An organic–inorganic hybrid based on an Anderson-type polyoxometalate immobilized on PVA as a reusable and efficient nanocatalyst for oxidative desulphurization of gasoline

Abstract

In the present work, an organic–inorganic hybrid based on an Anderson-type polyoxometalate ((C₄H₉)₄N)₆Mo₇O₂₄ was synthesized and immobilized on poly vinyl alcohol (PVA) via a sol–gel method. This synthesized nanocomposite was characterized by FT-IR, XRD, SEM and UV-vis spectroscopy. The catalytic activity of this hybrid nanocomposite was tested on oxidative desulphurization (ODS) of model sulfur compounds and actual gasoline. The ODS was performed using different polyoxometalates as catalyst and CH₃COOH/H₂O₂ as oxidant. The experimental results show that the supported polyoxometalate ((C₄H₉)₄N)₆Mo₇O₂₄/PVA catalyst is more active than the unsupported polyoxometalate catalysts. The oxidation reactivity of the catalysts depends on the type of countercation: ((C₄H₉)₄N)⁺ > NH₄⁺ > Na⁺. The sulfur-containing compounds, such as thiophene (Th), benzothiophene (BT) and dibenzothiophene (DBT) were oxidized to the corresponding sulfones. The reactivity order of the model sulfur compounds is: DBT > BT > Th. The effects of the reaction time, reaction temperature, dosage and nature of catalyst and concentration of hydrogen peroxide were investigated. The ((C₄H₉)₄N)₆Mo₇O₂₄/PVA also shows high selectivity for DBT oxidation desulphurization. The selective desulfurization ratio reaches 94% with ((C₄H₉)₄N)₆Mo₇O₂₄/PVA under the reaction conditions of 40 °C, 2 h. The kinetic parameters of the oxidation of model sulfur compounds were studied. The oxidation rate was interpreted with first-order kinetics. The advantages of this method lie in its mild conditions, low cost, large scale, simplicity and environmentally friendly route.