Surface characterization and catalytic properties of several graphite supported potassium-free and potassium-doped nickel catalysts

Abstract

Abstract Studies of the chemical preparation, activation energies of reduction by temperature-programmed reduction. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and catalytic activities of several graphite supported potassium-free and -doped nickel catalysts were carried out for the catalytic hydrogenation of 1,6-hexanedinitrile in a continuous process at 1 atm pressure, 443K, and in the absence of ammonia. Activation energies of reduction for the graphite supported non-stoichiometric NiO were higher than those from the unsupported non-stoichiometric NiO. Increasing potassium contents increase the activation energies of reduction. XRD measurements showed the presence of graphite, NiO and Ni phases, and also the loss of graphite due to gasification at temperatures higher than ca. 723 K. XPS showed the surface crystalline phases present and indicated the inhibiting effects of graphite and potassium upon the reducibility of NiO, the metallic nickel sintering and the graphite gasification at high temperatures. The catalytic conversions increase at higher NiO reduction degrees, potassium drives selectivity towards 6-aminohexanenitrile, and as graphite prevents metallic nickel from sintering, conversions remain high at temperatures of 723 K. 100% Selectivities with respect to 6-aminohexanenitrile were obtained at conversions higher than 50% for catalysts with potassium contents of 1.4·10−3 g K2O/g catalyst and 0.21 g Ni/g graphite. A mechanism is proposed.