Research On Preparation For Nano-Catalysts For Acetylene Selective Hydrogenation By W/O Microemulsion Method

Pd noble metal catalysts are widely applied to C2 fraction selective hydrogenation. Nanosize Pd particles on supported catalyst by the microemulsion method have such adventages on small particle size and narrow distribution etc. This improves the catalysis efficiency. So it was a very important significance that the paper researched.In this paper, we drew the pseudo-triangle phase diagram, researched wholly the characteristic of W/O microemulsion, studied the influence of the surfactant, the cosurfactant, and oil to the microemulsion phase regions, and found Tween80 / 1-propanol / cyclohexane / water microemulsion system for the preparation of catalyst. The experimental results show that: when the mass ratio of Tween80, propanol and cyclohexane is 1:1:1, there was the greatest amount water solubilization in the microemulsion system. The infiltration phenomenon wasn't appeared with the increasing of water content in this system. This system had high stability, and was suitable for the preparation of nano particles. There were well-dispersed Pd particles successfully prepared measuring 2nm-3nm without aggregation. The trend conductivity and viscosity were determined with the variation of the water content in the different microemulsion. Conductivity and viscosity changed dramatically from the microemulsion phase region into two continuous area , which were evidences to determine the phase structure. The structure parameters and the thermodynamic formation of the microemulsion system were studied by the dilution method , the results show that the formation of microemulsion system is a spontaneous process of heat. The experiment data from Nanometer particle diameter were well consistent the theoretical prediction based on this model.The effect of support and the different pyrolysis atmosphere on the performance of the catalyst are investigated. The pinion alpha Al₂O₃ support was more fit for the catalyst of the C2 selective hydrogenation. The catalyst performance of the high temperature decomposition in air atmosphere is better than that in nitrogen atmosphere. The effects of some preparation conditions such as different preparation route, water/surfactant molar ratio w were investigated, The performance of catalyst by the preparing route?and w=11.5 was the best. The Pd-Ag/Al₂O₃-?catalyst showed good activity and selectivity when the quantity contained Pd 0.05wt%, Ag 0.05wt%. When the temperature of reaction reached to 140?, the conversion of acetylene was 99.77% , the ethylene selectivity was 61.27% in a fixed microreactor. The performance of catalyst was better than the commercial catalyst. Catalyst characterization revealed the Pd noble particals were distributed in the surface of the support, the Pd average particle size of 4nm. In addition, it was found that the different Pd content and mass ratio of Pd to Ag had a great influence on the performance of the catalyst. the Pd was 0.03wt%, and Pd:Ag was 1:1, the catalyst showed the good activity and selectively.