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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.

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.

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.

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.

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.

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