Comparative study of β-nickel molybdate phase obtained by conventional precipitation and the sol-gel method

• Published in: Materials research bulletin 2004-04, Vol.39 (4), p.695-706
• Main Authors: Kaddouri, A., Tempesti, E., Mazzocchia, C.
• Format: Article
• Language: English
• Subjects: Activity; Metastable β-NiMoO 4; Reducibility; Sol-gel technique; Stabilised β-NiMoO 4
• ISSN: 0025-5408; 1873-4227
• DOI: 10.1016/j.materresbull.2003.11.005

Various samples of β-NiMoO 4 phase consisting of nickel and molybdenum in a stoichiometric ratio were prepared by precipitation from nickel nitrate hexahydrate and ammonium heptamolybdate, and also in presence of Si(OCH 3) 4 and Si(OEt) 3(CH 2) 3NH(CH 2)NH 2 using the sol-gel method. The stabilised β-NiMoO 4 phase is synthesised using the sol-gel technique. The development of this phase is achieved by using a direct crystallisation in the silica matrix due to a high dispersion of Ni and Mo salts into silica gels derived from silicon alkoxides hydrolysis and condensation reactions. The mutual influences in hydro-alcoholic solutions between the two growing phases, i.e. the molybdate crystallites ions and the silica colloidal oligomers particles, cause a dramatic increase in the gelation rate. The gel thermal treatment causes the ionic species migration to form highly dispersed nanometer-sized NiMoO 4 crystallites of ca.120 nm. XRD, Raman, TG-DTG, and XPS techniques were used for the characterisation of the material. The solids are semicrystalline materials with a surface area of 280 m 2 g −1. DTG and XPS analyses provide evidence for the interactions between SiO 2 and NiMoO 4 systems which are responsible for the stabilisation of β-NiMoO 4. Unsupported β-NiMoO 4 is a high-temperature metastable phase; it transforms (back transition) into α-NiMoO 4 at ca. 250 °C, while β-NiMoO 4 stabilised by a silica matrix does not.