Tania Montanari

Spectroscopic characterization of cobalt-containing solid catalysts

Abstract The nature of the cobalt centers in oxidized and reduced CoO x /Al 2 O 3 catalysts and in oxidized Co-H-mordenite (Co-H-MOR) have been characterized by UV-Vis spectroscopy and by IR spectroscopy. The UV-Vis spectroscopy of CoO x /Al 2 O 3 catalysts is dominated by the features of divalent cobalt in tetrahedral coordination. These sites can be reduced by hydrogen to cobalt metal centers that have been characterized by IR spectroscopy of adsorbed carbon monoxide. The surface of CoO x /Al 2 O 3 when it is in contact with CO/H 2 mixtures and works as the catalyst for hydrocarbon synthesis has also been characterized by IR. Surface formate species were detected that could act as reaction intermediates. The active sites of Co-H-MOR are also constituted by tetrahedrally coordinated Co 2+ that act as medium strong Lewis sites. The presence of Co species seems to cause a slight increase of the average Bronsted acidity of the residual hydroxy groups in Co-H-MOR samples.

Properties of sodium ions in zeolite materials: FT-IR study of the low temperature adsorption of carbon monoxide

The low temperature adsorption of CO has been investigated on NaX (Si/Al a. r. = 1.3), NaY (Si/Al a. r. = 2.4), NaMOR (Si/Al a. r. = 6.5) and NaFER (Si/Al a. r. = 25) zeolites by FT-IR spectroscopy. For comparison CO adsorption has also been investigated on Na-silica–alumina. Bands assigned to CO C-bonded and O-bonded to Na+ ions have been observed and discussed. A correlation between the position of the band and the siting and coordination state of Na+ ions has been observed for C-bonded species. Some effect of the cavity has been envisaged for O-bonded species. Low frequency bands corresponding to quite stable species have also been found and assigned to carbon monoxide bonded to two cations. This suggests that CO may also probe couples of the nearest Na+ ions, that may act in adsorption.

Preparation and characterization of silicon hydride oxide: a fully hydrophobic solid

Silicon hydride oxide, a white solid with composition Si2H2O3, has been prepared by hydrolysis and condensation of triethoxysilane HSi(OC2H5)3. This material is amorphous to XRD. The surface area is 195 m2 g−1. It is stable from the point of view of its chemical composition up to 550 K, as shown by TG-DTA analysis. IR spectra show that the amount of silanol groups at its surface is negligible. The interaction with polar organic compounds such as acetone is very weak and shows no significant hydrogen bonding. Its adsorption capacity towards hexane is definitely higher, while its adsorption capacity for water is smaller than for typical silica. This material appears as a highly hydrophobic silica-like solid. At temperatures higher than 673 K Si–H bonds progressively disappear and SiOH groups appear, in parallel to a significant decrease in surface area.