Shape Controlled Synthesis And Catalytic Activity Of Ruthenium Nanoparticles

The noble metal nanometer material have become one of the hot researchsubjects in the field of nanoscience and technology because of its outstandingcatalytic, electric, magnetic and optical properties. Their catalytic properties arestrongly dependent on their size and shape, as well as their composition, crystallinityand structure. As an important member of the platinum family metals, ruthenium iswell known as a novel catalyst for selective hydrogenation of aromatic compounds orthe unsaturated carbonyl compounds. Up to now, many effective methods focused onsize control for ruthenium nanoparticles. However, its morphology has been scarcelyreported. So, shape-controlled synthesis and the catalytical properties of Runanoparticles were investigated in this paper.By oil-bath method, stable flower-like Ru nano-flakes were synthesized withRuthenium chloride (RuCl3·xH2O) as a precursor, polyvinylpyrrolidone (PVP) as astabilizer, tetraethylene glycol (TEG) and Zn as a co-reductant in the presence of anappropriate amount of cetyltrimethylammonium bromide (CTAB), which was addedafter2h, at170°C for6h. The effect of CTAB adding time, CTAB concentration, aswell as the amount of Zn and the kind of surfactant on the morphologies of Runanoparticles were investigated. The results showed that the optimum molar ratio ofRuCl3/PVP/CTAB/Zn was1/20/1/1.5. The as-prepared Ru nanoparticles werecharacterized by transmission electron microscopy (TEM), UV-vis absorptionspectra(UV-Vis), X-ray powder diffraction (XRD) and X-ray photoelectronspectrometry (XPS).The little Ru nanoparticles were prepared with RuCl3·xH2O as a precursor, oilamine (C18H37N) as a protecting agent, toluene as a solvent and hydrogen as areducing agent. Ru nanoparticles with various morphologies can be obtained byadding oleic acid (C18H34O2) at the same time. Ru nanochaines or sea urchin-like Runanoparticles were synthesized with the molar ratio of oil amine/oleic acid of1/1,1MPa of H2pressure,160°C for4h or6h, respectively. The as-synthesized Runanoparticles were characterized by TEM, XPS,and XRD. The catalytic activities of SiO2-supported Ru nanoparticles with two kind ofmorphologies for the selective hydrogenation of phenol to cyclohexanone wereexamined. The effects of time, temperature, hydrogen pressure and on the catalyticactivities of Ru nanoparticles were investigated. The results showed that conversionrate of phenol was82.38%and the selectivity of cyclohexanone was92.95%when thereaction was conducted for6h at80°C with the molar ratio of phenol and catalyst of1001and1MPa of H2pressure. The flower-like Ru nano-flakes demonstrated ahigher conversion efficiency but lower selectivity, while a higher selectivity forpompon-like Ru nanoparticles.