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
Front. Chem. Sci. Eng. ›› 2015, Vol. 9 ›› Issue (4) : 450 -460.
Alkaline modification of ZSM-5 catalysts for methanol aromatization: The effect of the alkaline concentration
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.
ZSM-5 / alkaline treatment / dealumination / desilication / mesopores / methanol / aromatics
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Higher Education Press and Springer-Verlag Berlin Heidelberg
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