Hydrogen bonding versus coordination of adsorbate molecules on Ti-silicalites: a density functional theory study.
The present study discusses the results of theoretical calculations obtained at the B3LYP/ 6-31G level on the structural, electronic, and energetic properties of Ti-silicalites. Particularly, the relevance of 5T cluster models, either H- or OH-terminated, in large-scale calculations has been critically considered. It was shown that an open surface structure with one OH group and a closed-bulk structure with no bonded OH group at the Ti site are responsible for the observed UV-vis properties of Ti-silicalite materials. Both water and methanol can preferably interact with Ti-silicalites through the H-bonding mechanism, while ammonia can form either H-bonded or coordination complexes. The calculations support the existence of highly dispersed Ti sites in a tetrahedral environment only in Ti-silicalites because an increase in the coordination number of the Ti site by next-neighbor lattice oxygens is the energetically less favorable process.
Zhanpeisov
Nurbosyn U
NU
Department of Applied Chemistry, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531, Japan. nurbosyn@orgphys.chem.tohoku.ac.jp
Anpo
Masakazu
M