Colloidal Characteristics of Molybdenum Blue Nanoparticles Dispersion for Catalytic Applications

Molybdenum blue are oxygen-containing compounds of molybdenum of variable composition in which molybdenum is in oxidation states + 5 and + 6. Molybdenum-oxygen clusters represent a large class of polyoxometalates. Under certain conditions, it is possible to synthesize clusters of a certain shape and size. The nanosized of the clusters and their monodispersity make it possible to consider molybdenum blue as promising precursors for the synthesis of various catalysts, especially for preparation of refractory compounds - molybdenum carbides or nitrides.

For the synthesis of supported catalysts using dispersions of nanoparticles (sols), it is necessary to know their main colloidal-chemical properties, the most important of which are electro-surface characteristics, rheological properties and the conditions for maintaining aggregative stability.

The paper presents the results of a study of the colloidal-chemical properties of molybdenum blue, the dispersed phase of which is represented by toroidal particles of the class Mo₁₅₄-x. It was found that aggregate stable dispersions exist in the pH range from 0.8 to 3.0 pH units. In the investigated pH range, molybdenum blue particles are negatively charged, and the electrokinetic potential does not exceed 30 mV. Molybdenum blues have high aggregate stability and can be concentrated to a high concentration of the dispersed phase (20-30 wt%); at higher concentrations, a transition of the sol into a gel is observed. In a wide range of concentrations molybdenum blues are Newtonian liquids, the viscosity of which mainly depends on the concentration of the dispersed phase. It was found that dispersions are characterized by the presence of electro-viscous effects. The nature of the aggregate stability of the dispersions of molybdenum blue is discussed.