| Selective hydrogenation over supported noble metal catalysts is an important reaction in heterogeneous catalysis.A typical example is the selective hydrogenation ofα,β-unsaturated aldehydes to unsaturated alcohols,which have been widely used in the production of fine chemicals such as spices and pharmaceuticals.Compared with traditional processes using strong reductants such as Na BH4 and Li Al H4,selective catalytic hydrogenation using gaseous H2 as hydrogen source is more eco-friendly and atom economic.In the reaction of selective hydrogenation ofα,β-unsaturated aldehydes toα,β-unsaturated alcohols such as acrolein,pactonal,2-pentenal and cinnamaldehyde,the hydrogenation of C=C bond to saturated aldehydes is much easier than the hydrogenation of C=O bond to unsaturated alcohols in terms of thermodynamics and kinetics.Therefore,it is an important and challenging task to achieve high selectivity for unsaturated alcohols.In recent years,supported Pt-based catalysts have been widely used in the selective catalytic hydrogenation of crotonol to crotonol,but the selectivity and catalyst activity of crotonol still need to be improved.In this paper,supported Pt-based catalysts were prepared by different methods,and the effects of synthesis methods on their catalytic performance（activity,selectivity and stability）were investigated.This paper focused on the the relationship between catalyst carrier and its catalytic performance.And furthermore,the influence of non-noble metal doping on its catalytic performance also has been studied.The specific research content includes the following three parts:1.Overdipping method,sodium borohydride reduction method and equal volume dipping method are adopted respectively to synthesize Pt/Mo S2（E）,Pt/Mo S2（P）and Pt/Mo S2（D）catalysts.Selective hydrogenation of crotonaldehyde was used as a probe reaction.It was found that under the same reaction conditions（H2 pressure is 3.0 MPa;The reaction time was 4 h.The reaction temperature was 100°C）,and the performance of Pt/Mo S2（E）catalyst was better than Pt/Mo S2（P）and Pt/Mo S2（D）catalyst.With further optimization of reaction conditions the reaction time was 4 h and the reaction temperature was120°C,Pt/Mo S2（E）had the best catalytic performance(conversion rate of crotonaldehyde98.9%,selectivity of crotonol 70.8%,TOF is 488.1 h-1),and the catalytic performance remained unchanged after five cycles.The catalyst was characterized by XRD,BET,TEM,SEM,XPS and H2-TPD.The results showed that more Pt nanoparticles were loaded on the edge of two-dimensional Mo S2,and some Pt nanoparticles were anchored on the surface of two-dimensional Mo S2.The good catalytic performance of Pt/Mo S2（E）may be due to the existence of more Pt4+species in Pt/Mo S2（E）,the stronger Pt4+in two-dimensional Mo S2 edge,and the synergistic effect between Pt species and Mo S2 carrier.2.Pt M/CNTs（M stands for Co,Ni,Fe and Cu）,Pt/CNTs and Co/CNTs catalysts were synthesized by sodium borohydride reduction at room temperature.It was found that PtCo/CNTs and Pt Ni/CNTs of different metal doped catalysts were over-catalytic hydrogenation at H2 pressure of 3.0 MPa,reaction time of 4 h and reaction temperature of100°C,and the conversion rate was 100%and the selectivity to n-butanol was over 94%.The reason is that the reaction temperature is too high or the reaction time is too long,which makes the hydrogenation of carbon-carbon double bond or carbon-oxygen double bond become both,so that the selectivity of n-butanol becomes high.By reducing the reaction temperature and shortening the reaction time,it was found that the conversion of crotonaldehyde and selectivity of crotonol reached 83.5%and 91.3%,the TOF is 647.4 h-1 at2 h and 60°C,and the catalytic performance of PtCo/CNTs catalyst remained unchanged after five cycles.The catalysts were characterized by XRD,BET,TEM,SEM,XPS and H2-TPD.It was found that PtCo alloy was formed by Pt and Co in the PtCo/CNTs catalyst,and the PtCo alloy nanoparticles were uniformly loaded on the multi-walled carbon nanotubes.The reason why PtCo/CNTs have excellent hydrogenation performance of crotonaldehyde is that PtCo alloy particles formed by Pt and Co enhance the activation ability of hydrogen.The interaction between Pt and Co was beneficial to the vertical adsorption of crotonaldehyde.3.Pt Mx/SBA-15（M stands for Co,Ni,Zn and Cu）,Pt/SBA-15 and Co/SBA-15 catalysts were successfully synthesized by ultrasonic impregnation.The effects of reaction time,temperature,doping metal and metal ratio on crotonaldehyde hydrogenation were investigated.It is found that metal Co has more advantages in catalytic hydrogenation of croton aldehyde than other doped metals（Ni,Cu and Zn）.When H2 pressure is 3.0mpa,reaction time is 2 h,and reaction temperature is 80°C,the atomic ratio of doped metal Co in Pt:Co is 1:5,the catalytic performance of PtCo5/SBA-15 catalyst for the selective hydrogenation of crotonaldehyde to crotonol is the best(the conversion of crotonaldehyde is 100%and the selectivity of crotonol is 79.1%,the TOF is 910.5 h-1).The catalysts were characterized by XRD,BET,TEM,SEM,XPS and H2-TPD.It was found that PtCo alloy was formed in PtCo5/SBA-15 catalyst,and the PtCo alloy nanoparticles were uniformly loaded on the molecular sieve SBA-15.PtCo5/SBA-15 catalyst has better catalytic performance of crotaldehyde because of the strong interaction between PtCo alloy nanoparticles and molecular sieve SBA-15.The unique porous structure of SBA-15 and the interaction between Pt and Co are favorable for the adsorption of the C=O double bond of crotonaldehyde,thus improving the selectivity of C=O hydrogenation. |
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