ONSET OF CATALYTIC ACTIVITY OF GOLD CLUSTERS ON TITANIA WITH THE APPEARANCE OF NONMETALLIC PROPERTIES

Cold clusters ranging in diameter from 1 to 6 nanometers have been pre pared on single crystalline surfaces of titania in ultrahigh vacuum to investigate the unusual size dependence of the Low-temperature cataly tic oxidation of carbon monoxide. Scanning tunneling microscopy/spectr oscopy (STM/STS) and elevated pressure reaction kinetics measurements show that the structure sensitivity of this reaction on gold clusters supported on titania is related to a quantum size effect with respect to the thickness of the gold islands; islands with two Layers of gold are most effective for catalyzing the oxidation of carbon monoxide. Th ese results suggest that supported clusters, in general, may have unus ual catalytic properties as one dimension of the cluster becomes small er than three atomic spacings.