Nitric oxide reduction by Cu nanoclusters supported on thin Al2O3 films

The adsorption and reaction of NO on Cu clusters deposited on a 5 Å thick Al2O3 film, created by oxidation of a NiAl{110} crystal, have been studied using infrared, molecular beam, and scanning tunneling spectroscopies over the temperature range of 90–300 K. STM shows Cu clusters ranging in size from 20 to 40 Å and typically about 8 Å in height. Infrared spectra and molecular beam data show that the adsorption and reactivity of the particles are complex and very similar to those found on Cu single crystals. At 98 K, the infrared spectra are strongly coverage dependent and show the presence of monomeric NO adsorbed in two- and threefold sites, dimeric NO and N2O species. Molecular beam data show that during adsorption N2 and N2O are produced into the gas phase, even at 98 K. A reaction mechanism is derived from these data, which indicate the formation of NO dimers as precursors to the dissociation products.