Catalytic Behavior Of Zinc-based Catalysts For Acetylene Hydration To Acetaldehyde

Acetaldehyde is an important raw material and chemical intermediate,and the acetylene hydration is the dominant route of acetaldehyde production industry in China.However,the used mercury-containing catalyst is harmful to human health and pollutes environment because of its high toxicity and strong volatility.Thus,it is urgent to explore high performance and stability green non-mercuric catalysts for acetylene hydration to acetaldehyde.In this work,the synthesis and modification of zinc-based catalyst and its catalytic activity for acetylene hydration were studied.First,the effect of active components and carriers was investigated,and the appropriate active component is Zn Cl₂with the optimum 15 wt%loading,and molecular sieve（MCM-41）used as the carrier.Optimized reaction conditions included that the suitable reaction temperature was 220°C-260°C,a water gas molar ratio was 4 and water vapour activation enhanced catalytic performance of catalyst.In addition,the results showed that the main reasons for the rapid deactivation of Zn catalysts were loss of active components,carbon deposition and Zn particle agglomeration.The catalytic performance of a deactivated Zn catalyst could be restored by high temperature 550°C water vapour activation.Then,the influence of metal additives（Cu,Ni and La species）on the catalytic performance and stability of the Zn catalyst was investigated.The results indicated that the synergistic effect between metal additives and Zn components could improve the catalyst dispersion,increase the density of the electron cloud around Zn,reduce the loss of Zn components,inhibite the carbon deposition and improve the adsorption of acetylene reactant.Furthermore,the addition of metal additive La showed the optimal catalytic performance,which can improve the activity and stability of Zn-based catalyst in acetylene hydration reaction,and the optimal Zn&3La/MCM-41 catalyst showed over 80%C2H2 conversion and 70%selectivity to acetaldehyde.Finally,the effect of modified the zeolite carrier on the catalytic performance of the Zn catalyst was studied.The results showed that organic modification not only improved the dispersion of Zn catalyst,but also enhanced the interaction between Zn components and modified carrier,as a result of the improvement of catalytic activity for Zn-based catalyst,but the long-term catalytic stability of the catalyst was poor.On the other hand,more active sites and acid sites,higher dispersion,and stronger metal-support interaction were obtained over the Zn-based catalyst with transition-metal-doped zeolite,so remarkably improved the catalytic activity and stability of the catalyst.Additionally,transition metal Ti-doped was optimal,and when the Si/Ti=5,Zn/Ti-MCM-41-5 catalyst of acetylene conversion is 95%,acetaldehyde selectivity is 90%.