Browsing by Author "van Steen, E"
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- ItemRestrictedEffect of activation procedure and support on the reductive amination of ethanol using supported cobalt catalysts.(Elsevier, 1997) Sewell, G; O'Connor, C T; van Steen, EThe reductive amination of alcohols using ammonia catalyzed by supported cobalt catalysts has been studied. The catalytic activity for ethanol conversion is shown to be directly proportional to the exposed metal surface area, indicating that the activation of ethanol is metal-catalyzed and no metal-support effects were detected. The selectivity to the mono-, di-, and triethylamine varies with temperature, reactant partial pressures, and extent of reactant conversion generally as expected for a series-type reaction scheme. Both the activation procedure and the type of support also influence selectivity. Increasing the acidity of the support favors the formation of monoethylamine, probably due to disproportionation of diethylamine on the acid sites of the support indicating the bifunctionality of the catalyst.
- ItemRestrictedPreparation of supported nano-sized cobalt oxide and fcc cobalt crystallites(Elsevier, 2011) Fischer, N; van Steen, E; Claeys, MIn order to study the role of the crystallite size of an active phase in a catalytic reaction it is of utmost importance to be able to synthesise pure phases of crystallites in the desired size range with a narrow size distribution. In this paper we describe a new method to produce Co3O4 crystallites in the nanometer size range (average sizes: 3–10 nm) utilising reverse micelles as nano reactors. To prepare suitable model catalysts for studies on effects of crystallite size these crystallites can be deposited onto a variety of carriers, in this work an alumina support was used. It is further shown that the supported cobalt oxide crystallites prepared in this study do not undergo extensive sintering under reductive conditions (H2 flow and temperatures between 375 and 450 ◦C) so that also a series of model catalysts with metallic cobalt crystallites of varied size could be prepared. The resulting metal phase only shows the diffraction pattern of a face-centred cubic (fcc) crystal phase, while normally mixtures of fcc an hcp cobalt were obtained in previous studies. Furthermore, almost complete reduction of the catalyst could be obtained for all crystallite sizes and no Co-aluminate formation was observed. These model catalyst systems allow the study of structure sensitive reactions with an industrially relevant catalyst system in the absence of the commonly encountered difficulties like the formation of strong metal support interactions, co-existence of different metal crystallite phases, an incomplete reducibility and crystallite growth upon exposure to reduction/reaction conditions.
- ItemRestrictedUse of TPR/TPO for characterization of supported cobalt catalysts.(Springer, 1996) Sewell, G; van Steen, E; O'Connor, CThe extent of reduction of supported cobalt catalysts is difficult to determine using TPR due to the unknown stoichiometry of reduction and due to the dynamic nature of the measurement. A method is described where, by using a combined TPR/TPO technique, it is possible to determine the extent of cobalt reduction and obtain an estimate of the extent of cobalt-support species formation. The results showed that the extent of metal reduction following hydrogen reduction at 500°C is affected considerably by the type of metal carrier. In particular, the extent of metal reduction decreased with increasing aluminium content of the support material. Decreasing extents of metal reduction could be correlated with an increase in the temperature required for reduction of the nitrate ion during TPR. Increasing the time and temperature of hydrogen reduction results in increased extents of metal reduction.