Spectro-thermal investigation of the decomposition intermediates developedthroughout reduction of ammonium paratungstate

The thermal decomposition course of ammonium paratungstate (APT) in hydroge n was studied using thermogravimetric and differential thermal analyses. X- ray diffractometry, infrared spectroscopy and diffuse reflectance spectrosc opy were used to characterize and identify the intermediate solid products. It was found that ammonium paratungstate decomposes to tungsten metal W-0 through five main steps encompassing different tungsten intermediate compou nds. Ammonium tungsten bronze (NH4)(0.33)WO3, which precedes the formation of WO3, is relatively the most stable intermediate (250-550 degrees C) enco untered through reduction of APT to tungsten metal W-0. The influence of hy drogen spillover on the reduction behavior commences to be effective just a fter formation of the bronze intermediate. (C) 2000 Elsevier Science B.V. A ll rights reserved.