Sintering of Heterogeneous Catalysts

Sintering is a leading mechanism to catalyst deactivation. Direct observation of commercial catalysts is difficult due to their tortuous pore structure. Model catalytic systems consisting of Pd particles on flat oxide substrates provide a means for improving the catalyst visibility. The model supports that were used are alumina, quartz and yttria stabilized zirconia. Using a focused ion beam (FIB), the supports are marked with a grid to ensure that individual particles can be observed before and after experiments. Our experiments were performed in vacuum at 900°C to gain insight into the relative role of vapor phase versus surface transport of adatoms. The rate of metal evaporation predicted by the Langmuir model was compared to the observed loss of Pd and the results suggest that the surface transport pathway is dominant over atmospheric transport, even in vacuum.