Physico-chemical studies on synthetic disordered Ni-Fe layered double hydroxides

摘要

Layered double hydroxides (LDHs) possess positively charged brucite-like cationic layers (Jt = 0.3-0.5), with an-ions CO-14H2O intercalculated at the interlamellar space [1,2]. LDHs represent synthetic hydrotalcite-like compounds belonging to the anionic clay minerals and find extensive uses in antacid preparations, Zeigler-Natta catalyst supports, electrodes, magnetic materials, and selective oxidation catalysts for alcohol oxidations, epoxidations and polymerization etc. [3-6]. A number of iron-nickel hydroxide carbonates with reevesite-like structures are synthesized by coprecipitation with wide Ni-Fe mole ratios [7]. The oxide precursors from the Ni-Fe LDHs after calcinations were found to be metastable, and surface enrichment with Ni(II) and high oxygen to metal ratios were reported [8]. In our laboratory, NI(II)-Fe(III) LDHs with reevesite-like structures in 2:1 and 3:1 mole ratios were synthesized, which, upon controlled calcination, produced modified disordered Ni(II)-Fe(III) oxides to be used as catalysts for oxidation of alcohols. Measurements like magnetic susceptibility, specific surface area and pore volume variations with temperature on the calcined and normal LDHs were made in addition to the characterization analyses by X-ray diffraction (XRD), infrared (IR) spectroscopy and thermo-gravimetry (TG). Elucidation of the catalytic properties of the oxides on the oxidation of 2-methyl cyclohexanol through gas chromatography (GC) analyses of the products was undertaken. The results and discussion are outlined in this letter.