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Enhancing the aromatic selectivity of cyclohexane aromatization by CO₂ coupling

《化学科学与工程前沿（英文）》 2023年第17卷第11期页码 1801-1808 doi: 10.1007/s11705-023-2325-9

摘要： Improving the aromatic selectivity in the alkane aromatization process is of great importance for its practical utilization but challenge to make because the high H/C ratio of alkanes would lead to a serious hydrogen transfer process and a large amount of light alkanes. Herein, CO₂ is introduced into the cyclohexane conversion process on the HZSM-5 zeolite, which can improve the aromatic selectivity. By optimizing the reaction conditions, an improved aromatic (benzene, toluene, xylene, and C₉₊) selectivity of 48.2% can be obtained at the conditions of 2.7 MPa (CO₂), 450 °C, and 1.7 h⁻¹, which is better than that without CO₂ (aromatic selectivity = 43.2%). In situ transmission Fourier transform infrared spectroscopy spectra illustrate that many oxygenated chemical intermediates (e.g., carboxylic acid, anhydride, unsaturated aldehydes/ketones or ketene) would be formed during the cyclohexane conversion process in the presence of CO₂. ¹³C isotope labeling experimental results demonstrate that CO₂ can enter into the aromatics through the formation of oxygenated chemical intermediates and thereby improve the aromatic selectivity. This study may open a green, economic, and promising way to improve the aromatic selectivity for alkane aromatization process.

关键词： aromatics carbon dioxide aromatization coupling reaction ZSM-5 zeolite

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Alkaline modification of ZSM-5 catalysts for methanol aromatization: The effect of the alkaline concentration

Zhenhao Wei,Tengfei Xia,Minghui Liu,Qingsheng Cao,Yarong Xu,Kake Zhu,Xuedong Zhu

《化学科学与工程前沿（英文）》 2015年第9卷第4期页码 450-460 doi: 10.1007/s11705-015-1542-2

摘要： The effects of alkaline treatment on the physical properties of ZSM-5 catalysts and on their activities for methanol to aromatics conversion have been investigated. A mild alkaline treatment (0.2 and 0.3 mol/L NaOH) created mesopores in the parent zeolite with no obvious effect on acidity. The presence of mesopores gives the catalyst a longer lifetime and higher selectivity for aromatics. Treatment with 0.4 mol/L NaOH decreased the number of Brønsted acid sites due to dealumination and desilication, which resulted in a lower deactivation rate. In addition, more mesopores were produced than with the mild alkaline treatment. As a result, the lifetime of the sample treated with 0.4 mol/L NaOH was almost five times that of the parent ZSM-5. Treatment with a higher alkaline concentration (0.5 mol/L) greatly reduced the number of Brønsted acid sites and the number of micropores resulting in incomplete methanol conversion. When the alkaline-treated catalysts were washed with acid, some of the porosity was restored and a slight increase in selectivity for aromatics was obtained.

关键词： aromatics ZSM-5 alkaline treatment dealumination desilication mesopores methanol

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desilication for Al-rich HZSM-5 zeolite via steam-alkaline treatment and its application in methanol aromatization

Yuehua Fang, Fan Yang, Xuan He, Xuedong Zhu

《化学科学与工程前沿（英文）》 2019年第13卷第3期页码 543-553 doi: 10.1007/s11705-018-1778-8

摘要： The hierarchical HZSM-5 was prepared via dealumination and desilication of commercial Al-rich HZSM-5, and characterized by X-ray diffraction, Al magic-angle spinning nuclear magnetic resonance, inductively coupled plasma mass spectrometry, scanning electron microscope, transmission electron microscope, N adsorption-desorption, NH temperature-programmed desorption, performed thermogravimetric and Raman spectrum. The results showed that partial framework of HZSM-5 was removed after steam treatment at 0.15 MPa, 500°C for 3 h. HZSM-5 with high specific surface area and much mesoporosity was obtained by the subsequent alkaline treatment. The regulation of acid quantity was achieved by altering the concentration of alkaline. Dealumination and desilication of Al-rich HZSM-5 zeolites became more effective using a combination of steam and alkaline treatments than using alkaline treatment alone. Methanol aromatization reaction was employed to evaluate the catalytic performance of treated HZSM-5 at 0.15 MPa, 450°C and MHSV of 1.5 h . The results indicated that after steam treatment, HZSM-5 further treated with 0.2 mol/L NaOH exhibits the best catalytic performance: the selectivity of aromatics reached 42.1% and the lifetime of catalyst attained 212 h, which are much better than untreated HZSM-5.

关键词： steam treatment alkaline treatment hierarchical ZSM-5 methanol aromatization