Manganese containing MCM-41: Synthesis, characterization and catalytic activity in the oxidation of ethylbenzene

Abstract

A series of Mn-MCM-41 containing manganese from 2 to 10 wt.% were synthesized by impregnation method using aqueous manganese(II) acetate solution as the precursor. The samples were characterized by X-ray powder diffraction, nitrogen adsorption-desorption. FT-IR. TG-DTA. temperature programmed reduction, ESR, UV-vis diffuse reflectance spectra and solid state (29)Si NMR. X-ray diffraction patterns showed that the hexagonal mesopore structure is retained by Mn-MCM-41 after Mn impregnation. FTIR results indicated that Mn ions are incorporated into the Si-O framework. TPR patterns revealed the presence of highly dispersed manganese species on the surface of the support. ESR spectra exhibited a well-resolved sextet centered at g = 2.0 indicating distorted octahedral symmetry of Mn(II) species in Mn/MCM-41. UV-vis diffuse reflectance spectra showed co-existence of Mn(2+) and Mn(3+) in Mn-MCM-41 and co-ordinated to Si(IV) by disordered octahedral and tetrahedral environments, respectively. (29)Si NMR showed higher degree of condensation of materials in framework. Mn/MCM-41 materials possessed significant catalytic activity for oxidation of ethylbenzene using TBHP as oxidant under mild reaction conditions. 6/Mn-MCM-41 showed 57.7% ethylbenzene conversion, 82.2% and 18% selectivity for acetophenone and benzaldehyde, respectively. (C) 2009 Elsevier B.V. All rights reserved.