(392e) Sintering Studies on Model Catalytic Systems

A fundamental understanding of the mechanisms of sintering would help in making catalysts more sinter resistant. Direct electron microscopy observations of commercial catalysts are inherently difficult due to the tortuous pore structure of such materials. Model catalytic systems consisting of Pt particles on flat oxide substrates provide a means for improving the visibility of metal particles and to improve counting statistics. With such model samples, it is possible to perform observations of the catalyst before and after treatment to detect particle growth in a given area of the specimen. We use high resolution scanning electron microscopy (HRSEM) to observe the metal particles in the nano size regime relevant to heterogeneous catalysis. Samples were treated in air, under vacuum and under reducing conditions to elucidate the mechanisms of metal particle growth. The results help to establish if there is a connection between the vapor pressure of the metal and the rate of particle growth. Studies also analyze if the there is a chemical reaction between the atmosphere or surface of the support that enables the metal to sinter faster or slower. This is an attempt to establish if the metal catalyst ad-atoms are more mobile on the support surface or on the larger metal particles.