Issue 36, 2010

Aerobic methylcyclohexane-promoted epoxidation of stilbene over gold nanoparticles supported on Gd-doped titania

Abstract

Aerobic partial oxidations of alkanes and alkenes are important processes of the petrochemical industry. The radical mechanisms involved can be catalyzed by soluble salts of transition metals (Co, Cu, Mn…). We show here that the model methylcyclohexane/stilbene co-oxidation reaction can be efficiently catalyzed at lower temperature by supported gold nanoparticles. The support has little influence on gold intrinsic activity but more on the apparent reaction rates which are a combination of catalytic activity and diffusion limitations. These are here minimized by using gadolinium-doped titania nanocrystallites as support for gold nanoparticles. This material is obtained by mild hydrolysis of a new Gd4TiO(OiPr)14 bimetallic oxoalkoxide. It leads to enhanced wettability of the < 3 nm gold particles in the tert-butyl hydroperoxide (TBHP)-initiated epoxidation of stilbene in methylcyclohexane; Au/TiO2 : Gd3+ is in turn as active as the state-of-the-art hydrophobic Au/SiO2 catalyst. The rate-determining step of this reaction is identified as the gold-catalyzed homolytic decomposition of TBHP generating radicals and initiating the methylcyclohexane-mediated epoxidation of stilbene, yielding a methylcyclohexan-1-ol/trans-stilbene oxide mixture. Methylcyclohexan-1-ol can also be obtained in the absence of the alkene in the gold-catalyzed solvent-free autoxidation of methylcyclohexane, evidencing the catalytic potential of gold nanoparticles for low temperature C–H activation.

Graphical abstract: Aerobic methylcyclohexane-promoted epoxidation of stilbene over gold nanoparticles supported on Gd-doped titania

Supplementary files

Article information

Article type
Paper
Submitted
21 Apr 2010
Accepted
25 May 2010
First published
07 Jul 2010

Dalton Trans., 2010,39, 8457-8463

Aerobic methylcyclohexane-promoted epoxidation of stilbene over gold nanoparticles supported on Gd-doped titania

V. Mendez, K. Guillois, S. Daniele, A. Tuel and V. Caps, Dalton Trans., 2010, 39, 8457 DOI: 10.1039/C0DT00350F

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