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Lebarbier V.,CNRS Catalysis and Spectrochemistry Laboratory | Houalla M.,CNRS Catalysis and Spectrochemistry Laboratory | Onfroy T.,CNRS Surface Science Lab
Catalysis Today | Year: 2012

The development of Bronsted acidity and the relationship between acidity, catalytic performance and structure of niobium oxide were investigated for a series of samples prepared by calcination of niobic acid at temperatures between 423 and 823 K. All solids were active for propan-2-ol dehydration. The Bronsted acidity was monitored by adsorption of lutidine and CO followed by FT-IR. Low temperature CO adsorption measurements showed that all solids exhibit essentially the same medium Bronsted acid strength. A direct relationship between the abundance of Bronsted acid sites monitored by lutidine adsorption followed by desorption at 523 K and propan-2-ol dehydration activity was observed. © 2012 Elsevier B.V.


Meunier F.C.,CNRS Research on Catalysis and Environment in Lyon | Scalbert J.,CNRS Catalysis and Spectrochemistry Laboratory | Thibault-Starzyk F.,CNRS Catalysis and Spectrochemistry Laboratory
Comptes Rendus Chimie | Year: 2015

The combination of kinetic and thermodynamic analyses can provide an in-depth knowledge of the crucial steps of catalyzed reactions. Earlier examples are recalled to stress how a reaction mechanism can be supported or rejected based on trivial reactant and product concentration analyses. The method is then applied to the important reaction of alcohol condensation, the so-called Guerbet reaction, which enables converting ethanol, a renewable feedstock, into higher alcohols. Important conclusions regarding the design of ethanol condensation processes can be drawn, as the main reaction mechanism occurring at high temperatures (ca. 350-420 °C) appears to be different from that proposed at low temperatures (< 250 °C). In the former case, the pathway involving acetaldehyde is negligible, and therefore a multi-step process based on ethanol dehydrogenation followed by acetaldehyde self-aldolization would be irrelevant. © 2014 Académie des sciences. Published by Elsevier Masson SAS.


Aldana P.A.U.,CNRS Catalysis and Spectrochemistry Laboratory | Ocampo F.,University of Strasbourg | Kobl K.,University of Strasbourg | Louis B.,University of Strasbourg | And 5 more authors.
Catalysis Today | Year: 2013

Despite several studies, the use of CO2 as a chemical reactant is currently limited to a few processes. With the aim to formulate an efficient catalyst for CO2 conversion into methane, nickel was selected, being well known to be active for the catalytic COx methanation. Ceria-zirconia mixed oxide was chosen as a support because of its properties to activate CO2. Yields close to those predicted by thermodynamic were obtained with weak deactivation even after 90 h on stream. Interactions between Ni and the ceria-zirconia support seem to be a key parameter for the methanation reaction. The use of IR operando spectroscopy revealed that the main mechanism for CO2 methanation does not require CO as reaction intermediate. The better activity observed compared to Ni-silica can be explained by the importance of weak basic sites the adsorption of CO2. © 2013 Elsevier B.V. All rights reserved.


Van De Voorde B.,Catholic University of Leuven | Boulhout M.,Aix - Marseille University | Vermoortele F.,Catholic University of Leuven | Horcajada P.,University of Versailles | And 10 more authors.
Journal of the American Chemical Society | Year: 2013

The influence of the metal ion in the mesoporous metal trimesate MIL-100(Al3+, Cr3+, Fe3+, V3+) on the adsorptive removal of N/S-heterocyclic molecules from fuels has been investigated by combining isotherms for adsorption from a model fuel solution with microcalorimetric and IR spectroscopic characterizations. The results show a clear influence of the different metals (Al, Fe, Cr, V) on the affinity for the heterocyclic compounds, on the integral adsorption enthalpies, and on the uptake capacities. Among several factors, the availability of coordinatively unsaturated sites and the presence of basic sites next to the coordinative vacancies are important factors contributing to the observed affinity differences for N-heterocyclic compounds. These trends were deduced from IR spectroscopic observation of adsorbed indole molecules, which can be chemisorbed coordinatively or by formation of hydrogen bonded species. On the basis of our results we are able to propose an optimized adsorbent for the deep and selective removal of nitrogen contaminants out of fuel feeds, namely MIL-100(V). © 2013 American Chemical Society.


Vermoortele F.,U-Systems | Ameloot R.,U-Systems | Vimont A.,CNRS Catalysis and Spectrochemistry Laboratory | Serre C.,University of Versailles | De Vos D.,U-Systems
Chemical Communications | Year: 2011

After controlled pretreatment, some Zr-terephthalate metal-organic frameworks are highly selective catalysts for the cross-aldol condensation between benzaldehyde and heptanal. The proximity of Lewis acid and base sites in the amino-functionalized UiO-66(NH2) material further raises the reaction yields. © 2011 The Royal Society of Chemistry.


Yoon J.W.,Korea Research Institute of Chemical Technology | Seo Y.-K.,Korea Research Institute of Chemical Technology | Hwang Y.K.,Korea Research Institute of Chemical Technology | Chang J.-S.,Korea Research Institute of Chemical Technology | And 12 more authors.
Angewandte Chemie - International Edition | Year: 2010

"Figure Presented" Gas grabber: Reduction of the porous metal-organic framework MIL-100(Fe) (see picture; X-: OH- or F-; red: O of trimesate ligands) to form coordinatively unsaturated sites at iron(II) (depicted as a violet circle) is essential for selective gas purification or the selective removal of unsaturated gas impurities. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.angewandte.org.


