Liquid Phase Selective Hydrogenation Of Crotonaldehyde Over Over Supported Pt Catalysts

As an important organic intermediate, crotyl alcohol is widely used in medicine, paint and pesticide. It is a green route for the crotonaldydehyde hydrogenation over heteortous catalysts. However, gas phase methods of the selective hydrogenation of crotondehyde are reported in many references, the liquid phase methods are supplied in a few part. In this paper the supported Pt catalysts were prepared by an impregnation method, and were applied for the liquid phase selective hydrogenation of crotonaldehyde. By controlling reduction temperature, reaction temperature and pressure, higher catalytic activity and crotyl alcohol selectivity over Pt catalysts were got. Solvent effects and the second metal Fe doped into Pt/TiO2were examed in detail finally.The detailed studies are as follows:1. Pt/TiO2catalysts for the selective hydrogenation of crotonaldehydeUsing Titania (TiO2) as the support, a series of Pt/TiO2catalysts were prepared by an impregnation method, and were evaluated for the liquid phase selective hydrogenation of crotonaldehyde. The Pt/TiO2catalysts were characterizated with XRD, TEM, TPR, etc. The loading of Pt content, reduction temperature, reaction temperature and pressure were explored in detail. According to the experimental results,80%selectivity to crotyl alcohol with90%crotonaldehyde conversion over3%Pt/TiO2reached at80℃and0.6MPa H2after500℃reduction. Higher reduction temperature was favored for the selectivity to crotyl alcohol, which may be due to the larger particle size of platinum and the effect of electron-donor of Ti3+produded after high reudction temperature.2. The effect of solvent on the hydrogenation of crotonaldehydeIn liquid phase selective hydrogenation of crotonaldehyde, solvents can play a crucial role. The effects of different kinds of solvents on the hydrogenation of crotonaldehyde were examed in deatial:(1) for the polar protic solvents, ethanol can show a high catalytic activity, but it also easily reaches a excessive hydrogenation. The tert-butyl alcohol and isopropyl alcohol can give a high selectivity to crotyl alcohol, but benzyl alcohol has a very low activity and selectivity to crotyl alcohol;(2) for the polar aprotic solvents, THF shows a low catalytic activity and a high selectivity to crotyl alcohol (more than70%). Adding acidity to THF solvent, the selectivity to crotyl alcohol can be improved obviously (ca.85%); adding a little of ethanol, the activity and selectivity are both enhanced, and the yield of crotyl alcohol reached72%;.(3) for the non-polar solvents, cyclohexane show a higher catalytic activity than hexane.3. Pt-Fe/TiO2catalysts for the selective hydrogenation of crotonaldehydeBy adding the second metal Fe as a modifier, Pt-Fe/TiO2catalysts were prepared by co-impregnation method, and were evaluated in the liquid phase selective hydrogenation of crotonaldehyde. According to the experiment results, when the molar ratio of Pt and Fe was3:2, the selectivity to crotonyl alcohol was around70%. Adding excessive Fe to Pt/TiO2, the catalytic activity was decreased, which may be due to the cover of the Pt active sites with doped Fe. After redued at500℃, Pt-Fe/TiO2catalyst can givea good Crotonyl alcohol yield (70%). Comparing with liquid phase reduction, the ex-situ reduction with hydrogen atmosphere for Pt-Fe/TiO2catalyst can get better a catalytic activity and selectivity to crotonyl alcohol.