The grafting reaction of tetraneopentyl titanium on the surface of MCM-41 mesoporous molecular sieves dehydroxylated preliminary at 500 degrees C leads to formation of the well-defined bigrafted surface complex (&3bond; Si-O)(2)Ti(CH2CMe3)(2). On reaction with water or alcohol, the neopentyl ligands can be replaced selectively by alcoxy or hydroxy. On calcination at 500 degrees C, a well-dispersed titanium oxide supported on MCM-41 is obtained. In situ FTIR, DRS, and XAFS characterizations suggest that titanium is present as isolated tetrahedral species on the surface of MCM-41. This solid was used for the photocatalytic oxidation of ethylene in oxygen under UV irradiation, and its activity was compared to that of Ti-MCM-41 prepared by direct hydrothermal synthesis. The higher activity of the samples prepared by reaction with the organometallic complex is attributed to the good dispersion of titanium on the surface of MCM-41. (c) 2005 Elsevier Inc. All rights reserved.