Polyoxometalate@Periodic mesoporous organosilicas as active materials for oxidative desulfurization of diesels

Novel material catalysts based in the active zinc-substituted polyoxotungstate ([PW₁₁Zn(H₂O)₃₉]^5-, abbreviated as PW₁₁Zn) were efficiently used in the oxidative desulfurization of real and model diesels. These active catalytic center was strategically immobilized in a less hydrophilic periodic mesoporous organosilicas (PMOs), containing ethane-bridge (PMOE) and benzene-bridge (PMOB) walls, functionalized with (3-aminopropyl)triethoxysilane (aptes). The efficiency of the novel catalytic composites (PW₁₁Zn@aptesPMOE and PW₁₁Zn@aptesPMOB) was studied under oxidative desulfurization system (CODS) without the presence of an extraction solvent and also using a biphasic (diesel/extraction solvent) oxidative desulfurization system (ECODS). Both composites presented higher desulfurization efficiency under the solvent-free system, reaching ultra-low levels of sulfur compounds after only 1 h and using low ratio of H₂O₂/S = 4. The catalysts could be recycled without loss of activity for ten consecutive cycles. However, after the first desulfurization cycle complete desulfurization was achieved within only 30 min using PW₁₁Zn@aptesPMOE composite. Also, the structure of PW₁₁Zn@aptesPMOE demonstrated to be more stable than PW₁₁Zn@aptesPMOB, probably due to the occurrence of some PW₁₁Zn leaching from the PMOB surface, probably caused by the lower interaction of PW₁₁Zn with the benzene-bridge PMOB wall. The most robust catalyst PW₁₁Zn@aptesPMOE was used to desulfurize a real diesel achieving 75.9% of desulfurization after 2 h. The catalyst was further recycled with success to treat real diesel.