FT-IR Emission Spectroscopic Studies of the Thermal Decomposition of Ammonium Molybdate, Vanadate, and Tungstate

Abstract

The thermal decomposition of ammonium molybdate, vanadate, and tungstate has been studied by in situ Fourier transform infrared (FT-IR) emission spectroscopy and differential thermal analysis (DTA) in the temperature range of 100–500°C. The results indicated that ammonium vanadate directly converted into V2O5 with the simple loss of its ammonium ion at around 230°C; however, the ammonium ion of molybdate and tungstate decomposed in two steps at 230 and 330°C, respectively. The emission spectra are presented with a relative emittance value which was directly calculated from the single-beam emission spectra of the sample and reference at corresponding temperatures. The emission spectra in relative emittance were proved to be temperature independent and free of the distortion usually caused by radiation and absorption of the instrument and water vapor in the optical path. The study demonstrates that FT-IR emission spectroscopy is a potentially useful technique for the characterization of catalyst preparation.