The Study Of [Prmim][Cl]-Supported Palladium Nanoparticles As Catalysts For Selective Hydrogenation Of Acetylene

Ethylene is one of the largest chemical products and it makes great contributions to the national economy.It typically produced from oil cracking but the products always blended with about 0.3-3%acetylene impurity which could poison the following Ziegler-Natta catalysts and finally impacted the polyethylene quality.The main method to remove acetylene in ethylene is acetylene semi-hydrogenation.Supported palladium catalysts are generally chosen as the semi-hydrogenation catalysts but pure palladium catalysts confront several problems,including poor selectivity and short catalyst operating life.To solve the problems existed in the industrial palladium-based catalysts,1-propyl-3-methyl imidazolinium chloride?[Prmim][Cl]?ionic liquid?IL?was loaded on Pd/?-Al₂O₃ solid catalyst.A two-step impregnation approach is used to prepare a high selective Pd/[Prmim][Cl]/Al₂O₃ catalyst.The catalytic performance of ionic liquids-supported palladium catalyst was also investigated.It is shown that under the reaction conditions of Pd loading=0.1%,IL loading=30%,H₂ pre-reduction temperature=170?,H₂ pre-reduction time=1h and PdCl₂ as the precursor,the catalysts could exhibit the best catalytic performance.In order to improve the catalytic performance,Al₂O₃ were calcined at different heating temperature.The characterization results of XRD,BET,NH₃-TPD and C₂H₂-TPD revealed that the surface acid and adsorption capacity to C₂H₂ of Al₂O₃ had changed.The selective hydrogenation of acetylene was studied over the catalysts after support calcination.The results showed that there was a significantly improvement of activity and stability due to the lower surface acid of Al₂O₃ after calcination.By exploring the hydrogenation machanism of supported ionic liquid-palladium based catalyst,it was found that[Primim][Cl]could stabilize the structure of Pd particles during the pre-reduction and protect them from migration and aggregation.Due to the presence of IL,the unique properties of ionic liquids resulted in the difference of hydrogen and acetylene solubility in IL,there could be the“hydrogen-poor”environment in the active components layer.It caused a controlled amount of hydrogen to minimize overhydrogenation of C₂H₄ to C₂H₆.It was also shown that ethylene selectivity increased with hydrogen-bond basicity of anion increasing by modulating the type of IL'anion.