Surface configurations and infra-red studies on nickel oxide supported on η- and γ-Al2O3

Abstract

An infra-red investigation has been carried out of CO adsorbed onto Ni²⁺/η-Al₂O₃ and Ni²⁺/γ-Al₂O₃ catalysts. These contain a “surface spinel” phase in which nickel ions are present both in octahedral and tetrahedral sites. Their relative concentrations are primarily determined by the atmosphere (damp or dry) in which the preparation at 600°C has been carried out. Upon CO adsorption four bands appear in the 2250–2150 cm^–1 region due to molecules linked to coordinatively unsaturated surface cations. The relative intensities are related to the preliminary treatment of the sample and are therefore discussed in terms of the possible surface configurations and of the relative amounts of tetrahedral and octahedral sites occupied. The infra-red spectrum of CO adsorbed on hydrogen reduced samples has also been investigated and the importance of the preliminary treatment on the reducibility has been confirmed.