Toluene and Styrene Photo-Oxidation Quantum Efficiency: Comparison between Doped and Composite Tungsten-containing Anatase-based Catalysts

Abstract

In this work we analyze two series of samples containing tungsten and titania as cations with a W/Ti atomic ratio from 0 to 0.5. The samples are prepared by a single-pot procedure, rendering in all cases high surface area powders having a dominant anatase crystalline phase. The materials were characterized by a combination of X-ray diffraction and photoelectron spectroscopies, UV–vis and Raman spectroscopies and morphological measurements. Particular effort was carried out in analyzing the way tungsten and titani-um interact in the materials through a microscopy analysis combining dark field Scanning transmission electron microscopy (HAADF-STEM) an X-ray energy dispersive spectrometry (XEDS). Overall the results are able to spot out the samples that show a truly doped character with tungsten exclusively located at (surface and bulk) lattice positions of the anatase structure, from composite catalysts where nanosized tungsten entities are supported over the dominant anatase phase. Activity of the materials in toluene and styrene photo-transformation reactions was measured through the reaction rate and the quantum efficiency observables. The study shows that quantitative comparison requires the stringent calculation of the quantum efficiency and that both the reaction rate and the apparent quantum efficiency can lead to misleading results in terms of the most active sample(s) as well as the (positive/negative) magnitude with respect to the bare titania reference. The quantum efficiency shows that doped samples can always improve titania reference sample(s) while this is not the case for composite samples.