Adsorption of water in mordenite - An ab initio study

The adsorption of water in mordenite has been investigated using density fu nctional theory using gradient corrections to the exchange-correlation func tional. In the neutral complex water is strongly physisorbed through two di fferent hydrogen bonds, the stronger between the acid site and the water ox ygen atom, the weaker between a hydrogen atom of the adsorbed molecule and a framework oxygen atom. Strong polarizations and structural distortions of both the acid site and the molecule have been observed. To elucidate the q uestion if a chemisorbed complex (creation of a hydroxonium ion) is possibl e, ab initio molecular dynamics have bt en performed, indicating that a pro tonation of water occurs even for the low coverage of one water molecule Fc r unit call. However, this ionic configuration cannot be stabilized by the electrostatic field of the zeolite framework and is therefore not a minimum of the potential energy surface. (C) 2001 John Wiley & Sons, Inc.