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PreprintCC BY-NC-NDChemRxiv

Site-Specific Speciation of Vanadium Sites on γ-Al2O3 Facets and Edges from 51V SSNMR Spectroscopy

  • Weicheng Cao1,2
  • Charles Sidhoum1,2
  • Andri Florin1,2
  • Christophe Copéret1,2
  1. 1Department of Chemistry and Applied Biosciences
  2. 2Zürich
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Abstract

γ-alumina (γ-Al2O3) supported vanadium oxide represent a notable class of heterogenous catalysts used for the direct oxidative propane dehydrogenation (ODH) reaction. However, while the presence of highly dispersed VOx (V5+) species has been established, understanding the exact structure of surface sites and the role of supports remains a pivotal objective for establishing structure-property relationships. Considering the structural complexity of γ-Al2O3 surfaces, where distinct surface sites emerge as a function of specific facets and edges, clarifying how the support dictates vanadium speciation remains a key objective. In this work, we employ Surface Organometallic Chemistry (SOMC) approach to evaluate the impact of the γ-Al2O3 nanocrystals morphology on the nature and structure of surface vanadium sites. Specifically, we grafted vanadyl isopropoxide (VO(OiPr)3) on tailored γ-Al2O3 nanocrystals, namely Rhomboids, Laths and Needles, exposing varying distributions of (110), (100) and (111) facets along with characteristic edges sites. Subsequent calcination yields supported, organic-ligand-free, monomeric vanadia sites. Advanced 51V solid-state NMR spectroscopy combined with DFT calculations reveals that grafting on γ-Al2O3 partially dehydroxylated at 500 °C directly generate bipodal VO(OiPr) species, whose structures depend on the underlying surface facets and edge sites. Furthermore, the supported vanadia sites formed upon calcination are also characterized by distinct V-O coordination numbers and hydroxylation states, which are quantitatively resolved across γ-Al2O3 morphologies. This work not only elucidates the complex speciation of V supported on γ-Al2O3 support, but also offers fundamental insights into the reactive surface sites on γ-Al2O3 that stabilize isolated metal species.

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Cite

BibTeXRIS
BibTeX
@misc{cao2026sitespecific,
  title = {{Site-Specific Speciation of Vanadium Sites on γ-Al2O3 Facets and Edges from 51V SSNMR Spectroscopy}},
  author = {Weicheng Cao and Charles Sidhoum and Andri Florin and Christophe Copéret},
  howpublished = {ChemRxiv},
  year = {2026},
  month = sep,
  doi = {10.26434/chemrxiv.15008342/v1},
  url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008342/v1},
  note = {CC BY-NC-ND},
}
RIS
TY  - UNPB
TI  - Site-Specific Speciation of Vanadium Sites on γ-Al2O3 Facets and Edges from 51V SSNMR Spectroscopy
AU  - Weicheng Cao
AU  - Charles Sidhoum
AU  - Andri Florin
AU  - Christophe Copéret
PY  - 2026
DA  - 2026/09/04
PB  - ChemRxiv
DO  - 10.26434/chemrxiv.15008342/v1
UR  - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008342/v1
AB  - γ-alumina (γ-Al2O3) supported vanadium oxide represent a notable class of heterogenous catalysts used for the direct oxidative propane dehydrogenation (ODH) reaction. However, while the presence of highly dispersed VOx (V5+) species has been established, understanding the exact structure of surface sites and the role of supports remains a pivotal objective for establishing structure-property relationships. Considering the structural complexity of γ-Al2O3 surfaces, where distinct surface sites emerge as a function of specific facets and edges, clarifying how the support dictates vanadium speciation remains a key objective. In this work, we employ Surface Organometallic Chemistry (SOMC) approach to evaluate the impact of the γ-Al2O3 nanocrystals morphology on the nature and structure of surface vanadium sites. Specifically, we grafted vanadyl isopropoxide (VO(OiPr)3) on tailored γ-Al2O3 nanocrystals, namely Rhomboids, Laths and Needles, exposing varying distributions of (110), (100) and (111) facets along with characteristic edges sites. Subsequent calcination yields supported, organic-ligand-free, monomeric vanadia sites. Advanced 51V solid-state NMR spectroscopy combined with DFT calculations reveals that grafting on γ-Al2O3 partially dehydroxylated at 500 °C directly generate bipodal VO(OiPr) species, whose structures depend on the underlying surface facets and edge sites. Furthermore, the supported vanadia sites formed upon calcination are also characterized by distinct V-O coordination numbers and hydroxylation states, which are quantitatively resolved across γ-Al2O3 morphologies. This work not only elucidates the complex speciation of V supported on γ-Al2O3 support, but also offers fundamental insights into the reactive surface sites on γ-Al2O3 that stabilize isolated metal species.
ER  -