Study On Selective Catalytic Hydrogenation Of Acetylene Over PD/CTS Catalyst

It is a very important subject in the field of environmental engineering to control and utilize the environmental waste gas.Acetylene is a kind of exhaust gas because of the trace impurity gas acetylene in ethylene,and the ability of acetylene to cause greenhouse effect is more than 50 times that of carbon dioxide.Removal of acetylene from ethylene and its resource utilization are the key steps before the use of ethylene The use of selective catalytic hydrogenation is the main method for removing trace acetylene from ethylene.Therefore,it has been crucial to develop a catalyst which has a high conversion rate to acetylene and a high selectivity to ethyleneCompared with non-noble metal catalysts,Pd-based catalysts have high catalytic activity for acetylene,but catalysts with palladium as active component have lower selectivity to ethylene.Therefore,we modified Pd by using the functional group amino group on chitosan(CTS)to increase the selectivity of the catalyst for ethylene.At the same time,biomass chitosan has attracted more and more researchers’ attention because of its huge reserves,biodegradability,environmental pollution-free and abundant surface functional groups.In this paper,Pd/CTS catalysts were prepared by wet impregnation method,and the interaction between the active components and supports of the catalysts and the effect of supports on the hydrogenation activity of the catalysts were studied.At the same time,in-situ infrared and quantum chemical calculations were used to investigate the catalytic hydrogenation mechanism of the catalysts and the catalytic mechanism of the supports for the active components.We draw the following conclusions(1)Pd/CTS catalyst was prepared and used for selective catalytic hydrogenation of acetylene.The results show that the catalyst can convert acetylene to 100%at low space velocity and near room temperature,indicating that the catalyst has a high conversion rate for acetylene.Moreover,the selectivity of the catalyst for ethylene can reach more than 90%at the space velocity of 70 000 ml g-1 H-1 and the temperature of 90 C,which indicates that the catalyst has good selectivity to ethylene.(2)In this study,the active components of the catalyst were modified by amino groups on organic carriers to achieve the purpose of regulating the hydrogenation process of acetylene in the catalytic process.Studies have shown that the functional groups on the surface of chitosan(such as amino groups,hydroxyl groups)play a very good role in the dispersion of noble metals.Meanwhile,the amino group and palladium nanoparticles on chitosan can be known by X-ray energy spectroscopy.There is electron migration between them because the modification of the active component by the amino group on the carrier greatly increases the selectivity of the catalyst to ethylene.In this study,the interaction between support and active components was used to improve the catalytic hydrogenation performance of the catalyst,which provided a new way for the design of the catalyst.(3)The in-situ infrared characterization shows that acetylene will produce some transition states during the catalytic hydrogenation process.These transition states can interact with the amino and hydroxyl groups of the catalyst carrier chitosan,thus affecting the selective catalysis of the catalyst for acetylene process.Through in-situ infrared,we can also clearly see the acetylene molecules break on the surface of the catalyst.We suspect that in the selective catalytic hydrogenation of acetylene,acetylene and hydrogen molecules break simultaneously on the catalyst surface.(4)In this paper,the hydrogenation reaction process of acetylene was simulated by quantum chemical calculation.The results showed that the support chitosan could significantly reduce the reaction energy barrier of the active components,therefore improving the selectivity of the catalyst to ethylene.