Metal-free oxidative desulfurization with molecular oxygen by using N-enriched porous carbons derived from ionic liquid-loaded covalent-organic polymer

A microporous triazine polymer (MCTP) was prepared and loaded, for the first time, with an N-containing ionic liquid (IL) through a ship-in-a-bottle method. The composite material, IL@MCTP, was pyrolyzed under high temperature to get N-enriched carbonaceous materials. The obtained carbons (denoted ICDCs) were utilized as a metal-free catalyst for the aerobic oxidative desulfurization (ODS) of organic sulfur compounds like dibenzothiophene from a model fuel. The reactivity of ICDCs in ODS was dependent on the nitrogen content and porosity of the carbons. One selected material (ICDC(8)), because of high nitrogen content and adequate porosity, showed a remarkable performance in ODS or removal of dibenzothiophene with a very low activation energy of 23.7 kJ/mol. Radical scavenger experiments and ESR analysis revealed the important role of superoxide anion radicals (•O₂⁻) in oxidation. A plausible reaction mechanism to suggest an important role of nitrogen species in ICDCs to activate O₂ (via adsorption on C with a partial positive charge) was proposed. The ODS also can be carried out with air, and the catalyst was reusable for up to the fifth cycle by simple solvent washing. The ICDCs can be a competitive and environment-friendly (metal-free) ODS catalyst, especially using cheap oxidants like air or O₂.