Supported tungstic acid: Remarkable catalyst for room temperature oxidative denitrogenation of liquid fuel

Tungstic acid (TA, WO₃·H₂O) was synthesized for the first time on the porous polypyrrole-derived carbon (PpyrlDC) under mild hydrothermal conditions. The TA particles were uniformly distributed within the porous PpyrlDC support and the composite was used for the oxidative denitrogenation of several organonitrogen compounds (ONCs) from liquid fuel. The TA/PpyrlDC catalysts demonstrated remarkable efficiency in the oxidation of indole (one of the typical ONCs) with H₂O₂, even at room temperature and in the absence of any extractant or solvent. For example, one invented catalyst, TA(5)/PpyrlDC, had the lowest activation energy (22.6 kJ mol⁻¹ which is not far from the E_a of diffusion in the liquid phase), the highest turnover frequency, and the fastest kinetic constant, reported for W-based catalysts, in indole oxidation. Moreover, the catalyst can fully oxidize indole even at 25 °C and can be recyclable for several runs via simple soaking and washing with solvents. The oxidation mechanism could be suggested by analyzing the catalytic systems with the electron spin resonance and indole oxidation in the presence of radical scavengers.