Characterisation of Co/SiO2 catalysts prepared from Co(acac)(3) by gas phase deposition

Silica supported cobalt catalysts prepared by a chemical vapour deposition technique, atomic layer epitaxy (ALE), were characterised in order to study the interaction between cobalt species and silica. The catalysts were prep ared by chemisorption of cobalt(III)acetylacetonate from the gas phase onto silica. The metal loading on the catalysts varied from 5.7 to 19.5 wt.%. C oncentration profiles obtained with SEM/EDS showed that the cobalt species were evenly distributed through the catalyst particles. The dispersion was estimated by hydrogen chemisorption. The metallic cobalt was well dispersed on samples containing less than 6 wt.% cobalt but the dispersion decreased with increasing cobalt loading. XRD showed only weak reflections even for a sample containing 19.5 wt.%, which indicated weakly ordered cobalt specie s. The degree of reduction estimated by XPS was less than 30% on all sample s even after reduction at 550 degreesC for 7h. The low reducibility could b e explained by the formation of cobalt silicate during air calcination. The presence of silicates was also indicated by XRD and XPS. The catalysts wer e tested for gas phase toluene hydrogenation in a microreactor system. The reaction rate per gram sample increased with cobalt loading but the turn ov er frequency remained essentially constant on all samples. This indicated t hat the surface area of metallic cobalt is the main factor in determining t he overall activity of the catalysts in this reaction (C) 2001 Elsevier Sci ence B.V. All rights reserved.