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Số người truy cập: 107,064,220

 Brønsted Acid Characterization in 3D and 2D Zeolite
Tác giả hoặc Nhóm tác giả: Ho Viet Thang, Petr Nachtigall
Nơi đăng: 6th International FEZA Conference 2014, Leipzig University, Germany
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; Số: 2014;Từ->đến trang: 59;Năm: 2014
Lĩnh vực: Tự nhiên; Loại: Báo cáo; Thể loại: Quốc tế
TÓM TẮT
Zeolites, traditionally known as 3D crystalline solid structure, have been widely applied in heterogonous catalysis. While the small size of zeolite channels has a lot of advantages it also prevents optimized utilization of active sites in the whole zeolite volume in catalytic applications. One of the way to overcome this obstacle offers the concept of 2D layered zeolites1. The differences in properties of Brønsted acid sites in 3D and 2D material are investigated herein computational in order to understand the similarities and differences in catalytic properties of 2D and 3D zeolites. Periodic models of 3D and 2D zeolites MWW, UTL, and MFI are used together with dispersion-corrected density functional theory (DFT/CC). Vibrational frequencies of Brønsted OH groups and of adsorbed CO probe are described at the ω/r correlation level that accounts for anharmonic corrections. Relative energies of Brønsted sites in the vicinity of various framework Al positions are calculated. For the energetically most stable Brønsted sites the CO adsorption complexes are modeled. Vibrational frequencies are calculated for all investigated CO adsorption complexes. Vibrational frequencies and adsorption enthalpies calculated for corresponding 3D and 2D materials are very similar for majority of framework Al positions. However, in some cases larger decrease of OH frequency upon adsorption of CO is observed. This difference is due to the fact, that adsorption complex can easily adopt linear OH—CO geometry in 2D materials. It can be concluded that Brønsted acidity is not much influenced by the 3D to 2D transition.
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ABSTRACT
Zeolites, traditionally known as 3D crystalline solid structure, have been widely applied in heterogonous catalysis. While the small size of zeolite channels has a lot of advantages it also prevents optimized utilization of active sites in the whole zeolite volume in catalytic applications. One of the way to overcome this obstacle offers the concept of 2D layered zeolites1. The differences in properties of Brønsted acid sites in 3D and 2D material are investigated herein computational in order to understand the similarities and differences in catalytic properties of 2D and 3D zeolites. Periodic models of 3D and 2D zeolites MWW, UTL, and MFI are used together with dispersion-corrected density functional theory (DFT/CC). Vibrational frequencies of Brønsted OH groups and of adsorbed CO probe are described at the ω/r correlation level that accounts for anharmonic corrections. Relative energies of Brønsted sites in the vicinity of various framework Al positions are calculated. For the energetically most stable Brønsted sites the CO adsorption complexes are modeled. Vibrational frequencies are calculated for all investigated CO adsorption complexes. Vibrational frequencies and adsorption enthalpies calculated for corresponding 3D and 2D materials are very similar for majority of framework Al positions. However, in some cases larger decrease of OH frequency upon adsorption of CO is observed. This difference is due to the fact, that adsorption complex can easily adopt linear OH—CO geometry in 2D materials. It can be concluded that Brønsted acidity is not much influenced by the 3D to 2D transition.
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