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Oxygen Adsorption and H2-O2 Titration Method for Measurement of Ru Dispersion in Ru/gamma-Al2O3 Catalysts

Okal J.

Polish Journal of Chemistry

2007

Vol. 81, nr 12

2181-2194

Oxygen adsorption at room temperature (RT) and 0°C and H2-O2 titration were studied by volumetric technique on a colloidal 5.1% Ru/g-Al2O3 catalyst prepared from the RuCl3×3H2O precursor by a polyol reduction method. Adsorption properties of this catalyst were compared with those of the 4.6% Ru/g-Al2O3 catalyst prepared by incipient wetness impregnation method using the same metal precursor. The colloidal catalyst, in contrast to traditionally prepared one, was free of chlorine contamination. Characterization by TEM, XRD and XPS showed high dispersion of ruthenium in both catalysts. It was found that at RT the O2 adsorption coexists to some extent with the subsurface oxidation, but at 0°C the rate of the later, activated process was very low. In spite of this, the O2 adsorption at both temperatures can be successfully used to determine the ruthenium dispersion in the colloidal Ru/g-Al2O3 catalyst. Using a stoichiometry O/Rus = 2, good agreement was obtained between the aver age ruthenium particle sizes calculated from the O2 adsorption and from TEM. The H2-O2 titration data confirm the formation of the surface oxide of stoichiometry close to RuO2. In contrast, the presence of Cl ions in the traditionally prepared Ru/g-Al2O3 catalyst decreases the capacity of Ru to O2 adsorption (O/Rus less than 2), and causes large discrepancies between the aver age particle size estimated from the O2 up take, H2 chemisorption and TEM. The XPS data revealed that mainly Ru4+ was formed at the surface of the Ru particles a ter the O2 adsorption.