Fast (60 kHz) magic angle spinning solid-state NMR allows very sensitive proton detection in highly paramagnetic organometallic powders. We showcase this technique with the complete assignment of 1H and 13C resonances in a high-spin Fe(ii) polymerisation catalyst with less than 2 mg of sample at natural abundance.

Optimization of supported heterogeneous catalysts requires a careful control of their synthesis conditions and in particular of the metal impregnation step. This paper presents a theoretical and experimental study of both dry and diffusional impregnation of Ni/γ-Al2O3 catalysts. The advanced characterization technique Magnetic Resonance Imaging was used to monitor in-situ the impregnation step, which provided the necessary information to develop the model. The model accurately describes the active phase distribution during impregnation by taking into account capillarity (in the case of dry impregnation), diffusion in the fluid phase and adsorption/desorption phenomena. It was demonstrated that the adsorption of nickel ions on the alumina surface is extremely fast, favoring the removal of metal ions from the fluid phase. As a consequence, the limiting step of impregnation is the diffusion of nickel ions in the fluid phase. A good agreement between experimental and simulated results was achieved by adjusting only two parameters, namely total concentration of the active sites and adsorption equilibrium constant. By neglecting capillary action and using the same optimized parameters, the model also allowed describing diffusional impregnation, which illustrates its robustness. This model can predict the distribution of the active phase in the support as a function of the impregnation conditions and can therefore be applied as a new tool to optimize the impregnation step of heterogeneous catalysts.

An in situ characterization methodology based on the magnetic resonance imaging (MRI) and Raman imaging is applied to investigate the effect of citric acid in the impregnation step of molybdenum catalysts promoted with cobalt in the presence of phosphorus and supported on γ-alumina. MRI provides temporal and spatial information of the transport of species of the impregnation solutions within the porosity with a spatial resolution of 39 × 39 µm. Raman imaging gives information about the chemical nature of the species deposited on the support with a spatial resolution of 16.2 × 16.2 µm. The effect of citric acid strongly depends on the ratio between the additive and molybdenum used in the impregnation solution. For a ratio of 0.2, at the end of impregnation, molybdenum ions are in an egg-yolk distribution either in polymeric or monomeric form. For a ratio of 0.7, cobalt ions can be either in the form of aqua complexes in an egg-yolk distribution or in the form of H 2 PMo 11 CoO 40 5− heteropolyanion, which can improve the proximity between molybdenum and cobalt ions. This work gives new insights concerning the role of citric acid on the metal distribution profiles obtained at the end of impregnation, which can be used to control the final active phase distribution.

Nitrogen-containing compounds, present in gas oils (GO) or vacuum gas oils (VGO) cuts, affect many of the important petroleum processes such as hydrocracking and hydrotreating due to their nucleophilic character. Basic nitrogen compounds, which can inhibit the acidic sites of the catalysts, are mainly pyridine derivatives (6-membered-ring nitrogen compounds), and despite the use of highly resolutive methods, their characterization, especially in VGO, is still limited. Herein, we propose a new promising methodology, coupling the derivatization with BF3 of nonprotogenic nitrogen species and the use of NMR analysis. By crossing information from F-19, H-1, H-1-F-19 HMBC and F-19 DOSY, it is possible to determine the close environment of the nitrogen atom of the most nucleophilic nitrogen impurities in GO or in VGO cuts, independently of the sizes of the molecules. This approach allows the characterization and comparison of fingerprints of basic nitrogen impurities in charges or effluents.

Magnetic Resonance Imaging is applied, for the first time, to monitor in-situ the impregnation step of hydro treatment catalysts with an aqueous solution composed simultaneously of molybdenum, cobalt and phosphorus. This technique provides information about spatial distribution of all metal precursors inside the catalyst pellet with a significantly improved spatial resolution of 39 mu m x 39 mu m compared to the literature. Streamline Raman Imaging yields complementary information about molybdenum speciation at equilibrium. For a molybdenum based catalyst, a slow transport of molybdenum complexes through gamma-alumina is observed by Magnetic Resonance Imaging, which suggests a strong interaction between metal precursor and the support. Presence of polymeric molybdenum ions is found near the edges as well as the formation of an Anderson-type heteropolyanion. In the presence of phosphorus, interaction between molybdenum and gamma-alumina is weaken since a preferential adsorption to phopshorus is observed. This phenomenon results in an increase in the transport rate of molybdenum complexes. When phosphorus is added to a molybdenum based catalysts promoted by cobalt, preferential interactions between metal promotor and the support are observed rather than with molybdenum species. This innovative Magnetic Resonance Imaging -Streamline Raman Imaging methodology allows a better control of the deposition process during impregnation and to identify the descriptors that most influence this preparation step. Finally, this methodology can be applied to other type of supported catalysts.

