Temperature-programmed reduction of Ni-Mo oxides

Temperature-programmed reduction (TPR) has been employed to study Ni-Mo mixed oxides which were previously used as model hydrodesulphurization (HDS) catalysts, using compositions ranging from pure MoO₃ to pure NiO. An assignment of TPR signals to the different bulk phases was attempted. Good agreement between TPR spectra and structural data obtained previously from X-ray and electron diffraction was observed. TPR traces were consistent with proposed mechanisms of reduction of the bulk oxides MoO₃, MoO₂, NiO and NiMoO₄. The variations in TPR spectra were interpreted in terms of effects such as crystallite size, ageing of the samples, hydrous state and chemical interactions between the different species. The significance of these reducibility results for HDS catalysis is discussed.