Origin of weak Lewis acids on silanol nests in dealuminated zeolite Beta

Yi, Fengjiao; Chen, Yunlei; Tao, Zhichao; Hu, Caixia; Yi, Xiaoyan; Zheng, Anmin; Wen, Xiaodong; Yun, Yifeng; Yang, Yong; Li, Yongwang

doi:10.1016/j.jcat.2019.10.008

Cited by 74 publications

(40 citation statements)

References 75 publications

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“…It is known that zeolites with different acid site strengths and site densities may produce various types of mechanisms, and consequent activities. Furthermore, there is a synergic effect between acidity and porosity that causes shape selectivity in many hydrocarbon reactions [41] or other reactions in different solvents [42].…”

Section: Crystalline and Amorphous Aluminosilicate Materialsmentioning

confidence: 99%

Dehydration of Fructose to 5-Hydroxymethylfurfural: Effects of Acidity and Porosity of Different Catalysts in the Conversion, Selectivity, and Yield

et al. 2021

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There is a demand for renewable resources, such as biomass, to produce compounds considered as platform molecules. This study deals with dehydration of fructose for the formation of 5-hydroxymethylfurfural (HMF), a feedstock molecule. Different catalysts (aluminosilicates, niobic acid, 12-tungstophosphoric acid—HPW, and supported HPW/Niobia) were studied for this reaction in an aqueous medium. The catalysts were characterized by XRD, FT-IR, N2 sorption at −196 °C and pyridine adsorption. It was evident that the nature of the sites (Brønsted and Lewis), strength, quantity and accessibility to the acidic sites are critical to the conversion and yield results. A synergic effect of acidity and mesoporous area are key factors affecting the activity and selectivity of the solid acids. Niobic acid (Nb2O5·nH2O) revealed the best efficiency (highest TON, yield, selectivity and conversion). It was determined that the optimum acidity strength of catalysts should be between 80 to 100 kJ mol−1, with about 0.20 to 0.30 mmol g−1 of acid sites, density about 1 site nm−2 and mesoporous area about 100 m2 g−1. These values fit well within the general order of the observed selectivity (i.e., Nb2O5 > HZSM-5 > 20%HPW/Nb2O5 > SiO2-Al2O3 > HY > HBEA).

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Section: Crystalline and Amorphous Aluminosilicate Materialsmentioning

confidence: 99%

Dehydration of Fructose to 5-Hydroxymethylfurfural: Effects of Acidity and Porosity of Different Catalysts in the Conversion, Selectivity, and Yield

et al. 2021

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“…The residual LAS at 1450 cm −1 is likely a result of the electropositive hydrogen atoms in the silanol nests. 64 For 7% Zr-Beta, a tiny BAS band at 1545 cm −1 appears, which is likely related to the weak BAS of Zr-OH or structural Si-OH defects. 65,66 In contrast, a strong peak at 1445 cm −1 emerges due to LAS originating from Zr speices.…”

Section: ■ Results and Discussionmentioning

confidence: 97%

“…Additional bands at 1636 and 1620 cm –1 for BAS and 1597 and 1580 cm –1 for LAS were also detected on H-Beta. , The bands at 1636, 1620, 1597, 1580, 1545, and 1445 cm –1 almost vanished on Si-Beta, confirming Al was almost completely removed through dealumination. The residual LAS at 1450 cm –1 is likely a result of the electropositive hydrogen atoms in the silanol nests . For 7% Zr-Beta, a tiny BAS band at 1545 cm –1 appears, which is likely related to the weak BAS of Zr-OH or structural Si-OH defects. , In contrast, a strong peak at 1445 cm –1 emerges due to LAS originating from Zr speices.…”

Section: Resultsmentioning

confidence: 97%

“…Thus, the active sites for ketonization on Si-Beta are likely to be the silanol nests. Indeed, Yi et al showed that the silanol nests exhibited weak Lewis acidity due to hydrogen bonding (see Scheme ), which makes the H atoms in the nests more electropositive than those of isolated silanols . The TOF on Si-Beta by assuming each silanol nest has four LASs was calculated to be 0.0025 min –1 , significantly lower than the TOF on 3% Zr-Beta (0.19 min –1 ), due to the much weaker acidity of LAS in Si-Beta.…”

Section: Resultsmentioning

confidence: 99%

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Ketonization of Propionic Acid on Lewis Acidic Zr-Beta Zeolite with Improved Stability and Selectivity

Guo

et al. 2021

ACS Sustainable Chem. Eng.

