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

Abstract

Organic–inorganic hybrid materials [Rmim] 4 Mo 8 O 26 (1-alkyl-3-methylimidazolium polyoxomolybdate, alkyl = n -C 4 H 9, n -C 6 H 13, and n -C 8 H 17 ) 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 H 2 O 2 as the oxidant and acetonitrile (MeCN) as the extractant. Notably, these catalysts, initially insoluble in MeCN solution, fulfill a H 2 O 2 -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] 4 Mo 8 O 26 (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 H 2 O 2 -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.