Efficient metal-free aerobic oxidative desulfurization with nitrogen and sulfur co-doped covalent organic polymer-derived carbon

A nitrogen and sulfur co-doped carbon was prepared from a covalent-organic polymer named microporous triazine polymer (MCTP) for the first time by loading NH₄NO₃ and diphenyldisulfide followed by pyrolysis. The obtained carbons (named NSMDCs) were exploited as environment-friendly metal-free catalysts for oxidative desulfurization of organo sulfurous compounds (OSCs) from a dodecane-based simulated fuel using molecular oxygen (O₂) as an oxidizing agent. One of the materials showed a nearly complete conversion of an OSC, dibenzothiophene, after a reaction of 4 h at 100 °C which is one of the lowest temperatures among the metal-free ODS catalyses. A very low activation energy (E_a) of 30.4 kJmol⁻¹ was found for the DBT oxidation which is also lower than or competitive against most of other reported results (including the ones using metal-based catalysts). Radical scavenging investigations and ESR analyses showed the generation of superoxide anion radicals (O₂^–•) from O₂ that might have a dominant role in the oxidation or ODS. Moreover, DFT calculation revealed the generation of increased charge difference on the surface of the N and S co-doped catalyst. A plausible reaction mechanism including the effective activation of O₂ was proposed. The catalyst was effectively used for at least five runs without noticeable degradation with simple acetone soaking and further washing.