JOURNAL OF CATALYSIS 61, 19-28 (1980) An Infrared Study of CO Adsorption on Magnesia-Supported Ruthenium, Gold, and Bimetallic Ruthenium-Gold Clusters J. SCHWANK,' G.PARRAVANO,~ AND H.L. GRUBER~ Institut fiir Physikalische Chemie der Universitiit Innsbruck, A-6020 Innsbruck, Austria Received November 27, 1978; revised May 23, 1979 The adsorption of carbon monoxide on magnesia-supported ruthenium, gold, and bimetallic ruthenium/gold samples of varying composition was studied by infrared spectroscopy. The effects of different sample pretreatments, varying CO coverages, and coadsorption of hydrogen and oxygen on band frequencies and relative and integrated band intensities are reported. On the basis of these results and in comparison with results obtained for ruthenium on silica, consistent assignments have been made for all the bands observed in the spectra. Evidence for support-metal interaction in the oure metal samules. for metal-metal interaction in the bimetallic sample, and thus for the existence of bimetallic Ru-Au clusters is presented. INTRODUCTION Highly dispersed supported gold prepara- tions revealed considerable catalytic activ- ity in recent investigations of hydrogen and oxygen transfer reactions (1-4). The results of extended X-ray absorption fine structure spectroscopy (EXAFS) studies (5) and the significant differences in the selectivity and activity of gold catalysts supported on SiO*, Al,Os, or MgO, respectively (4), indicated the presence of strong metal-support in- teractions influencing the oxidation state of the highly dispersed gold. With regard to these findings and in order to elucidate fur- ther the role of electronic interactions be- tween gold and support materials it seemed to be of interest to extend the investigation to supported bimetallic systems, such as Au-Pt (6) and Au-Ru (this study). In any work on alloys or bimetallic clus- ters, the question of surface composition, possible metal segregation, and component interaction is of utmost importance. De- tailed reviews of the general principles and problems involved have been given by Sach- I Present address: Department of Chemical En- gineering, The University of Michigan, Ann Arbor, Michigan 48109. e Deceased on April 1, 1978. 3 To whom correspondence should be addressed. tler (7), Sinfelt (8), and Ponec (9). One means of characterization of the surface properties of bimetallic clusters is a study of the infrared spectra of adsorbed carbon monoxide as it was first applied to the Cu/Ni system by Eischens (ZO), to the Pd/Ag and the Cu/Ni system by Soma- Noto and Sachtler (II, 12), and to the Ru/Pt system by Brown and Gonzalez (13). The assignment of the infrared bands result- ing from the adsorption of carbon monoxide on a bimetallic system requires detailed knowledge of the behavior of carbon monoxide adsorbed on the single metal components. The peculiar role of ruthenium surfaces in the preferential formation of C-C bonds from mixtures of carbon monoxide and hy- drogen has been known for several decades. The behavior stands in contrast to that of all other metals and metallic compounds tested. In spite of the inherent practical interest in the production oflongchain hydro- carbons and oxygenated derivatives there is, as yet, no clarification of the effect in terms of known surface chemical and phys- ical phenomena. Previous infrared studies of CO adsorbed on alumina or silica- supported ruthenium catalysts contain con- flicting data and band assignments (14-21). Concerning gold there have been only a few 19 0021.9517/80/010019-10$02,00/O Copyright 0 1980 by Academic Press, Inc. All right of reproduction in any form reserved.