Preparation of polycarboxylic acid-functionalized silica supported Pt catalysts and their applications in alkene hydrosilylation

Abstract

A series of novel immobilized platinum catalysts was prepared by loading Pt onto silica particles modified with polycarboxylic acid groups such as diethylenetriaminepentaacetic acid (DTPA), nitrolotriacetic acid (NTA) and succinic acid (SA). The three modified heterogeneous Pt catalysts were characterized using infrared spectroscopy (IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS) and atomic absorption spectroscopy (AAS). The residual H₂PtCl₆ solutions were characterized using ultraviolet spectroscopy (UV). The polycarboxylic acid-functionalized silica supported Pt catalysts were used to catalyze alkene hydrosilylation and 1-hexene was chosen as a model alkene. The data indicated that the catalytic performance was strongly dependent on the properties of the polycarboxylic acid group bonded to the silica particles. Among them, DTPA-functionalized silica supported Pt (SiO₂-DTPA-Pt) showed the best catalytic activity and reusability. Furthermore, some hydrosilylation reactions between other linear alkenes (1-heptene, 1-octene, 1-decene, 1-do-decene, 1-tetra-decene, 1-hexa-decene, 1-octa-decene, styrene or cis-hex-2-ene), or ring type alkenes (norbornene) with methyldichlorosilane could be catalyzed in the presence of these three Pt catalysts. Their high activities were more than 90%, and their selectivities were more than 99%, which were apparently better than homogeneous Pt catalysts. In addition, reactions with cyclohexene were also successfully catalyzed by the Pt catalysts. These results indicate that the polycarboxylic acid-functionalized silica gel supported Pt catalysts have potential value in industrial hydrosilylation reactions.