All catalysts deactivate, some slow, some fast, but performance deteriorates inevitably with time. Ethylene oxidation catalysts, generally Ag metal dispersed on a-alumina, are no exception to this rule.  In this talk, we will examine the factors involved in metal particle sintering by introducing the basic mechanisms available.  These concepts will be then be used as the basis for an investigation into the critical factors in the deterioration of supported metal catalysts.In an attempt to sort out these processes on the very complex bulk catalysts, we decided first to study simplified, nearly 2-Dimensional systems.  A start was made using wafer spincoating, and electron beam lithographic (EBL) techniques to prepare model catalysts. While both are instructive, the advantage of EBL is that silver particles can be sized individually in addition to complete control over their mutual distance and arrangement. In that sense this methodology is unique for catalytic applications. In collaboration with the Delft Institute of Microelectronics and Submicron Technology (DIMES) several series of samples were designed, made and tested under various industrially relevant reaction conditions.  Changes in particle size distribution were monitored over time by a.o. scanning electron microscopy.  On top of that the fate of individual particles was followed over prolonged periods of time as well.Some selected results will be presented and discussed in the light of the prevalent sintering mechanisms: classic Ostwald ripening, dynamic and static coalescence.

Role of metal clusters in the sintering of silver epoxidation catalysts

247th National Meeting (2014)

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