2D-EXSY and PFG 129Xe NMR provide a powerful means for probing tortuosity and pore connectivity in bimodal alumina catalysts.

In petroleum refining, gamma-alumina is used as a solid support of molybdenum nickel/cobalt promoted catalysts for the hydrotreatment processes, such as hydrodesulfurization. The ever decreasing norms for the sulfur content in gasoline require better and more efficient catalysis, prompting extensive research on the materials and the factors influencing the activity, selectivity and stability of the catalytic processes. In the present study, Magnetic Resonance Imaging Single Point Imaging is tested as a tool to monitor the impregnation of fly-alumina pellets with Ni(NO3)(2) aqueous solutions at varying Ni2+ concentration. The method enables a study in the presence of paramagnetic elements in the alumina support, in the conditions of very fast T-1 and T-2. It is shown that at higher concentrations of metal ions a homogenous distribution in the support is attained faster. A non-linear dependence is observed and a minimum ion concentration of 0.2 M is necessary for achieving short impregnation times of alumina pellets of millimeter size scale. (C) 2015 Elsevier B.V. All rights reserved.

Crystalline mesoporous gamma-, delta-, and theta-alumina samples with complex porosity and various surface areas (70 to 330 m(2)/g) were characterized by Xe-129 NMR spectroscopy and nitrogen adsorption. Experimental conditions have been optimized to measure Xe-129 NMR chemical shifts independent of the nature of the surface and solely dependent on the pore size. Xenon adsorption constants have been determined from xenon adsorption isotherms and from the fit of the chemical shift versus volume to surface ratio (V/S) curves with a simple exchange model. The discrepancy observed between those values has been attributed to the rugosity of the alumina pore surface. A direct correlation between the observed chemical shift and the alumina pore diameter was obtained for the whole series of alumina samples.

A wheat straw soda lignin was characterized and converted into gases and liquids under H2 pressure, at 350°C over a supported NiMo sulfide catalyst, using tetralin as a hydrogen-donor solvent in a batch autoclave. The aim of this work was to evaluate the transformations occurring during the temperature increasing step to reach a pseudo-t0 and the impact of the catalyst presence in the mixture. A well-developed products separation protocol made possible to isolate and to characterize gases, organic liquid, lignin residue and solids (catalyst and char). A limited quantity of solids (or char) was produced however. As the lignin residue is one of the main intermediates of the lignin conversion pattern, the nature of this material has to be carefully determined. Thanks to several appropriate characterization techniques (GPC, NMR, FTIR), the conversion was followed and the lignin residue was compared to the initial lignin in order to understand the transformations occurring during the process.

Low temperature CO adsorption followed by IR spectroscopy (IR/CO) characterization was used to depict the MoS2 morphology change with sulfidation temperature on MoS2/Al2O3 catalyst. It is found that the morphology of MoS2 slabs on MoS2/Al2O3 catalyst under typical sulfidation temperature range (573 to 723 K) is a truncated triangle exposing both the M-edge and S-edge. Moreover, the IR/CO data indicate that the truncation degree (ratio of S-edge/M-edge) of MoS2 slabs gradually increases with increasing sulfidation temperature. This finding is in line with density functional theory calculation on model catalysts, providing IR evidence of MoS2 morphology change with sulfidation temperature on an Al2O3-supported catalyst. As a further step, it is also found that the MoS2 morphology is strongly influenced by MoS2-Al2O3 interactions under the same sulfidation temperature.