Guo Y.,Humboldt University of Berlin | Wuttke S.,Ludwig Maximilians University of Munich | Vimont A.,CNRS Catalysis and Spectrochemistry Laboratory | Daturi M.,CNRS Catalysis and Spectrochemistry Laboratory | And 3 more authors.
Journal of Materials Chemistry | Year: 2012

The fluorolytic sol-gel route sets a milestone in the development of synthesis methods for nanoscopic fluoride materials. They exhibit fundamentally distinct properties in comparison to classically prepared metal fluorides. To broaden this area, we report in this paper the first fluorolytic sol-gel synthesis of ZnF 2. The obtained sol was studied with dynamic light scattering (DLS). The dried ZnF 2 xerogel was investigated with elemental analysis, thermal analysis, powder X-ray diffraction (XRD), solid-state MAS NMR, and N 2 adsorption-desorption measurements. The characterisations revealed a remarkably high surface area of the sol-gel prepared ZnF 2. To determine key parameters deciding its prospects in future catalytic applications, we studied the surface acidity-basicity by using in situ FTIR with different probe molecules. Compared to the previously established MgF 2, weaker Lewis acid sites are predominant on the surface of ZnF 2 with some base sites, indicating its potential as a heterogeneous catalyst component. In short, we believe that the successful synthesis and detailed characterisation of nanoscopic ZnF 2 allow follow-up work exploring its applications, and will lead to studies of more metal fluorides with similar methods. © 2012 The Royal Society of Chemistry.


Goscianska J.,Adam Mickiewicz University | Ziolek M.,Adam Mickiewicz University | Gibson E.,CNRS Catalysis and Spectrochemistry Laboratory | Daturi M.,CNRS Catalysis and Spectrochemistry Laboratory
Catalysis Today | Year: 2010

Meso-macroporous tetragonal zirconia synthesised hydrothermally within this work and containing ca. 60% of mesopores and a surface area of 84 m 2/g is a highly basic material exhibiting both Brønsted and Lewis basicities (BBS and LBS). Moreover, it has Lewis acid sites and very weak BAS (bridged hydroxyls). Such ZrO2 was used as a matrix for niobium oxide species loaded as 0.3 and 1 monolayers. NbOx loading decreases basicity (both LBS and BBS) and the number of Lewis acid sites (LAS) and leads to an increase in the number of Brønsted acid sites (BAS). The loading with a 0.3 monolayer of NbOx leads to a very attractive support/catalyst because of the generation of active oxygen atoms at the interface between the NbOx and ZrO2 phases. Niobio-zirconia supports were modified by impregnation with chloroplatinic acid (1 wt% of Pt). Platinum modification further changes the acid-base properties of the supports, depending on the NbOx loading. The highest Pt dispersion is reached on the NbOxmonolayer because of the strong metal-support interaction. Structure and surface properties (acid-base) of the supports and platinum catalysts were characterized in detail by N2 adsorption, XRD, XPS, UV-vis, FTIR combined with the adsorption of probe molecules (pyridine, CO at room temperature and ∼100 K, CO2), and by test reactions (acetonylacetone cyclization and 2-propanol dehydration/ dehydrogenation). © 2009 Elsevier B.V. All rights reserved.


Seo Y.-K.,Korea Research Institute of Chemical Technology | Seo Y.-K.,Yonsei University | Yoon J.W.,Korea Research Institute of Chemical Technology | Lee J.S.,Korea Research Institute of Chemical Technology | And 14 more authors.
Advanced Materials | Year: 2012

Hierarchically porous metal-organic frameworks with mesoporous cages are demonstrated to behave as promising water adsorbents in energy-efficient dehumidification. Their low temperature desorption properties for water with huge sorption uptakes are essential for various water sorption applications including desiccant dehumidification and fresh water production. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Hensen E.J.M.,TU Eindhoven | Poduval D.G.,TU Eindhoven | Ligthart D.A.J.M.,TU Eindhoven | Chen W.,CNRS Catalysis and Spectrochemistry Laboratory | And 3 more authors.
Journal of Physical Chemistry C | Year: 2012

Surface characterization of amorphous silica-alumina (ASA) by CO ads IR, pyridine ads IR, alkylamine temperature-programmed desorption (TPD), Cs + and Cu(EDA) 2 2+ exchange, 1H NMR, and m-xylene isomerization points to the presence of a broad range of Brønsted and Lewis acid sites. Careful interpretation of IR spectra of adsorbed CO or pyridine confirms the presence of a few very strong Brønsted acid sites (BAS), typically at concentrations lower than 10 μmol/g. The general procedure for alkylamine TPD, which probes both Brønsted and Lewis acidity, is modified to increase the selectivity to strong Brønsted acid sites. Poisoning of the m-xylene isomerization reaction by a base is presented as a novel method to quantify strong BAS. The surface also contains a weaker form of BAS, in concentrations between 50 and 150 μmol/g, which can be quantified by CO ads IR. Cu(EDA) 2 2+ exchange also probes these sites. The structure of these sites remains unclear, but they might arise from the interaction of silanol groups with strong Lewis acid Al 3+ sites. The surface also contains nonacidic aluminol and silanol sites (200-400 μmol/g) and two forms of Lewis acid sites: (i) a weaker form associated with segregated alumina domains containing five-coordinated Al, which make up the interface between these domains and the ASA phase and (ii) a stronger form, which are undercoordinated Al sites grafted onto the silica surface. The acid catalytic activity in bifunctional n-heptane hydroconversion correlates with the concentration of strong BAS. The influence of the support electronegativity on the neopentane hydrogenolysis activity of supported Pt catalysts is considerably larger than that of the support Brønsted acidity. It is argued that strong Lewis acid sites, which are present in ASA but not in γ-alumina, are essential to transmit the Sanderson electronegativity of the oxide support to the active Pt phase. © 2012 American Chemical Society.

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