JOURNAL OF CATALYSIS
·
2023
·
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
·
物理化学
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF CATALYSIS
·
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
·
材料科学
✓ 已验证
产品关联
DOI
高影响因子
MICROPOROUS AND MESOPOROUS MATERIALS
·
2022
·
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
·
绿色化学
·
催化化学
✓ 已验证
产品关联
DOI
高影响因子
Materials Chemistry Frontiers
·
2021
·Vol. 5
·期 16
·6101-6113
·
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
·
材料科学
·
催化
✓ 已验证
产品关联
DOI
高影响因子
危险品化学品经营许可证（带存储）