Oxidative desulfurization of liquid fuel with tungsten-nitride@porous carbon, derived from MAF-6(Zn) loaded with phosphotungstic acid and melamine

A tricomponent composite comprising metal–azolate framework-6 (MAF6), melamine (Mela), and phosphotungstic acid (PWA), i.e., Mela(x)PWA(15)@MAF6, was developed and used as a precursor to prepare tungsten nitride@porous carbon (Mela(x)PWA(15)@C) materials upon carbonization under N₂ atmosphere. The crystal phase of the W species and the size of the tungsten nitride (W₂N) nanoparticles in the Mela(x)PWA(15)@C nanocomposites could be controlled by tuning the loaded quantity of Mela. Very small W₂N nanoparticles (~2–7 nm), well-dispersed on porous carbon, were obtained via single step carbonization of Mela(x)PWA(15)@MAF6 composites without feeding external N sources. The obtained Mela(x)PWA(15)@C materials were applied as heterogeneous catalysts for oxidative desulfurization (ODS) of liquid fuel, and the Mela(x)PWA(15)@C catalysts, especially the Mela(10)PWA(15)@C, exhibited very remarkable performance (~100% of dibenzothiophene removal) compared to other W based catalysts. Thus, the turnover frequency of Mela(10)PWA(15)@C, 110 h⁻¹, was around 3.1 times that of conventional WO₃/ZrO₂ catalysts. Moreover, the Mela(10)PWA(15)@C catalyst could be easily recycled with no loss of performance. Oxidation experiments in the presence of radical scavengers suggest that the oxidation reaction proceeds via a nonradical mechanism that involves the facile formation of active pseudo cyclic W peroxo species, facilitated by the N atom of W₂N. The present W₂N@porous carbons can be recommended as highly effective catalysts for the ODS of liquid fuel.