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Deactivation of Sn-Beta zeolites caused by structural transformation of hydrophobic to hydrophilic micropores during aqueous-phase glucose isomerization

Cordon, Michael J. and Hall, Jacklyn N. and Harris, James W. and Bates, Jason S. and Hwang, Son-Jong and Gounder, Rajamani (2019) Deactivation of Sn-Beta zeolites caused by structural transformation of hydrophobic to hydrophilic micropores during aqueous-phase glucose isomerization. Catalysis Science and Technology, 9 (7). pp. 1654-1668. ISSN 2044-4753. https://resolver.caltech.edu/CaltechAUTHORS:20190313-090938903

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Abstract

The structural changes underlying the deactivation of Sn-Beta zeolites under aqueous-phase reaction conditions at elevated temperatures (373 K) are investigated using spectroscopic characterization and site titration techniques together with turnover rates for glucose isomerization, a well-understood probe reaction for which changes in measured rates can be ascribed to specific changes in catalyst structure. In the case of hydrophobic, low-defect Sn-Beta zeolites (Sn-Beta-F), treatment in hot liquid water (373 K) for short times (<1 h) prior to reaction causes glucose–fructose isomerization turnover rates (per open Sn site, 373 K) to increase, while longer-term exposure (>3 h) to hot liquid water causes turnover rates to decrease and approach values characteristic of hydrophilic, defect-rich Sn-Beta zeolites (Sn-Beta-OH). In contrast, turnover rates on hydrophilic Sn-Beta-OH zeolites are insensitive to the duration of hot liquid water exposure prior to reaction. Activation and deactivation phenomena on Sn-Beta-F zeolites occur concomitantly with the formation of silanol defects (by ∼2–10×) with increasing durations (0–24 h) of hot water treatment, despite negligible differences in open and closed Sn site speciation as quantified ex situ by CD_3CN IR spectra. Mechanistic interpretations of these phenomena suggest that silanol groups present at low densities serve as binding sites for water molecules and clusters, which confer enthalpic stability to kinetically-relevant hydride-shift transition states and increase turnover rates, while silanol groups present in higher densities stabilize extended hydrogen-bonded water networks, which entropically destabilize kinetically-relevant transition states and decrease turnover rates. Intraporous voids within hydrophobic Sn-Beta-F zeolites become increasingly hydrophilic as silanol groups are formed by hydrolysis of framework siloxane bridges with increasing durations of water treatment, thereby decreasing aqueous-phase glucose isomerization turnover rates (per open Sn site). These findings suggest design strategies that suppress framework hydrolysis would attenuate the deactivation of Lewis acid zeolites in aqueous media.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1039/c8cy02589dDOIArticle
http://www.rsc.org/suppdata/c8/cy/c8cy02589d/c8cy02589d1.pdfPublisherSupplementary Information
ORCID:
AuthorORCID
Cordon, Michael J.0000-0002-5675-8027
Hall, Jacklyn N.0000-0003-4960-1344
Harris, James W.0000-0001-6760-9951
Bates, Jason S.0000-0002-7603-9687
Hwang, Son-Jong0000-0002-3210-466X
Gounder, Rajamani0000-0003-1347-534X
Additional Information:© 2019 The Royal Society of Chemistry. The article was received on 23 Dec 2018, accepted on 04 Mar 2019 and first published on 05 Mar 2019. We acknowledge the financial support provided by the Purdue Process Safety and Assurance Center (P2SAC). We also thank Juan Carlos Vega-Vila for helpful technical discussions and comments on this manuscript. The NMR facility at the California Institute of Technology was supported by the National Science Foundation (NSF) under Grant Number 9724240 and partially supported by the MRSEC Program of the NSF under Award Number DMR-520565. There are no conflicts to declare.
Funders:
Funding AgencyGrant Number
Purdue UniversityUNSPECIFIED
NSFDMR-9724240
NSFDMR-520565
Issue or Number:7
Record Number:CaltechAUTHORS:20190313-090938903
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190313-090938903
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:93760
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:13 Mar 2019 16:28
Last Modified:03 Oct 2019 20:57

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