Speciation, Structural Refinement, and Distribution of Ti Sites in Titanium Silicalite‐1 From ^47/49 Ti NMR Crystallography at 28.2 Tesla

Abstract

ABSTRACT Titanium silicalite‐1 (TS‐1) is industrially used for selective oxidation processes. Despite being discovered over 40 years ago, TS‐1 is seeing an increase in use in the chemical industry. The catalyst structure, especially the Ti speciation and local environment in the zeolitic framework, as well as the nuclearity of the Ti sites in the pristine zeolite material, are still debated. Here, we address this issue by applying high field (28.2 T) 47/49 Ti NMR and 17 O NMR spectroscopy for an array of TS‐1 catalysts. For extra‐framework‐free TS‐1 catalysts, the Ti sites are associated with a distinct NMR signature—δ iso ( 49 Ti) = −900 ppm; C Q,0 ( 49 Ti) = 7.2 MHz—which can be translated into structural parameters and a dominant first coordination environment according to an extended Czjzek model. With the implementation of a 47/49 Ti NMR crystallography protocol, benchmarked on molecular models, this signature was assigned to the presence of mononuclear Ti framework sites in pristine TS‐1 structures. The observed distribution of the NMR parameters presumably originates from variations of mononuclear Ti framework sites in the first and second coordination sphere, likely due to the occupancy of several T‐sites.