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    Tailoring the First Coordination Shell of Isolated Ti(IV) Active Sites in Zeolite Frameworks Boosting Catalytic Activity in Epoxidation
    (2025-05-08)
    Klinyod, Sorasak
    ;
    Yomthong, Krissanapat
    ;
    Suttipat, Duangkamon
    ;
    Pornsetmetakul, Peerapol
    ;
    Kidkhunthod, Pinit
    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 NH<inf>4</inf>F 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 NH<inf>4</inf>F concentration in the synthesis precursor, the formation of open Ti(OSi)<inf>3</inf>OH and Ti(OSi)<inf>3</inf>F active species can be precisely controlled. To elucidate the relationship between various Ti active species, including closed Ti(OSi)<inf>4</inf>, open Ti(OSi)<inf>3</inf>OH, and open Ti(OSi)<inf>3</inf>F 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)<inf>4</inf> < open Ti(OSi)<inf>3</inf>OH < open Ti(OSi)<inf>3</inf>F, correlate with enhanced catalytic performance in MO epoxidation. However, an excessive proportion of Ti(OSi)<inf>3</inf>F species in the framework can diminish catalytic performance by promoting undesired side reactions. Therefore, we propose an optimized balance between open Ti(OSi)<inf>3</inf>OH and open Ti(OSi)<inf>3</inf>F species in the zeolite structure to maximize the catalytic activity of epoxidation.
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    Effects of zeolite frameworks and hierarchical structures on catalytic bioethanol dehydration: In-situ DRIFTS and DFT studies
    (2023-04-15)
    Iadrat, Ploychanok
    ;
    Yomthong, Krissanapat
    ;
    Rodaum, Chadatip
    ;
    Pornsetmetakul, Peerapol
    ;
    Thivasasith, Anawat
    Herein, the combined in-situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory studies were employed to investigate the effects of different zeolite frameworks and hierarchical structures on catalytic bioethanol dehydration. The findings reveal that different zeolite frameworks enable the formation of distinct intermediates, hence promoting different mechanistic pathways. Interestingly, the FER is highly selective to ethylene and inhibits the formation of by-products thanks to the confined porous structure of the FER. Although the pristine small pore FER often suffers from fast catalyst deactivation, the incorporation of hierarchical structures in the FER framework can mitigate this significantly. Accordingly, the catalytic stability of the hierarchical FER was improved remarkably with a high ethylene yield (∼95%), whereas the pristine FER suffers from fast deactivation. Additionally, coke formation over the hierarchical FER catalyst was also reduced significantly compared to that of the pristine FER. Importantly, the in-situ DRIFTS studies reveal that the different reaction pathways over hierarchical and commercial FER have been observed in which the hierarchical one promotes the monomeric pathway due to the facile desorption of corresponding products and intermediates, whilst the pristine one promotes bioethanol conversion via both pathways of monomeric and dimeric pathways to produce ethylene and diethyl ether, respectively.
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