JOURNAL OF CATALYSIS
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2023
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IF 7.3
Zijun Yang,Qiang Yu,Hua Wang,Qingfeng Ge,Xinli Zhu
Ketonization of propionic acid has been investigated on Lewis acidic TS-1 and Ti-Beta zeolites to understand the reaction mechanism and effects of pore topology and hydrophobicity. Characterizations showed that TS-1 and Ti-Beta (Si/Ti = 40) exhibited a similar acidity whereas TS-1 was more hydrophobic than the silanol-rich Ti-Beta. TS-1 showed higher activity, selectivity, stability and was more resistance to H 2 O than Ti-Beta. A combination of infrared spectroscopic, isotopic and kinetic studies showed that the molecularly adsorbed monodentate propionic acid is the most abundant reactive intermediate, and C-C coupling is the rate-determining step. The mechanism of ketonization of propionic acid at isolated tetrahedral Ti centers can be described by a Langmuir-Hinshelwood model. The turnover rate on TS-1-40 is ∼ 1.3 times higher than that on Ti-Beta-40, which is consistent with the lower fitted free activation energy, i.e., the energy difference between C-C coupling transition state and two co-adsorbed propionic acids at a Ti center. The slightly lower activation enthalpy on Ti-Beta-40 than TS-1-40 is over-compensated by much larger entropy penalty, due to more silanol groups and hydrogen bonded propionic acids in close proximity to the Ti center for Ti-Beta-40, which impose additional steric hindrance to bulkier C-C coupling complex at transition state and outweigh the difference of steric hindrance of pore confinement between MFI and BEA frameworks. This work provides insight into the ketonization mechanism on Lewis acidic zeolites, and indicates that moderate pore size with hydrophobic property promotes ketonization of carboxylic acid at isolated tetrahedral Ti centers confined in zeolites.
研究领域:
催化化学
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材料科学
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DOI
高影响因子
JOURNAL OF CATALYSIS
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2024
·
IF 6.5
Bowen Xu,Mengshan Deng,Kehang Lin,Yuexia Wang,Xinqing Lu,Rui Ma,Yanghe Fu,Weidong Zhu
Ti-Beta zeotypes, possessing three-dimensional 12-membered ring pore-opening channels, have shown some superior catalytic performance in the epoxidation of bulky cycloalkenes with hydrogen peroxide (H 2 O 2 ) in comparison with other titanosilicate zeotypes. However, some further improvement on the catalytic activity and selectivity of Ti-Beta zeotypes is still demanded for the industrialization of cycloalkenes epoxidation. In the present work, the catalytic performance of Ti-Beta in cyclohexene epoxidation was significantly improved via the transformation of their closed Ti(OSi) 4 sites into the open Ti(OSi) 3 OH ones by a simple NH 4 F treatment. Based on the extensive characterization results, it is found that the NH 4 F-treated Ti-Beta zeotypes with open Ti(OSi) 3 OH sites, named OH-Ti-Beta, possess a stronger Lewis acidity that is favorable to the production of cyclohexene oxide (CHO) from the epoxidation of cyclohexene with H 2 O 2 , compared to the parent Ti-Beta with closed Ti(OSi) 4 sites. Moreover, OH-Ti-Beta catalysts are reusable after the calcination of the deactivated zeotypes. Hence, it is expected that the current developed NH 4 F treatment can obtain efficient OH-Ti-Beta catalysts industrially applied in cyclohexene epoxidation.
