Nature of ruthenium-copper catalysts

Abstract

The chemisorption and catalytic properties of ruthenium-copper catalysts with a metal dispersion of the order of 1%, in which the dispersion refers to the fraction of metal atoms present in the surface, were investigated and compared with previously published data on supported ruthenium-copper clusters of much higher dispersion. Ruthenium and copper are essentially completely immiscible in the bulk, but there is evidence of definite interaction between the two in ruthenium-copper catalysts. The presence of copper decreases the capacity of ruthenium for hydrogen chemisorption and also suppresses markedly the catalytic activity for hydrogenolysis of ethane to methane. The ethane hydrogenolysis activity of a ruthenium-copper catalyst is strikingly related to its capacity for strong hydrogen chemisorption, the latter being defined as the amount of chemisorbed hydrogen retained by the catalyst after evacuation at room temperature. The interaction between copper and ruthenium occurs at the surface and is likened to that which would exist if copper were chemisorbed on ruthenium. The state of dispersion of a ruthenium-copper catalyst has a major influence on the effect of the copper. The atomic ratio of copper to ruthenium required for a given degree of coverage of the surface by copper increases with increasing dispersion, as is clearly reflected by the results on hydrogen chemisorption and ethane hydrogenolysis.