Alkane and cycloalkane reactions on rhodium, rhodium–copper and related films

Abstract

Catalytic reaction of n-hexane/hydrogen mixtures on homogeneous rhodium–copper alloy films at ∼570 K shows a dehydrocyclization/hydrogenolysis product ratio one order of magnitude or more greater than found on 100 % Rh films. 1,5-Cyclization occurs on Rh–Cu films but not on 100 % Rh and this feature is clearest in the reaction of n-pentane. A similar influence is found with tin and with gold as alloying partners in promoting 1,5-cyclization.Ring enlargement of methylcyclopentane (to benzene) and of 1,1-dimethylcyclopentane (to toluene) takes place at ∼540 K upward on both Rh and Rh–Cu films. Rates on 100 % Rh films are much greater than rates of rearrangement of isopentane or of neohexane, both chosen as acyclic structural equivalents to these cyclopentanes. It is inferred that ring enlargement on rhodium is by a mechanism different from that by which bond-shift isomerization of simple alkanes takes place.