Chemistry of Tungsten Oxide Bronzes

Abstract

Ammonium paratungstate (APT) is the generally accepted starting material in tungsten manufacturing. The dopants, which are responsible for the non-sag properties, are given to some tungsten oxide bronze (TOB)-type compounds which are formed by thermal reductive decomposition of APT. The doped TOB is reduced in a H 2 atmosphere to tungsten metal grains. The powder metallurgical processing and the following thermomechanical treatment of the metal powder result in the formation of the non-sag wire.The bronze forming compounds (M z x ) in this case are NH4 or H + ions, or both of them, but the degree of reduction, i.e. the oxygen deficiency, may vary in the W0 3 , therefore, the description of the possible compounds seems to be necessary.We have the general formula of M ( / ) W0 3 _ > ,+z.Jt/2, where y^zx/2 conditions are possible. We also give a phase diagram in which we have located the possible types of compounds.The preparation methods of oxide bronzes (OBs) and the general structural characterization of OBs are described with special attention to ATOB and HTOB compounds. Because many experiences prove the advantages of ionexchange doping, such properties of TOBs have also been discussed.

Mechanism of Hydrogen Spillover on WO3(001) and Formation of HxWO3 (x = 0.125, 0.25, 0.375, and 0.5)

“…2, 4, 6, and 8 H atoms are populated into the bulk model to form H x WO 3 ( x = 0.125, 0.25, 0.375, and 0.5) (Figure S5). In the present work, phase transition that might accompany with the increase of bronze content was not considered. The average ( E av ) and sequential ( E seq ) H absorption energies were obtained (Table ), according to E av = (1/ x )[ E (H x WO 3 ) – E (WO 3 )] and E seq = (1/0.125)[ E (H x +0.125 WO 3 ) – E (H x WO 3 )], respectively.…”

Pd@HyWO3–x Nanowires Efficiently Catalyze the CO2 Heterogeneous Reduction Reaction with a Pronounced Light Effect

“…20−22 The introduction of a hydrogen dissociation catalyst such as Pd onto the surface of WO 3 enhances hydrogen bronze formation via the hydrogen spillover reaction. 23−27 Protons and electrons are inserted throughout the bulk of the WO 3 lattice and become stabilized as Brønsted acidic OH groups and W(V) sites, respectively, 28,29 reduction of CO 2 . In addition, oxygen vacancies formed in nonstoichiometric WO 3−x enable the light-assisted stoichiometric extraction of O atoms from CO 2 to form CO. 30 The integration of Pd, a hydrogen spillover catalyst on WO 3 , inspires the possibility that Pd@H y WO 3−x could contain highly active sites for CO 2 hydrogenation on the entire H y WO 3−x surface rather than being limited to the vicinity of Pd.…”

Self-Organized Transformation from Hexagonal to Orthorhombic Bronze of Cs–Nb–W–O Mixed Oxides Prepared Hydrothermally

“…Mo-based bronzes have been extensively studied because of their interesting physical properties. In particular, their highly anisotropic transport properties [2][3][4][5]7 are of interest in applications such as electrochromic devices, batteries, solar cells, sensors, or electrocatalysts. 1,2,7−10 More recently, they have been used as efficient catalysts as well, 10−16 especially those corresponding to the so-called M1 phase, with orthorhombic symmetry and nanoscale 5-, 6-, and 7-fold channels, 11−16 which are very selective catalysts in the oxidation and ammoxidation of propane 10−15 and in the oxidative dehydrogenation of ethane to ethylene.…”