Subnanometer cobalt oxide clusters as selective low temperature oxidative dehydrogenation catalysts

Abstract

The discovery of more efficient, economical, and selective catalysts for oxidative dehydrogenation is of immense economic importance. However, the temperatures required for this reaction are typically high, often exceeding 400 °C. Herein, we report the discovery of subnanometer sized cobalt oxide clusters for oxidative dehydrogenation of cyclohexane that are active at lower temperatures than reported catalysts, while they can also eliminate the combustion channel. These results found for the two cluster sizes suggest other subnanometer size (CoO) x clusters will also be active at low temperatures. The high activity of the cobalt clusters can be understood on the basis of density functional studies that reveal highly active under-coordinated cobalt atoms in the clusters and show that the oxidized nature of the clusters substantially decreases the binding energy of the cyclohexene species which desorb from the cluster at low temperature.

Oxidative Dehydrogenation of Cyclohexane by Cu vs Pd Clusters: Selectivity Control by Specific Cluster Dynamics

“…In previous studies of supported‐clusters which explored the reaction profile by including O 2 , the direct participation via adsorption of O 2 on the cluster or hydrocarbon was not pursued. In other, surface‐mediated, reactions the dynamics of pressure‐dependent O 2 may lead to increased production of CO 2 , but in other systems where the oxidative state of Cu is of interest, the presence of O 2 followed by introduction of cyclohexane has led to greater production of benzene while the reverse led to CO 2 . These experimental studies merely reinforce the complexity of O 2 ’s presence and likewise our theoretical calculations uncover a range of interactions.…”

“…Previously proposed mechanisms for the ODH of cyclohexane to hydrocarbon products such as cyclohexene, cyclohexadiene, and benzene occur via dehydrogenation in a step‐wise fashion (intermediate hydrocarbons formed through sequential C−C/C−H bond breaking) or direct dehydrogenation to benzene . In zeolites, the presence of the Cu 2+ oxidation state has been linked to adsorption of oxygen as the rate limiting step, leading to increased production of benzene . Mochida, et.…”

Operando XAS/SAXS: Guiding Design of Single‐Atom and Subnanocluster Catalysts

“…pointed out that the oxidized nature of the under‐coordinated cobalt atoms in clusters substantially decreases the cyclohexene species′ binding energy during oxidative dehydrogenation of cyclohexane. [ 77 ] Besides, the synergistic effect of two different valence states at the same metal site exhibits improved catalytic activity. For example, the coexistence of Cu(I) and Cu 0 species leads to an increase in ethanol selectivity during the CO 2 RR by enhancing CO dimerization.…”

Synthetic strategies of supported atomic clusters for heterogeneous catalysis

“…In this antechamber, the electrocatalytic performances of supported atomic clusters for oxygen reduction or ethanol oxidation can be explored 73 . Vajda et al have focused on UHV and in situ reaction conditions of heterogeneous catalytic reactions, including dehydrogenation, epoxidation, and Fischer-Tropsch synthesis 74,75 . It is noteworthy that the gap between ideal UHV and realistic reaction conditions is not easy to be addressed.…”