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By combining multinuclear 1H, 29Si, 27Al and 51V solid-state NMR experimental measurements with reactivity and selectivity data, as well as first-principles calculations, for ternary bi-layered supported VO x /Al 2 O 3 /SiO 2 catalysts, the structure of the dehydrated surface vanadia species was determined for each combination of supported VO x and AlO x active components. The specific structure of the surface vanadia sites in the ternary bi-layered supported VO x /Al 2 O 3 /SiO 2 catalyst system have been investigated for the first time. The following vanadia sites are proposed based on the current findings: At low vanadia content, surface VO(OH)(OSi) 2 sites form on the alumina-free surface of the SiO 2 support in the bi-layered supported VO x /Al 2 O 3 /SiO 2 catalyst system. In addition, two types of VO(OSi) 3 surface species are likely present in this system. On small alumina clusters, weakly bonded surface VO(OH)(OAl) 2 sites also form, along with the sites containing mixed Si/Al pods VO(OH)(OAl)(OSi). As the size of alumina clusters increases, strongly bonded VO(OAl) 3 centers form, alongside the surface sites containing mixed pods VO(OAl) 2 (OSi) and VO(OAl)(OSi) 2. The content of these sites increases with the loading of vanadia. Comparing supported VO x /SiO 2 , VO x /Al 2 O 3 , and bi-layered VO x /Al 2 O 3 /SiO 2 catalyst systems revealed differences in catalytic activity due to the presence of new sites with different pods, with OH groups as well as the influence of Al-O-Si bonds on the electronic structure of surface vanadia sites on the alumina clusters. During the formation of dimethyl ether (DME), the turnover frequency (TOF DME) of the catalysts decreases with increasing domain size of the alumina clusters on SiO 2. Addition of surface VO x sites, however, slightly decreases the TOF DME with the higher vanadia content weakening the activity of the alumina clusters. When surface VO x exists predominantly as V/Al 1 and V/Al 2 , TOF redox depend on the vanadia content with lower vanadia content resulting in higher the TOF redox values. The 51V NMR spectra show that this decrease in redox TOF value correlates with the appearance of vanadia sites associated with silica pods. The activity of the catalysts was tested in methanol conversion reactions. [Display omitted] • Various VO x sites were studied in bi-layered supported VO x /AlO x /SiO 2 catalysts. • VO(OH)(OSi) 2 and VO(OSi) 3 sites are formed at low and high VO x loading on SiO 2 • VO x sites weakly and strongly bound to AlO x clusters are formed in ternary system. • Weakly bound VO(OH)(OAl) 2 and mixed pods VO(OH)(OAl)(OSi) sites have OH groups. • VO(OAl) 3 and mixed pods VO(OAl) 2 (OSi), VO(OAl)(OSi) 2 are strongly bonded sites. [ABSTRACT FROM AUTHOR]

Biomass pyrolysis by solid acid catalysts is one of many promising technologies for sustainable production of hydrocarbon liquid fuels and value‐added chemicals, but these complex chemical transformations are still poorly understood. A series of well‐defined model SiO2‐supported alumina catalysts were synthesized and molecularly characterized, under dehydrated conditions and during biomass pyrolysis, with the aim of establishing fundamental catalyst structure–activity/selectivity relationships. The nature and corresponding acidity of the supported AlOx nanostructures on SiO2 were determined with 27Al/1H NMR and IR spectroscopy of chemisorbed CO, and DFT calculations. Operando time‐resolved IR–Raman–MS spectroscopy studies revealed the molecular transformations taking place during biomass pyrolysis. The molecular transformations during biomass pyrolysis depended on both the domain size of the AlOx cluster and molecular nature of the biomass feedstock. These new insights allowed the establishment of fundamental structure–activity/selectivity relationships during biomass pyrolysis. Defining the relationship: A series of well‐defined model SiO2‐supported alumina catalysts were synthesized and molecularly characterized with the aim of establishing fundamental catalyst structure–activity/selectivity relationships. The nature and acidity of the supported AlOx nanostructures on SiO2 were determined with 27Al/1H NMR and IR spectroscopy of chemisorbed CO, and DFT calculations. [ABSTRACT FROM AUTHOR]

