Hydrophobic Modification\nof Halloysite Nanotubes Loaded\nwith a Small Amount of Tungsten Oxide for Efficient Oxidative Desulfurization

Transition metal oxides can be used as efficient multiphase\ncatalysts\nin the field of catalysis. In this study, a hydrophobic halloysite\nnanotube (HNT) catalyst was designed and prepared with a low loading.\nTungsten oxide was immobilized on the inner surface of the HNT, through\nelectrostatic adsorption and calcination. Furthermore, a dual-functional\nW/HMT/M catalyst was prepared by hydrophobic modification of the outer\nsurface of HNT through a harmless and nontoxic method. The catalyst\nwas applied in the oxidative desulfurization (ODS) of dibenzothiophene\n(DBT), and characterized by inductively coupled plasma (ICP), contact\nangle tests, and other methods. Systematic characterization further\nconfirmed that W/HNT/M has a low loading (0.48 wt %) and a relatively\nhigh contact angle of 92.6°. Oxidative desulfurization experiments\ndemonstrated that the high contact angle corresponds to good hydrophobicity.\nThe low loading and high activity of the catalyst enabled it to achieve\na removal efficiency of 100% for DBT under conditions of 60 °C\nand an O/S = 4. The hydrophobic surface of HNT allowed better dispersion\nin the oil phase, while its hydrophilic inner cavity could adsorb\nH<sub>2</sub>O<sub>2</sub> and the converted dibenzothiophene sulfoxide,\nthereby reducing the subsequent extraction steps after oxidative desulfurization\nand enhancing the reaction environment for reactants and active oxygen.\nW/HNT/M maintained high activity for at least 5 cycles. Additionally,\nthe potential mechanism of the catalyst in the aqueous ODS reaction\nwas proposed. This study demonstrates that HNT-supported metal oxides\nhave desulfurization potential and provides ideas for improving ODS\ncatalytic activity of the ODS through low loading, high activity,\nand unique hydrophobicity design.