Characterization of Sulfided Ni‐Mo/γ‐Al2O3 Catalysts by O2 and NO Chemisorption. Influence of the Method of Preparation

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Abstract
Two Ni‐Mo/γ‐Al2O3 catalyst series prepared by sequential or simultaneous impregnation with a Mo content of ca. 8 wt% MoO3 and NiO content ranging between 0 and 8.9 wt% were studied in their sulfided state. Quantitative determination of irreversible chemisorption of NO at room temperature and of O2 at ‐78°C indicated that NO uptake was much higher than that of O2 for both catalyst series. Besides, NO uptake increased with promoter content until Ni/Mo ca. 0.8 and then leveled off, whereas O2 uptake steadily increased with increasing Ni/Mo ratios. Absorbance of IR band of NO chemisorbed on Ni atoms at 1840–1845 cm−1 were always higher for the sequentially impregnated catalysts. The absorbance of NO in both series vs. Ni/Mo ratio followed volcano‐type curves, such as those found for hydrodesulfurization (HDS) activity. A possible correlation between HDS activity and both, NO‐ and O2‐ uptake and NO absorbance on Ni atoms is attempted.