Carbon nanospheres as novel support in the nickel catalyzed gas phase hydrogenation of butyronitrile

Abstract

Three nickel catalysts supported on carbon nanospheres have been prepared by deposition-precipitation with urea (Ni/CNS DP) and standard impregnation (Ni/CNS IMP-1 and Ni/CNS IMP-2). The CNS support was characterized by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), Raman spectroscopy and N 2 adsorption/desorption, exhibiting a graphitic structure and limited porosity. Ni/CNS catalysts were characterized by temperature-programmed reduction (TPR), XRD, TEM and N 2 adsorption/desorption. Surface area weighted mean Ni particle diameters (post activation at 623 K) were comparable in the case of Ni/CNS DP and Ni/CNS IMP-1 (10.4–12.7 nm) and shifted to 36.6 nm in the case of Ni/CNS IMP-2. The three catalysts were tested in the gas phase hydrogenation of butyronitrile where 463 K < T < 583 K. All the catalysts exhibited a temporal drop of activity an approached the steady state after 12 hours-on-stream. Extracted specific reaction rates followed the sequence: Ni/CNS DP < Ni/CNS IMP-1 < Ni/CNS IMP-2, where those Ni particles presenting a lower electron density conducted to a stronger adsorption of the reactant ( via C N bond) making it more difficult to hydrogenate. Selectivity to the primary amine was favoured in those catalysts presenting a higher electron density, while a lower electron density enhanced condensation reactions leading to higher amines. The three catalysts presented an activity maximum in the temperature interval studied, associated to a change in reactant surface coverage.