Eric van Steen
MSc (Eng) Eindhoven, PhD Karlsruhe
Professor, Head of Department
Department of Chemical Engineering
Faculty of Engineering and the Built Environment
Email: Eric van Steen
The kinetics of heterogeneous catalysed reactions are generally interpreted on the basis of the chemical reactions which take place on the surface of the solid catalyst. The relationship between the rates of reaction at the solid and the physical properties of these materials is however poorly understood. The physical characterisation of catalysts is usually performed ex-situ, i.e. under non-reacting conditions with the fresh, unused catalysts. Catalysts normally show some change in activity and selectivity during the initial stage of reaction, which might be ascribed to a change in the catalyst structure and hence their physical properties. The main question then remains, whether the catalyst under reaction conditions is the same as either the fresh or the spent catalyst. We try to characterise the fresh catalysts, to determine the change in the rate of the various reactions occurring at the surface of the solid catalyst as a function of time on stream behaviour, to interpret this as a function of the change in the catalyst structure, and to correlate this with the characteristics of the spent catalyst. The ultimate aim is to understand the kinetics of heterogeneous catalysed reactions in terms of the physical properties of the catalysts in order to be able to design better catalysts.
A large effort of our research is directed towards the Fischer-Tropsch synthesis, because of its importance to the South African chemical industry. In this reaction the in initial activity is not the steady state activity, implying large changes in the properties of catalysts. It is attempted to understand these changes in terms of the thermodynamic possible changes in the structure of the catalyst. The obtained selectivity obtained with cobalt based Fischer-Tropsch catalysts is understood in terms of mass transport limitations of the product components, and hence the location and the density of active sites in the catalyst are of paramount importance in the catalyst design.