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Comparative Investigation of Ga- and In-CHA in the Non-Oxidative Ethane Dehydrogenation Reaction

Published

Author(s)

Jian Pan, Jason Lee, Muyuan Li

Abstract

Ga- and In-exchanged chabazite (CHA) zeolites with Si/Al ratio of 6 and metal/Al ratio of 0.7 were prepared via the incipient wetness impregnation method, were characterized using N2 adsorption, electron microscopy, temperature-programed reactions and were evaluated for the ethane dehydrogenation reaction using flow microreactors. Ga-CHA has higher reaction rates, a lower activation energy (Ea = 107 kJ/mol), lower initial selectivity (96.5%) and carbon balance than In-CHA (Ea = 175 kJ/mol and 98.3%, respectively). Rietveld refinement of the X-ray powder diffraction pattern of dehydrated In-CHA shows that the In+ cation is predominantly located above the 6-ring of the CHA cage. For Ga-CHA, higher Ga/Al ratio leads to higher specific reaction rates, and higher turnover frequency is observed with higher Si/Al ratio. It is proposed that the reaction proceeds through the so-called alkyl mechanism based on stability of alkyl hydride intermediates for both In- and Ga-CHA as determined using DFT calculations. The oxidative addition of ethane to the metal shows much lower Gibbs free energy for Ga-CHA (+27.95 kJ/mol) vs. In-CHA (+124.85 kJ/mol), a result consistent with the higher reactivity of Ga-CHA. These results, together with the measured lower activation energy and higher reaction rates of Ga- vs. In-CHA, indicate that the energetics of oxidative addition are more important than the elimination steps in the rate of ethane dehydrogenation in these materials.
Citation
Journal of Catalysis
Volume
413

Keywords

Zeolites, catalysis, intercalation, oxidative addition, sustainable chemistry, alkane dehydrogenation

Citation

Pan, J. , Lee, J. and Li, M. (2022), Comparative Investigation of Ga- and In-CHA in the Non-Oxidative Ethane Dehydrogenation Reaction, Journal of Catalysis, [online], https://doi.org/10.1016/j.jcat.2022.07.018, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=934536 (Accessed March 1, 2024)
Created August 1, 2022, Updated January 23, 2024