A novel synthesis of MnO2, nanoflowers as an efficient heterogeneous catalyst for oxidative desulfurization of thiophenes

Abstract

[Mn<inf>2</inf>(bit)<inf>4</inf> (H<inf>2</inf>O)<inf>2</inf>] complex was used in this study as a novel precursor for the synthesis of MnO<inf>2</inf> nanoflowers. The inorganic precursor was synthesized from the reaction between chloride salt of Mn(II) and benzisothiazolinate. The chemical composition and the nanostructure of the prepared MnO<inf>2</inf> catalyst was characterized using several identification techniques (XRD, Thermal gravimetry, FTIR, N<inf>2</inf>-physisorption, and SEM-EDX). The results showed that the new precursor is a suitable Mn source for the synthesis of highly crystalline MnO<inf>2</inf> nanoflowers of a small particle size with a large surface area. Manganese dioxide nanoflowers were examined for its catalytic ability in the oxidative desulfurization process of a model and real diesel fuels. Oxidative desulfurization conditions have been found to influence the removal efficiency of thiophene, 4,6-dimethyldibenzothiophene and dibenzothiophene. The optimum desulfurization parameters were examined, and the results show that the amount of catalyst is 0.5 g, extraction solvent/ oil ratio is 6, reaction time is 35 min, reaction temperature is 65°C and oxidant: sulfur (O/S) mole ratio is 4. Under these optimum conditions, the MnO<inf>2</inf> catalyst is capable of removing more than 95% of thiophenes from commercial and crude diesel, in the presence of tert-butyl hydroperoxide (TBHP) as an oxidant. The newly prepared catalyst is recyclable for seven sequential oxidative desulfurization runs without the requirement for reactivation steps. This catalytic reaction including TBHP as an effective oxidant was presented through a suggested mechanistic pathway. © 2019 Elsevier B.V., All rights reserved.