Exchange reactions of cyclopentane (250 K) and of 2,2-dimethylpropane (322 K and above) with deuterium were studied using static reactors on a well-characterised series of silica-supported Rh–Ir catalysts containing 1.06 × 10^–4 mol metal g^–1. Hydrogenolysis of 2,2-dimethylpropane was carried out at 427 K. The initial product distributions from the exchange reactions showed little variation with catalyst composition but gave considerable information about adsorbed intermediates. The change of activity with catalyst composition for reactions of 2,2-dimethylpropane was interpreted in terms of ensembles – a small ensemble for exchange and a larger one for hydrogenolysis for which rhodium was 80 times more active than iridium.

The rate of cyclopentane exchange increased by a factor of 180 from iridium to rhodium and substantial changes in activity were associated with small quantities of one metal in the other. These effects could not readily be explained in terms of ensembles but were thought to be attributable to electronic interactions.