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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.
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 November 5, 2024)