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Preparation and Characterization of the Colloidal Ru/g-Al2O3 Catalysts

Okal J.

Polish Journal of Chemistry

2009

Vol. 83, nr 2

293-302

Highly dispersed ruthenium nanoparticles were prepared by a microwave-assisted polyol heating process and supported on g-alumina. The structure of the Ru/g-Al2O3 catalysts with different metal loadings was investigated using BET, XRD, TEM and HRTEM. The chemisorption of hydrogen and oxygen on the resultant supported metal materials was investigated as a means of determining the dispersion of the samples. Electron microscopy showed that the Ru nanoparticles were uniformly distributed on the alumina surface and their mean size slightly increased from 1.3 to 2.1 nm with Ru loading rising from 1.2 to 8.6 wt.%. For all samples, oxygen adsorbtion at RT was somewhat higher than at 0°C indicating some subsurface oxidation of small Ru nanoparticles. This process does not, however, affect significantly the Ru dispersion calculated from the O2 up takes at 0°C or at RT. Assuming a stoichiometry O/Rus = 2, good agreement was obtained between the average Ru particle size calculated from O2 and H2 adsorbtion and TEM data. The formation of the surface oxide with stoichiometry close to RuO2 on the surface of the Ru metal nanoparticles after O2 up take measurements was established, but no such phase was detected by HRTEM. Much lower value of O/Rus < 1 was found, however, for the catalyst with the high est Ru loading. A large discrepancy between the results of O2 adsorbtion and TEM for this sample was interpreted as an indication of partial encapsulation of the Ru particles with the support and/or that the metal surface was not reduced completely.