Theoretical study of adsorption of methyl tert-butyl ether on the substituted tetrahedral surface of dickite

The adsorption of methyl tert-butyl ether (MTBE) on the substituted tetrahedral surface of dickite has been studied using the n-layered integrated molecular orbital and molecular mechanics (ONIOM) approach and Becke's three-parameter exchange functional and the gradient-corrected functional of Lee, Yang, and Paar (B3LYP)/6-31G(d):PM3 approximation. Two Si atoms of the tetrahedral side were substituted by Al atoms in three different mutual arrangements (1,2-, 1,3-, and 1,4-substitution). The negative charge of the layer originating from the substitution was compensated by the exchangeable Mg²⁺ cation. Initially the Mg²⁺ cation was placed above the center of the six-member ring with the tetrahedral structure of the mineral fragment. The Mg²⁺ cation plays a crucial role in the adsorption of MTBE on the substituted surface of dickite. Methyl tert-butyl ether is adsorbed due to the formation of a chemical bond between the oxygen atom of MTBE and the Mg²⁺ cation and due to the formation of multiple weak C-H…O hydrogen bonds between the C–H groups of MTBE and the surface oxygen atoms. The adsorption results in changes in the structural parameters of MTBE that are the most significant in the case of the 1,3-substituted system. The interaction energies of MTBE adsorbed on the substituted surface of dickite corrected by basis set superposition error were predicted. The values of adsorption energies range from −42.8 kcal/mol (1,2-substitution) to −45.9 kcal/mol (1,3-substitution) to −47.2 kcal/mol (1,4-substitution). © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004