Preparation Of Nanoporous Metals And Their Applications In Organic Synthesis

The nano-porous metal material prepared by alloying is a kind of self-supporting material with three-dimensional bicontinuous nano-porous structure.They have the advantages of significant surface effect,high specific surface area,high porosity,low density,uniform structure stability,corrosion resistance,resistance to fatigue,easy preparation and reusable.They have received the widespread attention in various fields,such as sensing,biology,analysis,energy storage,filtration and adsorption media.Among the characteristics of nano-porous metals,the properties of high specific surface area,no load,easy preparation,good reproducibility and repeatability make them show broad prospects in the field of organic catalysis.Compared with conventional supported nanomaterials,porous metal nanomaterials can help us to better understand the catalytic activity of nanomaterials in organic reaction catalysis.At the same time,the existence of low coordination atoms on the pore wall of porous metal nano-materials,could make the nano-catalysts of porous metal show higher catalytic activity than the traditional supported catalysts.The stable and uniform self-supporting structure of nano-porous metal materials could preserve their original morphology and original catalytic activity in the catalytic process,which largely solves the problem of deactivation caused by the changes in morphology,size and distribution of traditional supported nano-catalysts after the reaction.Therefore,unsupported nano-porous metal catalysts are considered as a kind of green catalysts with broad prospects in organic synthesis and industrial production.Nano-porous metal catalysts can be divided into precious metal nano-porous catalyst and non-precious metal nano-porous catalyst.At present,there are many researches on precious metals,especially nano-porous gold,but precious metals have the inherent defects of high cost and limited stock.To solve this problem,we can start from two aspects: the development of non-precious metal nano-porous catalysts and the development of polymetallic nano-porous catalysts doped with precious and non-precious metals.This paper is focus on the nano-porous gold,one kind of the nano-porous metal nano-porous catalysts,on this basis,two kinds of nano-porous catalysts containing non-noble metals including nano-porous copper/ cuprous oxide complexes and nano porous palladium-copper complexes were studied.The details are as follows:(1)The reduction of aromatic nitro groups is an important reaction in organic synthesis and industrial production.The reported catalytic aromatic nitro reduction systems often have problems of harsh reaction conditions,flammable and explosive hydrogen sources.It is still challenging to prepare the corresponding aromatic amine by catalytic aromatic nitro reduction under mild conditions,and such a mild catalytic system is of great significance in organic synthesis and industrial production.We found that the nano-porous gold exhibited high catalytic activity and selectivity for aromatic nitryl reduction by using the ammonia borane as a hydrogen source,and the aromatic nitryl could be selectively reduced to the corresponding aromatic amine under normal temperature and pressure,furthermore,the catalytic activity was not significantly reduced after five cycles.In the further study,we found that the nano-porous copper-cuprous oxide complexes could also complete the catalysis of this reaction,but the two catalysts showed slight differences in selectivity and reaction mechanism.We believe that the green heterogeneous catalysts represented by nano-porous gold and nano-porous copper-cuprous oxide complexes are expected to play an important role in organic reactions in the future.(2)To realize the growth of carbon chain by coupling reaction plays an important role in the fields of organic synthesis,biopharmaceutical,polymer industry.Among them,the Suzuki-Miyaura reaction is the commonly used coupling reaction in this field.In the traditional catalytic system,Pd and Ni catalysts are commonly used to catalyze the Suzuki-Miyaura reaction.Inspired by this,the nano-porous palladium-copper catalyst shows good catalytic activity and substrate universality for the Suzuki-Miyaura reaction,as well as no obvious attenuation of the catalytic activity for multiple cycles.However,further studies are needed to explain the reaction mechanism.