SPECTROSCOPIC STUDIES OF SURFACE COPPER SPINELS - INFLUENCE OF PRETREATMENTS ON CHEMICAL-STATE OF COPPER

The nature of copper species of a series of alumina-supported copper samples was investigated by the kinetics of reduction, x-ray photoelectron spectroscopy, temperature-programmed desorption-mass spectrometry of chemisorbed NO and infrared spectroscopy of chemisorbed NO and CO probes. The role of these copper species was also examined in the catalytic decomposition of NO. The surface properties of copper were found to depend strongly on both Cu loading and calcination treatment. At Cu contents as low as 0.6 wt.%, Cu2+ ions form a well-dispersed interacting phase at the alumina surface, which upon calcination forms a surface spinel CuAl2O4. At copper contents up to 3.2 wt.%, both the surface spinel CuAl2O4 and a segregated CuO phase were clearly distinguished. The partial reduction of these species upon thermal treatment under high vacuum, the ability of the surface sites to chemisorb NO and CO probes and their implications in the catalytic decomposition of NO are discussed.