Metal-Organic-Framework-Derived Co/Cu-Carbon Nanoparticle Catalysts for Furfural Hydrogenation

The transformation of Co, Cu, and mixed Co/Cu MOF-74 crystals into bimetallic, carbon-supported Co-Cu catalysts is investigated via high-temperature pyrolysis. Mixed-metal MOFs prepared via a one-step solvothermal synthesis of MOF-74 are transformed into high metal content (48-63 wt %) catalysts by pyrolysis in N-2 at atmospheric pressure and elevated temperatures (300-900 degrees C). Comprehensive catalysis and structural characterization studies (temperature-programmed reduction, N-2 physisorption, transmission electron microscopy, scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and in situ X-ray absorption spectroscopy) are reported using a range of CoxCu1-x (0.33 < x < 0.95) catalyst compositions. The data suggest MOF precursor restructuring occurs to increasingly favor, at higher pyrolysis temperatures, formation of bimetallic nanoparticles with a Co-rich core and Cu-rich shell (Co@Cu core-shell) and suggest a metallic active site in furfural hydrogenation. For differential furfural conversion reactions of the bimetallic catalysts, furfuryl alcohol selectivities between 66 and 89% and 2-methylfuran selectivities of 10-25% are obtained at 180 degrees C and a W/F of 3.6 g(cat)/(mol.h) (specific rates of 50-530 mu mol/(g(cat).min)). Higher Co:Cu ratios tend to increase activity and shift selectivity toward production of 2-methylfuran. Catalysts formed at elevated pyrolysis temperatures (>= 600 degrees C) display more complete Cu-shells, while at lower pyrolysis temperatures some Co atoms are still present on the nanoparticle surface, resulting in lower furfuryl alcohol selectivity and higher conversion.