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

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). However, 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 andmore » 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 imply design strategies that suppress framework hydrolysis would attenuate the deactivation of Lewis acid zeolites in aqueous media.« less
Authors:
ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [1]
  1. Purdue Univ., West Lafayette, IN (United States)
  2. California Inst. of Technology (CalTech), Pasadena, CA (United States)
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Catalysis Science and Technology
Additional Journal Information:
Journal Volume: 9; Journal Issue: 7; Journal ID: ISSN 2044-4753
Publisher:
Royal Society of Chemistry
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
OSTI Identifier:
1505311

Cordon, Michael J., Hall, Jacklyn N., Harris, James W., Bates, Jason S., Hwang, Son-Jong, and Gounder, Rajamani. Deactivation of Sn-Beta zeolites caused by structural transformation of hydrophobic to hydrophilic micropores during aqueous-phase glucose isomerization. United States: N. p., Web. doi:10.1039/c8cy02589d.
Cordon, Michael J., Hall, Jacklyn N., Harris, James W., Bates, Jason S., Hwang, Son-Jong, & Gounder, Rajamani. Deactivation of Sn-Beta zeolites caused by structural transformation of hydrophobic to hydrophilic micropores during aqueous-phase glucose isomerization. United States. doi:10.1039/c8cy02589d.
Cordon, Michael J., Hall, Jacklyn N., Harris, James W., Bates, Jason S., 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". United States. doi:10.1039/c8cy02589d.
@article{osti_1505311,
title = {Deactivation of Sn-Beta zeolites caused by structural transformation of hydrophobic to hydrophilic micropores during aqueous-phase glucose isomerization},
author = {Cordon, Michael J. and Hall, Jacklyn N. and Harris, James W. and Bates, Jason S. and Hwang, Son-Jong and Gounder, Rajamani},
abstractNote = {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). However, 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 CD3CN 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 imply design strategies that suppress framework hydrolysis would attenuate the deactivation of Lewis acid zeolites in aqueous media.},
doi = {10.1039/c8cy02589d},
journal = {Catalysis Science and Technology},
number = 7,
volume = 9,
place = {United States},
year = {2019},
month = {3}
}

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