Freeze-Dried Precursor-Based Synthesis of Nanostructured Cobalt−Nickel Molybdates Co_1-xNi_xMoO₄

Abstract

A simple processing route to nanostructured mixed cobalt−nickel molybdates, Co1 - x Ni x MoO4 (0 ≤ x ≤ 1), has been developed. It is based on the use of precursors resulting from the freeze-drying of aqueous solutions of the appropriate common metal salts. Thermal decomposition of amorphous freeze-dried powders at low temperatures produces the nanostructured mixed oxides. A study of the influence of the preparative variables on the outcomes of this procedure is presented. The resulting materials have been characterized by X-ray powder diffraction, elemental analysis, scanning electron microscopy, thermogravimetry under oxygen flow, and physisorption measurements. Co1 - x Ni x MoO4 grains (obtained by calcination below 773 K) are aggregates of nanometric particles (with diameters typically around 30−40 nm) and have relatively high specific surface areas (20−40 m2/g). The catalytic activity of the nanostructured cobalt and nickel molybdates for the oxidative dehydrogenation of propane has been evaluated. The performance of these nanostructured catalysts in this process is higher than those reported for homologous oxides prepared through conventional procedures.

Electrochemical performance of Ni x Co1-xMoO4 (0 ≤ x ≤ 1) nanowire anodes for lithium-ion batteries

“…However, as can be seen in Figure 3f, both end-members had α- and β-phases corresponding to each material together. It is known that single-phase β-CoMoO 4 and α-NiMoO 4 can be formed by fast cooling and by slow cooling, respectively, to room temperature after post-annealing of their hydrates [14,17,18]. Meanwhile, D. Vie et al reported that the α-CoMoO 4 phase became detectable as a minority phase after heat treatment of the amorphous solid precursor at a temperature above 700°C [17].…”

“…It is known that single-phase β-CoMoO 4 and α-NiMoO 4 can be formed by fast cooling and by slow cooling, respectively, to room temperature after post-annealing of their hydrates [14,17,18]. Meanwhile, D. Vie et al reported that the α-CoMoO 4 phase became detectable as a minority phase after heat treatment of the amorphous solid precursor at a temperature above 700°C [17]. On the basis of these reports, we believe that the coexistence of α- and β-phases in CoMoO 4 and NiMoO 4 nanowires can be attributed to the medium cooling rate (≈10°C/min to 30°C/min) applied after post-annealing or to a change of phase transition temperature with the unique morphologies of the samples.…”

Nanostructured Oxide Catalysts for Oxidative Activation of Alkanes

“…In spite of its inherent interest, little attention has been paid in the literature on the use of nano sized oxide catalysts for ODH. The catalytic performance for the ODH of propane of the nano-sized molybdates of cobalt and nickel [13,14] has been compared to their homologues prepared by the conventional citrate method (to obtain similar surface areas). The freeze-drying method has been applied to obtain isomorphically substituted Co x Ni 1-x MoO 4 in the whole 0 B x B 1 range [14].…”

“…The catalytic performance for the ODH of propane of the nano-sized molybdates of cobalt and nickel [13,14] has been compared to their homologues prepared by the conventional citrate method (to obtain similar surface areas). The freeze-drying method has been applied to obtain isomorphically substituted Co x Ni 1-x MoO 4 in the whole 0 B x B 1 range [14]. Monophasic molybdates, with particle sizes \50 nm and BET specific areas 20-40 m 2 /g, were prepared from amorphous precursors obtained from mixed solutions of nitrates of Ni or Co and ammonium heptamolybdate, calcined at T C between 300 and 700°C.…”

Polyol‐Mediated Synthesis and Properties of Nanoscale Molybdates/Tungstates: Color, Luminescence, Catalysis

“…Studies on the synthesis, characterization, and properties of nanoscale metal molybdates and tungstates, however, have comparably limited to date. Most often nanoscale molybdates and tungstates have been gained via simple water-based precipitation, [ 3 ] freeze-drying, [ 8 ] hydrothermal/solvothermal reactions, [ 9 ] thermal combustion, [ 10 ] or mechanochemical treatment. [ 11 ] Quite often the described materials were obtained with comparably large diameter (i.e., greater than 80 nm), and broad size distribution.…”