Speaker
Dr
Andrei Khodakov
(UCCS, CNRS, Université Lille 1, ENSCL, Ecole Centrale de Lille)
Description
Cobalt Fischer-Tropsch catalysts are typically prepared by impregnation, followed by calcination in oxidizing atmosphere and activation in hydrogen. Decomposition of cobalt nitrate is a crucial step in the genesis of active phase and could involve several short-living intermediate species. In the present work, in-situ quick X-ray absorption spectros-copy (QXAS) in combination with other techniques has been used to investigate the genesis of active phases in silica-supported cobalt catalysts prepared using either activa-tion under 5%NO/He or sub-stoichiometric addition of sorbitol.
Cobalt nitrate decomposition in air or helium proceeds via dehydrated species at 140°C. These species convert into Co3O4 crystallites below 200°C. In diluted NO, in contrast to activation in air or He, an intermediate cobalt (II) hydroxynitrate phase is detected by both XANES and EXAFS above 110°C, before the formation of Co3O4. The quantitative QXAS results are consistent with FEFF, in-situ Raman and ex-situ XAS and XRD.
In the catalysts prepared with sorbitol addition, the in-situ XANES/EXAFS is indicative of higher temperature of cobalt nitrate decomposition in the presence of sorbitol. Organic acids produced during sorbitol oxidation stabilize cobalt precursor. The in-situ QXAS at Ru K-edge suggests incorporation of Ru ions into mixed CoRu oxides in the calcined catalysts, better catalyst reducibility and formation of CuRu bimetallic particles in the reduced catalysts.
Primary authors
Dr
Andrei Khodakov
(UCCS, CNRS, Université Lille 1, ENSCL, Ecole Centrale de Lille)
Dr
Anne Griboval-Constant
(UCCS)
Dr
Eric Marceau
(LRS, UMPC, Paris, France)
Dr
Jean-Sébastien Girardon
(UCCS)
Dr
Jingping Hong
(UCCS)
Co-authors
Dr
Camille La Fontaine
(Synchrotron Soleil)
Dr
Valérie Briois
(Synchrotron Soleil)
