Preparation And Catalytic Performance On Hydrogenation For Novel Egg-Shell Nano-Catalyst

A novel egg-shell nano-SiO2was used as the support to prepare egg-shell shaped nano-catalysts. The structure of the egg-shell Pd-based catalysts and their catalytic performance in the reaction of selective hydrogenation of acetylene were studied systematically. In addition, egg-shell Cu-based catalysts were prepared and tested in the methanol synthesis from CO hydrogenation.Egg-shell nano-SiO2was synthesized with nano CaCO3as template. Then egg-shell shaped unpromoted and Ce/Ag promoted Pd-based catalysts were prepared by an impregnation method using the egg-sheii SiO2as supports and PdCl2as the precursor. TEM, XRD and ICP results showed that Palladium was loaded to the support in the form of PdO with good dispersion and small particle size. TEM, XRD and TPR results reflected that Ag and Pd formed Pd-Ag alloy on the egg-shell shaped support and the Ag promoter inhibited some of the Palladium active sites.The catalytic performance of Palladium catalytst in the selective hydrogenation of acetylene was also investigated. It was found that the optimal space velocity of the Pd-based catalysts with0.04%Pd content was19200mL·g·h-1and the suitabe H2/C2H2of the catalyst is2:1. In addition, Palladium catalysts promoted with Ce were prepared by a co-impregnation and a sequent impregnation, respectively. The effects of the preparation method and the reduction temperature were investigated. The results showed that Ce promoted catalysts prepared by sequent impregnation, which could be reduced at lower temperature compared with that prepared by co-impregnation method, exhibited better catalytic activity and selectivity. As far as for the Ag promoted palladium catalysts is concerned, Ag promoter could improve the acetylene selectivity while lower the ethylene conversion at the same time in the reaction of selective hydrogenation of ethyne.In addtion, egg-shell CuO/ZnO/Si02and Cu0/ZnO/Ce/SiO2catalysts supported with porous hollow silica have been prepared by the two-step precipitation method combined with addition of surfactant in this work. The catalytic performances of the prepared catalysts for methanol synthesis from CO hydrogenation were investigated, and the catalyst structure was characterized by TEM, BET, XRD and XPS. The results showed that the catalysts supported with porous hollow silica had large surface areas and the CuO and ZnO particles with a size of～13nm were well dispersed on the support. The Ce promoter could improve the catalytic activity and the yield of methanol significantly, probably by two reasons:Ce can lower the binding energy of Cu2p3/2and Zn2p3/2and thus facilitating the reduction of CuO to Cu by hydrogen; the presence of Ce might enhance the interaction between Cu and Zn, and improve the dispersion of the active components by preventing the Cu particles from aggregating.