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-polar 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) over bar 0), whereas only the molecular chemisorption of NH3 on Cu2O(111) has been considered. Calculations include the evaluation of surface relaxation 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) surface occurs only molecularly and that the adsorbate is more tightly bound to Cu(I) than to Zn(II) sites. The agreement with available experimental data is satisfactory. (C) 1999 Elsevier Science B.V. All rights reserved.