The Quantity of Reduced Nickel in Synthetic Takovite: Effects of Preparation Conditions and Calcination Temperature

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Abstract
Takovi te, Ni6A12(OH)t6CO 3. 5H20 , with molar Ni/A1 ratios of 2.5 and 3 is prepared by pre- cipitation at pH levels of 7 and 10, periods of reaction of 3 and 20 hr, and calcination temperatures varying between 120 ~ and 853~ The quantity of reduced Ni is determined as a function of the calcination temperature, and the solid phases remaining after reduction are determined with XRD. The Ni/A1 ratio, pH of precipitation, and calcination temperature are important preparation conditions. A precursor of a Ni/A1 ratio of 2.5 precipitated at a pH-level of 10 exhibits on reduction metallic Ni particles of about 15 nm irrespective of the drying or calcination temperature. After reduction, a considerable amount of NaA102 is present. Metallic Ni particles of 6 nm are present in a reduced precursor of Ni/A1 ratio of 2.5 precipitated at a pH-level of 7. The size of the Ni particles present in a reduced precursor of Ni/A1 ratio of 3 precipitated at a pH-level of 10 rises from 4-8 nm to 16 nm after calcination at temperatures increasing from 120* to 853"C. The last precursor contains much less sodium, and shows after reduction a disordered NiO phase containing some alumina. Especially, the takovite with the molar Ni/A1 ratio of 2.5, thoroughly washed to remove Na, and calcined at T < 260"C before reduction of Ni provides a promising catalyst for the production of hydrogen-carbon monoxide flows out of methane and steam.