Study On Supported Cobalt Catalysts For Selective Hydrogenation Of Cinnamaldehyde To Cinnamyl Alcohol

Cinnamyl alcohol is one ofα,β-unsaturated alcohols,which is conventionally used in cosmetics,pharmaceuticals and pesticides.Selective hydrogenation of cinnamaldehyde is a green processing route to synthesize cinnamyl alcohol.Up to now,however,the catalysts used in this hydrogenation are mainly noble metals,which are expensive and rare.In order to get high yeld of cinnamyl alcohol,the conversation of cinnamaldehyde and the hydrogenadtion selectivity to cinnamyl alcohol should be enhanced.However,selective hydrogenation of cinnamaldehyde to cinnamyl alcohol is a difficult reaction,because the C=C bond is more reactive than the C=O bond for hydrogenation.So the key work is to develop cheap and high selective catalysts for the hydrogenation.In this paper,a series of supported cobalt catalysts were prepared by incipient wetness impregnation method.The activity and the selectivity of the catalysts were investigated.The effects of supports,cobalt content, calcination and reduction temperatures,and reduction time on the catalytic performance were studied.The catalysts were characterized using the technologies of X-ray diffraction(XRD)and infrared spectroscopy(IR).It is found that the cobalt-based catalyst supported on TiO₂-SiO₂ with the cobalt content of 15wt%which was calcinated at 823K and reduced for 3h at 823K in hydrogen respectively,shows the best activity and selectivity to cinnamyl alcohol.Additionally,the addition of La into Co/TiO₂-SiO₂ can enhance the activity for 16.25%compared with the catalyst without La.Based on the above results,the reaction conditions were optimized over Co-La/TiO₂-SiO₂ catalyst.Uniformity design experiments method and step by step regression means were adopted.Meanwhile,a B-P neural network was used to optimize the catalytic reaction conditions.The results show that catalyst amount,hydrogen pressure and reaction temperature are the main factors on the catalytic activity,and hydrogen pressure and reaction temperature are the main factors on the selectivity.These results agreed with the results predicted by BP artificial neural network.The B-P neural network for the reaction shows that the highest activity would reach 100%under the following reaction conditions:catalyst amount 0.25 g/mL CAL to 0.3 g/mL CAL,reaction temperature 368 K to 373 K,and hydrogen pressure 2.5 MPa to 3 MPa;the highest selectivity would reach 72%under the following reaction conditions:solvent amount 70 mL, reaction temperature 353 K,and hydrogen pressure 1 MPa to 1.5 MPa.