AI Article Synopsis
- Titanosilicalite-1 (TS-1) is a key industrial oxidation catalyst, but its active site structure remains unclear, especially regarding defect sites and extraframework Ti.
- Research using a novel MAS CryoProbe has revealed that the Ti signature in dehydrated TS-1 is similar to molecular analogues, confirming a tetrahedral Ti environment, but with larger quadrupolar coupling constants suggesting asymmetry.
- Computational studies indicate that NMR signatures of Ti are sensitive to small structural changes, which could help differentiate specific Ti locations, although distinguishing between mono- and dinuclear sites may be challenging.
Article Abstract
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 extraframework Ti. Here, we report the Ti signature of TS-1 and molecular analogues [Ti(OTBOS)] and [Ti(OTBOS)(OPr)] using novel MAS CryoProbe to enhance the sensitivity. While the dehydrated TS-1 displays chemical shifts similar to those of molecular homologues, confirming the tetrahedral environment of Ti consistent with X-ray absorption spectroscopy, it is associated with a distribution of larger quadrupolar coupling constants, indicating an asymmetric environment. Detailed computational studies on cluster models highlights the high sensitivity of the NMR signatures (chemical shift and quadrupolar coupling constant) to small local structural changes. These calculations show that, while it will be difficult to distinguish mono- vs dinuclear sites, the sensitivity of the Ti NMR signature should enable distinguishing the Ti location among specific T site positions.
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| http://dx.doi.org/10.1021/jacs.2c09867 | DOI Listing |
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