Preparation And Catalytic Performance Of Porous Bimetallic Catalysts

In recently, porous bimetal materials already become the focus because of the existence of synergistic effect, bifunctional mechanism and unique properties of porous catalyst.In this thesis, we mainly focus on the preparation and catalytic performance (selective oxidation of benzyl alcohol) of hierarchically porous thin films catalyst (HPAFs). Besides, there is also the fabrication of surface porous Cu-based bimetallic monolithic wire mesh AuxCuyPFs/Cu and AgxCuyPFs/Cu catalysts. The main information is as follows:1. Preparetion and catalytic performance of HPAFsHierarchically porous Au-Cu thin films (HPAFs) with tunable ligament-pore sizes and Cu residue were fabricated on Au-Cu alloy surface by an alloying/dealloying process. This highly porous structure is composed of large-sized ligament-channels (several micrometers) coupled with small-sized ligament-pores (tens nanometers) interpenetrating the big architectures. The existence of Cu residue in Au-rich ligament spontaneously created an Au-Cu2O heterostructure which is likely highly active for the oxidative dehydrogenation of benzyl alcohol by facilitating the activation of molecular oxygen. The cooperative effect of Au and Cu2O and the hierarchically porous architecture contribute to both high activity and selectivity for HPAFs materials toward the aerobic oxidation of benzyl alcohol to benzaldehyde. It is likely this catalysis process proceeded via the commonly accepted oxidative dehydrogenation mechanism of alcohol oxidation by Au-based catalysts. The reaction can be initiated with a small amount of O2added and the maximum conversion was achieved around the stoichiometric O2/alcohol ratio. Further kinetics studies indicated that the oxidative dehydrogenation is fast enough that the pore diffusion may play a role in benzyl alcohol oxidation over HPAFs as the rate-limiting step. The hierarchically and surface thin-layer structure is likely to enable the decrease of internal diffusion resistance and the improvement of the catalytic performance.2. Fabication and catalytic performance of AuxCuyPFs/Cu AuxCuyPFs/Cu (where x and y is atomic ratio of Au to Cu in electroplating solution) were fabricated in Cu wire by the hydrogen templated electrodeposition. The electrodeposition of AuxCuy foams using a dynamic hydrogen template results in the formation of3-D porous structures. The surface ratio of Au to Cu atom was controlled by adjusting corresponding ions in the solution. This method can control the content of precious metals under0.5%, so as to ensure the dispersion of precious metals, improving utilization. From the study on the catalytic performance of HPAFs for selectivity oxidation of benzyl alcohol, AuxCuy (x=1,y=1) catalysts showed the best catalytic activity. Research shows grown Cu2O phase in the porous structure by oxidation pretreatment was the key to obtain high catalytic activity. The reaction can be initiated with a small amount of O2added and the maximum conversion was achieved around the stoichiometric O2/alcohol ratio.3. Fabication and catalytic performance of AgxCuyPFs/CuAgxCuyPFs/Cu(x and y is atomic ratio of Ag to Cu in electroplating solution)were fabricated by the hydrogen templated electrodeposition. The electrodeposition of AgxCuy foams using a dynamic hydrogen template results in the formation of3-D porous structures. The surface ratio of Ag to Cu atom was controlled by adjusting corresponding ions in the solution. Controlled surface silver copper ratio of1:1, AgCu showed the best catalytic performance at240℃for benzyl alcohol oxidation with conversion74.5%. Notablely, The material prepared by method of hydrogen templated electrodeposition can controlled precious metal content under0.5%, so as to ensure the dispersion of precious metals, improving utilization. Research shows that grown Cu2O phase in the porous structure by oxidation pretreatment was the key to obtain high catalytic activity. The reaction can be initiated with a small amount of O2added and the maximum conversion was achieved around the stoichiometric O2/alcohol ratio. In addition, relatively small size of pore wall nanoparticles of AgxCuyPFs/Cu, given its much higher catalytic activity than AuxCuyPFs/Cu. It also proves that for the Cu-base surface porous structure foams of AuxCuyPFs/Cu and AgxCuyPFs/Cu catalyst, the membrane structure of micro porous-nanoparticles is conducive to its high catalytic activity.