JOURNAL OF CATALYSIS 93, 256-269 (1985) Fischer-Tropsch Synthesis on Bimetallic Ruthenium-Gold Catalysts A. K. DATYE~ AND J. SCHWANK~ Department of Chemical Engineering, The University of Michigan, Ann Arbor, Michigan 48109 Received June 8, 1984; revised January 8, 1985 The effect of Au in the behavior of Ru as a Fischer-Tropsch catalyst was studied. Two series of catalysts were investigated, one supported on Si02 and the other on MgO. Au did not seem to alter the product distribution on Ru at pressures up to 1 MPa and in the temperature range 490-570 K. However, the turnover frequencies for both CO hydrogenation and methanation showed a precipi- tous drop with the Au content in the Si02-supported catalysts, whereas on the MgO series a maximum in activity was observed at an intermediate Au content. These activity patterns were correlated with extensive physical characterization placing major emphasis on analytical electron microscopy. The activity trends as a function of Au content were remarkably similar to those previously reported for the structure-sensitive ethane hydrogenolysis reaction. In both reactions, the effect of Au appears to be due to a dilution of the active Ru ensembles. o 1985 Academic PKSS, I~C. INTRODUCTION While Ru is one of the most active cata- lysts for the CO hydrogenation reaction (I), it has not found significant commercial ap- plication as a Fischer-Tropsch catalyst (2). One disadvantage is its higher cost com- pared to Fe or Co which are commonly used as Fischer-Tropsch catalysts. Never- theless, it’s catalytic behavior is quite inter- esting. For example, a large yield of high- molecular-weight waxes can be obtained at low temperatures and high pressures. In contrast to Fe, the yield of oxygenates on Ru is relatively low. Thus, there is a strong motivation to study the behavior of Ru and to explore the effects of promoters or addi- tives on product selectivities. We chose to investigate the Ru-Au sys- tem in view of the interesting behavior of Au in terms of its interaction with catalyst support materials (3-6). A particularly in- triguing aspect of this interaction is the in- creased mobility of support oxygen found in isotopic oxygen exchange experiments i Present address: Department of Chemical and Nu- clear Engineering, University of New Mexico, Albu- querque, N.M. 87131. 2 To whom correspondence should be addressed. on Au/MgO (7). One objective of this study was to explore whether this oxygen mobil- ity in the MgO support would influence the selectivity toward oxygenates. Second, catalysts that do not dissociate CO, such as Pd, yield predominantly meth- anol while Ru which can dissociate CO un- der reaction conditions catalyzes the chain growth yielding mainly oxygenate-free products (8). Adsorption of CO on group Ib metals, such as Au, is weak and reversible and involves a molecularly adsorbed linear CO species (9, 10). The availability of weakly held undissociated CO on Au adja- cent to active Ru sites might play a similar role to that of CO on Pd. Further, the most widely used methanol synthesis catalyst in- volves another group Ib metal, namely Cu/ ZnO. It has been suggested that the active form of the catalyst involves an oxidized state where the Cu species interact elec- tronically with ZnO (11, 22). In the Au/ MgO system, EXAFS results gave evi- dence for the existence of a highly dispersed Au/MgO phase with a formal Au oxidation state of + 1 (3), thus making it interesting to study the effect of this elec- tronically interacting Au species as a pro- moter. 256 0021-9517/85$3.00 Copyright 0 I985 by Academic Press, Inc. All rights of reproduction in any form reserved.