Issue 18, 2021

K+ located in 6-membered rings of low-silica CHA enhancing the lifetime and propene selectivity in MTO

Abstract

Methanol-to-olefins (MTO) technology presently serves as a key to convert coal or natural gas to valuable hydrocarbons, in particular lower olefins. This work focuses on developing a low cost and environmentally benign MTO catalyst from low-silica CHA zeolite. Its moderate acidity and reaction space have been balanced by tuning the residual K+ cations in the cavity via controlled ammonium ion-exchange. The structure-dependent catalytic performances have been assessed, summarized and discussed by using various characterization techniques. The crystalline structure and crystal morphology of CHA were well preserved during the NH4+ exchange. N2 physisorption demonstrated that the pore volume and specific surface area increased substantially after K+ cations were exchanged as a result of pore opening. NH3 temperature-programmed desorption (TPD) and NH3-adsorption IR spectra showed that the amount and strength of acid sites were regulated by the exchange level of K+ with NH4+, which was closely related to the K+ location according to NO and acetonitrile adsorption IR spectra. The completely exchanged CHA (>98% K+ exchange level) deactivated rapidly in MTO at 400 °C, whereas CHA (65% K+ exchange level) with moderate acidity showed the best catalytic performance. The moderate acidity in the open cage facilitated the formation of higher methylbenzene intermediates, giving propylene (45%) as the predominant product.

Graphical abstract: K+ located in 6-membered rings of low-silica CHA enhancing the lifetime and propene selectivity in MTO

Supplementary files

Article information

Article type
Paper
Submitted
19 Apr 2021
Accepted
12 Jul 2021
First published
20 Jul 2021

Catal. Sci. Technol., 2021,11, 6234-6247

K+ located in 6-membered rings of low-silica CHA enhancing the lifetime and propene selectivity in MTO

J. Zhang, L. Ren, Y. Mi, P. Luo, H. Xu, Y. Guan, H. Peng, S. Song, W. Song, H. Wu, M. He and P. Wu, Catal. Sci. Technol., 2021, 11, 6234 DOI: 10.1039/D1CY00691F

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