Study On Gold Catalysts For Selective Hydrogenation Of Cinnamaldehyde

Gold catalysts are a kind of promising catalysts for selective hydrogenation based on their good activity and selectivity for the reduction of many compounds. Finding good methods to tune the active sites and the selective adsorption sites is crucial for the further research and development of the gold catalysts.In this paper, a series of colloidal gold catalysts stabilized by poly( N-vinyl-2-pyrrolidone) (PVP) have been synthesized by the liquid reduction of HAuCl4. A series of Au/MxOy-TiO₂ catalysts and Au-M/TiO₂ bimetallic catalysts were prepared by deposition-precipitation (DP) method. All the catalysts were tested in cinnamaldehyde hydrogenation, and characterized by XRD, TEM and XPS techniques.The results showed that the gold nanoparticle catalysts are active for the reduction of carbon-carbon double bond in cinnamaldehyde. Au nanoparticles with quite narrow size distribution and small diameters (ca. 10nm ) prepared at the conditions of the mol ratio of surfactant to Au at 20:1, and the molor ratio of KBH4 to Au at 3:1, exhibits excellent catalytic activity and selectivity for the hydrogenation of cinnamaldehyde. The conversion of cinnamaldehyde and the selectivity to hydrocinnamaldehyde are 98.82% and 63.78%, respectively.The property of intrinsic support plays a key role for the supported colloidal gold catalysts. Colloidal gold supported on SiO₂ shows high selectivity for the reduction of carbon-carbon double bond, the same as unsupported Au nanoparticle catalyst. Colloidal gold supported on TiO₂ followed reduction treatment using H2 behavior an opposite selectivity to the unreduced PVP-Au/TiO₂ catalyst,selective for the reduction of carbon-oxygen double bond. The reduction process facilitates electron transfer from support to gold, and the multielectron gold particles are responsible for the selectivity adsorption of the carbon oxygen double bond.The supported catalysts prepared by deposition-precipitation (DP) method are selective for cinnamaldethyde hydrogenation to cinnamyl alcohol. The type, dosage and adding method of metal oxide modifier significantly affect on the performance of Au/MxOy-TiO₂ catalysts via the different interaction between gold species and the support. Pre-deposition and pre-impregnating could make the zirconium modifier finely dispersed on the supports. The Au/5%ZrO₂-TiO₂ catalyst, prepared by decomposition of ZrO₂ on TiO₂ followed by loading gold, shows comparable performance in cinnamaldethyde hydrogenation.The addition of cobalt can influence the performance of Au/TiO₂ catalyst. Au-Co/TiO₂ catalyst synthesized by the pre-decomposition of cobalt followed by loading gold showed comparable performance in cinnamaldethyde hydrogenation. While the cobalt added by co-deposition with Au could lead to congregating of the gold nanoparticle, which is inert for cinnamaldethyde hydrogenation.