Study On The Controlled Synthesis Of Ruthenium Nanocrystals Under Microwave And Their Catalytic Properties

During recent years, nobel metal nanomaterials had attracted much attentionbecause of their widespread applications in the field of electricity, optics, magnetismand especially catalyst. Research showed that the unique physical chemistryproperties of the nanomaterials depended on their morphology, surface structure andsize. Therefore, many researchers attempted to control the synthesis of metalnanoparticles of specific morphology and size to optizime their applications.Ruthenium had became the research focus due to their superior performance in manycatalyst field, however, most of the literature focus on the size controls of rutheniumnanoparticles and discussed the size dependent catalytic capability, there were fewreports on the morphology control and the self-assembly of the rutheniumnanostructures.This thesis focused on the morphology and size control ofdendrimer-like ruthenium nanocrystal and the self-assembly ruthenium nanaosphereusing alcohol heating method. The prepared ruthenium nanocrystals werecharacterized by transmission electron microscopy （TEM）, X-ray powder diffraction（XRD）, X-photoemission-spectroscopy （XPS） and UV-Visible absorptionspectroscopy. The effects of the reducing agent, protecting agent PVP, theconcentration of precursor, reaction time and heating method on the synthesis wereinvestigated. The mechanism of formation of dendrimer-like ruthenium nanocrystalsand the self-assembly nanostuctures were also explored. The dendrimer-likeruthenium nanocrystals were used as the catalyst of the hydrogenation of aromaticnitrocompound, and the catalyst performance were evaluated.The dendrimer-like ruthenium nanocrystals with a mean size of approximately19.6nm were synthesized by heating RuCl₃in the presence of PVP as protectingagent and benzyl alcohol as reducing agent under microwave irradiation for360s, theconcentration of precursor RuCl₃and protecting agent PVP were0.03mol/L and0.15mol/L, respectively, keeping their mole ratio as1:5. The as-synthesizeddendrimer-like ruthenium nanocrystals were characterized by TEM, XRD, XPS andUV-Vis. The molecular weight and concentration of PVP, reducing agent species,concentration of precursor also with the reaction time can greatly influence themorphology and size of dendrimer-like ruthenium nanocrystals.Self-assembly ruthenium nanosphere with a mean size of about32.7nm wereprepared by heating RuCl₃in the presence of PVP as protecting agent and benzylalcohol mix glycerin as reducing agent under microwave irradiation for240s. theconcentration of precursor RuCl₃and protecting agent PVP were0.03mol/L and0.15 mol/L, respectively, kepping the volume ratio of benzyl alcohol and glycerin as1:4.The as-synthesized ruthenium nanosphere were characterized by TEM, XRD, XPSand UV-Vis, which showed that the ruthenium nanosphere was assembly of initialruthenium nanoparticles with a size of about2-3nm. It was found that the heatingmethod, reducing agent species, different volume ratio of benzyl alcohol and glycerin,concentration of PVP and reaction time can greatly influence the morphology and sizeof self-assembly ruthenium nanosphere. Then the mechanism of the self-assemblyruthenium nanostructures were also discussed.The as-synthesized dendrimer-like ruthenium nanocrystals was using as thecatalyst of the hydrogenation of4-chloronitrobenzene. With the conversion of4-chloronitrobenzene can reach72.81%and100%selectivity for p-chloroanilineachevied under suitable condition. Comparing the5%Ru/C and Ru nanoparticles witha size of2.5nm, the selectivity of p-chloroaniline can be100%under dendrimer-likeruthenium nanocrystals, which was due to the effects of the dendrimer-likemorphology and size. The as-synthesized dendrimer-like ruthenium nanocatalyst canbe cycled for more than4times, without changing the morphology and size.