Wyniki wyszukiwania - BazTech

1

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

Okal J.

Polish Journal of Chemistry

|

2009

|

Vol. 83, nr 2

293-302

EN

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.

2

The Effect of Chlorine and Support Dissolution on Hydrogen Chemisorption on Ru/Al2O3 Catalyst

Okal J.

Polish Journal of Chemistry

|

2007

|

Vol. 81, nr 1

69-77

EN

Hydrogen chemisorption at 20–200°C was studied volumetrically on Ru/gamma-Al2O3 catalysts (4.6 and 10.8% of Ru) prepared from ruthenium chloride. The structure of the catalysts was determined by ICP-AES, BET, TEM and XRD methods. Large amount of Cl– was retained on the catalysts after H2 reduction at 500°C. Ruthenium dispersion determined by the hydrogen chemisorption technique was found to be inaccurate due to the contamination of the ruthenium surface – during preparation of the catalysts – by chlorine from precursor and/or aluminum ions from the support. For the Ru/-Al2O3 catalystswith high chlorine content, the mean particle sizes estimated from irreversible H2 chemisorption at 100°C, were much greater than that obtained by TEM and XRD. The difference was much smaller for the catalysts subjected to washing procedure removing chlorine ions.

3

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

EN

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.

4

Spectroscopic and dielectric characteristics of nickel-doped porous silica glasses

Macalik B., Suszyńska M., Rysiakiewicz-Pasek E., Krawczyk L., Morawska-Kowal T., Okal J.

Optica Applicata

|

2005

|

Vol. 35, nr 4

761-767

EN

The direct current conduction and electrical relaxation currents in nickel-doped porous silica glasses were investigated by using the thermally stimulated polarisation and depolarisation current techniques in a wide temperature range. Optical absorption measurements and transmission electron microscopy observations accompanied these studies. All characteristics were found to be affected by the porous matrix and the material filling the pores.

5

Hydrogen and Oxygen Adsorption on Re/gamma-Al2O3 catalyst of Low Metal Content

Okal J.

Polish Journal of Chemistry

|

2002

|

Vol. 76 / nr 10

1505-1508