In this study, reaction pathway of a woody biomass under hydrothermal conditions is investigated in order to further understand reactions that occur during the thermochemical liquefaction of a lignocellulosic biomass. A multitechnique analytical approach combining chromatographic and spectroscopic techniques has been developed in order to characterize both chemical structure and molecular weight of the products. From our experiments, we can assume that the holocellulosic and the ligneous fractions of biomass have different reactivity under hydrothermal condition. Although hydrothermal conversion of holocellulose and lignin occur both according to a complex pathway composed of competitive fragmentation and condensation reactions, holocellulose reacts first by total fragmentation to low molecular weight compounds followed by the condensation of the fragment to heavy molecular weight compounds, whereas lignin reacts essentially by partial depolymerisation. Since compounds produced from both the holocellulosic cind the ligneous fraction are together in the reaction medium then they condense each other during the conversion of lignocellulosic material.

MoS2 catalysts were firstly prepared over three different alumina supports γc-Al2O3, γT-Al2O3, and δ-Al2O3 with the same Mo loading per nm2. Then, using various deposition methods and different Co-precursors as Co(NO3)2, Co(acac)2 and Co(CO)3NO, Co-promoted MoS2 catalysts were obtained. The different catalytic systems were tested in hydrodesulfurization (HDS) reactions of thiophene and 4.6-dimethyldibenzothiophene (4,6-DMDBT) under atmospheric and high pressure (4 MPa), respectively. For the non-promoted catalysts, we observed for δ-alumina supported system a higher intrinsic catalytic activity than for γc-Al2O3 and γT-Al2O3. For the Co-promoted systems, the use of cobalt organometallic complex allowed obtaining catalysts which exhibit higher intrinsic activity than the catalysts prepared by impregnation of Co inorganic salts on supported Mo sulfide. Furthermore, the intrinsic catalytic activities of promoted systems obtained with δ-alumina support were always higher than for the classical γ-alumina. This support effect can be partially explained and supported by physicochemical characterization results of XPS and IR of adsorbed CO at low temperature (77 K).

The aim of this work was to investigate the influence of the catalyst acidity in vacuum residues hydroconversion processes. To achieve this goal, a grafting procedure was applied in order to incorporate silicon at the surface of alumina carriers. The corresponding NiMoP catalysts with different silicon amounts in the support were evaluated in order to assess the conversion rate and mechanism of a Safaniya vacuum residue in a batch reactor at 370 degrees C. A multi-techniques set of analyses was used, in order to characterize both the sulphided active phase (TEM, XPS, IR-CO, model molecules test) and acidity (IR-CO, model molecules tests). We also confirm that support texture was not modified by the incorporation of silicon.Grafting procedure allows to both control textures but also hydrogenation rate, the one being assessed by toluene hydrogenation. In addition, acidity strength of the catalysts was slightly increased. Nevertheless, it remains obvious that nickel disponibility (i.e. in surface of the catalyst) must be affected with higher concentration of silicon. It leads to significant modifications in the active phase features. As a matter of fact, NiMoP catalysts with same texture, same hydrogenating power, but also different level of acidity reveal no change in conversion (chi 370+ and chi 540+ and HDAsC7) or hydrogenation performance (HDS, HDV). Nevertheless, it is proved that acidity can enhance the cracking of aliphatic chains of asphaltenes without increasing their aromaticity. It could provide an original way of cracking of asphaltenes different from the well known thermal mechanisms. This new way of transformation opens the way to a complete change of reactivity over the whole HDT processes. (C) 2013 Elsevier B.V. All rights reserved.

The hydrothermal conversion takes advantage of the singular physico-properties of the hot and compressed water which can be considered as a green solvent. The hydrothermal conversions of an alkali lignin and of phenolic model compounds (vanillin, monobenzone, 2,2'-biphenol) have been studied at 370 and 390 degrees C, at 25 MPa between 5 and 40 min. Polydispersity of products in term of both chemical structures and molecular weights has been characterized through a new analytical approach combining chromatographic (GC) and spectrometric techniques (Fourier transform ion cyclotron mass spectrometry FT-ICR/MS, NMR). From our experiments, it is clear that lignin conversion occurs via a complex reaction pathway where competitive fragmentation and condensation reactions occur. An original reaction pathway has been suggested from the main emphasized reactions. (C) 2012 Elsevier Ltd. All rights reserved.

