An Adsorption Study of CH4 on ZSM-5, MOR, and ZSM-12 Zeolites

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• 作者：Yiwei Zhang ; JingYe Yu ; Yu-Hao Yeh ; Raymond. J. Gorte ; Srinivas Rangarajan ; Manos Mavrikakis
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：December 31, 2015
• 年：2015
• 卷：119
• 期：52
• 页码：28970-28978
• 全文大小：411K
• ISSN：1932-7455

文摘

CH₄ adsorption was studied experimentally and theoretically on ZSM-5, MOR, and ZSM-12 zeolites using calorimetric measurements at 195 K and plane wave DFT calculations. Differential heats measured on four different H-ZSM-5 samples were determined to be 22.5 ± 1 kJ/mol, independent of Br?nsted site density or defect concentration. However, DFT calculations performed using various functionals and on the most stable Br?nsted site indicated that CH₄ should bind to this site by an additional 1–7 kJ/mol, a discrepancy that is due to the inability of standard DFT methods to capture hydrogen-bonding effects accurately with CH₄. Differential heats for CH₄ in MOR were 30 ± 1 kJ/mol at low coverages, falling to 25 kJ/mol for coverages above one molecule per 8-membered-ring side pocket, while differential heats on ZSM-12 were initially 22.5 kJ/mol, decreasing to 21 kJ/mol with coverage. DFT calculations on the siliceous form of the zeolites were able to predict these values within 5 kJ/mol in most cases. The results indicate that CH₄ is an excellent probe molecule for characterizing the pore structure of zeolites.