Education, training, and development:

1. GOALI/FRG: Structural Properties of Alumina and Adsorbed Metal ParticlesSergey N. Rashkeev, Vanderbilt University,DMR-0111841 Although nanocatalysis in chromia/alumina powders is widely used for dehydrogenation of alkanes, the details of the process are still unknown. We combined theoretical and experimental tools to demonstrate that only dispersed CrOx species at the alumina surface play active roles in catalysis while crystalline Cr2O3 clusters inhibit the process. Cr atoms act as the binding centers for active oxygen atoms, which serve as hydrogen traps. Small differences in bulk vacancy distribution between different Al2O3 spinel polytypes dramatically change the likelihood of agglomeration of the individual CrOx, thus affecting the catalytic activity.The structural stability of catalysts is also investigated. Nature Materials 3, 143-146 (2004); Science (to be submitted). Z-contrast images (shown on several different length scales) and EELS spectra of Cr-doped -Al 2O3 demonstrate that the formation of crystalline Cr2O3 (brighter spots) correlates with diminishing of the catalytic activity.

2. GOALI/FRG: Structural Properties of Alumina and Adsorbed Metal ParticlesSergey N. Rashkeev, Vanderbilt University,DMR-0111841 Education, training, and development: Two undergraduates, one graduate student, and three postdocs contributed to this work. The universities and industry benefited from visits to each other. A very productive collaboration with scientists from the Russian Academy of Sciences and Moscow State University has been established and maintained.. Other specific products: This project has stimulated the upgrade of the existing scanning transmission electron microscopy (STEM) facilites at Oak Ridge National Laboratory. At present, the STEM has the world's highest resolution (0.78 Å) for both Z-contrast imaging and EELS. This facilitates the direct imaging of dopant and impurity sites both on the alumina surface and in the bulk. A new facility, the ORNL Advanced Microscopy Lab has been recently constructed to house these upgraded instruments. Z-contrast image for a Si film with <112> orientation: a direct resolution at 0.78 Å is observed. From: Nellist et al., Science 305. 1741 (2004).