Preparation Of Nano Core-shell Bimetallic Catalyst By Hydrogen Reduction And Research Of Catalytic Performance For VOCs Oxidation

With the development of modern industry,environmental problems are becoming more and more serious,which have brought great influence on people’s life,work and health.Among them,Volatile organic compounds（VOCs）are the major component of air pollution from a larger variety of sources,such as transport,industrial process and household products,et al.VOCs are also important precursors for the formation of particulate matter（PM）,ozone and photochemical smog,which greatly threaten to the environment and human health due to their toxic,mutagenic and teratogenetic characteristics.It is of great significance to develop an efficient and low-energy for VOCs removal method.Until now,the main approaches for removing VOCs include adsorption,absorption,photocatalysis,biodegradation,pulse corona,catalytic oxidation,etc.Among these methods,catalytic oxidation is considered to be one of the most effective and commonly used methods for eliminating VOCs.However,the catalyst is the core content in the catalytic oxidation process.This paper is mainly aimed at the in-depth study of the catalytic oxidation of VOCs,which is of great significance.In this paper,Au and Pt nanoparticles were prepared by hydrogen reduction in liquid phase,and the preparation conditions were studied systematically.On this basis,the two-step liquid-phase hydrogen reduction method was innovatively proposed,that is,the shell of another metal was grown on the monometallic core,thus the Au@Pt nano-catalyst with bimetallic core shell structure was successfully prepared.In addition,the catalytic properties of monometallic Au,Pt and bimetallic Au@Pt core-shell catalysts were studied,and the intrinsic relationship between catalyst structure and catalytic properties was also discussed.The specific results are as follows:The preparation conditions of Au nanoparticles have found that the precursor concentration,hydrogen pressure,reduction temperature and reduction time of the Au nanoparticles can influence the size and distribution of the monometallic Au nanoparticles,thus affecting the activity of the monometallic Au catalyst.The high concentration of Au precursor and reaction temperature in a certain range led to an increase in size of Au nanoparticles and even caused agglomeration of Au nanoparticles,which reduced catalytic activity.The increase of preparation pressure was favor of the reduction of the metal precursor HAuCl₄·4H₂O,and could inhibit agglomeration of Au nanoparticles.Appropriate reaction time could promote the reduction of precursors,form uniformly dispersed nanoparticles and improve their activity.In conclusion,the optimum preparation conditions for Au nanoparticles were as follows:preparation concentration of 1.0 mg/mL,preparation pressure of 4 MPa,preparation temperature of 40℃,preparation time of 2 h.Secondly,the preparation conditions of Pt nanoparticles are studied in the same way,and the optimal preparation conditions of Pt nanoparticles were as follows:preparation concentration of 2.0 mg/mL,preparation pressure of 4 MPa,preparation temperature of 40℃,preparation time of 3 h.On the basis of preparing monometallic nanoparticles,the bimetallic core-shell structure was prepared by a two-step liquid phase hydrogen reduction method.The Au@Pt core-shell structure prepared by Au as core and Pt as shell,which showed higher activity for the catalytic oxidation of toluene than monometallic Pt or Au catalyst.By adjusting the molar ratio of the bimetal,it was found that the catalytic activity for toluene was given in the order of Au₁Pt₂≥Au₁Pt₃>Au₁Pt₁>Au₂Pt₁>Au₃Pt₁≥Pt>Au.Among the catalysts,the Au₁@Pt₂/Al₂O₃ exhibited higher catalytic activity(T₉₈=195℃)and better stability.The XPS results suggested that the electron transfer from Au to Pt enhanced the catalytic activity of the bimetallic catalyst.In addition,the active components of the catalyst mainly existed in the form of Au⁰and Pt⁰,and the strong interaction between the nanoparticles and the support was also an important factor to improve the catalytic activity.The preparation of Pt@Au core-shell catalyst corresponding to Au@Pt core-shell structure catalyst was Pt as core and Au as shell.In this paper,Pt core was prepared by hydrogen reduction method using organometallic Pt₂（dba）₃ as precursor.Then Au nanoparticles were grown on the Pt core.The Pt@Au core-shell bimetallic catalysts were prepared without any protective agent.The structure of the catalyst was characterized systematically.Bimetallic Au@Pt and Pt@Au core-shell nanoparticles were successfully prepared by two-step liquid phase hydrogen reduction.In the core-shell preparation process,the preparation method is simple,and does not require any protective agent,structure directing agent and blocking agent.Compared with the conventional method,the method not only can effectively control the particle size,but also can effectively control the particle size.Bimetallic Au@Pt core-shell nano-catalysts have higher activity for catalytic oxidation of VOCs than monometallic metal.The present synthesis concept could provide new insights into other double or multi-layer noble metal（transition metal）core-shell nanocatalysts and have potential applications in catalytic,optics,electronic,sensing,energy conversion,storage,biomedicine and other fields.