Study On Preparation Of Confined Pt-Fe And Their Catalytic Performance For Hydrogenation Of Chloronitrobenzene

Chloroaniline（CAN）are important organic intermediates,which are widely used in the synthesis of medicine,pesticide,dye,rubber and photosensitive materials.At present,most of CAN are prepared by the reduction of chloronitrobenzene（CNB）.Catalytic hydrogenation reduction has attracted great attention due to its advantages of advanced technology,high yield and less waste discharge.Among the reported catalysts,Pt catalysts,especially activated carbon supported Pt-Fe catalyst,exhibit excellent activity and selectivity for hydrogenation of CNB to CAN.However,the poor catalytic stability of the catalyst for the reaction limits its practical application.In this dissertation,based on the analysis of the present research status of the catalysts for CNB hydrogenation to CAN,we systematically studied the preparation of confined Pt-Fe and their catalytic performance for hydrogenation of CNB.The main research contents and conclusions are as follows.1.Spherical TiO₂ precursor was synthesized through a controlled hydrolysis of titanium tetraisopropoxide.The urchin shell TiO₂ support（u-TiO₂）was prepared by etching the spherical TiO₂ precursor under the protection of a polyvinylpyrrolidone coating and calcination.Pt-Fe/u-TiO₂catalysts were prepared by impregnation-reduction method.It was found that the 0.3%Pt-4%Fe/u-TiO₂ show high activity,selectivity and stability for hydrogenation of CNB to CAN.The p-chloroaniline was obtained with a yield of 100%under 30 ^oC,1.0 MPa H₂ and p-CNB to catalyst mass ratio of 50 for 90 min.The catalyst retained 51.3%activity after the third recycle.TEM and XPS results show that the u-TiO₂as a support makes Pt-Fe particle dispersion better,and there is a strong electron interaction between Pt and Fe and the confinement effect of u-TiO₂on Pt-Fe,which are probably the reason why the0.3%Pt-4%Fe/u-TiO₂ catalyst showed good performance for the catalytic hydrogenation of p-CNB to p-CAN.2.0.3%Pt-4%Fe loaded inside carbon nanotubes（0.3%Pt-4%Fe@CNTs）catalyst was prepared by impregnating carbon nanotubes（CNTs）with H₂Pt Cl₆ and Fe（NO₃）₃ethanol solution.0.3%Pt-4%Fe loaded outside CNTs（0.3%Pt-4%Fe/CNTs）catalyst was synthesized by impregnation CNTs using H₂Pt Cl₆ and Fe(NO₃3) aqueous solution after ethanol saturation.Compared with the 0.3%Pt-4%Fe/CNTs catalyst,the0.3%Pt-4%Fe@CNTs catalyst show better performance for the hydrogenation of CNB to CAN.The p-chloroaniline was obtained with a yield of 100%under under 30^oC,1.0 MPa H₂ and p-CNB to catalyst mass ratio of 50 for 50 min,and the activity of the 0.3%Pt-4%Fe@CNTs catalyst didn’t decrease obviously even after the third recycle.XPS characterization shows that there is a strong electron interaction between Pt and Fe₂O₃ confined in CNTs,which makes the Pt nanoparticles in the0.3%Pt-4%Fe@CNTs catalyst an electron-deficient state and generates Fe³⁺/Fe²⁺redox couple.The electron-deficent Pt can reduce the extension of electron feedback to benzene ring and inhibit the dehydrochlorination reaction.The Fe³⁺/Fe²⁺redox couple is favorable for hydrodeoxidation of-NO₂.The confinement effect of CNTs on Pt-Fe may be responsible for excellent performance of the 0.3%Pt-4%Fe@CNTs catalyst for p-CNB hydrogenation to p-CAN.Higher H₂ pressure and reaction temperature are favorable to the catalytic hydrogenation of p-CNB to p-CAN over the0.3%Pt-4%Fe@CNTs.3.0.3%Pt-4%Fe/MgAl-LDH catalyst was prepared by a co-precipitation method.Compared with the 0.3%Pt-4%Fe/u-TiO₂ and 0.3%Pt-4%Fe/CNTs catalysts The0.3%Pt-4%Fe/MgAl-LDH exhibited lower catalytic activity for hydrogenation of p-CNB to p-CAN,but the catalyst showed excellent stability,almost no decrease in catalytic activity even after the third recycle.