A DFT study of the effect of NNN Al atom on strength of Brönsted acid sites of HY zeolite

Mo, Zhousheng; Li, Qiang; Qin, Yucai; Duan, Linhai; Zhang, Xiaotong; Song, Lijuan

doi:10.1080/08927022.2015.1135332

Cited by 8 publications

(7 citation statements)

References 65 publications

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“…This interesting finding suggests that the Brønsted acidity at the specific BAS site not only depends on the Si/Al ratio but also relies on the local Al distributions (locations) around the Al c site. This NNN location-dependent acidity of the HY zeolite might be attributed to the variation of local electric field strength induced by the distribution of two protons. ,, It is noted that this trend is similar for the HY zeolite with the low Si/Al ratio (Si/Al = 7). As shown in Figure b, for the 1 NNN Al atom located at the hexagonal column cage (Al 1 –Al 3 ) and the super cage (Al 8 –Al 9 ), the ammonia adsorption energies are decreased to the range from −111.3 kJ/mol (Al 3 ) to −100.1 kJ/mol (Al 9 ), compared to the calculated ammonia adsorption of −116.7 kJ/mol (Al c ) for the 0 NNN Al zeolite.…”

Section: Results and Discussionmentioning

confidence: 87%

“…The number of NNN Al atoms around the Al c site is increased by successively replacing the NNN Si with Al until all nine NNN T sites on the HY zeolite framework are substituted. Previous theoretical DFT studies , indicate that the substituting preference for the NNN Al atoms follows the order of the hexagonal column cage > the β cage > the super cage. Herein, the unchanged Si/Al ratio during the NNN Si substitution by Al is named the low Si/Al ratio-7.…”

Section: Results and Discussionmentioning

confidence: 91%

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Effects of Next-Nearest-Neighbor Aluminum Location on the Brønsted Acidity of HY Zeolites

et al. 2022

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The distribution of aluminum (Al) on the H-form zeolite framework strongly affects the Brønsted acidity, resulting in the corresponding acid-catalyzed reactivity of zeolite catalysts. In the present work, the effects of next-nearest-neighbor (NNN) Al locations and numbers on the acidity for the specific Brønsted acid sites (BAS) inside the channel and on the external surface of the HY zeolites with two Si/Al ratios were investigated using density functional theory calculations. The Gibbs free energy of ammonia adsorption at the BAS site with different local NNN Al environments was used to characterize the Brønsted acidity. It has been found that an NNN Al atom on the β cage slightly enhances the acidity, while NNN Al atoms at the hexagonal column and super cages significantly decrease the acidity. With the increasing number of NNN Al atoms, the acidity of the specific BAS becomes weaker. The effects of the NNN Al location and numbers on the Brønsted acidity are further confirmed using pyridine, indole, and quinoline as probe molecules.

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Section: Results and Discussionmentioning

confidence: 87%

Section: Results and Discussionmentioning

confidence: 91%

Effects of Next-Nearest-Neighbor Aluminum Location on the Brønsted Acidity of HY Zeolites

et al. 2022

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“…As can be seen from the total acidity in Table , the total acidity of the synthesized HY zeolite samples decreases in the following order: HY-0.15D > HY-0.1D > HY-0.05D > HY-0.2D > HY-0D. Y zeolites with smaller crystal sizes have more acid sites because there are more Si–OH–Al linkages or unsaturated coordinated Al caverns in small-crystal Y zeolites, , indicating that DTAB can promote the exposure of acid sites.…”

Section: Resultsmentioning

confidence: 94%

Synthesis of Small Crystal Size Y Zeolite Catalysts with High Hydrocracking Performance on n-Hexadecane

Wang

Sun

et al. 2022

Energy Fuels

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A series of in situ dodecyl trimethyl ammonium bromide (DTAB)-modified small-crystal Y zeolites have been successfully synthesized by DTAB addition to the seed synthesis procedure, which was used to create the small crystal size Y zeolites. Compared to the Y zeolites prepared without DTAB, the Y zeolites prepared with DTAB have a uniform morphology and mesoporous structure, a larger specific surface area (up to 32.3 m 2 g −1 increase), a smaller crystal size (up to 66 nm reduction), and more Bronsted acid sites (up to 55 μmol/g increase). After loading with NiW, the corresponding NiW catalysts were utilized in the hydrocracking of n-hexadecane. It is evident from the catalytic performance that the catalysts containing DTAB-modified smallcrystal zeolites have a higher yield and selectivity of primary cracking products compared with the Y zeolites without DTAB modification. Moreover, the conversion of n-hexadecane is also higher due to its low mass-transfer resistance, high dispersion, and sulfation of W species. When the molar ratio of DTAB/Al 2 O 3 is 0.15, the corresponding catalyst has the optimum balance between cracking and hydro−dehydrogenation activity. Therefore, it has the most excellent catalytic performance and a 7.3% increase in C 8 −C 12 yield.

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“…The distribution of Al in the framework will affect its acid strength. Mo et al found that the Brønsted acid strength of Y-type zeolites decreased linearly with the increase of the NNN-Al atom number using density functional theory. Therefore, compared with the microporous Y-type zeolite, the increase in the ratio of SiO 2 /Al 2 O 3 and the reduction of Si (2Al), Si (3Al), and Si (4Al) structures of hierarchical zeolites lead to the decrease in the number of acid sites.…”

Section: Resultsmentioning

confidence: 99%

Catalytic Upgrading of Coal Pyrolysis Gaseous Tar over Hierarchical Y-Type Zeolites Synthesized Using a Microwave Hydrothermal Method

Yan

Liu

et al. 2019

Ind. Eng. Chem. Res.

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In this work, a series of hierarchical Y-type zeolites were rapidly synthesized using organosilane as templates through a microwave hydrothermal method. The effects of hierarchical Y-type zeolites on the product composition and the yield of light aromatics in gaseous tar from coal pyrolysis were studied. The results showed that the hierarchical Y-type zeolites showed better catalytic properties than the traditional microporous zeolite in the catalytic conversion of gaseous tar and can greatly increase the yield of light aromatics in the pyrolysis products. The hierarchical Ytype zeolite has abundant mesopores, which contribute to the access of bulky molecules into the porous channel and the contact of active sites. Meanwhile, the mesopores reduce the diffusion length of the reaction products, thus promoting the conversion of heavy components in gaseous tar to light aromatics.

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A DFT study of the effect of NNN Al atom on strength of Brönsted acid sites of HY zeolite

Cited by 8 publications

References 65 publications

Effects of Next-Nearest-Neighbor Aluminum Location on the Brønsted Acidity of HY Zeolites

Effects of Next-Nearest-Neighbor Aluminum Location on the Brønsted Acidity of HY Zeolites

Synthesis of Small Crystal Size Y Zeolite Catalysts with High Hydrocracking Performance on n-Hexadecane

Catalytic Upgrading of Coal Pyrolysis Gaseous Tar over Hierarchical Y-Type Zeolites Synthesized Using a Microwave Hydrothermal Method

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