THE CHEMISTRY OF WATER ON ALUMINA SURFACES - REACTION DYNAMICS FROM FIRST PRINCIPLES

Aluminas and their surface chemistry play a vital role in many areas o f modern technology. The behavior of adsorbed water is particularly im portant and poorly understood, Simulations of hydrated alpha-alumina ( 0001) surfaces with ab initio molecular dynamics elucidate many aspect s of this problem, especially the complex dynamics of water dissociati on and related surface reactions. At low water coverage, free energy p rofiles established that molecularly adsorbed water is metastable and dissociates readily, even in the absence of defects, by a kinetically preferred pathway. Observations at higher water coverage revealed rapi d dissociation and unanticipated collective effects, including water-c atalyzed dissociation and proton transfer reactions between adsorbed w ater and hydroxide, The results provide a consistent interpretation of the measured coverage dependence of water heats of adsorption, hydrox yl vibrational spectra, and other experiments.