QUANTUM-CHEMICAL SIMULATION OF METHANOL-ADSORPTION COMPLEXES WITH LEWIS-ACID SITES AT THE OXIDE SURFACES AND THE MECHANISM OF HETEROLYTIC DISSOCIATION OF METHANOL

The electronic structure and geometry of methanol-adsorption complexes on the acid-base pair that includes the aluminum atom of a Lewis acid site and the oxygen atom connected to aluminum, modeled by the simple st Al(OH)3 cluster, is analyzed using the ab initio SCF MO LCAO method with the 3-21 G basis set. Two local minima corresponding to the two- point adsorption of methanol molecules are found on the potential-ener gy hypersurface of the Al(OH)3 + CH3OH system. It is shown that dissoc iation with abstraction of the hydrogen atom from the carbinol group r esulting in a bridging OH group is energetically possible, whereas a h igh energy barrier should be overcome for realization of the route inv olving the abstraction of the carbinol group and resulting in a basic- terminal OH group. The effect of geometry relaxation on the energetics of the processes studied is considered.