Surface characterization and hydrogenation properties of several nickel/α-alumina catalysts

Abstract

Studies of the chemical preparation, X-ray photoelectron spectra (XPS), activation energies of reduction, temperature-programmed reduction (TPR), X-ray diffraction (XRD) and catalytic activities of several nickel/α-alumina catalysts have been carried out for the catalytic hydrogenation of hexanedinitrile, in a continuous process at 1 atm pressure, 443 K, and in the absence of ammonia. XPS results show complete reduction of non-stoichiometric NiO on α-alumina at temperatures higher than 623 K and higher surface nickel dispersion with increasing nickel content and decreasing reduction temperatures. Activation energies of reduction for the α-alumina-supported non-stoichiometric NiO were higher than those of the unsupported non-stoichiometric NiO. TPR results show that the initial and final temperatures of reduction of the α-alumina-supported non-stoichiometric NiO are higher with unsupported NiO, confirming the inhibiting effect of α-alumina on NiO reduction. XRD measurements show the presence of α-alumina, NiO and Ni phases, and also the increase in crystallite size with increasing reduction temperature. Catalytic conversions increase with the nickel content and selectivities toward 6-aminohexanenitrile increase at lower nickel contents, high space velocities, and higher metallic sintering, probably owing to the presence of a higher content of specific crystal sites responsible for the production of 6-aminohexanenitrile. A mechanism is proposed.