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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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Dealumination and desilication for Al-rich HZSM-5 zeolite via steam-alkaline treatment and its application

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    

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Using ultrasound to improve the sequential post-synthesis modification method for making mesoporous Y zeolites

Rongxin Zhang, Peinan Zhong, Hamidreza Arandiyan, Yanan Guan, Jinmin Liu, Na Wang, Yilai Jiao, Xiaolei Fan

《化学科学与工程前沿（英文）》 2020年 第14卷 第2期   页码 275-287 doi: 10.1007/s11705-019-1905-1

摘要： Mesoporous Y zeolites were prepared by the sequential chemical dealumination (using chelating agents such as ethylenediaminetetraacetic acid, H EDTA, and citric acid aqueous solutions) and alkaline desilication (using sodium hydroxide, NaOH, aqueous solutions) treatments. Specifically, the ultrasound-assisted alkaline treatment (i.e., ultrasonic treatment) was proposed as the alternative to conventional alkaline treatments which are performed under hydrothermal conditions. In comparison with the hydrothermal alkaline treatment, the ultrasonic treatment showed the comparatively enhanced efficiency (with the reduced treatment time, i.e., 5 min vs. 30 min, all with 0.2 mol·L NaOH at 65°C) in treating the dealuminated Y zeolites for creating mesoporosity. For example, after the treatment of a dealuminated zeolite Y (using 0.1 mol·L H EDTA at 100°C for 6 h), the ultrasonic treatment produced the mesoporous zeolite Y with the specific external surface area ( ) of 160 m ·g and mesopore volume ( ) of 0.22 cm ·g , being slightly higher than that by the conventional method (i.e., = 128 m ·g and = 0.19 cm ·g ). The acidic property and catalytic activity (in catalytic cracking of -octane) of mesoporous Y zeolites obtained by the two methods were comparable. The ultrasonic desilication treatment was found to be generic, also being effective to treat the dealuminated Y zeolites by citric acid. Additionally, the first step of chemical dealumination treatment was crucial to enable the effective creation of mesopores in the parent Y zeolite (with a silicon-to-aluminium ratio, Si/Al= 2.6) regardless of the subsequent alkaline desilication treatment (i.e., ultrasonic or hydrothermal). Therefore, appropriate selection of the condition of the chemical dealumination treatment based on the property of parent zeolites, such as Si/Al ratio and crystallinity, is important for making mesoporous zeolites effectively.

关键词： zeolite Y     mesoporous zeolite     post-synthesis treatment     ultrasound     chemical dealumination treatment     alkaline desilication treatment    

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标题 作者 时间 类型 操作

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

期刊论文

Dealumination and desilication for Al-rich HZSM-5 zeolite via steam-alkaline treatment and its application

Yuehua Fang, Fan Yang, Xuan He, Xuedong Zhu

期刊论文

Using ultrasound to improve the sequential post-synthesis modification method for making mesoporous Y zeolites

Rongxin Zhang, Peinan Zhong, Hamidreza Arandiyan, Yanan Guan, Jinmin Liu, Na Wang, Yilai Jiao, Xiaolei Fan

期刊论文