The performance of Ti-MCM-41 in aqueous media and after mechanical treatment studied by in situ XANES, UV/Vis and test reactions

The influence of water on the epoxidation of cyclohexene with H2O2 and tert-butyl hydroperoxide (tbhp) on Ti-MCM-41 molecular sieves prepared by post-synthetic modification of the support with titanium alkoxides was investigated. The catalytic performance depends on the hydrophilicity/hydrophobicity of the MCM-41 surface, but also on the interactions between titanium centers and oxidants. Using XANES, a higher coordination number and an irreversible transformation of isolated into oxide-like titanium species was observed when the reaction was performed with H2O2 compared to tbhp. The mechanical treatment of Ti-MCM-41 in a ball mill or press did not influence the local environment around the titanium centers, whereas the MCM-41 structure was damaged causing a decrease of the conversion of cyclohexene. (C) 2002 Elsevier Science B.V. All rights reserved.