Theoretical investigation of the chemisorption of H2 and CO on the ZnO(10(1)over-bar0) surface

Density functional molecular cluster calculations have been used to study the adsorption of CO and H-2 on the ZnO(10 (1) over bar 0) surface. Substrate and adsorbate geometry modifications,adsorption energies and adsorbate vibrations are computed in good agreement with experiment. For CO, the influence of Cu surface impurities has been also considered. Despite the limited size of the adopted clusters, surface relaxations computed for the clean and undoped ZnO(10 (1) over bar 0) agree well with experimental measurements. The chemisorption of CO on ZnO(10 (1) over bar 0) relieves some of the relaxation of the Lewis acid site (L-s(a)); nevertheless, the L-s(a) electronic structure is negligibly affected by the interaction with CO. At variance to that,the stronger interaction of CO with copper impurities significantly influences both the geometry and the electronic structure of L-s(a), extending its effects to the adjacent Lewis base site (L-s(b)). The dissociative adsorption of H-2 is found to be exothermic by 23 kcal/mol, and it implies the L-s(a)-L-s(b) bond breaking.