Oxidative denitrogenation with TiO₂@porous carbon catalyst for purification of fuel: Chemical aspects

In order to investigate the possible denitrogenation of fuels, oxidation of organonitrogen compounds (ONCs) was carried out by using H₂O₂ green oxidant over a TiO₂-containing carbon catalyst, prepared by the pyrolysis of an MOF-composite [ZIF-8(30)@H₂N-MIL-125] (named as MDC-C). Neutral ONCs, including indole (IND) and its derivatives, especially those with high electron density on the nitrogen of the ONCs, different from basic ONCs, could be effectively oxidized, especially in the presence of a suitable extracting solvent CH₃COOH. MDC-C showed a high turnover frequency in the oxidation of IND as compared with various commercial or synthesized TiO₂ nanoparticles. The used catalyst could be recycled by simple solvent washing up to the fourth run without severe deactivation. Therefore, it could be confirmed that MDC-C is very effective in oxidative denitrogenation to remove ONCs, especially neutral ones, from fuels in the presence of H₂O₂ and a suitable extractant. Importantly, oxidation of IND derivatives was performed firstly under similar conditions in order to understand the mechanism of the reaction. The results showed that high electron density (that calculated in this study) on the nitrogen of the IND and its derivatives is very important, suggesting that the electrophilic addition of oxygen atoms onto the substrates (via N on the INDs) might play a crucial role in the oxidation, even though further study is essential to support this assumption.