Properties and structure of NiO-Al2O3 catalysts

Summary It was shown by x-ray and magnetochemical methods that the formation of spinel from coprecipitated nickel and aluminum hydroxides by thermal treatment consists of the following stages: a) formation of a solid solution of nickel and aluminum hydroxides or nickel hydroaluminate by coprecipitation; b) decomposition of the gel and crystal formation in the range 100–250°, accompanied by a sharp decrease in the water content; c) rearrangement of the crystal lattice at 250–300° to a cubic, face-centered spinel-type lattice; d) ordering of the crystal lattice at 300–700° without noticeable redistribution of Ni²⁺ ions, accompanied by a gradual decrease in water content; and e) further ordering of the crystal lattice at 700–1200° with redistribution of Ni²⁺ ions in accordance with the reversibility coefficient of spinel NiAl₂O₄.