The objective of this work was to study the adsorption and separation of the most important families of hydrocarbon compounds on metal-organic frameworks (MOFs), in comparison with zeolites. For this purpose, we have selected four probe molecules, each of them representing one of these families, i.e., o- and p-xylene as aromatics, 1-octene as an alkene, and n-octane as an alkane. The separation of these four molecules was studied by binary breakthrough experiments. To represent the large diversity of MOF structures, the experiments were carried out with (i) two MOFs with coordinatively unsaturated metal sites (CUS), i.e., Cu-btc (HKUST-1) and CPO-27-Ni, (ii) a MOF with an anionic framework and extraframework cations, i.e. RHO-ZMOF, and (iii) two rather apolar zeolitic imidazolate framework (ZIF) materials with different pore sizes, i.e. ZIF-8 and ZIF-76. Zeolite NaY and zeolite β were used as polar and apolar reference adsorbents, respectively. The results can be briefly summarized as follows: ZIFs (not carrying any polar functional groups) behave like apolar adsorbents and exhibit very interesting and unexpected molecular sieving properties. CUS-MOFs behave like polar adsorbents but show the specificity of preferring alkenes over aromatics. This feature is rationalized thanks to DFT+D calculations. MOFs with extraframework cations behave like polar (cationic) zeolites.

The nature of acid sites on amorphous silica–alumina (ASA) is strongly debated, as well as their infrared signature. We report a combined experimental and computational study to unravel this challenging question at the atomic scale, focusing on proton transfer from ASA to lutidine (2,6-dimethylpyridine), an experimentally widely used molecule for probing Brønsted acid sites. The ASA surface model obtained by density functional theory (DFT) calculations is validated by the comparison of infrared frequencies of OH-groups with experimental spectra. The bands observed are assigned to the various OH-groups present, as a function of their hydrogen-bond donor character and of the proximity of silanols toward aluminum atoms. The affinity of lutidine (2,6-dimethylpyridine) for each site of the ASA surface is then evaluated by sampling the DFT model and varying the experimental pretreatment conditions. A general rule is established for Brønsted acidity of ASA, by comparison with calculations on reference silica, alumina, and mordenite models: the driving force for the proton transfer from OH-groups to lutidine is the stabilization of the conjugated base (after deprotonation) of the hydroxyls, more than the intrinsic acidity of the OH-group. Pseudo-bridging silanols (PBS) are thus found to be capable of proton transfer, thanks to the stabilization of silanolate species by the formation of additional O–Al and O–Si bonds. A prominent role of water molecules adsorbed on Al atoms is also shown: they act as a proton reservoir to express intrinsic acidity and to promote the acidity of neighboring silanols. Finally, we suggest that the ν˜8a and the ν˜8b modes of lutidinium species are inverted with regards to lutidine, contrary to what was previously thought on the basis of empirical data.

1H DOSY NMR experiments were used to investigate the macrostructure of the asphaltenes of Maya, Athabasca, and Buzurgan feedstocks in toluene-d8 at 20 °C. The influence of the concentration of asphaltenes on their diffusion coefficients is presented for the three asphaltenes. A separation between two classes of aggregates—one diffusing quickly and one diffusing more slowly—was observed at an onset concentration that is dependent upon the origin of the sample. This illustrates that the chemical interactions (and, hence, the chemical structures) are different for the three asphaltenes. Because asphaltenes are a continuum of both archipelago and continental asphaltenes, the interactions in the solutions differ, depending on the repartition between archipelago- and continental-type asphaltenes in the feed. Maya and Buzurgan asphaltenes show similar diffusion properties in the dilute regime, while Athabasca asphaltenes diffuse more slowly. Results obtained from DOSY experiments data seem to indicate that Buzurgan asphaltenes show a more continental character than the two other asphaltenes, while Athabasca asphaltenes seem to contain more archipelago asphaltenes. 1H and 13C NMR experiments were also performed to determine the average structural parameters of asphaltenes. Average sizes and molecular weights were determined from the 1H-DOSY NMR diffusion coefficients and compared to size exclusion chromatography (SEC) data.