Selective hydrogenation of crotonaldehyde on Au/HSA-CeO2 catalysts

The gas-phase hydrogenation of crotonaldehyde was carried out over Au supported on high-surface area (HSA) CeO2, previously reduced at 120 degrees C. The products analyzed during the initial, nonequilibrium stage showed the formation of large amounts of ethanol, which rapidly decreased with time on stream and were replaced by a combination of condensation products (mainly 2,4,6-octatrienal) under equilibrium conditions. The production of crotyl alcohol largely exceeded that of butanal at any time on stream. Under steady-state conditions, the crotyl alcohol-to-butanal ratio was equal to 1.7. When the catalyst was recalcined in air at 300 degrees C, just before the reduction treatment, the formation of ethanol in the initial stage and that of condensation products under steady state decreased. Besides, notable increase in the production of crotyl alcohol was observed, whereas butanal formation was unaffected. Finally, Au/HSA-CeO2 is a highly selective catalyst for C=O bond hydrogenation when crotyl alcohol/butanal ratio is equal to 3 under a steady-state regime. These results were compared to those obtained for Au/TiO2 [R. Zanella, C. Louis, S. Gorgio, R. Touroude, J. Catal. 223 (2004) 328]. The role of acid-base sites, as well as that of the redox centers of HSA-CeO2, is evaluated. Even though ceria sites are engaged in the reaction, the catalytic properties of Au/HSA-CeO2 are attributed mainly to the gold nanoparticles. (c) 2006 Elsevier Inc. All rights reserved.