The adsorption and catalytic oxidation of carbon monoxide on evaporated palladium particles

Palladium crystallites, evaporated in UHV on a α-Al₂O₃ single crystal support and characterized by transmission electron microscopy (TEM), have been used as catalysts for the low pressure oxidation of carbon monoxide between 450 and 550 K. Average particle diameters varied between 1.5 and 8 nm. The turnover rate N, i.e. the number of molecules of CO₂ made per second per surface palladium atom was measured. The number of surface palladium atoms was determined by combining TEM and temperature programmed desorption of CO. Values of N, under constant conditions, were practically identical on all samples. It is noted that the reaction studied is structure insensitive on palladium.