SOMC grafting of vanadium oxytriisopropoxide (VO(OⁱPr)₃) on dehydroxylated silica; analysis of surface complexes and thermal restructuring mechanism

Abstract

VO(OiPr)3 was grafted on highly dehydroxylated silica by a surface organometallic chemistry approach and its thermal evolution was analyzed with support of DFT calculations.

Understanding the Synthesis of Supported Vanadium Oxide Catalysts Using Chemical Grafting

“…The isotropic shift position, linewidth, and C Q values for peak 2 in the V+ i PrOH/SiO 2(700) and V+ i PrOH/TMS‐SiO 2(700) spectra are all consistent with a monopodal 51 V site with a weak fifth coordination to a nearby Si−O− i Pr group (Figure , inset), as we have suggested previously . Other groups using different synthesis procedures have proposed a bipodal vanadium site with two surface bonds, however C Q values were not reported for these species …”

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

“…A 1 H NMR spectrum acquired on a 700 MHz spectrometer using a 1.3 mm rotor and a spinning rate of 50 kHz (Figure A) shows detailed features that were not observed in previous studies , due to the poorer resolution resulting from the use of typical, albeit low, rotor spinning rates (ca. 10 kHz) .…”

“…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. , …”

“…No additional sharp signal at −630 ppm is observed, consistent with the absence of remaining physisorbed molecular precursor. 31,32 We then further analyzed this sample by correlation spectroscopy in view of the greatly improved resolution and sensitivity gained on the 1 H spectrum under these fast MAS conditions. A 2D DQ−SQ 1 H− 1 H correlation spectrum was acquired within a couple of hours using a single rotor period of recoupling using the BABA sequence 37 (Figure 2C), where the signals at around 2 ppm show a correlation with 4 ppm in the indirect dimension and can therefore be attributed with its self-correlation that can therefore be assigned the methyl groups.…”

Increasing the Efficiency of Optimized V-SBA-15 Catalysts in the Selective Oxidation of Methane to Formaldehyde by Artificial Neural Network Modelling

“…Different methods for preparation are known in the literature, yielding catalysts with varying properties and distribution of VO x species. The most prominent ones are wet and incipient wetness impregnation [8,9] and ion exchange [10,11] of vanadium salts, grafting of molecular precursors [12][13][14] and direct preparation via in situ methods during silica synthesis. The latter was applied for different kinds of V-SiO 2 materials as the successful synthesis of V-SBA-15 [5,6,[15][16][17], V-SBA-3 [18], V-MCM-41 [5,19,20], V-MCM-48 [21] or V-MCF [22] catalysts for different catalytic applications demonstrates.…”