Chromium and Lanthanum on Transition Alumina Surfaces: The Role of Bulk Point- Defect Distributions on Catalytic Activity

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 γalumina 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 ηalumina than in γalumina, i.e., ηalumina is a more durable support for chromium catalyst.