The Preparation And Application Of Supported Noble Metal Composite Catalysts

There are some problems in the application of noble metal catalysts prepared by conventional methods,such as low catalytic activity,low selectivity,more harmful byproducts,low catalyst reuse utilization and other shortcomings.The supported noble metal catalysts with higher catalytic activity and better cycle stability have attracted more and more attention,which have been widely used in the catalysis of alkane dehydrogenation,aromatic nitro hydrogenation,and other electrocatalytic oxidation reaction.Therefore,to explore the preparation of the supported noble metal catalysts with good dispersibility and high utilization of atomic has a very important significance value.Based on the current researchs of supported noble metal catalysts,the hotspots mainly include the following aspects:on one hand,to control the preparation of noble metal nanoparticles,many studies have confirmed that the catalytic activity of the noble metal nanoparticle was closely related to its size,morphology,exposure of crystal face and surface properties.As a result,changing the experimental methods could directly controll the size,morphology and exposure of crystal face of nanoparticles,so as to prepare supported noble metal catalysts with ultrasmall size,good dispersion,high activity and good stability;on the other hand,the carriers are an important part of the supported noble metal catalysts as well,not only can it support the noble metal nanoparticles,but also it improve the dispersion of the noble metal on the support.Meanwhile,the carrier may have the strong interaction with the active species.The last aspect is to form the bimetallic alloy.Recently,preparing precious metal alloys or transition metal alloys has attracted more and more attention.Alloys always have a strong synergistic effect between them,which can greatly enhance the catalytic activity of the catalyst.In this paper,the research results are as follows:1.Pt/Al₂O₃ and Pt₃Sn/Al₂O₃ catalysts by a simple pyrolysis of platinum carbonyl was synthesized.Then,we used XRD,TEM and other methods to characterize the composite materials,and propane dehydrogenation was investigated.Experimental results showed that Sn additives could significantly increase the degree of dispersion and thermal stability of platinum particles,and significantly improve the conversion and selectivity of propane dehydrogenation.2.The Pt/RGO by a simple pyrolysis of platinum carbonyl was prepared.Then,we used XRD,TEM,Raman,IR,XPS and other methods to characterize the composite materials.We examined the effects of the pyrolysis temperature and gas atmosphere on the size of platinum particle.Nitrobenzene hydrogenation,as a model reaction,was used to evaluate the reactivity of the catalyst prepared.Firstly,the impacts of the carriers?activated carbon,carbon nanotubes,aluminum oxide and graphene oxide?on the catalytic activity were studied.It was found that Pt/RGO could catalyze nitrobenzene into aniline with 100%of conversion and selectivity at room temperature for 0.5h.Then,Pt particles with various sizes were obtained by changing the decarbonylation reaction conditions.Then the activities of Pt catalysts with different particle size for hydrogenation of nitrobenzene were tested.The results showed that the smaller the Pt particle is,the higher activity the catalyst has.Last,we tested the cycle stability of the catalysts.After recycled six times,aniline conversion rate dropped to 92%,which indicated catalysts had good cycling stability.3.Using acid refluxing method,glucose as the carbon source,the carbon dots with different sizes was prepares.As there are a lot of functional groups?such as hydroxyl and carboxyl?on the carbon quantum dot surface,which could in-situ reduce the noble metal?Ag,Pd,Au,Pt?,then heterodimers were formed.Then we used XRD,TEM,Raman,IR,XPS and other methods to characterize the composite materials.The activities of the catalysts were evaluated through the hydrogenation of nitrobenzene phenol.Experimental results showed that AgPd@Carbon dots showed higher hydrogenation activity compared with Pd@Carbon dots and Ag@Carbon dots,and that is the highest activity among all the reported results.At last,we tested the cycle stability of the catalysts.After recycled six times,their catalytic activitives just fell a little,reflecting the high catalytic activity and excellent stability.