In this paper, transition metal (Zn, Cu, Fe and Co) Schiff base complexes modified SiO₂ [SiO₂-M(NNOO)] were prepared with 3-chloropropyltrimethoxysilane (CPTMS) as the coupling agents by ultrasonic technique under mild conditions for the first time. The character and catalytic activity of the sample were also compared with those of the sample prepared by traditional methods. The samples were characterized by IR and UV-Vis spectroscopy. The results showed that the characteristic absorption bands of amidocyanogen and Schiff base groups appeared in IR spectroscopy of the samples prepared by the two methods. The presence of complex structure was confirmed by UV-Vis. The catalytic activity of the samples was tested in selective oxidation of styrene to benzaldehyde with H₂O₂ as oxidant. The influences of reaction time and catalysts on styrene conver-sion and production selectivities were also studied. The results showed that both high styrene conversion (＞90%) and benzaldehyde selectivity (93.5%) could be obtained. The production selectivities were influenced not only by reaction time but also by the kinds of transition metal in the catalysts.

Key words: SiO₂, ultrasonic technique, grafting, Schiff base complex, styrene, benzaldehyde, catalytic activ-ity