Hydrotalcites supported on carbon nanofibers as solid base catalysts for the synthesis of MIBK

Mechanically strong carbon nanofiber spheres of millimeter size were grown from methane over a preshaped Ni/SiO2 catalyst. Mg-Al hydrotalcites (HTs) were precipitated in the porous carbon bodies by consecutive impregnation of the reactants and an aging step. In a single sequence, HT loadings as high as 16 wt% were obtained. HTs turned out to be present as platelets with a lateral size of ∼20 nm supported on the carbon nanofibers. After activation by heat treatment and subsequent rehydration, a high number of accessible Brønsted base sites were found (0.7-0.9 mmol g−1HT), as determined by CO2 adsorption measurements. High specific activity of the supported HTs was found in the self-condensation of acetone, more than four times higher than that of unsupported catalysts. The greatly improved efficiency of the supported HTs was ascribed to the high number of active edge sites. Results show no loss of HTs from the carbon bodies after catalysis and demonstrate that the used catalyst can be easily reactivated by the thermal activation procedure. An efficient and mechanically strong catalyst for the single-stage liquid-phase synthesis of methyl isobutyl ketone from acetone and H2 at 331 K was obtained with the deposition of Pd and HTs on the same support.