Acid site densities and reactivity of oxygen-modified transition metal carbide catalysts

Mark M. Sullivan; Aditya Bhan

doi:10.1016/j.jcat.2016.09.012

Acid site densities and reactivity of oxygen-modified transition metal carbide catalysts

Mark M. Sullivan, Aditya Bhan

Chemical Engineering and Materials Science

Research output: Contribution to journal › Article › peer-review

31 Scopus citations

Abstract

Acidic properties of β-Mo₂C, α-Mo₂C, W₂C, and WC were quantified by assessing the kinetics of isopropanol (IPA) dehydration at 415 K either (i) under inert He/Ar atmosphere or (ii) with 13 kPa O₂ co-feed. Dehydration kinetics were zero-order with respect to IPA for all catalysts and under all reaction conditions. Intrinsic activation energies were similar across all catalysts (89–104 kJ mol⁻¹). Acid site densities calculated via in situ 2,6-di-tert-butylpyridine (DTBP) titration were used to normalize dehydration turnover frequencies (TOF). O₂ co-feed increased dehydration rates per gram by an order of magnitude for all catalysts tested, but TOF remained invariant within a factor of ∼2. Mo- and W-based carbides showed similar dehydration kinetics regardless of O₂ co-feed, and O₂ co-feed did not alter bulk carbidic structure as noted by X-ray diffraction. Brønsted acid site provenance results from the oxophilicity of Mo and W carbides.

Original language	English (US)
Pages (from-to)	53-58
Number of pages	6
Journal	Journal of Catalysis
Volume	344
DOIs	https://doi.org/10.1016/j.jcat.2016.09.012
State	Published - Dec 1 2016

Bibliographical note

Funding Information:
This research was supported by Office of Basic Energy Sciences, the U.S. Department of Energy under award number no. DE- SC0008418 (DOE Early Career Program). Part of this work was carried out in the College of Science and Engineering Characterization Facility, University of Minnesota, which has received capital equipment funding from the NSF through the MRSEC program. We thank Javier Garcia Barriocanal for assistance with the X-ray diffraction studies, Rick Knurr for assistance with the ICP-OES characterization, and Bing Luo for assistance with the XPS characterization.

Publisher Copyright:
© 2016 Elsevier Inc.

Keywords

Brønsted acid
Catalysis
Dehydration
Interstitial carbide
Molybdenum carbide
Oxophilic
Site density
Transition metal
Tungsten carbide

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title = "Acid site densities and reactivity of oxygen-modified transition metal carbide catalysts",

abstract = "Acidic properties of β-Mo2C, α-Mo2C, W2C, and WC were quantified by assessing the kinetics of isopropanol (IPA) dehydration at 415 K either (i) under inert He/Ar atmosphere or (ii) with 13 kPa O2 co-feed. Dehydration kinetics were zero-order with respect to IPA for all catalysts and under all reaction conditions. Intrinsic activation energies were similar across all catalysts (89–104 kJ mol−1). Acid site densities calculated via in situ 2,6-di-tert-butylpyridine (DTBP) titration were used to normalize dehydration turnover frequencies (TOF). O2 co-feed increased dehydration rates per gram by an order of magnitude for all catalysts tested, but TOF remained invariant within a factor of ∼2. Mo- and W-based carbides showed similar dehydration kinetics regardless of O2 co-feed, and O2 co-feed did not alter bulk carbidic structure as noted by X-ray diffraction. Br{\o}nsted acid site provenance results from the oxophilicity of Mo and W carbides.",

keywords = "Br{\o}nsted acid, Catalysis, Dehydration, Interstitial carbide, Molybdenum carbide, Oxophilic, Site density, Transition metal, Tungsten carbide",

author = "Sullivan, {Mark M.} and Aditya Bhan",

note = "Funding Information: This research was supported by Office of Basic Energy Sciences, the U.S. Department of Energy under award number no. DE- SC0008418 (DOE Early Career Program). Part of this work was carried out in the College of Science and Engineering Characterization Facility, University of Minnesota, which has received capital equipment funding from the NSF through the MRSEC program. We thank Javier Garcia Barriocanal for assistance with the X-ray diffraction studies, Rick Knurr for assistance with the ICP-OES characterization, and Bing Luo for assistance with the XPS characterization. Publisher Copyright: {\textcopyright} 2016 Elsevier Inc.",

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N2 - Acidic properties of β-Mo2C, α-Mo2C, W2C, and WC were quantified by assessing the kinetics of isopropanol (IPA) dehydration at 415 K either (i) under inert He/Ar atmosphere or (ii) with 13 kPa O2 co-feed. Dehydration kinetics were zero-order with respect to IPA for all catalysts and under all reaction conditions. Intrinsic activation energies were similar across all catalysts (89–104 kJ mol−1). Acid site densities calculated via in situ 2,6-di-tert-butylpyridine (DTBP) titration were used to normalize dehydration turnover frequencies (TOF). O2 co-feed increased dehydration rates per gram by an order of magnitude for all catalysts tested, but TOF remained invariant within a factor of ∼2. Mo- and W-based carbides showed similar dehydration kinetics regardless of O2 co-feed, and O2 co-feed did not alter bulk carbidic structure as noted by X-ray diffraction. Brønsted acid site provenance results from the oxophilicity of Mo and W carbides.

AB - Acidic properties of β-Mo2C, α-Mo2C, W2C, and WC were quantified by assessing the kinetics of isopropanol (IPA) dehydration at 415 K either (i) under inert He/Ar atmosphere or (ii) with 13 kPa O2 co-feed. Dehydration kinetics were zero-order with respect to IPA for all catalysts and under all reaction conditions. Intrinsic activation energies were similar across all catalysts (89–104 kJ mol−1). Acid site densities calculated via in situ 2,6-di-tert-butylpyridine (DTBP) titration were used to normalize dehydration turnover frequencies (TOF). O2 co-feed increased dehydration rates per gram by an order of magnitude for all catalysts tested, but TOF remained invariant within a factor of ∼2. Mo- and W-based carbides showed similar dehydration kinetics regardless of O2 co-feed, and O2 co-feed did not alter bulk carbidic structure as noted by X-ray diffraction. Brønsted acid site provenance results from the oxophilicity of Mo and W carbides.

KW - Brønsted acid

KW - Catalysis

KW - Dehydration

KW - Interstitial carbide

KW - Molybdenum carbide

KW - Oxophilic

KW - Site density

KW - Transition metal

KW - Tungsten carbide

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ER -

Acid site densities and reactivity of oxygen-modified transition metal carbide catalysts

Abstract

Bibliographical note

Keywords

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