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Tailoring the First Coordination Shell of Isolated Ti(IV) Active Sites in Zeolite Frameworks Boosting Catalytic Activity in Epoxidation
Author(s)
Klinyod, Sorasak
Yomthong, Krissanapat
Suttipat, Duangkamon
Pornsetmetakul, Peerapol
Kidkhunthod, Pinit
Namuangruk, Supawadee
Wattanakit, Chularat
Date Issued
May 8, 2025
Type
Article
Abstract
We present a strategy to precisely tune the local structure of the tetrahedrally coordinated titanium (Ti) sites incorporated in the zeolite framework via a one-pot hydrothermal synthesis with the aid of NH4F without any further postmodification step. This approach effectively prevents typical issues observed in postsynthetic methods, such as Ti leaching and zeolite framework degradation. By optimizing the NH4F concentration in the synthesis precursor, the formation of open Ti(OSi)3OH and Ti(OSi)3F active species can be precisely controlled. To elucidate the relationship between various Ti active species, including closed Ti(OSi)4, open Ti(OSi)3OH, and open Ti(OSi)3F sites and their catalytic performances in methyl oleate (MO) epoxidation, we employed ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), fluorine X-ray absorption near edge structure spectroscopy (F-XANES), and density functional theory (DFT) calculations. Our findings reveal that increased positive charges on Ti active centers, in the order of closed Ti(OSi)4 < open Ti(OSi)3OH < open Ti(OSi)3F, correlate with enhanced catalytic performance in MO epoxidation. However, an excessive proportion of Ti(OSi)3F species in the framework can diminish catalytic performance by promoting undesired side reactions. Therefore, we propose an optimized balance between open Ti(OSi)3OH and open Ti(OSi)3F species in the zeolite structure to maximize the catalytic activity of epoxidation.
Citation
Chemcatchem, 17(9), 2025