| Because of the unique small size, large specific surface area and otheradvantages, noble metal nanoparticles have been extensively studied in the optical,electrical, magnetic, mechanical and catalytic fields, unique physical and chemicalproperties of which have valuable application in these filed. The size, shape anduniform dispersion of particles will affect the surface chemical activity, magnetic andelectrical performance. Changing the surface structure by controlling the size and themorphology has gradually become a research hotspot. Pt, Rh and Rh are the mainactive component of the three-way catalysts. However, the precious metal resourcesare scarce and expensive. The new environmental standards are also increasinglystringent, so the filed of motor vehicle exhaust catalytic science faces an importantissue to reduce precious metal consumption and improve the activity of catalytic.Nano-catalyst technology provides a feasible technology roadmap for solving thisproblem, while the important prerequisite of the nano-catalysis is to find thecontrollable preparation of the metal nanoparticles. This project, through the design ofexperiments, we found the controllable preparation conditions of Pt, Rh, Pdnanoparticles and described the influence of the law of the synthesis parameters onparticle size and found the controllable law of bimetallic Au/Rh and Pd@SiO2nanoparticles, Which would provide a theoretical foundation and technical support forthe preparation on the excellent performance of nano metal catalysts and nanothree-way catalyst.First of all, through accessing the journal of other workers’ and trackingdomestic and international cutting-edge, we determined the experimental program: bythe polyol reduction method, ethylene glycol as the reducing agent and chief solvents,PVP as protective agent and stabilizers, and chloroauric acid, palladium chloride,chloroplatinic acid and rhodium chloride precursor solutions, the concentrations ofwhich were20,50,20,10and20mM respectively. According to the journals, wedeveloped a test series of the concentration range of experimental conditions andparameter settings.And then, we explored synthesis conditions of Pt, Rh and Pd nanoparticlesprepared by polyol approach with designing experiments. Uv-vis, TEM and laserparticle size analyzer of Pt, Rh and Pd nanoparticles were characterized to determine the the best conditions and synthesis parameters of preparation by ethylenealcoholreduction method, including the effect of the concentration of the precursor solutionand PVP content on the particle size. The experimental results showed that the particlesize of Pt, Rh, of Pd nanoparticles were monodisperse and the distribution is narrow,the morphology of which was spherical. The size of Pt nanoparticles increased withthe raise of metal precursor concentration （0.1,0.3,0.6,1.2,2.4mM）, as followed by:3.2,4.6,5.7,6.1and6.4nm; similarly, Rh and Pd nanoparticles were also increasedwith increasing concentration, respectively: corresponding to0.1,0.2,0.4,0.8,1.6,3.2mM of Rh concentration, the particle size were2.4,2.7,2.9,3.2,4.0and5.1nm;corresponding to0.12,0.24,0.48,0.96,1.92,3.84mM of Pd concentration, theparticle size were3.2,3.3,4.0,4.4,4.8and5.3nm. The size of Pt, Rh, and Pdnanoparticles, first decrease and then increased trend with the increasing amount ofthe PVP. So, The optimal conditions for the fabrication of Pt, Rh, and Pdnanoparticles with uniform distribution were at a temperature of190°C, stirringspeed612r min-1, the precious metals and PVP molar ratio of1:10and preciousmetal concentration of1×10-4,1×10-4and1.24×10-4mol L-1, respectively. Themorphologies of the Rh nanoparticles with the size of5.1nm were polygons,including hexagons, pentagons, and triangles. Which offer the possibility to explorethe relationship of nano-size and catalytic activity for the size of the optimal activity.Controllable preparation of the bimetallic AuRh nanoparticles was studied basedon the end of the dimension of the polyol reduction method. In the process ofexperiment, ethylene glycol as the reaction solvent and reducing agent, PVP as thestabilizer, we prepared the size about7-30nm of AuRh nanoparticles well dispersedin polar solvents. The effect of the concentration of gold chloride acid and rhodiumchloride precursor solution, the proportion of gold and rhodium, and the amount ofPVP on the particle size were investigated. The prepared nanoparticles werecharacterized by means of UV-vis, TEM, HAADF, and STEM-EDS. The resultsproved that nano-particles was alloy and showed that the when the precursorconcentration was0.1mM, the size of nanoparticles were small; as the ratio of goldand rhodium was3:1, the alloy number was more; the amount of PVP indeed theparticle size had a little large. In addition, we also studied the controllable preparationof Pd@SiO2nanoparticles, and the result indicated that adjusting the percentage of thevolume of the silicon source TEOS could control the thickness of the SiO2parcellayer, which provided technical support for the improvement of controllable preparation and stability of nano-catalyst. |
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