Insights into the sintering resistance of RuO2/TiO2–SiO2 in the Deacon process: role of SiO2

Abstract

The sintering of RuO₂ is the main reason for the deactivation of supported RuO₂ catalysts in the oxidation of HCl to Cl₂ with O₂ as the oxidant, i.e., the Deacon process. Although RuO₂/TiO₂–SiO₂ as an industrial catalyst for HCl oxidation is more sintering-resistant than RuO₂/TiO₂, the stabilizing role of SiO₂ has not been clearly illustrated yet. In the present work, several TiO₂–SiO₂ supports with different amounts of SiO₂ dispersed on TiO₂ were prepared via a post-synthesis method using tetraethylorthosilicate (TEOS) as the Si source, and then RuO₂/TiO₂–SiO₂ catalysts were prepared by a dry impregnation method. The prepared supports and their supported RuO₂ catalysts were extensively characterized using various techniques, and the catalysts were evaluated in HCl oxidation. The results show that the properties of these Deacon catalysts are closely related to the amount of SiO₂ dispersed on TiO₂. Compared with RuO₂/TiO₂, RuO₂/TiO₂–SiO₂ with an appropriate amount of SiO₂ exhibits some significantly enhanced sintering-resistant properties, because of the geometric effects of SiO₂ on the dispersion of RuO₂ on the surface of TiO₂ (rutile), i.e., the SiO₂ nanoparticles can geometrically separate the RuO₂ nanoparticles and thus prevent the sintering of RuO₂ on the surface of TiO₂. The current investigation, therefore, not only elucidates the role of SiO₂ in the catalyst, but also provides some guidance in the development of Deacon catalysts with a long-term stability.