MODELING OF CHEMISORPTION ON COPPER-OXIDE SUPPORTED ON ALUMINA

Transition metals supported on alumina are widely used as catalysts, and over the last few decades a large amount of experimental work has been done to characterize such systems. While it is generally believed that the catalytic reactions occur on and near the surface, knowledge of the reactions and the adsorption sites on the surface and related energetics is seriously lacking, especially at the atomic structure level. We have used a combination of the film linearized muffin-tin orbital (FLMTO) method and an ab initio molecular quantum cluster method to model the use of the system of CuO/gamma-Al2O3 as a regenerable adsorbent of SO2 (of interest for flue-gas cleanup). The modeling and calculations with the FLMTO method show that the copper atoms are adsorbed at the surface octahedral vacant sites of the alumina. The modeling and calculations with the ab initio cluster method rule out the adsorption of the SO2 molecule with sulfur-copper bonding and indicate that the SO2 molecule is adsorbed via oxygen-copper bonding; and accordingly we investigate some pertinent geometrical configurations including ''bridge'' arrangements providing bonding between the oxygen atoms of the SO2 molecule and the surface copper or aluminum atoms.