FIRST PRINCIPLES STUDY OF NA ADSORPTION ON TIO2 (110) SURFACE

The activation of the (110) TiO2 rutile surface by deposition of alkal i metal atoms has been the subject of some recent experimental studies . These results indicate a reduction of the surface when sodium atoms are deposited on it. In the present work, this process has been studie d by means of ab initio embedded cluster calculations combined with mo lecular dynamics simulations. Several surface sites have been consider ed and our calculations show that reduction occurs selectively on five fold coordinated titanium atoms. Geometry optimization of a representa tive Na-surface clusters leads to a structure in which the Na atom is symmetrically coordinated to three oxygen atoms (two protruded and one basal) in excellent agreement with models proposed from experimental data. A mechanism for the adsorption process in which a long-distance electron transfer from atomic Na toward a fivefold coordinated surface titanium atom followed by physisorption of the Na+ cation on the surf ace is proposed. (C) 1998 John Wiley & Sons, Inc.