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Title: Propene Metathesis over Supported Tungsten Oxide Catalysts: A Study of Active Site Formation

Abstract

A detailed investigation was conducted on the factors influencing the properties of silica-supported tungsten oxide catalysts for propene metathesis. A principal goal of this work was to identify the processes involved in the formation of catalytically active sites. To probe the influence of dispersion, samples were prepared across a range of W loadings using two methods of catalyst preparation: incipient wetness impregnation of amorphous silica and ion exchange of mesoporous SBA-15. The samples were characterized by nitrogen adsorption, UV-vis, Raman, and X-ray absorption spectroscopy (XAS). Catalytic activity was observed to increase with W surface concentration up to the point where WO 3 nanoparticles formed. The catalytic performance of all samples was enhanced 2-fold by pretreatment in He, in comparison to pretreatment in air. In situ characterization of samples pretreated in He by Raman and XAS shows an increase in the relative concentration of isolated dioxo W(6+) species relative to mono-oxo W(6+) species, and in situ XAS data collected during propene metathesis indicated that a similar conversion occurs for air-pretreated samples in the presence of propene. For both air- and He-pretreated catalysts an activation period was observed, during which the activity increased and attained steady-state activity. This period was significantly longermore » for air-pretreated catalysts and was accompanied by the transient formation of acetone. While acetone was not observed during the much shorter transient of He-pretreated samples, in situ XAS provided evidence of reduction occurring in these samples upon contact with propene. In conclusion, it is also notable that, independent of the manner of catalyst preparation or pretreatment, the rate of propene metathesis is first order in propene and exhibits an activation energy of 200 kJ/mol. A model is proposed to explain why only a fraction of the isolated tungstate species is active for propene metathesis (~5%) and why this fraction increases with increasing concentration of W dispersed on silica.« less

Authors:
 [1];  [1];  [1]
  1. Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Chemical Sciences Division
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1377571
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 6; Journal Issue: 11; Journal ID: ISSN 2155-5435
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; butene; catalyst activation; metathesis; propene; silica; tungstate species

Citation Formats

Howell, John G., Li, Yi-Pei, and Bell, Alexis T. Propene Metathesis over Supported Tungsten Oxide Catalysts: A Study of Active Site Formation. United States: N. p., 2016. Web. doi:10.1021/acscatal.6b01842.
Howell, John G., Li, Yi-Pei, & Bell, Alexis T. Propene Metathesis over Supported Tungsten Oxide Catalysts: A Study of Active Site Formation. United States. doi:10.1021/acscatal.6b01842.
Howell, John G., Li, Yi-Pei, and Bell, Alexis T. Thu . "Propene Metathesis over Supported Tungsten Oxide Catalysts: A Study of Active Site Formation". United States. doi:10.1021/acscatal.6b01842. https://www.osti.gov/servlets/purl/1377571.
@article{osti_1377571,
title = {Propene Metathesis over Supported Tungsten Oxide Catalysts: A Study of Active Site Formation},
author = {Howell, John G. and Li, Yi-Pei and Bell, Alexis T.},
abstractNote = {A detailed investigation was conducted on the factors influencing the properties of silica-supported tungsten oxide catalysts for propene metathesis. A principal goal of this work was to identify the processes involved in the formation of catalytically active sites. To probe the influence of dispersion, samples were prepared across a range of W loadings using two methods of catalyst preparation: incipient wetness impregnation of amorphous silica and ion exchange of mesoporous SBA-15. The samples were characterized by nitrogen adsorption, UV-vis, Raman, and X-ray absorption spectroscopy (XAS). Catalytic activity was observed to increase with W surface concentration up to the point where WO3 nanoparticles formed. The catalytic performance of all samples was enhanced 2-fold by pretreatment in He, in comparison to pretreatment in air. In situ characterization of samples pretreated in He by Raman and XAS shows an increase in the relative concentration of isolated dioxo W(6+) species relative to mono-oxo W(6+) species, and in situ XAS data collected during propene metathesis indicated that a similar conversion occurs for air-pretreated samples in the presence of propene. For both air- and He-pretreated catalysts an activation period was observed, during which the activity increased and attained steady-state activity. This period was significantly longer for air-pretreated catalysts and was accompanied by the transient formation of acetone. While acetone was not observed during the much shorter transient of He-pretreated samples, in situ XAS provided evidence of reduction occurring in these samples upon contact with propene. In conclusion, it is also notable that, independent of the manner of catalyst preparation or pretreatment, the rate of propene metathesis is first order in propene and exhibits an activation energy of 200 kJ/mol. A model is proposed to explain why only a fraction of the isolated tungstate species is active for propene metathesis (~5%) and why this fraction increases with increasing concentration of W dispersed on silica.},
doi = {10.1021/acscatal.6b01842},
journal = {ACS Catalysis},
number = 11,
volume = 6,
place = {United States},
year = {2016},
month = {10}
}

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