MOF-derived hcp-Co nanoparticles encapsulated in ultrathin graphene for carboxylic acids hydrogenation to alcohols.

[Display omitted] • Few-layer graphene encapsulated hexagonal closed-packed Co particles were prepared. • The hcp-Co@G400 achieved outstanding performance in carboxylic acid hydrogenation. • The TOF values of hcp-Co@G were one magnitude higher than that of fcc-Co countparts. • DFT calculation elucidates reaction mechanism of carboxylic acid hydrogenation. • Acetic acid vertically adsorbs at hcp-Co (0 0 2) facet with low adsorption energy. Highly efficient conversion of carboxylic acids to valuable alcohols is a great challenge for easily corroded non-noble metal catalysts. Here, a series of few-layer graphene encapsulated metastable hexagonal closed-packed (hcp) Co nanoparticles were fabricated by reductive pyrolysis of metal-organic framework precursor. The sample pyrolyzed at 400 °C (hcp-Co@G400) presented outstanding performance and stability for converting a variety of functional carboxylic acids and its turnover frequency was one magnitude higher than that of conventional facc-centered cubic (fcc) Co catalysts. In situ DRIFTS spectroscopy of model reaction acetic acid hydrogenation and DFT calculation results confirm that carboxylic acid initially undergoes dehydroxylation to RCH 2 CO* followed by consecutive hydrogenation to RCH 2 CH 2 OH through RCH 2 COH*. Acetic acid prefers to vertically adsorb at hcp-Co (0 0 2) facet with a much lower adsorption energy than parallel adsorption at fcc-Co (1 1 1) surface, which plays a key role in decreasing the activation barrier of the rate-determining step of acetic acid dehydroxylation. [ABSTRACT FROM AUTHOR]