ELECTRONIC-STRUCTURE OF ADSORBED PYRIDINE AND AMMONIA COMPLEXES ON GAMMA-AL2O3

The adsorbed pyridine and ammonia complexes with optimized geometry on aluminum oxide were calculated as clusters by the CNDO/2 method. The interaction energy between the Lewis acid centers and the adsorbate was shown to depend on the structure and mobility of the A1 surroundings. Calculation of the pyridine interaction with the exposed A1 surfaces accounting for reconstruction of the surface does not give noticeable bonding, i.e., these centers are unsuitable for adsorption. Bonding of the pyridine is observed for A1 ions which are protruding from the surface of the oxide, which is energetically unfavorable, or which have a hydroxyl group environment, A1(OH)2. The last center is outside the lattice and the OH groups are rather mobile: in the adsorbed pyridine complex the A1 environment approaches tetrahedral.