Understanding the Synthesis of Supported Vanadium Oxide Catalysts Using Chemical Grafting

Abstract

The complexity of variables during incipient wetness impregnations ynthesiso fs upported metal oxides precludes an in-depth understandingo ft he chemical reactions governing the formation of the dispersed oxide sites. This contributiond escribes the use of vapor phase deposition chemistry (also known as grafting) as at ool to systematically investigate the influence of isopropanol solvento nV O(O i Pr) 3 anchoring during synthesis of vanadiumo xide on silica. The availability of anchorings ites on silicaw as found to depend not only on the pretreatment of the silica but also on the solventp resent. H-bond donors can reduce the reactivity of isolateds ilanols whereas disruption of silanoln estsb yHbond acceptors can turn unreactive H-bonded silanols into reactivea nchoring sites. The models uggested here can inform improved syntheses with increased dispersion of metal oxidesons ilica.

Proton-Detected Multidimensional Solid-State NMR Enables Precise Characterization of Vanadium Surface Species at Natural Abundance

“…Here we present the use of multidimensional 1 H-detected solid-state NMR (ssNMR) experiments at high spinning rates in conjunction with computational studies to identify surface sites using supported vanadium compounds prepared via surface organometallic chemistry as a prototypical example because they are an important precursor to model supported vanadium oxide catalysts used in a broad range of applications − and because their structure is still debated in the literature. , In this work, we demonstrate how proton-detected ssNMR spectroscopy enables acquiring high-quality NMR spectra for low-abundant (<1%) surface species without the need for labeling. As a showcase example, we will focus on elucidating the local environment of grafted vanadium species. , …”

“…Reference appeared during the course of the evaluation process, where similar detection schemes were used, albeit at lower spinning frequencies, thus not allowing high proton resolutions.…”

“…As a showcase example, we will focus on elucidating the local environment of grafted vanadium species. 33,34 We thus first prepared supported V(V) species via SOMC by grafting VO(O i Pr) 3 on partially dehydroxylated silica at 700 °C that contains mostly isolated OH groups. 35 Figure 1 shows the general scheme and the potential structures that are formed after grafting the precursor on dehydroxylated silica.…”

The Molecular and Electronic Structure of Isolated Platinum Sites Enabled by Expedient Measurement of 195Pt Chemical Shift Anisotropy

“…However, direct NMR experiments on the metal nucleus of supported catalysts are challenging because of the typically low metal loadings. Consequently, NMR experiments have traditionally been limited to highly receptive isotopes of metals such as aluminum, 39 scandium, 21 vanadium, [40][41] niobium 18 and/or isotopically enriched materials. 22,[42][43] Recently, sensitivity-enhancement by dynamic nuclear polarization (DNP) or proton detection has enabled NMR experiments on catalysts featuring unreceptive nuclei.…”

The photoelectron-imaging spectroscopic study and chemical bonding analysis of VO2−, NbO2− and TaO2−

“…In addition, these investigations and valuable reactions inspired us to design supported metal oxide catalysts at the molecular level. [4][5][6] As the reactivity of supported catalysts is known to depend on the particle size of catalysts, there has been a focus on the chemistry of gas-phase size-selected oxide clusters as model catalytic systems. [7][8][9][10][11][12][13] Moreover, vanadium, niobium and tantalum oxides have been extensively studied in the gas phase and solid matrices via spectroscopy.…”