INIFTA   05425
INSTITUTO DE INVESTIGACIONES FISICO-QUIMICAS TEORICAS Y APLICADAS
Unidad Ejecutora - UE
artículos
Título:
DFT Investigation of Intermediate Steps in the Hydrolysis of alfa-Al2O3(0001)
Autor/es:
VICTOR A. RANEA, IAN CARMICHAEL AND WILLIAM F. SCHNEIDER
Revista:
The Journal of Physical Chemistry C
Referencias:
Año: 2009 vol. 113 p. 2149 - 2158
Resumen:
The R-Al2O3(0001) surface is well-known to become hydroxylated in the presence of water, and thishydroxylation is important to subsequent alumina surface chemistry. Here, we use plane-wave, supercelldensity functional theory to examine the progression of multiple water dissociation steps from the hydrogenfreestoichimetric surface to the fully hydroxylated, gibbsite-like surface. Consistent with earlier reports, wefind that water molecules adsorb and dissociate exothermically and with a small activation barrier atunhydroxylated and coordinatively unsaturated surface Als sites and that the formation energy of thesehydroxylated Als is coverage-independent. Subsequent water dissociations at a singly hydroxylated Als site,steps necessary to liberate Als and reach the fully hydroxylated surface, are approximately thermoneutral atany surface hydroxyl coverage. Further, within the pathways we are able to identify, these subsequentdissociation steps proceed along more complex reaction coordinates and have higher activation energies thanthe first water dissociation step. Although the fully hydroxylated surface is the thermodynamic ground statein the presence of water, the actual R-Al2O3(0001) surface composition under any particular conditions mayexhibit strong dependence on sample history.