Comparison of the activity stabilities of nanosized and microsized zeolites based Fe-Mo/HZSM-5 catalysts in the non-oxidative CH₄ dehydroaromatization under periodic CH₄-H₂ switching operation at 1073 K

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• 作者：Yuebing Xu ; Yoshizo Suzuki ; Zhan-Guo Zhang ; ^{z.zhang@aist.go.jp}
• 关键词：Methane dehydroaromatization ; Mo/HZSM-5 ; Nanosized zeolite ; Fe modification ; Carbon nanotube
• 刊名：Applied Catalysis A: General
• 出版年：2013
• 出版时间：15 February, 2013
• 年：2013
• 卷：452
• 期：Complete
• 页码：105-116
• 全文大小：2279 K

文摘

The activities and stabilities of three series of Fe-modified 5 % Mo/HZSM-5 catalysts based on a nano-zeolite and two micro-zeolites in the fixed-bed non-oxidative CH₄ dehydroaromatization reaction were compared at the condition of 1 atm, 1073 K and 10,000 mL/g/h under periodic CH₄-H₂ switch operation mode. The activity evaluation tests showed that 0.1-2 wt % Fe co-impregnated modification improves remarkably the benzene formation activity stability of the nanosized zeolite-based catalyst while it had little influence on those of the two microsized zeolites-based catalysts. Then, another series of Fe-modified 5 % Mo/HZSM-5 catalysts based on a ball-milled, nanosized zeolite sample were prepared and tested at the same condition. The results confirmed that the maximum improving effect of Fe modification achieves at a properly small Fe addition of 0.5 wt % . SEM observation of all fresh and spent catalyst samples revealed that carbon nanotubes formed over all Fe-modified catalysts but disagglomeration of zeolite agglomerates caused by carbon nanotube formation and growth occurred only to the nano-zeolite based, Fe-modified catalysts. Further, TPO measurement of all spent samples revealed that the amounts of accumulated coke per unit external surface area in the spent nano-zeolite based catalysts were much smaller than those in the micro-zeolite based catalysts. Moreover, well consistent BET measurement confirmed that all nano-zeolite based, Fe-modified catalysts exhibited a similarly smaller degree of decrease in their microporosity than all micro-zeolite based catalysts. All these suggest that the preferential coke formation on the external surfaces and/or in the outer layers of zeolite agglomerates took place under the test condition and enhanced the deactivation of the nano-zeolite based, Fe-unmodified catalysts, and that the disagglomeration of zeolite agglomerates caused by Fe-induced carbon nanotube formation and growth in the reaction was the origin of Fe modification improving the activity stability of the nano-zeolite based Mo/HZSM-5 catalysts. The improvement mechanism is discussed in detail in the article.