Title: Investigation of Silica-Supported Vanadium Oxide Catalysts by High-Field ⁵¹V Magic-Angle Spinning NMR

Abstract

Supported V₂O₅/SiO₂ catalysts were studied using solid-state ⁵¹V magic-angle spinning NMR at a sample spinning rate of 36 kHz and at a magnetic field of 19.975 T to provide a better understanding of the coordination of the vanadium oxide as a function of environmental conditions. Structural transformations of the supported vanadium oxide species between the catalyst in the dehydrated state and hydrated state under an ambient environment were revisited to examine the degree of oligomerization and the effect of water. The experimental results indicate the existence of a single dehydrated surface vanadium oxide species that resonates at –675 ppm and two vanadium oxide species under ambient conditions that resonate at –566 and –610 ppm. No detectable structural difference was found as a function of vanadium oxide loading on SiO₂ (3% V₂O₅/SiO₂ and 8% V₂O₅/SiO₂). Quantum chemistry simulations of the ⁵¹V NMR chemical shifts on predicted surface structures were used as an aid in understanding potential surface vanadium oxide species on the silica support. The results suggest the formation of isolated surface VO₄ units for the dehydrated catalysts with the possibility of dimer and cyclic trimer presence. The absence of bridging V–O–V vibrations (~200–300 cm^–1) in previous Raman spectra, however, indicatesmore » that the isolated surface VO₄ sites are the dominant dehydrated surface vanadia species on silica. Upon exposure to water, hydrolysis of the bridging V–O–Si bonds is most likely responsible for the decreased electron shielding experienced by vanadium. In conclusion, no indicators for the presence of hydrated decavanadate clusters or hydrated vanadia gels previously proposed in the literature were detected in this study.« less

Authors:

Jaegers, Nicholas R. ^[1]; Wan, Chuan ^[2]; Hu, Mary Y. ^[2]; Vasiliu, Monica ^[3]; Dixon, David A.  ^[3];

• Search DOE PAGES for author "Dixon, David A."
• Search DOE PAGES for ORCID "0000-0002-9492-0056"

Walter, Eric ^[2]; Wachs, Israel E. ^[4]; Wang, Yong ^[1]; Hu, Jian Zhi  ^[2]

• Search DOE PAGES for author "Hu, Jian Zhi"
• Search DOE PAGES for ORCID "0000-0001-8879-747X"

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+ Show Author Affiliations

1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Washington State Univ., Pullman, WA (United States)
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
3. The Univ. of Alabama, Tuscaloosa, AL (United States)
4. Lehigh Univ., Bethlehem, PA (United States)

Publication Date:

Mon Feb 27 00:00:00 EST 2017

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Center for Understanding and Control of Acid Gas-induced Evolution of Materials for Energy (UNCAGE-ME)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division; USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1388368

Grant/Contract Number:  

SC0012577; AC06-76RL01830

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Physical Chemistry. C

Additional Journal Information:

Journal Volume: 121; Journal Issue: 11; Related Information: UNCAGE-ME partners with Georgia Institute of Technology (lead); Lehigh University; Oak Ridge National Laboratory; University of Alabama; University of Florida; University of Wisconsin; Washington University in St. Louis; Journal ID: ISSN 1932-7447

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; catalysis (heterogeneous); defects; membrane; carbon capture; materials and chemistry by design; synthesis (novel materials); synthesis (self-assembly); synthesis (scalable processing)