Adsorption and reaction on strained-metal overlayers Cu/Ru(0001)

Abstract

These studies have addressed the adsorption of CO on very thin (submonolayer to multilayer) deposits of Cu on an Ru(0001) single crystal as well as the measurement of the high-pressure kinetics of the methanation, ethane hydrogenolysis and cyclohexane dehydrogenation reactions on this model bimetallic catalyst. Temperature-programmed desorption (t.p.d.) spectra of CO at submonolayer Cu coverages show a monotonic diminution of features due to CO adsorbed on Ru with a concomitant apperance of new t.p.d. peaks, which can be assigned to desorption from the top and edges of [1 × 1]‘strained-layer’ Cu islands. Importantly, these new CO features have significantly higher desorption temperatures than those observed on bulk Cu(111), indicating a stabilization relative to bulk Cu of CO on monolayer Cu films supported on Ru. This behaviour can be correlated with LEED, ARUPS and work-function measurements, which indicate the unique character of the first layer of Cu on Ru(0001).

For methanation and ethane hydrogenolysis the overall surface activity is found to decrease monotonically with decreasing Ru surface area upon Cu addition. For cyclohexane dehydrogenation, however, the Ru specific activity is observed to increase by ca. 40 at a copper coverage of 0.75 of a monolayer. The rate enhancement observer for submonolayer Cu deposits may relate to the modified activity of the strained Cu overlayer owing to its altered geometric and electronic properties.