Tungsten Oxide in Catalysis and Photocatalysis: Hints from DFT

Despite the importance of tungsten oxide in various areas of materials science including catalysis and photocatalysis, relatively few systematic theoretical studies have been devoted to this system. In this review we report the results of first principle density functional theory calculations based on a hybrid functional that properly reproduces the band gap and other fundamental properties of WO₃. We briefly describe the dependence of the band gap on the crystalline phase of WO₃. Then, we address the nature of defects and dopants in bulk WO₃. As WO₃ can be easily reduced to WO_3−x , we first discuss the nature of isolated O vacancies showing that three different situations arise from the removal of one O atom along each of the three crystallographic directions of RT monoclinic WO₃. The data provide insight into the origin of electrochromism of this material. Then we discuss the role doping of WO₃ with substitutional atoms in order to increase the activity for water splitting and we show that Hf is a promising dopant. The redox properties of WO₃ are discussed also in relation to H₂ adsorption on the WO₃(001) surface. Finally, the role of nanostructuring is analyzed by studying the properties of (WO₃)₃ cyclic clusters deposited on the rutile TiO₂(110) surface. Charge transfers at the (WO₃)₃/TiO₂ interface and their role on the activity of this heterogeneous catalyst are discussed.