Support-dependent performance of size-selected subnanometer cobalt cluster-based catalysts in the dehydrogenation of cyclohexene

The evolution of the chemical state and change in the morphology of subnanometer cobalt clusters during the dehydrogenation of cyclohexene was investigated in terms of metal-support interactions. The model catalyst systems were prepared by deposition of size selected subnanometer Co 27±4 clusters on various amorphous metal oxide supports (Al 2O 3, ZnO, and MgO), as well as on a carbon-based support (UNCD=ultrananocrystaline diamond). The reactivity, oxidation state, and sintering resistance of the clusters were monitored by temperature programmed reaction (TPRx), insitu grazing incidence X-ray absorption spectroscopy (GIXAS), and grazing incidence small angle X-ray scattering (GISAXS), respectively. The reactivity and selectivity of cobalt clusters show strong dependency on the support used, with clusters supported on UNCD possessing the highest activity at 300°C. The evolution of the oxidation state of metal cluster during the reaction reveals that metal-support interaction plays a key role in performance of the subnanometer catalyst. A reversible assembly of clusters into a nanostructure which evolves with reaction temperature was observed on the MgO support. Assemble together, catalyze together: The catalytic activity and selectivity of subnanometer 27±4 atom cobalt clusters in the dehydrogenation of cyclohexene shows strong support dependency. The support-cluster interactions reflect in the evolution of the oxidation state of the clusters during the course of the reaction, as well as in the formation of a dynamically evolving nanoassembly on the MgO support.