Two sets of silica-supported nickel phosphide catalysts with a nickel content of about 2.5 and 10 wt % and Ni/P molar ratio 2/1, 1/1 and 1/2 in each set, were prepared by way of a temperature-programmed reduction method using (Ni(CH3COO)2) and ((NH4)2HPO4) as a precursor. The NixPy/SiO2 catalysts were characterized using chemical analysis N2 physisorption, XRD, TEM, 31P MAS NMR. Methyl palmitate hydrodeoxygenation (HDO) was performed in a trickle-bed reactor at 3 MPa and 290 °C with LHSV ranging from 0.3 to 16 h-1. The Ni/P ratio was found to affect the nickel phosphide phase composition, POx groups content and catalytic properties in methyl palmitate HDO with the TOF increased along with a decline of Ni/P ratio and a growth of POx groups' content. Taking into account the possible routes of methyl palmitate conversion (metal-catalyzed hydrogenolysis or acid-catalyzed hydrolysis), we proposed that the enhancement of acid POx groups' content with the Ni/P ratio decrease provides an enhancement of the rate of methyl palmitate conversion through the acceleration of acid-catalyzed hydrolysis. [ABSTRACT FROM AUTHOR]

Abstract: In this article we will discuss the potentiality of solid-state 51V NMR technique to characterize heterogeneous catalysts containing paramagnetic cations located on the surface or incorporated in the bulk of heterogeneous catalysts. 51V NMR data for a number of 3d and rare earth vanadates, where paramagnetic effects are caused by the presence of paramagnetic cations, are considered. We also summarize results available for vanadium bronzes, where some vanadium is in a paramagnetic V4+ state, and for some vanadium compounds, where closely spaced paramagnetic centers form diamagnetic pairs. The comprehensive 51V chemical shift scale (database) for paramagnetic solids was compiled. [Copyright &y& Elsevier]

Vanadium and niobium species (together and separately) were loaded on gamma alumina, and the resulting catalysts were run in the methanol conversion. This reaction was studied by both GC analysis and FTIR study in the flow system. The catalytic properties are discussed based on the combined FTIR and 27Al, 51V and 1H MAS NMR studies. The NMR studies revealed a different mechanism of interaction between Nb and Al2O3 than that between V and Al2O3. This predetermines the structure of vanadium sites in bimetallic VNb/Al samples. The effect of coverage was considered for various metal loadings ranging from below to above monolayer. One of our most interesting findings is that the surface Nb oxide species exhibited a redox character below monolayer but were acidic above monolayer. 27Al MAS NMR revealed a strong alumina–Nb interaction that may account for its redox performance. Moreover, the role of sulfate from vanadium precursor is evidenced. [Copyright &y& Elsevier]

Abstract: A series of catalytic filamentous carbons (CFC) obtained from gas phase reaction on iron subgroup metal catalysts was studied by 129Xe NMR. A connection between 129Xe NMR parameters and structural, textural and paramagnetic properties of CFC was discussed. The chemical shift (δ) was shown to depend on the structure of the CFC surface formed by edge, basal or both (edge and basal) graphite faces. This dependence follows a general trend of the chemical shift to increase with adsorption potential of a surface. The term describing Xe–Xe interaction (δ Xe–Xe) in confined space decreased with the average pore size of CFC granule. For hollow multi-wall carbon nanotubes two 129Xe NMR signals were attributed to voids inside nanotubes and to interstices between the interlaced nanotubes. However, analysis of experimental data is complicated due to the presence of paramagnetic metal particles necessary to the filament growth. Therefore, ESR data are given and correlated with 129Xe NMR results. [Copyright &y& Elsevier]