Properties and structure of NiO-Al₂O₃ catalysts Communication 2. X-ray study of the effect of the proportions of components and the conditions of thermal treatment on phase composition and crystal structure

Summary

An x-ray investigation was made of coprecipitated (pH 8) NiO-Al₂O₃ catalysts containing 0–100 moles percent of NiO and of the structural changes occurring in them when submitted to various thermal treatments in the range 400–900°.

• 1. Unlike catalysts described in [2], all the catalysts prepared under the conditions indicated are crystalline. It was shown, therefore, that the conditions of preparation affect the structure of the catalysts to a greater extent than the quantitative proportions of components.

• 2. Catalysts containing less than 50 moles percent of NiO are one-phase systems and do not contain free NiO. By measurement of the parameter of the crystal lattice and its variation with NiO concentration it was shown that these one-phase catalysts consist of solutions of the spinel NiAl₂O₄ in excess of γ-Al₂O₃.

• 3. The results of phase and structural analysis were compared with the catalytic properties of NiO-Al₂O₃ [1]: it was shown that there are optimum spinel lattice parameters for dehydration in the range 7.90–7.95 A.