Efficient Oxidative Desulfurization over [Mo8O26]4–-Based Hybrids: Phase Transfer Catalysis

Abstract

Organic–inorganic hybrid materials [Rmim]4Mo8O26 (1-alkyl-3-methylimidazolium polyoxomolybdate, alkyl = n-C4H9, n-C6H13, and n-C8H17) were prepared, and various characterization techniques have proven the hybrids’ successful synthesis. Meanwhile, the oxidative desulfurization (ODS) performance of both model and real diesel has been evaluated with H2O2 as the oxidant and acetonitrile (MeCN) as the extractant. Notably, these catalysts, initially insoluble in MeCN solution, fulfill a H2O2-responsive phase transfer into the MeCN phase to improve the ODS performance, facilitating the S compound extraction to the MeCN phase. After the ODS reaction, the hybrids precipitated from the MeCN phase, completed the heterogeneous separation, and regenerated simply by drying. Hybrid materials [Omim]4Mo8O26 (1-octyl-3-methylimidazolium polyoxomolybdate) with the longest alkyl chain displayed the highest desulfurization efficiency, achieving 99.8% dibenzothiophene (DBT) removal at the optimum reaction conditions of 50 °C, O/S = 5, Mo/S = 1:1, and V(MeCN/diesel) = 1:5. Even for real diesel, the hybrid exhibited more than 97% sulfur removal in diesel with sulfur contents of 3000 μg/g through the two-stage extraction-coupled oxidation desulfurization (ECODS) process. High catalytic recycling capability has been manifested by no obvious decrease in ODS activity after five cycles. This extraction-promoted H2O2-responsive phase transfer catalysis guarantees a promising industrial ODS system, not only substantially improves the catalytic desulfurization activity but also shows superior recycling performance with a simple catalyst regeneration method.