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Effect of Heteroatom Concentration in SSZ-13 on the Methanol-to-Olefins Reaction

Deimund, Mark A. and Harrison, Luke and Lunn, Jonathan D. and Liu, Yu and Malek, Andrzej and Shayib, Ramzy and Davis, Mark E. (2016) Effect of Heteroatom Concentration in SSZ-13 on the Methanol-to-Olefins Reaction. ACS Catalysis, 6 (2). pp. 542-550. ISSN 2155-5435. doi:10.1021/acscatal.5b01450.

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SSZ-13 materials have been synthesized with varying amounts of Al to produce samples with different concentrations of Brønsted acid sites, and consequently, these SSZ-13 materials contain increasing numbers of paired Al heteroatoms with increasing Al content. These materials were then characterized and tested as catalysts for the methanol-to-olefins (MTO) reaction at 400 °C and 100% methanol conversion under atmospheric pressure. A SAPO-34 sample was also synthesized and tested for comparison. SSZ-13 materials exhibited significant differences in MTO reactivity as Si/Al ratios varied. Reduced Al content (higher Si/Al ratio) and, consequently, fewer paired Al sites led to more stable light olefin selectivities, with a reduced initial transient period, lower initial propane selectivities, and longer catalyst lifetime. To further support the importance of paired Al sites in the formation of propane during this initial transient period, a series of experiments was conducted wherein an H-SSZ-13 sample was exchanged with Cu^(2+), steamed, and then back-exchanged to the H form. The H-SSZ-13 sample exhibited high initial propane selectivity, while the steamed H-SSZ-13, the Cu^(2+)-exchanged SSZ-13 sample, and the steamed Cu-SSZ-13 sample did not, as expected since steaming selectively removes paired Al sites and Cu^(2+) exchanges onto these sites. However, when it was back-exchanged to the proton form, the steamed Cu-SSZ-13 sample still exhibited the high initial alkane selectivity and transient period typical of the higher Al content materials. This is attributed to protection of paired Al sites during steaming via the Cu^(2+) cation. Post-reaction coke analyses reveal that the degree of methylation for each aromatic species increases with increasing Si/Al in SSZ-13. Further, SAPO-34 produces more polycyclic species than SSZ-13 samples. From these data, the paired Al site content appears to be correlated with both MTO reaction behavior and coke species formation in SSZ-13 samples.

Item Type:Article
Related URLs:
URLURL TypeDescription Information
Malek, Andrzej0000-0002-1608-9375
Davis, Mark E.0000-0001-8294-1477
Additional Information:© 2015 American Chemical Society. This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Received: July 10, 2015; Revised: December 11, 2015; Published: December 22, 2015. The authors thank The Dow Chemical Company for financial support of this project. The authors also thank Cassie Fhaner for analytical work associated with the GC-MS data. The authors declare no competing financial interest.
Funding AgencyGrant Number
Dow Chemical CompanyUNSPECIFIED
Subject Keywords:methanol-to-olefins; CHA; zeolite; silicoaluminophosphates; hydrocarbon pool
Issue or Number:2
Record Number:CaltechAUTHORS:20160125-134417395
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Official Citation:Effect of Heteroatom Concentration in SSZ-13 on the Methanol-to-Olefins Reaction Mark A. Deimund, Luke Harrison, Jonathan D. Lunn, Yu Liu, Andrzej Malek, Ramzy Shayib, and Mark E. Davis ACS Catalysis 2016 6 (2), 542-550 DOI: 10.1021/acscatal.5b01450
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:63934
Deposited By: Tony Diaz
Deposited On:25 Jan 2016 22:19
Last Modified:10 Nov 2021 23:23

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