Silylated MgAl LDHs intercalated with MnO2 nanowires: Highly efficient catalysts for the solvent-free aerobic oxidation of ethylbenzene

Abstract

A novel method for the preparation of silylated MgAl layered double hydroxides (LDHs) intercalated with MnO2 nanowires is presented. The method involves functionalizing the calcined MgAl LDHs (LDOs) with mercaptopropyltrimethoxysilane (MPTS), and then treating the silylated LDOs in the aqueous solution of KMnO4. The results obtained from XRD, FTIR, ICP, XPS and TEM showed that MPTS could be successfully grafted on LDOs via the reaction between –Si(OCH3)3 groups on the silane and the –OH groups on LDOs. LDOs grafted with MPTS could reconstruct their original layered structure by treating them in the aqueous solution of KMnO4, and in the same time, small amount of MnO4− anions were reduced to MnO2 by the grafted –SH groups on MPTS. The formed small amount MnO2 could further catalyze the decomposition of MnO4− in the interlayers of the reconstructed MgAl LDHs to MnO2. The formed MnO2 was finely dispersed on the LDH support in the form of nanowires (about 1.4nm in diameter). The MnO2/MgAl-LDH composites prepared by this method exhibited high catalytic activity, stability and reusability in the solvent-free aerobic oxidation of ethylbenzene.