Comparison of liquid-phase olefin epoxidation catalysed by dichlorobis-(dimethylformamide)dioxomolybdenum(VI) in homogeneous phase and grafted onto MCM-41

A mesoporous silica-supported molybdenum oxide catalyst with a loading of 0.17Mo/nm2 was prepared by liquid phase deposition ofMoO2Cl2(dmf)2 (1) onto MCM-41 (dmf = dimethylformamide). Powder X-ray diffraction and N2 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, 13C and 29Si MAS NMR, and Mo K-edge EXAFS, the Mo atoms in this catalyst are mainly present as isolated {MoO2[(–O)3SiO]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 ◦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 -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.

Keywords

MCM-41 Mesoporous materials EXAFS Molybdenum Oxidation Heterogeneous catalysis

URI

http://hdl.handle.net/10400.1/2056

Citation

Monteiro, Bernardo; Balula, Salete S.; Gago, Sandra; Grosso, Carla; Figueiredo, Sónia; Lopes, André D.; Valente, Anabela A.; Pillinger, Martyn; Lourenço, João P.; Gonçalves, Isabel S. Comparison of liquid-phase olefin epoxidation catalysed by dichlorobis-(dimethylformamide)dioxomolybdenum(VI) in homogeneous phase and grafted onto MCM-41, Journal of Molecular Catalysis A: Chemical, 297, 2, 110-117, 2009.