| Ethylene is a crucial intermediate in many industrial reactions.In general industry,ethylene is mostly produced by thermal cracking or catalytic cracking of higher hydrocarbons,but this process will produce a small amount of acetylene impurities,which will poison the catalyst.In order to prevent catalyst poisoning,the acetylene concentration needs to be lower than 5 ppm.The most common method to reduce the concentration of acetylene in industry is the selective hydrogenation of acetylene on a palladium-based catalyst.However,the precious metal palladium is expensive,and excessive hydrogenation of ethylene and ethane oligomerization will occur during the reaction,thereby reducing ethylene selectivity.The purpose of this thesis is to seek a green,environmentally friendly,low-cost catalyst to increase the selectivity of ethylene under the premise of ensuring the conversion of acetylene.The first part of the work in this paper is to use tetraethylammonium hydroxide and sodium fluoride as the dual template,and use the hydrothermal synthesis method to successfully prepare the BEA/MOR composite molecular sieve catalyst,and then use the pure phase BEA,MOR and BEA/MOR composite Molecular sieve was used as the carrier,and the loading of nickel was fixed at 0.5 wt%,1 wt%,2 wt%,and 3 wt%to explore the influence of different supports and different metal loadings on the reaction.The results show that 2 wt% Ni/BEA/MOR has the highest hydrogenation activity for acetylene at 250 °C.At this time,the conversion rate of acetylene is 100%,and the selectivity of ethylene is 69.5%.The catalyst activity is excellent when the composite molecular sieve is used as the carrier.Use pure phase molecular sieve as carrier.This reaction has phenomena of excessive hydrogenation and acetylene polymerization,and the nickel catalyst has poor stability to this reaction.Based on this,we introduced the metal promoters Sn and Ag into the single metal catalyst,and explored the influence of the metal promoter on the reaction.The experimental results show that metallic silver is more beneficial to increase the selectivity of the catalyst.When the ratio of nickel to silver is 7 and the reaction temperature is 250 °C,the catalyst has the best catalytic performance.At this time,the acetylene conversion rate is 100% and the ethylene selectivity is 95.2 %.In addition,the stability of the catalyst is greatly improved compared to the single metal catalyst.This is because charge transfer occurs between silver and nickel to form an alloy,which is beneficial to improve the catalytic activity of the catalyst. |
