining high metal-support interactions and dispersion efficiency. Under optimal reaction conditions (1 h, 70 °C, and H(2)O(2)/S molar ratio = 6), the 15MoPSBC catalyst exhibited high DBT conversion (>99.3%) in 10 000 ppm DBT model fuel. When tested on real gas oil with 1715 ppm sulfur, formic acid-promoted 10MoPSBCF, where formic acid acts as an in situ oxidant precursor to boost the Mo active site turnover, reduced the total sulfur content to about 89 ppm (94.6% sulfur removal), showing practical applicability to real-world feedstocks. Mechanistic studies revealed that the reversible Mo(4+)/Mo(6+) redox cycle produced highly electrophilic oxoperoxo-molybdenum species as primary active sites, while the graphitic biochar surface enabled π-π stacking interactions for refractory dibenzothiophene (DBT) sequestration, as revealed by FTIR and SEM characterization. Kinetic studies validated pseudo-first-order kinetics with respect to the concentration of DBT. These results demonstrate the potential of MoPSBC as a cost-effective, biomass-derived catalytic platform for advanced fuel purification, providing a scalable solution for ULSD production.