HCl catalytic oxidation over Ru/Ti-Sn oxide catalysts: The influence of supports' crystal and surface structures on catalytic performance

RuO2 supported on rutile TiO2 or SnO2 has been proved extremely effective for catalyzing the oxidation of HCl into Cl-2. The supports play a crucial role in the catalyst systems. In this work, Ti-Sn oxides with different Sn/(Sn + Ti) molar ratios (0-0.2) were synthesized by a facile co-precipitation method as supports. The corresponding Ru/Ti-Sn oxide catalysts were investigated in HCl catalytic oxidation and systematically characterized to elucidate the role of Ti-Sn oxide supports on the process. The diffraction, spectroscopy and microscopy results reveal the crystal and surface structures of supports and catalysts. Among all the RuO2/Ti(1-x)SnxO(2) catalysts, RuO2/Ti0.97Sn0.03O2 exhibits the best catalytic activity of 2.6 g(Cl2).g(cat)(-1).h(-1) with only 0.5% Ru loading and excellent stability on stream. Differed from the previous understanding, Ti0.8Sn0.2O2 support containing the most rutile phase shows unsatisfying performance. The excessive Sn content renders more crystal disorder and volatile substrate, inevitably lowering the dispersion and stabilization of RuO2 active phase. However, moderate Sn addition induces well-dispersed SnO2 and rutile TiO2 film, facilitating the dispersion of RuO2 phase on the support surface with more active oxygen species. A large number of oxygen vacancies on Ti0.97Sn0.03O2 can act as an active oxygen reservoir and boost catalytic performance.