NIO REDUCIBILITIES - STRUCTURAL AND CATALYTIC PROPERTIES OF THEIR PURE AND POTASSIUM-DOPED REDUCED FORMS

The study of the activation energies of reduction of stoichiometric and nonstoichiometric potassium-free and potassium-doped NiO was carried out by means of temperature-programmed reduction experiments, using two compared theoretical methods. Nonstoichiometric NiO shows the lower initial activation energy of reduction, whereas stoichiometric NiO shows a higher initial activation energy for starting the autocatalytic nucleation. Studies of the chemical preparation, BET surface areas, X-ray diffraction, X-ray photoelectron spectra, scanning electron microscopy, and measurements of catalytic activities of the nickel samples for the catalytic hydrogenation of 1,6-hexanedinitrile, in a continuous process at 1 atm pressure and 443 K, in the absence of ammonia, were also carried out. Surface areas dcrease when NiO reduction temperature increase. XRD, XPS, TPR, and SEM measurements detect NiO incipiently reduced between 463 and 498 K, a NiO reducibility inhibitor character for potassium, and 99.9% reduction above 573 K for all NiO forms. 100% selectivities with respect to 6-aminohexanenitrile may be obtained at 60% conversions for catalysts with potassium contents of 10.5 × l0-4 g K2O/g Ni on reduced nonstoichiometric NiO. A mechanism for the continuous process is proposed. © 1993 Academic Press, Inc.