Platinum supported on [60]fullerene-grafted silica as a new potential catalyst for hydrogenation

摘要

A Pt-based catalyst supported on a silica grafted with [60]fullerene was prepared and evaluated in the liquid-phase hydrogenation of cinnamaldehyde. Silanization of a large-pore silica was carried out with diethoxymethylsilane. [60]Fullerene was anchored on the modified silica through a hydrosilylation reaction with Si-H bonds, mediated by a Pt-0 Karsted catalyst. IR, Si-29 and C-13 MAS NMR spectroscopies, and N-2 adsorption-desorption provided evidence that [60]fullerene was covalently bonded onto the silica surface. [60]Fullerene was released at ca 950, 750, and 800 K in He, air, and H-2, respectively, even in the presence of 0.8 wt% Pt. The very high density of [60]fullerene grafting confers a strong hydrophobic character to the surface. A fairly good selectivity to cinnamyl alcohol was observed on this catalyst at cinnamaldehyde conversion above 90%. This behavior might be better explained by a specific interaction between the phenyl ring of cinnamaldehyde and the grafted [60]fullerene film than by a modification of the Pt d-band. The IR spectroscopy of adsorbed CO did not provide any evidence of an enhanced, or reduced, back-donation to 2 pi* antibonding orbitals of CO, with respect to classical supported Pt catalysts. (C) 1998 Academic Press. [References: 20]