Thermal and reductive decomposition of ammonium thiomolybdates

Abstract:

Thermal decomposition and hydrogen reduction of ammonium thiomolybdates of formulas: (NH<inf>4</inf>)<inf>2</inf>[MoS<inf>4</inf>] (I), (NH<inf>4</inf>)<inf>2</inf>[Mo<inf>2</inf>(S<inf>2</inf>)⁶] · 2H<inf>2</inf>O (II) and (NH<inf>4</inf>)<inf>2</inf>[Mo<inf>3</inf>S(S<inf>2</inf>)<inf>6</inf>] · 1.85H<inf>2</inf>O (III), were investigated using thermogravimetric analysis (TGA), either in pure N<inf>2</inf> or in 10% H<inf>2</inf> in N<inf>2</inf>, and temperature-programmed reduction (TPR). The thiomolybdate compounds were characterized by several physicochemical techniques, including FTIR, PAS/FTIR, UV-visible spectroscopy, XRD and CHNS elemental analyses. The decompositions of (I) and (II) proceed in a similar way independently of the type of gas phase, with production of MoS<inf>3</inf>. However, the anion cluster of (III) is decomposed at lower temperatures in the presence of H<inf>2</inf>. The amorphous MoS<inf>3</inf> compound is very sensitive to the presence of H<inf>2</inf>, which also lowers the onset of its decomposition. These results seem to support a model for the structure of MoS<inf>3</inf> consisting of triangular Mo<inf>3</inf> cluster units, similar to those present in (III). TPR could be used as a "fingerprint" technique for identification of the complexes, as they present strong differences in the shapes and characteristic temperatures of the reductograms. © 1995.

Año de publicación:

1995

Keywords:

• Reductive decomposition
• Reducibility
• TPR
• TGA
• decomposition
• Thiomolybdate

Fuente:

scopus

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