Preparation Of Supported Gold Catalysts And Their Performance For Selective Hydrogenation Of Cinnamaldehyde

Supported gold catalysts are a kind of promising catalysts for selective hydrogenation based on their good activity and selectivity for the reduction of many compounds.In this paper, using several metal oxides doped TiO₂ as supports, which were prepared by the sol-gel method, a series of gold catalysts were prepared by the deposition-precipitation (DP) method. Additionally, a series of Au/La(OH)₃ catalysts were prepared by cocipitation (CP) method. All the catalyst were tested in cinnamaldehyde hydrogenation. Their phisico-chemical properties were investigated by XRD, TEM, XPS, BET and TPR techniques. The reaction conditions of cinnamaldehyde selective hydrogenation were optimized.The results show that the performance of Au/TiO₂ catalyst is influenced by the type and the content of additives. Among the metal oxide promoters tested, La₂O₃ modified Au/TiO₂ shows the best selectivity for the reduction of carbon-carbon double bond in cinnamaldehyde. The moderate amount of La₂O₃(10 wt%) can obviously improve the catalytic activity and selectivity of Au/TiO₂ for cinnamaldehyde hydrogenation. The presence of La₂O₃ in TiO₂ restrains the growth of TiO₂ crystallites, increases the surface area of catalysts and makes the particle size distribution of Au crystallites more evenly. The gold on the surface of Au/TiO₂ exists mainly as Au0, but on the La₂O₃ doped catalyst there is a small portion of Au3+ species besides Au0, which may benefit the activation of the C=O bond of cinnamaldehyde.The results show that La(OH)₃ supported gold catalyst shows high selectivity for the reduction of carbon-carbon double bond. With the characterization results, the reason of the high selectivity is that the supporter La(OH)₃ and Au interact to form a unique structure. The preparation conditions of Au/La(OH)₃ catalyst are optimized as follows: 2 wt% of gold content, calcination temperature 100°C and reduction temperature 150°C.The reaction conditions of cinnamaldehyde selective hydrogenation over Au/La(OH)₃ catalyst are optimized as follows: reaction temperature 180°C, reaction pressure 2.0 MPa, catalyst dosage 0.25 g, solvent isopropanol. Under the optimal conditions, the conversion of cinnamaldehyde and the selectivity to cinnamyl alcohol can reach 100% and 75.7%, respectively, after reaction 22 h.