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

The sintering of RuO2 is the main reason for the deactivation of supported RuO2 catalysts in the oxidation of HCl to Cl-2 with O-2 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.