Adsorption and Formation of BaO Overlayers on Gamma-Al2O3 Surfaces
First-principles density functional theory slab calculations were used to investigate adsorption, clustering and overlayer formation of BaO on the gamma-Al2O3 surfaces. Multiple stable adsorption configurations were identified for the adsorbed BaO molecule and (BaO)2 on both (100) and (110) surfaces of gamma-Al2O3. Adsorption of BaO and (BaO)2 induces significant relaxation of the gamma-Al2O3 surfaces. At high BaO coverage, up to the ratio of BaO units to surface Al atoms being unity, the adsorbed BaO molecules were organized to form a buckled monolayer-like overlayer on the surface. Aggregation energy was used to characterize the organization of adsorbed BaO on the surface. Our results showed that the initial BaO adsorption configuration had a strong effect on clustering and overlayer formation. A weakly adsorbed BaO molecule will thermodynamically favor clustering over being isolated. On the fully dehydrated gamma-Al2O3(100) surface, the formation of BaO overlayer was thermodynamically unfavorable until 4.26 BaO/nm2 if the additional BaO was from the most stable site, corresponding to a low BaO loading, whereas aggregation became favorable if the additional BaO was from less stable sites, corresponding to a high BaO loading. On the fully dehydrated gamma-Al2O3(110) surface, the formation of a BaO dimer was found to have the highest energy cost. On the other hand, the presence of hydroxyls on the surface enhances the stability of the adsorbed BaO molecules. As such, isolated BaO islands, rather than a complete BaO overlayer, were expected on the hydroxylated gamma-Al2O3 surfaces, consistent with recent experimental observations. Pacific Northwest National Laboratory operated by Battelle for the U. S. Department of Energy.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 946367
- Report Number(s):
- PNNL-SA-61350; 20691; 19800; TRN: US200903%%322
- Journal Information:
- Journal of Physical Chemistry C, 112(46):18050–18060, Vol. 112, Issue 46
- Country of Publication:
- United States
- Language:
- English
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