MODELING OF CHEMISORPTION ON COPPER-OXIDE SUPPORTED ON ALUMINA

Transition metals supported on alumina are widely used as catalysts, a nd over the last few decades a large amount of experimental work has b een 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 e nergetics is seriously lacking, especially at the atomic structure lev el. We have used a combination of the film linearized muffin-tin orbit al (FLMTO) method and an ab initio molecular quantum cluster method to model the use of the system of CuO/gamma-Al2O3 as a regenerable adsor bent of SO2 (of interest for flue-gas cleanup). The modeling and calcu lations with the FLMTO method show that the copper atoms are adsorbed at the surface octahedral vacant sites of the alumina. The modeling an d calculations with the ab initio cluster method rule out the adsorpti on of the SO2 molecule with sulfur-copper bonding and indicate that th e SO2 molecule is adsorbed via oxygen-copper bonding; and accordingly we investigate some pertinent geometrical configurations including ''b ridge'' arrangements providing bonding between the oxygen atoms of the SO2 molecule and the surface copper or aluminum atoms.