Preparation Of Nano-Pd@PS Core-shell Catalyst And Its Application In Hydrogenation Reaction

In this paper,aldehyde-based polystyrene(PS)functional microspheres were prepared by dispersion polymerization.The effect of binary copolymerization ratio was investigated on the particle size of PS functional microspheres.Pd@PS core-shell microsphere catalyst was prepared by directional reduction of Pd2-ions to Pd nanoparticles by the reaction of aldehyde radicals on the surface of PS functional microspheres with Pd salt precursors.The effects of reaction time on the loading and dispersion of Pd nanoparticles on the surface of Pd @ PS core-shell microspherc catalyst were investigated.Catalytic hydrogenation of nitrobenzene was selected as the basic theory to explore the catalytic performance and recycling application prespect of naropd@PS core-shell mierospberes catalyst Catalytic hyJrogenation and electrochemical reduction methods were used to investigate the catalytic reaction of core-shell microsphcres for the preparation of aniline from nitrobenzene.The catalytic activity of nano-Pd@PS core-shell microspheres was characterized by the yield of aniline.With Pd@PS nano-core-shell microspheres as catalyst,the reaction of catalytic hydrogenation of nitrobenzene to polyaniline was studied.Response Surface Methodology(RSM)optimization test was carried out with Design-Expert software to determine the optimum conditions for the preparation of polyanilinc.The results show that the nano-Pd@PS core-shell material synthesized in this paper is a kind of highly active catalyst.It still has good catalytic activity after many catalytic reactions,which is conducive to the recycling of the catalyst and saves resources.In this paper,the preparation of polyaniline is a step-by-step condensation polymerization reaction.It belongs to a different polymerization mechanisn from the traditional oxidation-coupling lethod.It can not only provide a new scheme for the synthesis of polyaniline,but also reduce the environmental pollution of oxidation-coupling polymerization and simplify the reaction process of polyaniline synthesis.The main research contents include the following aspects:(1)With polyvinylpyrrolidone(PVP)as dispersant,ethanol/watcr as dispersing medium,styrene and acrolein as monomers and azodiisobutyronitrile as initiator,monodisperse PS-CHO functional microsphcres with uniform particle size were prepared by dispersion polymerization The effect of styrene/acrolein copolymerization ratio on the particle size of PS-CHO functional microspheres was studied.Palladium chloride and potassium palladitc chloride as precursors of palladium,PdDPS core-shell microspheres loaded with Pd nanoparticles were prepared by directional reduction reaction with PS-CHO functional microspheres.The effects of reaction temperature,reaction pH,reaction speed,reaction time,particle size of PS-CHO functional microspheres and PdCl2 concentration on the dispersion and loading of Pd@PS nano-core-shell microspheres were mvestigated.The results show that when the particle size of PS-CHO functional microspheres is larger than 300 nm,the loading rate of Pd nanoparticles is high and the dispersion is good.The loading degree of Pd nanoparticles increases first and then decreases with the change of reaction temperature,reaction pH,reaction time,reaction speed and PdCb concentration.The optimum reaction conditions are as follows:reaction temperature 70?,pH 1.38,rotation speed 315 r/min,PdCl2 concentration 2.05 mmol/L,reverse reaction.The response time was 10 to 15 minutes.(2)The prepared Pd@PS nano-core-shell microspheres were used as catalyst,nitrobenzene as raw material,cetyltrimethylammonmum bromide as emulsifier and sodium borohydride as hydrogen source,the reaction of nitro catalytic hydrogenation to aniline was investigated by chemical method.The results show that aniline is willow-shaped,closely arranged and cross-distributed in solution.The effects of reaction temperature,catalytic ratio(m(Pd):m(nitrobenzene))and reaction time on the yield of aniline are investigated.With the increase of reaction temperature,catalytic ratio(m(Pd):m(nitrobenzene))and reaction time,the yield of aniline first increases and then decreases.There is an optimum reaction value:m(Pd):m(nitrobenzene)=1:1273,reaction temperature 30?.reaction time 8h.Under these conditions,Pd@PS nano-core-shell microspheres had the highest activity and the highest yield of aniline.Pd@PS nano-core-shell microsphere catalyst has not been inactivated after three cycles of recycling,and can be reused to save resources.Aniline was prepared by electrochemical reduction using Pd@PS nano-core-shell microspheres as catalyst,nitrobenzene as raw material and dilute sulfuric acid as electrolyte.The effects of Pd@PS nano-core-shell microsphere catalyst concentration,electrolyte type,electrolyte concentration and nitrobenzene concentration on the electrocatalytic reduction of nitrobenzene were investigated.The results showed that the redox peaks appeared at-0.43V and 0.43V,respectively.The characterization showed that the reductive products were aniline.(3)The preparation of polyaniline by catalytic hydrogenation of nitrobenzene with Pd@PS nano-core-shell microspneres as catalyst,nitrobenzene as raw material,cetyltrnmethylammonium bromide as emulsifier and sodium borohydride as hydrogen source was studied.The results show that polyaniline is chain-like in solution and its structure is regular.According to the characterization of mass spectrometry,C-spectrum and H-spectrum,the polyaniline prepared in this paper is a oligomer with three monomer units,a polymer with seven monomer units and a polymer with ten monomer units.The end groups of the polymer are-NHOH and-H.Response Surface Methodology(RSM)optimization experiments were carried out by using Design-Expert software.To explore the yield of Polyaniline and determine the reaction conditions for the maximum yield of polyaniline:m(Pd):m(nitrobenzene)=25:1,C(NaBH4)=37.5g/L,reaction time is 6.67h.Under these conditions,the yield of polyaniline is 0.3664g.(4)The engineering process of Pd@PS nano-core-shell microsphere catalyst catalytic reaction was preliminarily studied by simulating the continuous hydrogen source at room temperature and atmospheric pressure in industrial production.The simulation results show that under the optimum conditions:i.the yield of aniline is 0.1500g,the yield is 80.50%.ii.the yield of polyaniline is 0.05152g,which provides a theoretical basis for the industrial application of the catalyst and preliminarily discusses the prospect of its industrial application.