Epsilon Cobalt Nanoparticles as Highly Performant Catalysts in Cinnamaldehyde Selective Hydrogenation

Epsilon cobalt nanoparticles are underexplored in catalysis due to the fact that they are accessible only through wet-chemical approaches, which employ ligands as stabilizing agents. Ligands may play a significant role in determining the structure and catalytic performances of nanoparticles, which complicates their comparison in catalysis. Here, we present catalytic performances in cinnamaldehyde hydrogenation of freestanding and few-layer graphene-supported ε-Co nanoparticles and hexagonal close-packed (hcp)-Co nanorods, which are stabilized by the same ligands. We show that while hcp-Co nanorods exposing a majority of {112̅0}-type facets are the most active, the supported spherical ε-Co nanoparticles combine high activity and excellent selectivity for the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. The concentration-dependent ligand conformation on the surface of the nanostructures influences their catalytic performances, with higher concentrations favoring both activity and selectivity to cinnamyl alcohol. These results should incite the interest in the implementation of ε-Co nanoparticles in other catalytic reactions where the cobalt crystal structure may play an important role.