Model oxide supports for studies of catalyst sintering at elevated temperatures

Sintering is one of the most important causes for loss of catalytic activity when catalysts are subjected to elevated temperatures, as in automotive exhaust or during catalytic combustion. Herein we report a novel form of model catalyst for sintering studies at elevated temperatures. These model catalysts based on disks of SiO₂ (quartz) and Al₂O₃ (sapphire) allow sintering temperatures of > 900 °C to be studied. High resolution scanning electron microscopy (SEM) was used for the study of these catalysts. Using modern in-lens backscatter electron detection operating at low voltages, high contrast images can be obtained of the metal catalyst on these model oxide supports. Model catalysts make it possible to observe the same area of the sample, before and after sintering, which is essential to gain mechanistic insights into the sintering phenomena. Our results show that while Ostwald ripening is the dominant mechanism for Pd sintering at 900 °C, we see evidence for the migration of particles as large as 50 nm on the alumina surface.