In Situ SERS Technique To Monitor The Catalytic Reduction Reaction Of Nitrobenzene On Metal Catalyst Surfaces

The catalytic hydrogenation of nitrobenzene to produce aniline is an important industrial production process.The catalytic hydrogenation process generally recognized by researchers is proposed by Haber,which is divided into direct hydrogenation route and coupled hydrogenation route.In this reaction process,important reaction intermediates with high added value such as phenylhydroxylamine,azobenzene and azobenzene oxide are produced,as well as the product aniline,which has very high application value in chemical industry,medicine and dyes.Because the reduction process of nitrobenzene is very complex,many by-products are generated in the reaction,and the selectivity is difficult to control effectively.Therefore,it is still a challenging topic to obtain specific products through selective control of efficient hydrogenation catalysts.It has important application value to improve the selectivity of a specific product in the hydrogenation of nitrobenzene by designing different catalysts.The product selectivity of catalytic hydrogenation of nitrobenzene is closely related to the structure and properties of the catalyst.The interaction of catalytic reactants,intermediates and products in the catalyst process is helpful to understand the reaction mechanism of the selective hydrogenation of nitrobenzene catalyzed by different catalysts.At present,there are many detection methods commonly used for the catalytic hydrogenation of nitrobenzene,such as ultraviolet-visible spectroscopy,high performance liquid chromatography and nuclear magnetic resonance,which are offline and final state detection,difficult to detect the catalytic reaction process.So,in situ real-time monitoring of the catalyst surface interface was performed.However,in situ infrared spectroscopy also greatly limits the monitoring of the heterogeneous catalytic reaction process due to its strong water absorption in aqueous systems.Electrochemical research methods have weak adsorption capacity for reactant intermediates,and it is difficult to conduct in-depth research on various electrochemical phenomena and reaction mechanisms.Surface-enhanced Raman spectroscopy(SERS)is a highly sensitive,non-destructive spectroscopic technique that enables in situ analyze of substances and provide spectral information of reaction intermediates and products at the molecular level in real time.It is a powerful tool to real-time in situ monitor the reaction process and further reveal the reaction mechanism.Therefore,in this thesis,we used SERS technology to study the interaction between the surface and interface of Au@Au and Au@Au Cu catalysts and the catalytic reduction reaction system of nitrobenzene,which was used for the selective control of the catalytic hydrogenation of nitrobenzene.mechanism research.In this thesis,the first chapter reviews the research significance of nitrobenzene catalytic reduction and the research status of catalyst selectivity regulation and expounds the detection methods of the reaction process and the research status of SERS on the surface interface reaction.The research idea of using SERS technology to monitor the selective control process of catalytic hydrogenation of nitrobenzene is proposed.In Chapter 2,we synthesized bifunctional Au@Au catalysts with SERS-enhanced and catalytic activity for in-situ real-time monitoring of the Au@Au-catalyzed nitrobenzene catalytic hydrogenation process using in-situ SERS.It was observed that the catalytic hydrogenation of nitrobenzene under the catalysis of Au@Au selectively generated azobenzene intermediates and further obtained the product aniline.By combining density functional theory(DFT)calculations,the mechanism of the selective reduction pathway of the interaction between the reactant and product molecules and the surface of the Au@Au catalyst was analyzed from the perspectives of the structural properties of nano materials and the Gibbs free energy.In Chapter 3,we explored the effect of Au@Au Cu catalyst selectivity using in situ SERS.Au Cu alloy catalysts with different molar ratios were formed by doping non-precious metal Cu,and it was observed that the doping of Cu made the azobenzene intermediate disappear in the catalytic hydrogenation path of nitrobenzene,the intermediate N-phenylhydroxylamine is directly converted to aniline.The interaction of Au@Au Cu alloy catalyst on reactants,reaction intermediates and product molecules were further analyzed by DFT.In summary,in situ monitoring of the catalytic hydrogenation process of nitrobenzene by in situ SERS,the interaction between the catalyst and the reaction system was studied,and the selectivity of the catalyst for the reduction process of nitrobenzene with different compositions and structures was revealed.mechanism of influence.The research provides a new method for indepth understanding of the reaction mechanism of catalytic hydrogenation of nitrobenzene and providing guidance for the design of new efficient catalysts.