Mn(Salen)Cl complexes immobilized on SBA-15 functionalized with amine as an efficient, selective and recyclable catalyst for benzyl alcohol oxidation by TBHP: the effects of Mn loading and reaction conditions

Abstract

In this work, SBA-15 molecular sieves were functionalized with propylamine. A series of Mn(Salen)Cl complexes immobilized on amine functionalized SBA-15 (SBA-15-pr-NH2) with different loading of Mn in range of 0.293–0.765 mmol Mn/g catalyst were prepared. These samples were characterized by BET, XRD, TGA–DSC, UV–Vis and FT-IR. The catalytic activity of immobilized Mn(Salen)Cl complexes was evaluated in the oxidation of benzyl alcohol in the liquid phase using tert-butylhydroperoxide (TBHP) as the oxidant. It was found that Mn(Salen) complexes immobilized on the SBA-15-pr-NH2 are an efficient catalyst for the oxidation of benzyl alcohol and showed high catalytic activity and selectivity to benzaldehyde. As we expected, the leaching of manganese complexes from the support during the reaction was negligible, because of strong interaction between Mn(Salen)Cl complexes and the amine groups on the surface. The effects of Mn loading and various solvents on the conversion and selectivity were studied. A second order function for the variation in catalytic activity with respect to the loading of Mn(Salen)Cl in different catalyst samples was observed. The activity of the SBA-15-pr-Mn(Salen)Cl catalyst differs with the type of the solvent, and, in this case, acetonitrile gives the best conversion results. The influences of reaction temperature, reaction time, solvent, reusability, amount of catalyst and TBHP to benzyl alcohol molar ratio were investigated. Under optimized conditions, 73.5 % conversion of benzyl alcohol and 100 % selectivity to benzaldehyde was achieved.