Spectro-thermal investigation of the decomposition intermediates developed throughout reduction of ammonium paratungstate

The thermal decomposition course of ammonium paratungstate (APT) in hydrogen was studied using thermogravimetric and differential thermal analyses. X-ray diffractometry, infrared spectroscopy and diffuse reflectance spectroscopy were used to characterize and identify the intermediate solid products. It was found that ammonium paratungstate decomposes to tungsten metal W0 through five main steps encompassing different tungsten intermediate compounds. Ammonium tungsten bronze (NH4)0.33WO3, which precedes the formation of WO3, is relatively the most stable intermediate (250–550°C) encountered through reduction of APT to tungsten metal W0. The influence of hydrogen spillover on the reduction behavior commences to be effective just after formation of the bronze intermediate.