NMR Signatures and Electronic Structures of Ti-sites in Titanosilicalite-1 from solid-state 47/49Ti NMR Spectroscopy

Although titanosilicalite-1 (TS-1) is among the most successful oxidation catalysts used in industry, its active site structure is still debated. Recent efforts have mostly focused on understanding the role of defect sites and extra-framework Ti. Insights into the positions and distributions of framework tetrahedral Ti sites remain scarce, in part due to the lack of direct characterization techniques with sufficient sensitivity. Here, we report the 47/49Ti solid-state NMR characterization of TS-1 and its molecular models, [Ti(OTBOS)4] and [Ti(OTBOS)3(OiPr)]. Analysis of their spectroscopic signatures, augmented by computational studies, shows pronounced differences that originate from specific arrangements of the second coordination sphere of Ti atoms, yielding information on titanium siting in TS-1.