JOURNAL OF CATALYSIS 63, 415-424 (1980) Isotopic Oxygen Exchange on Supported Ru and Au Catalysts J. SCHWANK,’ S. GALVAGNO,~ AND G. PARRAVANO~ Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109 ReceivedSeptember 4, 1979; revised January 9, 1980 The isotopic exchange reaction of molecular oxygen is applied to supported ruthenium and gold catalysts. The results on supported ruthenium are similar to those on Ruq. The exchange reaction seems to be unaffected by differences in particle size or nature of the support (MgO or Siq, respectively). The heterogeneous exchange kinetics deviate from an exponential law. This indicates the presence of nonuniformities on the catalyst surface and/or a contribution of oxygen diffusion. On supported gold, high exchange activity and massive uptake of labeled oxygen by the solid phase are observed. Au/MgO is one order of magnitude more active than Au/SiOZ. The activation of support oxygen for the isotopic exchange reaction is related to an interaction between gold and support. INTRODUCTION In previous investigations, supported ru- thenium and gold catalysts have been ex- tensively characterized and tested in sev- eral hydrogen and oxygen transfer reactions (Z-9). From all the accumulated data, it could be concluded that the sup- ported gold catalysts deviated markedly from known bulk properties of gold and behaved in an exceptional manner, espe- cially when oxygen-bearing molecules were involved in the reaction. Gold, supported on magnesia, for instance, was two orders of magnitude more active in the oxygen transfer between CO and CO2 (8, /U) than supported ruthenium and gave the same turnover number as silica-supported plati- num. In an infrared study of CO adsorption on Au/MgO, the CO band maximum was shifted to a significantly lower wavenumber in comparison to the band position on Au/SiO, or Au films (7). It was suggested that the observed phe- nomena could be related to an interaction between gold and the support. Additional ’ To whom correspondence should be addressed. * Permanent address: Istituto Donegani, Novara, Italy. 3 Deceased on April 1, 1978. evidence for this interaction came from an extended X-ray absorption fine structure spectroscopy (EXAFS) study which indi- cated the presence of a bond between gold and support oxygen (.?, 5, 8). Information about the oxygen bond strength, the mobility of solid-phase oxy- gen, and presence of nonuniformities on a surface can be obtained by measuring the kinetics of the isotopic exchange of molecu- lar oxygen (11, 14). In the present work, this reaction is applied to supported gold and ruthenium catalysts in order to learn more about the role of oxygen in these catalytic systems and to get more insight into the nature of the above-mentioned metal-support interaction. Theoretical and experimental aspects of the isotopic oxygen exchange reaction as a technique for the study and characterization of supported catalysts have been discussed previously (15). In the past, the isotopic exchange reac- tion of molecular oxygen was mainly stud- ied on metal oxides. Considerably less data are available for unsupported metals, such as Pt, Pd, Ni, and Ag, in the form of powders, films, or wires. The pertinent literature has been reviewed by Boreskov (II, 16) Novakova (17), and Ozaki (18). 415 0021-9517/80/060415-10$02.00/O Copyright 0 1980 by Academic Press, Inc. All rights of reproduction in any form reserved.