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Organic-Free Synthesis of CHA-Type Zeolite Catalysts for the Methanol-to-Olefins Reaction

Ji, Yuewei and Deimund, Mark A. and Bhawe, Yashodhan and Davis, Mark E. (2015) Organic-Free Synthesis of CHA-Type Zeolite Catalysts for the Methanol-to-Olefins Reaction. ACS Catalysis, 5 (7). pp. 4456-4465. ISSN 2155-5435. doi:10.1021/acscatal.5b00404.

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Chabazite (CHA)-type zeolites are prepared from the hydrothermal conversion of faujasite (FAU)-type zeolites, dealuminated by high-temperature steam treatments (500–700 °C), and evaluated as catalysts for the methanol-to-olefins (MTO) reaction. The effects of temperature and partial pressure of water vapor during steaming are investigated. Powder X-ray diffraction (XRD) and Ar physisorption data show that the steam treatments cause partial structural collapse of the zeolite with the extent of degradation increasing with steaming temperature. ^(27)Al MAS NMR spectra of the steamed materials reveal the presence of tetrahedral, pentacoordinate, and octahedral aluminum. NH_3 and i-propylamine temperature-programmed desorption (TPD) demonstrate that steaming removes Brønsted acid sites, while simultaneously introducing larger pores into the CHA materials that make the remaining acid sites more accessible. Acid washing the steamed CHA-type zeolites removes a significant portion of the extra-framework aluminum, producing an increase in the bulk Si/Al ratio as well as the adsorption volume. The proton form of the as-synthesized CHA (Si/Al = 2.4) rapidly deactivates when tested for MTO at a reaction temperature of 400 °C and atmospheric pressure. CHA samples steamed at 600 °C performed the best among the samples tested, showing increased olefin selectivities as well as catalyst lifetime compared to the unsteamed CHA. Both lifetime and C_2–C_3 olefin selectivities are found to increase with increasing reaction temperature. At 450 °C, CHA steamed at 600 °C reached a combined C_2–C_3 olefin selectivity of 74.2% at 100% methanol conversion, with conversion remaining above 80% for more than 130 min of time-on-stream (TOS) before deactivating. More stable time-on-stream behavior is observed for 600 °C-steamed CHA that underwent acid washing: conversion above 90% for more than 200 min of TOS at 450 °C with a maximum total C_2–C_3 olefin selectivity of 71.4% at 100% conversion.

Item Type:Article
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URLURL TypeDescription Information
Davis, Mark E.0000-0001-8294-1477
Additional Information:© 2015 American Chemical Society. ACS AuthorChoice - 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: February 24, 2015; Revised: May 1, 2015; Publication Date (Web): June 23, 2015. The authors thank the Dow Chemical Company for financial support of this work. The authors also thank Drs. Andrzej Malek, Jonathan Lunn, and Yu Liu from the Dow Chemical Company for helpful discussions. The authors declare no competing financial interest.
Funding AgencyGrant Number
Dow Chemical CompanyUNSPECIFIED
Subject Keywords:methanol-to-olefins; CHA; zeolite; organic-free; steaming
Issue or Number:7
Record Number:CaltechAUTHORS:20150701-133219784
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Official Citation:Organic-Free Synthesis of CHA-Type Zeolite Catalysts for the Methanol-to-Olefins Reaction Yuewei Ji, Mark A. Deimund, Yashodhan Bhawe, and Mark E. Davis ACS Catalysis 2015 5 (7), 4456-4465 DOI: 10.1021/acscatal.5b00404
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58739
Deposited By: Tony Diaz
Deposited On:08 Jul 2015 19:41
Last Modified:10 Nov 2021 22:09

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