Study Of Selective Hydrogenation Of Crotonaldehyde Over Noble Metal Catalysts

As an important organic intermediate,crotyl alcohol is widely used in medicine, paint and pesticide.Presently,the production of crotyl alcohol involves the reduction of crotonaldehyde using NaBH₄ or AlLiH₄,which causes difficulty in product separation and serious environment pollution.By using heterogeneous catalysts,the gaseous selective hydrogenation of crotonaldehyde to crotyl alcohol can overcome such drawbacks.Here,we have designed supported gold and platinum catalysts and evaluated these catalysts for the selective hydrogenation of crotonaldehyde to crotyl alcohol.Furthermore,the reaction mechanism and active sites of the catalysts were explored by means of characterization techniques,such as XRD,FT-IR,TEM,Raman and CO-chemisorption.The detailed studies are as follows:1.Au/TiO₂ catalysts for the selective hydrogenation of crotonaldehydeUsing titania(TiO₂) with different crystal phases,a series of Au/TiO₂ catalysts were prepared and evaluated for the reaction of crotonaldehyde hydrogenation.It was found that the selective hydrogenation of crotonaldehyde over Au/TiO₂ catalysts was influenced by different crystal phases of TiO₂.Comparing to the pure phase(anatase or rutile),the mixed phase TiO₂ containing rutile and anatase could improve both the catalytic activity of gold catalysts and the selectivity to crotyl alcohol.2.Pt/CeO₂ catalysts for the hydrogenation of crotonaldehydeThe catalytic properties of Pt/CeO₂ catalysts prepared by a deposition-precipitation method were evaluated for the reaction of crotonaldehyde hydrogenation.It was found that the particle size of platinum nano-particles and the effect of electron-donor of Ce³⁺ are the main reasons for a higher selectivity of crytal alcohol.Comparing the fresh and used Pt/CeO₂ catalysts,it was found that the Ce³⁺ of the support could gradually change to high-valent Ce⁴⁺ during the reaction,which led to carbon deposition on the catalyst and consequently covered the active sites and decreased the catalytic activity.3.Pt/Pr₆O₁₁ catalysts for the hydrogenation of crotonaldehydeThe catalytic properties of Pt/Pr₆O₁₁ catalyst prepared by a deposition-precipitation method were evaluated for the reaction of crotonaldehyde hydrogenation.The selectivity of crotyl alcohol was higher than 70%when the Pt/Pr₆O₁₁ catalysts were reduced at high temperature(700℃).Based on the TPR and FT-IR characterizations, it was found that the selectivity of crotyl alcohol can be enhanced by the presence of Pr³⁺.However,Raman characterization indicated that the presence of Pr³⁺ can also cause the carbon deposition on the catalyst.