Characterization of several γ-alumina-supported nickel catalysts and activity for selective hydrogenation of hexanedinitrile

Abstract

Studies of the Chemical preparation, Temperature-programmed reduction (TPR), powder X-ray diffraction (XRD), X-ray photoelectron (XP) spectra and catalytic activities of several Nickel/γ-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. The TPR measurements detect the inhibiting effect of γ-alumina on NiO reduction and also the formation of some kind of nickel aluminate at the NiO/γ-alumina interface at calcination temperatures > 623 K, which affects the final degree of reduction of the catalysts. The XRD detects the nickel phases present except that of the non-crystalline nickel aluminate. The XPS results indicate the presence of surface Ni²⁺ and reduced nickel, presumably in the form of nickel aluminate underneath the reduced surface nickel crystallites, particularly for higher nickel loadings. Catalytic conversions increase significantly with increase in nickel content and degree of reduction of the catalysts; the latter was highly resistant to metallic sintering. Selectivities of 100% towards azacycloheptane were obtained, where nickel aluminate may play a role in a decoration mechanism.