研究领域:
催化化学
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材料科学
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DOI
高影响因子
MICROPOROUS AND MESOPOROUS MATERIALS
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2022
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IF 5.876
Haoyi Lin,Jiaqi Wang,Boxin Gao,Kaixuan Yang,Guojun Lv,Shixue Qi,Zhiguo Zhu,Hongying Lü
Solvent-free and low-template synthesis of zeolite materials is the future direction of zeolite production, which meets the requirements of green chemistry. Ti-Beta zeolite with opened channel systems of the 3-dimensional 12-membered ring is a promising industrial catalyst in the field of selective oxidations . Herein, nanosized Ti-Beta zeolites were successfully synthesized via interzeolite transformation of siliceous MOR zeolite using sample and commercially available tetraethylammonium hydroxide (TEAOH) as organic structure-directing agents under solvent-free and low-template-content (TEAOH/SiO 2 = 0.2) conditions within a short crystallization time. The crystallization mechanism and Ti coordinated state were thoroughly investigated by numerous characterization techniques. It was found that the hydrothermal synthesis of Ti-Beta-M zeolites obeyed a liquid crystallization mechanism, during which pre-dissolution of the silicon source MOR zeolite was a critical step in achieving successful crystallization. Ti 4+ ions mainly existed in the form of tetrahedrally coordinated states in zeolite framework. Thus Ti-Beta zeolites showed remarkable activity and reusability during the oxidative desulfurization of fuel oil. Moreover, the deactivated mechanism and regenerated method were also studied in detail. This work provides new guidance for solvent-free and low template content synthesis of metallosilicate zeolites.
研究领域:
材料科学
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绿色化学
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催化化学
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DOI
高影响因子
JOURNAL OF CATALYSIS
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2023
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IF 7.3
Zhiwei He,Qifeng Lei,Weili Dai,Hongbo Zhang
Alkene epoxidation is a very important reaction process for the selective generation of chiral products, usually performed in some solvent(s) with different polarity, solubility and proton properties. These physical properties are entangled and do not explain very well whether they are mainly against population or stability of the reaction intermediates during catalysis. Here, we investigate how different solvents with known polarity properties (CH 3 CN, (CH 3 ) 2 CO, CH 3 OH, etc.) affect the C 6 H 10 transformation over Ti-Beta catalysts. Combining kinetic measurements, thermodynamic investigations and isotope experiments, the solvent was found not to change the reaction path or mechanism, with C 6 H 10 epoxidation most likely following the Eley-Rideal mechanism and C 6 H 10 O hydration following a Langmuir-Hinshelwood mechanism, and both nucleophile and carbonium were found to be involved in the transition state (c.a. SN 2 process) of hydration. However, in the epoxidation reaction of C 6 H 10 with CH 3 CN and (CH 3 ) 2 CO as solvents, the reaction order of [C 6 H 10 ] is subtly different and the epoxidation rate increases with increasing volumetric fraction of CH 3 CN in the binary mixture, which indicates that the solvent affects the concentration of dissolved C 6 H 10 surrounding the active sites and leads to the corresponding differences in activity and product selectivity. Nevertheless, the measured apparent reaction barrier (energy difference between transition state and MASIs) spans the elementary step of solvent modification, thus allowing for the observation of negligible solvent thermodynamic modification. Collectively, these findings provide clear evidence of solvent effects on alkene epoxidation and can be easily extended to some other reactions in solvents.
研究领域:
催化化学
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物理化学
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DOI
高影响因子
Materials Chemistry Frontiers
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2021
·Vol. 5
·期 16
·6101-6113
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IF 6.482
Haikuo Ma,Haoyi Lin,Xiuquan Liu,Hongying Lü,Zhiguo Zhu
Fabricating hierarchical porosity in a metallosilicate zeolite crystal is a facile and efficient approach to increase the accessibility of active sites and to enhance the diffusion performance in the process of catalytic reactions, particularly those involving bulky guest organics. The straightforward and efficient synthesis of hierarchical metallosilicate zeolites was intensively limited by the high-cost mesoporogen, complicated and tedious synthesis procedures, broad mesoporous size distribution, restricted zeolite topologies, and low solid yield. Herein, an innovative hydrothermal synthesis methodology of a hierarchical heteroatom-containing zeolite, in this case of Ti-Beta, via in situ structural reconstruction was proposed. Tetraethylammonium hydroxide (TEAOH) played significant roles of not only as base source, functioning etching effect, but also as structure directing agent (SDA), reconstructing the framework structure in this hydrothermal synthesis. The mesoporosity and Ti4+ species coordinate state could be regulated by varying the TEAOH content, which was closely related to the catalytic activity in oxidative desulfurization. The optimal hierarchical Ti-Beta zeolite with a mesopore size of 7.8 nm and a high solid yield of more than 96% exhibited outstanding catalytic oxidation performance, far outperforming the hydrothermally synthesized Ti-Beta zeolite and postsynthesized Ti-Beta zeolite. This work provides a straightforward and facile methodology for rationally constructing the hierarchical Ti-Beta zeolite, which is promising to be an extension to synthesize other hierarchical heteroatom-containing zeolites without the assistance of a mesoporogen in a short time.
