Study On The Hydrogenation Mechanism Of Nitrobenzene Over Pt-based Catalysts

Aromatic amines are important raw materials for the synthesis of pharmaceuticals,rubber,herbicides,dyes,pigments,chemicals and other chemical fine chemicals and are of great value in industrial production.The hydrogenation of aromatic nitrocompounds in liquid phase is one of the ways to produce aromatic amines.The results show that different kinds of catalysts with different morphology have important influence on the hydrogenation process of nitrobenzene.Among them,the low-cost Cu-based and Ni-based catalysts show good activity in the reaction,but they have relatively strict requirements on reaction conditions and are easily poisoned and inactivated.but they had relatively strict requirements on reaction conditions and were prone to poisoning and inactivation.The noble metal catalyst has the characteristics of high activity and long life.Therefore,the design of noble metal catalysts with special functions and special morphology,in-depth exploration of the mechanism and influencing factors of nitrobenzene hydrogenation reaction under different catalyst systems,in order to complete the low temperature reaction while maintaining a high level of catalytic performance,has become an urgent problem to be solved in the sustainable development of this industry.In this paper,the hydrogenation of nitrobenzene was used as the template reaction,including two parts:1.Pt/CeO₂ catalyst was selected as the research object to explore the reasons behind the influence of the carrier morphology and reduction temperature on the hydrogenation performance of nitrobenzene;2.Pt₃Fe was taken as the research object to explore how Fe addition and octadecene content affected the catalyst performance.It mainly includes the following contents and conclusions:1.We successfully synthesized CeO₂ carriers with different morphologies by adding alkaline solution Na OH and using simple hydrothermal method.By studying the pore structure,crystal plane orientation,oxygen defect concentration and infrared reduction of CO reduction of catalysts with different morphologies The reason for the difference in the performance of Pt metal supported on different morphologies on the hydrogenation of nitrobenzene was explored.It was concluded that due to the high dispersion of Pt/CeO₂-R catalyst metal Pt,its catalytic activity was the highest.Among them,for the particle catalyst,the rod-shaped and cubic catalyst have regular{100}crystal planes and exhibit better redox properties,resulting in better activity.At the same time,the adsorption characterization results of CO₂-TPD,XPS and nitrobenzene show that nitrobenzene is mainly adsorbed on the CeO₂ carrier,in which the content of Ce³⁺on the carrier is positively correlated with the catalytic activity,because the conversion of Ce⁴⁺to Ce³⁺will form oxygen vacancies,while oxygen The vacancy as a Lewis basic site is conducive to the adsorption of-NO₂,resulting in the greater the content of Ce³⁺,the stronger the adsorption capacity of the catalyst for nitrobenzene and the higher the nitrobenzene hydrogenation activity.The in-situ infrared of CO shows that Pt/CeO₂-R-600 exposes more metal active sites,which is also the reason why the rod catalyst has the best activity.By studying the oxygen defect concentration,nitrobenzene adsorption,CO reduction infrared and hydrogen overflow effects of Pt/CeO₂-R catalysts at different reduction temperatures,the reasons for the difference in the hydrogenation history of nitrobenzene at different reduction temperatures were explored,and Pt/CeO₂-R-300 has a smaller metal particle size and dispersibility,so that the conversion rate of p-nitrobenzene in the early stage of the reaction is greater than Pt/CeO₂-R-600.However,when it reached the late stage of the reaction,the adsorption capacity of Pt/CeO₂-R-600 to N-phenylhydroxylamine was greater than that of Pt/CeO₂-R-300 and the hydrogen overflow rate,resulting in the late Pt/CeO₂-R-600 to intermediate products.The conversion rate of N-phenylhydroxylamine is faster.By controlling the p H of the surface layer of the washing liquid during the preparation of the carrier,the Na content on the surface of the carrier and the acidity and alkalinity were studied.On,thereby improving the catalytic activity.When studying the reaction process,it is concluded that the initial product of nitrobenzene hydrogenation is not nitrosobenzene,but N-phenylhydroxylamine.2.Taking the Pt₃Fe catalyst as the research object,the effect of the residual octadecene on the catalyst on the catalytic activity and the effect of doping the second metal Fe on the electronic structure of the metal are compared.Hydrogen,it is concluded that the proper amount of octadecene remaining on the surface of the catalyst is conducive to the activity of Pt₃Fe catalyst nitrobenzene hydrogenation.CO adsorption showed that the addition of transition metal Fe changed the electronic structure of the Pt surface,making the active center Pt surface rich in electrons,which was conducive to the activation of-NO₂ and further greatly improved its catalytic hydrogenation activity.Studies on the activity of different substituents show that when the side group is an electron-withdrawing group,it is conducive to high-NO₂ catalytic activity.