Study On The Preparation Of CNTs Supported Pt, Pd Catalysts And Catalytic Performance For The Selective Hydrogenation Of α, β-unsaturated Aldehyde

α,β-Unsaturated aldehydes are the source materials for many important products in the chemical industry,including polymers and fine chemicals.The semi-hydrogenated products such asα,β-unsaturated alcohol and saturated aldehyde are important fine chemicals and intermediates especially in perfume industry and medicine manufacture.Study on the selective hydrogenation ofα,β-unsaturated aldehydes is of great importance in potential industrial applications and theoretical aspects.Cinnamaldehyde(CMA),a member ofα,β-unsaturated aldehydes.It is easier for the hydrogenation of C=C group than hydrogenation of C=O group on the hydrogenation of CMA.More activated adsorptive hydrogen and more active sites for the hydrogenation of unsaturated bond on catalyst's surface improve catalytic activity and selectivity on the hydrogenation of CMA.The selective hydrogenation has been attention for its lower impact on the environment.From the point of view of green chemistry,the development of industrial processes for direct production of organic intermediates using heterogeneous catalysts is an industrially meaningful target,since the catalysts could be easily removed from the reaction mixtures and wastes could be largely diminished.Since the discovery at the beginning of the last decade,carbon nanotubes(CNTs)have received an increasing interest both from a fundamental point of view and for potential industrial applications.Based on the rule of selective hydrogenation of CMA,we mainly design a series of Pt,Pd catalysts supported by CNTs.They show better hydrogenation properties on the selective hydrogenation of CMA.Some specific conclusions are drawn from this work as follows:1 The selective hydrogenation properties of CMA have been studied over Al₂O₃,ZrO₂, TiO₂,active carbon(AC),Graphite(G)and carbon nanotubes(CNTs)supported Pt catalysts.Among these catalysts,Pt/CNTs catalyst shows the highest selectivity of the hydrogenation of C=O bond,and no production of by-products due to the special nanosized channel structure of the CNTs.2 Effect of transition metals(Cr,Mn,Fe,Co,Ni and Cu)on the hydrogenation properties of CMA over Pt/CNTs catalyst are investigated systematically for the first time.The results show that the addition of Co and Ni improve the catalytic activity of Pt/CNTs catalyst.The 0.5%Pt-0.17%Co/CNTs catalyst exhibits the higher hydrogenation selectivity for C=O bond,97.0%for the conversion of CMA and 94.5% for the selectivity of CMA to cinnamyl alcohol(CMO)at 70℃under 2.0MPa H2 pressure with the reaction time of 2.5h,which is one of the best results reported until now.The 0.5%Pt-0.34%Ni/CNTs catalyst exhibits the higher hydrogenation selectivity for C=C bond,98.6%for the conversion of CMA and 88.4%for the selectivity of CMA to hydrocinnamaldehyde(HCMA)at 70℃under 2.0MPa H₂ pressure with the reaction time of 1.5h.3 The influence of reaction conditions on the selective hydrogenation of CMA over PtCo/CNTs and PtNi/CNTs catalysts has been studied.The results show that the catalytic activity of the catalysts increases with the increasing of reaction temperature and hydrogen pressure.It is to improve the hydrogenation for C=C bond as increasing the reaction temperature and to improve the hydrogenation for C=O bond as increasing the H₂ pressure.Both of the catalysts show better hydrogenation properties in polar solvent than litter-polar solvent.The selective hydrogenation for C=O bond over PtCo/CNTs catalyst increases while the selective hydrogenation for C=C bond over PtNi/CNTs catalyst increases with the increasing of solvent polarity.The addition of trace amount of acid,base and salt have very different effect on the hydrogenation properties of CMA over PtCo/CNTs and PtNi/CNTs catalysts.For the PtCo/CNTs catalyst,the hydrogenation rate of CMA increases significantly in the presence of trace NaAc,HAc and HNO₃ promoters and exhibits the highest selectivity(96.5%)of CMO when the NaAc amount is 0.10mmol,while the addition of organic base (CH₃CH₂)₂NH and inorganic base NaOH inhibit the catalytic activity.For the 0.5%Pt-0.17%Ni/CNTs catalyst,the hydrogenation rate of CMA increases significantly in the presence of trace NaAc,NaOH,HAc and HNO₃ promoters and the addition of NaAc and NaOH remarkably increase the catalytic activity and the hydrogenation selectivity for the C=C bond.The best result(91.8%for conversion of CMA and 96.1%for selectivity of HCMA)is obtained at 60℃,under 1.5MPa H₂ pressure with the reaction time of 1.5h.The results of primary kinetic investigation of the PtCo/CNTs reaction system show that the activation energy is 26.5KJ/mol.4 The influence of preparation condition such as reduction methods,precursor and impregnation modes on the selective hydrogenation of CMA over PtCo/CNTs and PtNi/CNTs catalysts has been studied.The results show that the catalyst reduced by KBH₄ show higher catalytic activity than catalyst reduced by hydrogen,formaldehyde and hydrazine hydrate which maybe due to the effect of the remained element B from KBH₄.The prepared catalyst exhibits the best catalytic activity when Pt(NH₃)₄Cl₂ is used as the Pt precursor,while the impregnation mode of the promoter has little effect on the catalytic property of the catalysts.5 Microemulsions have been investigated as reaction media for the selective hydrogenation of CMA.The water/ethanol/reactant microemulsion system can influence reaction regioselectivity due to orientation of reactants at the interfacial region by the attraction of the C=O end because of the polarity of the water which deeply increases the trend of the selective hydrogenation of C=O.The conversion of CMA is 87.4%and the selectivity of CMA to CMO is 92.4%at 70℃,under 2.0MPa H₂ pressure with the reaction time of 1.5h in the reaction media of ethanol.While the conversion of CMA is 97.3%and the selectivity of CMA to CMO is 90.8%at the same reaction condition in the water/ethanol/reactant microemulsion system.6 Hydrogenation properties of CMA have been studied overγ-Al₂O₃,ZrO₂,TiO₂, active carbon(AC),Graphite(G)and carbon nanotubes(CNTs)supported Pd catalysts. Different support materials have great influence on catalytic activity and selectivity. The order of the catalytic activity of the catslysts is:Pd/TiO₂(IⅠ＞Pd/7-Al₂O₃(â… )＞Pd/ZrO₂(â… )＞Pd/AC(â… )＞Pd/CNTs(â… )＞Pd/G(â… ).Among these catalysts, Pd/CNTs shows the highest selectivity of the hydrogenation of HCMA.80.6%for the conversion of CMA and 92.7%for the hydrogenation of CMA to HCMA at 30℃under atmosperic H₂ pressure with the reaction time of 4h.The influence of reduction methods and reaction conditions on the selective hydrogenation of CMA over different supports supported Pd/CNTs catalysts has been studied.The results show that catalyst reduced by KBH₄ shows higher catalytic activity and which also benefit for the hydrogenation of C=C bond.All of the catalysts show better hydrogenation properties in polar solvent than litter-polar solvent.It is to improve the hydrogenation for C=O bond with the increasing of solvent polarity.The order of the catalytic activity of the solvents is:ethanol＞n-butanol＞toluene.The hydrogenation rate of CMA increases significantly in the presence of trace HAc and HNO₃ promoters while the by-products increases when the acid is strong acidity.The addition of trace bases inhibit catalytic activity while improve the hydrogenation selectivity of CMA to HCMA.