Thermal Decomposition of Ammonium Paratungstate in Hydrogen

Thermal decomposition of ammonium paratungstate (APT) in air has been investigated previously. The thermal decomposition of ammonium paratungstate (APT) in hydrogen (H2) now has been studied to investigate the decomposition process.

The experimental procedures are as follows:

Ammonium paratungstate (denoted APT, 99%) in a finely divided form was prepared as the starting material. APT was calcined at 400°C for 5h to get crystalline WO3. The crystalline WO3 was further heating to Nitrogen gas further heating to 1000°C in an atmosphere of hydrogen with a nominal purity of 99%. They were subjected to the appropriate deoxygenating and drying procedures prior to application.

Later, thermogravimetry (TG) and differential thermal analysis (DTA) curves were recorded on heating up to 1000°C at various rates (β= 2-20°C min^-1) in a dynamic atmosphere (30 ml min^-1), using a model 30H Shimadzu thermal analyzer (Japan). Small portions (20-40mg) of test samples were used in the TG experiments, and a highly sintered α-Al2O3was the thermally inert reference for the DTA measurements.

Finally, the result show that Heating APT in H2 atmosphere establishes a thermal decomposition course to the formation of WO3 near 400” and a subsequent reduction course of the oxide to metallic W”. The reduction is completed somewhere between 680 and 800 °C, depending on the heating rate.

H2 does not affect the thermal decomposition of APT at 1400 °C, except for insignificant shifts in the operational temperature regions of the events involved. The reductive effects commence following the formation of WO3. After the complete decomposition of APT into WO3, near 400°C and lead eventually to the formation of W” at 700-800°C. Thus, it was concluded that a pre-calcination of APT-containing materials might develop upon reduction to monolayer-type W” catalysts.

• < Prev
• Next >