The Study On The Catalytic Performance Of Newly-structured Pt-Cu Nanocomposite For Selevtive Hydrogenation Of P-chloronitrobenzenes

Platinum group elements(PGE)is a kind of important metal materials,being able to use as the active materials for drug and gas sensors,which can be intensively applied as catalysts for electrocatalysis,catalytic hydrogenation and catalytic cracking reactions.To controllably modify the catalytic performance of Pt group elements is an important issue because of not only their extensive industrial application fields but its great scientific interests.Presently,the way to modify the catalytic performance of PGE mainly includes decorating with small molecules,adding supports and introducing the second metal.The added metal exerts the influence on the catalytic performance of PGE catalysts in two ways,i.e.geometric effect and electronic effect.However,it is difficult to know how much contribution of geometric effect and electronic effect of added metal to PGE catalysts' performance,because the ratio of metal to PGE,geometric effect and electronic effect are hard to be tuned independently in the metal-PGE alloy or core-shell structure.To realize the target of controllable modification of bimetallic catalysts is still a big challenge.To develop newly structured bimetallic catalysts is a viable way.This theme focuses on the design,preparation and catalytic performance of bimetallic catalysts in order to pave the way for controllably modifying the catalytic performance of Pt group elements.The catalytic performance of Pt/C and Cu/C in the hydrogenation of p-chloronitrobenzene was studied.The activity of Pt/C is very high,and the reaction rate can reach 11.85 molCNB molPt-1 s-1.However,the chlorination reaction can be clearly observed.The Cu/C is not active for this reaction.Based on above work,two kinds of model Pt-Cu catalysts are designed and prepared to explore the contribution of geometric effect and electronic effect from copper to the catalytic performance of Pt nanoparticles in the selective hydrogenation of p-chloronitrobenzene(p-CNB).One model Pt-Cu catalyst(called Cu/C-Pt)is Pt nanoparticles depositing on ultra-small copper particles decorated active carbon,and another is copper particles decorated Pt/C catalyst(called Pt/C-Cu).During all the preparation process,the samples were placed at room temperature and the reducing reagent was NaBH4.After incorporating with copper,the crystalline structure of Pt nanoparticles still remains.Cu/C-Pt catalyst has lower activity than Pt/C,but the selectivity of the desired product p-chloroaniline(p-CAN)on Cu/C-Pt catalyst is much higher than that on Pt/C.The selectivity of p-chloroaniline can reach 99.5%.The increase of Cu loading led to the lower catalytic activity and better selectivity for Cu/C-Pt.Over Pt/C-Cu catalyst,p-CNB cannot be completely converted into p-CAN.More interestingly,the dechloronation reaction of p-CAN on Pt/C-Cu cannot be observed.The newly-structured catalysts were prepared at very mild conditions.The interaction between Pt nanoparticles and Cu nanoparticles at room temperature was explored(the experimental details can be seen in supporting information).First we prepared PVP encapsulated Cu nanoparticles(Cu-PVP)and Pt nanoparticles(Pt-PVP).The results revealed that diffusion of solid copper into Pt nanoparticles at room temperature was difficult and that PtCu alloy can be easily produced by reducing cationic state of Cu with NaBH4 on Pt nanoparticles at room temperature.The most important work in this theme is exploring the influence of geometric effect and electronic effect on the catalytic performance of Pt nanoparticles in the selective hydrogenation of p-chloronitrobenzene(p-CNB).The ex-situ XPS results revealed that the decrease of binding energy of Pt in Cu/C-Pt and Pt/C-Cu with a value of 0.2 eV.The same electronic effect can be deduced,which led to the decrease of catalytic performance of Pt nanoparticles.The exposed surface of Pt is close to that of Pt/C,but most of the surface of Pt nanoparticles in Pt/C-Cu is covered by copper,which caused by the difference in preparation method.Much more surface of Pt was covered by Cu in Pt/C-Cu,leading to the big change in the surface geometric structure and lower catalytic activity than that of Cu/C-Pt.This theme investigated the influence of geometric effect and electronic effect on the catalytic performance of Pt nanoparticles,which can help us to understand the factors influencing the catalytic reactions and to design the composition and structure of the catalysts.This work move a key step to realize the target of controllably modifying the catalytic performance of catalysts.