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Ketonization reactions provide a feasible approach to remove oxygen and increase carbon chain length for conversion of biomass derived carboxylic acids. However, the reaction suffers from fast catalyst deactivation and low ketone selectivity. In this work, Lewis acidic heteroatom Ti-, Zr-, Ce-, and Sn-Beta zeolites were prepared using a twostep post-synthesis method and applied in vapor phase ketonization of propionic acid at 350 °C. Among these zeolites, Zr-Beta shows both the highest activity and selectivity. Characterizations indicate that Zr prefers the vacant tetrahedral site when the Zr content is < 7%, corresponding to the maximal fraction of vacant sites produced from dealumination of the parent H-Beta with a Si/Al ratio of 19. Extraframework Zr may also form at a Zr content ≥ 7%. The tetrahedrally coordinated framework Zr species (mainly in the structure of open sites) show Lewis acidic characteristic, and their density can be linearly correlated with the ketonization activity, indicating that these sites are active sites for ketonization. In contrast to rapid deactivation of H-Beta, the 7% Zr-Beta is stable for ketonization over 60 h, maintaining a conversion of ∼50% and a 3-pentanone selectivity > 96% at a space time of 2 h. The amount of coke deposition on Zr-Beta is about 1/3 of that on H-Beta, and the structure of Zr-Beta is preserved after 60 h of reaction. The results of this work indicate that Zr-Beta zeolite is a promising catalyst for ketonization with good stability and high selectivity toward ketone.

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“… 47 This Lewis acid site is mainly generated by structural defects such as silanol groups and extra-framework hexacoordinated aluminum. 48 − 50 It is known that both the Brønsted and Lewis acidities are important in polymer degradation. 51 *BEA-type (Beta) zeolite is suitable for the catalytic decomposition of polymers because they have many Lewis acid sites derived from structural defects as well as Brønsted acid sites.…”

Section: Introductionmentioning

confidence: 99%

Design of Zr- and Al-Doped *BEA-Type Zeolite to Boost LDPE Cracking

et al. 2022

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Nowadays, the increase in plastic waste is causing serious environmental problems. Catalytic cracking has been considered a promising candidate to solve these problems. Catalytic cracking has emerged as an attractive process that can produce valuable products from plastic wastes. Solid acid catalysts such as zeolites decompose the plastic waste at a lower temperature. The lower decomposition temperature may be desirable for practical use. Herein, we synthesized both Zr- and Al-incorporated Beta zeolite using amorphous ZrO 2 –SiO 2 . The optimized Zr content in the dry gel allowed the enhancement of Lewis acidity without a significant loss of Brønsted acidity. The enhancement of Lewis acidity was mainly due to Zr species incorporated into the zeolite framework. Thanks to the enhanced Lewis acidity without any significant loss of Brønsted acidity, higher polymer decomposition efficiency was achieved than a conventional Beta zeolite.

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Origin of weak Lewis acids on silanol nests in dealuminated zeolite Beta

Cited by 74 publications

References 75 publications

Dehydration of Fructose to 5-Hydroxymethylfurfural: Effects of Acidity and Porosity of Different Catalysts in the Conversion, Selectivity, and Yield

Dehydration of Fructose to 5-Hydroxymethylfurfural: Effects of Acidity and Porosity of Different Catalysts in the Conversion, Selectivity, and Yield

Ketonization of Propionic Acid on Lewis Acidic Zr-Beta Zeolite with Improved Stability and Selectivity

Design of Zr- and Al-Doped *BEA-Type Zeolite to Boost LDPE Cracking

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