Interactions of M(CO)(6) (M = Cr, Mo, W) with surfaces sites of Al2O3: a theoretical study

In the present work, the first interaction steps of Group VI hexacarbonyls with different surface sites of alumina were modelled by a computational, n on-local, density-functional theory method. Octahedral and tetrahedral Lewi s acid sites were considered as active sites for M(CO)(6) (M = Cr, Mo, W) a dsorption. An interaction with a Lewis base site took place with the cleava ge of one CO ligand of the metal carbonyl and with the formation of the met al-oxygen bond. The results show that the interaction is stronger with Lewi s base sites than with acidic ones. On the Lewis base site, the interaction energy is higher for the octahedral aluminium coordination than for tetrah edral coordination. On the contrary, on a Lewis acid site, the interaction is stronger with the tetrahedrally coordinated aluminium. Neutralisation of Lewis base sites diminishes the interaction of the metal complex with the surface. Comparison of the results in the metal series reveals that chromiu m and molybdenum carbonyls interact with the surface sites similarly, while for the tungsten analogues the interaction is somewhat stronger. (C) 1999 Elsevier Science B.V. All rights reserved.