<br/>The ability to describe a reaction sequence and the associated elementary steps during catalytic turnovers is critical in advancing catalytic science. When developing a mechanistic framework, thermodynamic consistency of the proposed sequence and associated elementary rate and thermodynamic constants are often being considered. It is, however, much more difficult to verify rigorously the thermodynamic consistency on experimentally measured rates, as rate data may be corrupted by transport, changes in the identity of the most abundant surface intermediates, surface coverages, and kinetically relevant step. Here, we apply De Donder Relations to interrogate and then confirm the intrinsic kinetics for two reaction pairs of: (1) reforming-methanation and (2) dehydrogenation-hydrogenation, each of these pairs contains two reactions that occur in the same catalytic cycle, but proceeds in the exact opposite direction of each other. We show how the measured rates, kinetic implications, and rate and equilibrium constants must obey the De Donder Relations, even under conditions far away from chemical equilibrium. For methane reforming-CO<sub>x</sub> methanation reactions, the initial C-H bond activation and its reverse, C-H bond formation, are the kinetically relevant steps in the forward and reverse catalytic reactions, respectively. This step occurs via either a H adatom transfer on metal or a proton transfer on O* covered transition metal surfaces. The ratio of the effective rate constants for these reactions, after accounting for the effects of coverage, gives the equilibrium constant of the reaction. Similarly, for ethane dehydrogenation-ethylene hydrogenation reactions, the rate constant ratio for the forward and reverse reactions gives the equilibrium constant for the dehydrogenation reactions. This method, which requires interrogating both the forward and reverse reactions, provides a rigorous method to scrutinize experimental rate data and its mechanistic conclusions, confirming that the proposed mechanism, elementary steps, and rate constants meet the thermodynamically requirements.

Application of the De Donder relations to scrutinize experimental rate data and its mechanistic conclusions: Alkane conversion on transition metal and metal oxide surfaces

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.