Formation and Stability of μ2-Peroxo on Titanosilicates, Anatase and Rutile: Implications for Zeotype Catalysts

Extra-framework TiO2 in titanosilicate oxidation catalysts has generally been linked with low selectivity and great emphasis has been put on developing synthetic protocols that yield anatase-free materials. Here, using 17O solid-state NMR spectroscopy, we investigate the formation and stability of μ2-peroxo groups on both titanosilicates containing or not containing extra-framework TiO2 as well as TiO2 polymorphs. By comparison with TiO2 nanoparticle references, H2O2 activation (e.g. peroxo formation) and decomposition is proposed to be related to the presence of rutile-like extra-framework TiO2. In fact, μ2-peroxo species can form and remain stable on anatase, whereas they decompose quickly on rutile. According to DFT calculations, the high stability of μ2-peroxo surface species on anatase is due to the specific arrangement of μ2-oxo groups on the 101 surface that allows for stabilization of key-intermediates through H-bonding. Notably, the μ2-peroxo species formed on titanosilicates and anatase display distinct 17O NMR spectroscopic signatures, that relates directly to the Ti coordination environments, and can thus be distinguished.