Chromium and lanthanum on transition alumina surfaces: The role of bulk point-defect distributions on catalytic activity

2002 Fall Proceedings, 751, p. Z2.7.1 - Z2.7.6.We employ a combination of Z-contrast scanning transmission electron microscopy (ZSTEM) and first-principles density-functional calculations to investigate the interaction between metal atoms and cubic alumina catalytic supports. We show that there are two observed La sites at the porous γ- alumina surface, and that single La atoms do not exhibit a tendency to cluster. Cr behaves very differently from La - it has a tendency to cover the alumina surface in ordered, periodic raft-like patches. The degradation of the chromia/alumina catalyst is related to the possibility for the chromium to move away from the surface into the bulk, and the activation barrier for such a process is higher in η- alumina than in γ- alumina, i.e., η- alumina is a more durable support for chromium catalyst