The kinetics of H/D exchange in cyclopentane

The exchange of hydrogen for deuterium (H/D exchange) in cyclopentane (CP) is a promising test reaction for studying support effects in heterogeneously metal-catalyzed reactions, such as differences in stability and activity in, e.g., benzene or tetralin hydrogenation reactions. In order to employ this test reaction, a full understanding of the H/D exchange mechanism is essential. However, clear insight in the observed kinetics and selectivities is lacking in the literature. In this paper, a kinetic model that adequately describes the observed activity and orders in CP and D2 is developed. It is shown that the selectivity is determined in a series of reactions after the rate-determining step. To understand the observed selectivities a Monte Carlo model is developed which accurately simulates the observed exchange patterns and reveals the relative contributions of four competitive intermediates. One intermediate (a π-bonded η2-cyclopentene) can rotate in a nonactivated mechanism via an allylic intermediate. The model reveals the number of rotations each intermediate experiences and can be as high as ∼ 20, even if only 5 D atoms are observed in the product. This number of rotations is a better measure of the H/D exchange than the conventional “multiplicity.” The H/D exchange of CP together with these insights can now be applied to investigate in detail the influence of the support on the catalytic properties of supported metal particles.