研究领域:
化学工程
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材料科学
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催化
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DOI
高影响因子
AICHE JOURNAL
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2024
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IF 3.5
Dong Lin,Xiuhui Zheng,Ze Zong,Yang Xu,Qiuming He,Zhe Ma,De Chen,Chaohe Yang,Xiang Feng
Comprehensive mechanistic explorations and profound understandings of the interactions between water molecules and active intermediates harbors tremendous significance in the field of zeolite catalysis. Herein, we envision a strategy to accelerate alkene epoxidation reactions (e.g., 1-pentene, 1-hexene, cyclohexene, cyclooctene) with preformed H 2 O 2 inside confined channels of Ti-beta by water molecules. Combined with in situ UV–vis, kinetic experiments, and DFT calculations, it is found that keen control of water molecules could effectively enhance H 2 O 2 adsorption and stabilize crucial oxygen intermediates (Ti-OOH) by hydrogen bonding interactions. As a result, the yields of corresponding epoxides increased up to 20.5%. However, excessive water clusters construct a dense and robust hydrogen-bond network, blocking the activation of reactants and further epoxidation over Ti sites. This finding not only sheds new light on the mechanism of water-accelerated reaction, but also opens up new opportunities to enhance the efficiency of industrial epoxidation reactions involving H 2 O 2 .
研究领域:
催化化学
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材料科学
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理论化学
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产品关联
DOI
高影响因子
MICROPOROUS AND MESOPOROUS MATERIALS
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2021
·
IF 5.455
Zijun Yang,Qiang Yu,Yonghua Guo,Xiaoxia Wu,Hua Wang,Jinyu Han,Qingfeng Ge,Xinli Zhu
Heteroatom metal-zeolite, with heteroatom metal (oxide) dispersed in the zeolite framework, enables the reactions typically catalyzed by bulk metal oxide counterpart but with maximized the atomic utilization. However, the distribution of heteroatoms in the framework is strongly influenced by the preparation method. In this work, Ti-Beta zeolites were postsynthesized using the recrystallization (Ti-Beta-Re) and solid-state ion-exchange (Ti-Beta-SSIE) methods. Characterizations showed that more Ti species were incorporated in the tetrahedral framework site of Ti-Beta-Re to form Lewis acid sites than in that of Ti-Beta-SSIE. In addition, intra-crystallite mesopores were developed in Ti-Beta-Re due to partial dissolution of BEA framework during alkaline etching and subsequent recrystallization of the etched framework. These zeolites were then tested for ketonization of biomass derived propionic acid at 350 °C and atmospheric pressure. The turnover frequency of ketonization was found to be 25% higher on Ti-Beta-Re (0.25 min −1 ) than on Ti-Beta-SSIE (0.20 min −1 ), whereas the apparent activation energy of 80 kJ/mol on Ti-Beta-Re is lower than 95 kJ/mol on Ti-Beta-SSIE. Moreover, the selectivity of 3-pentanone kept > 95% on Ti-Beta-Re while it dropped to ∼63% on Ti-Beta-SSIE with increase of reaction time at a space time of 2 h. This work demonstrated that the tetrahedrally coordinated Ti species are the active sites and the presence of intra-crystallite mesopores facilitates selective ketonization of carboxylic acids.
研究领域:
催化化学
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材料科学
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产品关联
DOI
高影响因子
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