Theoretical Investigation of H2 Combustion on aAl2O3 Support

Report No. ARl-TR-4642
Authors: Jennifer Synowczynski, Jan W. Andzelm, and D. G. Vlachos
Date/Pages: November 2008; 22 pages
Abstract: Based on Density Functional Theory - Generalized Gradient Approximation (DFT-GGA) calculations, we provide a theoretical model for the effect of the catalytic support (alpha alumina oxide (aAl2O3)) on the dissociation of molecular hydrogen (H2), molecular oxygen (O2), hydroxyl (OH), water (H2O), and the surface diffusion of oxygen and hydrogen species along the aAl2O3 (0001) surface. These processes are key to understanding the "inverse spillover effect" that occurs during hydrogen combustion on alumina surfaces. Our results indicate the dissociation of O2 is not thermodynamically favored on the aAl2O3 surface. However, both H2 and H2O can dissociate, forming hydroxyls with oxygen atoms in the second atomic layer. Once dissociated, oxygen species can diffuse locally but encounter a large barrier to long-range surface diffusion in the absence of defects or other species. In contrast, the barrier to the long-range surface diffusion of hydrogen is modest under ideal conditions.
Distribution: Approved for public release
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Last Update / Reviewed: November 1, 2008