Spectroscopic characterization of cobalt-containing solid catalysts

The nature of the cobalt centers in oxidized and reduced CoOx/Al2O3 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 CoO2/Al2O3 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 CoOx/Al2O3 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 Co2+ 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. (C) 2003 Elsevier Science B.V. All rights reserved.