abstract
A mesoporous silica-supported molybdenum oxide catalyst with a loading of 0.17 Mo/nm(2) was prepared by liquid phase deposition of MoO(2)Cl(2)(dMf)(2) (1) onto MCM-41 (dmf = dimethylformamide). Powder X-ray diffraction and N(2) adsorption studies of Mo-MCM-41 indicate that the texture properties of the support were preserved during the grafting experiment. On the basis of evidence from FTIR spectroscopy, (13)C and (29)Si MAS NMR, and Mo K-edge EXAFS, the Mo atoms in this catalyst are mainly present as isolated {MoO(2)[(-O)(3)SiO](2)(dmf)(2)} species, with a small contribution from oxo-bridged dimers. Catalysis tests show that complex 1 and Mo-MCM-41 are highly active oxidation catalysts for liquid-phase epoxidation of unfunctionalised olefins using tert-butylhydroperoxide as oxidant, from ambient to 55 degrees C. The high stability and recyclability of the heterogeneous Mo-MCM-41 catalyst is attributed to the strong metal oxide-support interaction. With cyclooctene, 1-octene, trans-2-octene and norbornene substrates, the corresponding epoxides were the only observed reaction products. The reactions of the other substrates gave by-products such as 8,9-p-menthen-1,2-diol from (R)-(+)-limonene, campholenic aldehyde from alpha-pinene, and benzaldehyde from styrene. The addition of dichloromethane as a co-solvent had a beneficial effect on catalytic performance, and in the case of (R)-(+)-limonene allowed the epoxide to be formed as the only reaction product. (C) 2008 Elsevier B.V. All rights reserved.
keywords
SUPPORTED MOLYBDENUM OXIDE; RAY-ABSORPTION-SPECTROSCOPY; CURVED-WAVE THEORY; MESOPOROUS SILICA; PARTIAL OXIDATION; SELECTIVE OXIDATION; RAMAN-SPECTROSCOPY; EXAFS CALCULATIONS; MOLECULAR-SIEVES; COMPLEXES
subject category
Chemistry
authors
Monteiro, B; Balula, SS; Gago, S; Grosso, C; Figueiredo, S; Lopes, AD; Valente, AA; Pillinger, M; Lourenco, JP; Goncalves, IS
our authors
Anabela Tavares Aguiar Valente
Principal Researcher
Isabel Maria de Sousa Gonçalves
Associate Professor
Martyn Pillinger
Principal Researcheracknowledgements
We are grateful to the FCT, POCI 2010, OE and FEDER for funding (Project POCI/QUI/56109/2004). The CCLRC Daresbury Laboratory Synchrotron Radiation Source (SRS) is acknowledged for providing beamtime at station 16.5 under award number 47105. We also wish to acknowledge Paula Esculcas for assistance in the NMR experiments and Rosario Soares for collecting the powder X-ray diffraction patterns. B.M., S.S.B. and S.G. thank the FCT for grants.