A comparative study of the NH3 chemisorption on ZnO(1010) and Cu2O(111) non-polar surfaces

The chemisorption of NH3 on the ZnO(10 (1) over bar 0) and Cu2O(111) non-po lar surfaces is theoretically investigated to look into the different Lewis acidity of exposed, unsaturated Zn(II) and Cu(I) ions. Both molecular and dissociative processes have been taken into account for NH3 on ZnO(10 (1) o ver bar 0), whereas only the molecular chemisorption of NH3 on Cu2O(111) ha s been considered. Calculations include the evaluation of surface relaxatio n before/after chemisorption, optimized adsorbate geometries, chemisorption energies and adsorbate vibrational frequencies. Theoretical data indicate that the chemisorption of NH3 on the defect free ZnO(10 (1) over bar 0) sur face occurs only molecularly and that the adsorbate is more tightly bound t o Cu(I) than to Zn(II) sites. The agreement with available experimental dat a is satisfactory. (C) 1999 Elsevier Science B.V. All rights reserved.