- LCS Valoris
Cold VCl3-plasma is employed for the preparation of highly dispersed vanadium oxide clusters on nanosized zeolite. Different types of zeolite, such as EMT, FAU (z.X) and Beta are used. The activity of thus prepared catalysts is studied in the selective photooxidation of methanol under polychromatic visible and UV irradiations. The physicochemical properties and catalytic performance of plasma treated zeolite Beta (P-V2O5@Beta) catalyst is compared with zeolite Beta (V2O5@Beta) and amorphous silica (V2O5@SiO2) impregnated vanadium oxide catalysts. Pure V2O5 is used as a reference material. The set of catalytic data shows that plasma prepared zeolite Beta based catalyst displays the highest activity. Complementary characterization techniques including XRD, N2-sorption, FTIR, ionic exchange, pyridine adsorption, Raman, NMR, TPR and EDX-TEM are used to study the impact of the preparation approach on the physicochemical properties and catalytic performance of photocatalysts.
K-F zeolite nanocrystals (structure code EDI) are synthesized from a template-free Al2O3–SiO2–K2O–H2O precursor system. The use of a very reactive organic-template-free gel system (4SiO2: 1Al2O3: 16K2O: 160H2O) enables the crystallization of EDI-type nanosized zeolite to accomplish within 3 h at 100 °C. The K-F zeolite crystals have flattened cuboid shape morphology (ca. 27 nm) and they tend to agglomerate and form secondary spherical particles (ca. 310 nm). The K-F zeolite nanocrystals have high alumina content (Si/Al ratio = 1.10) and high crystalline solid yield (79%) offering a promising route for large-scale production of hydrophilic zeolite nanoparticles.
Partenariat entre Normandie AeroSpace et l’institut Carnot ESP Le 16 février 2017, Normandie AeroSpace (NAE)1 et l’institut Carnot ESP2 (Energie et Systèmes de Propulsions) ont signé un partenariat afin de mutualiser leurs efforts pour accélérer la recherche et le développement en Energie et Systèmes de Propulsion sur le territoire Normand. Cet accord vise à faciliter […]
Atomic substitutions are a central feature of the physicochemical properties of an increasing number of solid-state materials. The complexity that this chemical disorder locally generates in otherwise crystalline solids poses a major challenge to the understanding of the relationships between the structure and properties of materials at the atomic and molecular level. Strategies designed to efficiently explore the ensemble of local chemical environments present in disordered crystals and predict their signatures in local spectroscopies such as solid-state nuclear magnetic resonance (NMR) are therefore essential. Focusing on the Ga/Si disorder in the framework of rubidium-exchanged gallosilicate natrolite zeolite (Rb-PST-1) with a high Ga content (Si/Ga = 1.28), we show how the structure-generation approach implemented in the new program supercell (Okhotnikov et al., J. Cheminf. 2016) provides an excellent basis for the understanding of complex experimental spectroscopic data. Furthermore, we describe how exhaustive explorations of atomic configurations can be performed to seek local structural ordering and/or disordering factors. In the case of Rb-PST-1, we more specifically explore the possibility to form and to detect the presence of thermodynamically unfavorable Ga-O-Ga connectivity. While particularly adapted to the description of dense materials, we demonstrate that this approach may successfully be used to reproduce and interpret the distributions of local structural distortions (i.e., the geometrical disorder) resulting from the chemical disorder in systems as complex as microporous zeolites.
An optical detection of volatile organic compounds (VOCs) using nanosized zeolites functionalized with pyrylium salts is presented. Nanosized zeolite crystals firstly are functionalized with pyrylium salt (para-dimethylamino-2,4,6-triphenylthiopyrylium tetrafluoroborate, PNS). Then the optical response of the pyrylium-functionalized nanozeolites towards volatile organic compounds is investigated. Two possible modes of zeolite functionalization are proposed based on: (1) ion exchange between the pyrylium and sodium cations (Na+) in the zeolite (Si-O−-Al active sites), and (2) adsorption via electrostatic interaction between the electron lone-pair of amine of the PNS and the orbital vacancy of Al on the zeolite surface (Lewis acid sites). The experimental results verify that the great number of Lewis acid sites of the nanozeolites led to a significant adsorption of the PNS (mode 2) causing the hypsochromic (band shift to lower wavelength) shift in the visible light absorbance. Pyrylium-functionalized nanozeolites demonstrate a good sensitivity and reversibility toward volatile organic compounds investigated in this work.
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Coupler comprising side-polished optical fiber and tantalum pentoxide (Ta2O5) waveguide coated with 330 nm hydrophobic MFI-type zeolite films was utilized as chemical sensor for acetone vapors. The thickness of the zeolite films was selected through theoretical modeling of the resonant wavelength shift in order to achieve the highest possible sensitivity. The spectral positions of the resonances were determined through solving of the characteristics equations for the coupled waveguides and finding their mode effective refractive indices. The optical quality of the coupler surface, that is responsible for the proper operation of the device, was controlled through 3D optical imaging prior to and after deposition of the zeolite films. The application of side-polished optical fiber–Ta2O5 waveguide coupler covered with hydrophobic zeolite film for acetone vapor sensing was demonstrated and discussed.
Communiqué de Presse du CNRS Le 22 avril prochain, les citoyens du monde entier sont appelés à participer à une grande marche pour les sciences. Cette initiative a été lancée par des scientifiques américains pour faire face à « de nouvelles politiques (qui) menacent d’entraver davantage la capacité des chercheurs de mener à bien leurs […]
Among NOX emission sources, the automotive industry and specifically Diesel engines are the main pollutants. Selective catalytic reduction by Hydrocarbons (HC-SCR) may lead to efficiencies as high as 70% in reducing NOX into N2 specially by using economical catalysts (zeolites). We report here an HC-SCR study using acetylene (C2H2) as a reducing agent that presents intersting activity at low temperatures. A ferrierite zeolite catalyst was used and modified by the introduction of either copper or iron and the NOX reduction activity was analysed by InfraRed (IR) operando techniques subsequent to a preliminary IR in-situ characterization. The later technique allowed the identification of the species formed on the surface after NO or C2H2 adsorption at room temperature. The thermal stability of adsorbed acetylene was also investigated. The obtained information on vibrational bands typical for adsorbed species served as an input for the IR operando study. Cu-HFER catalyst presents a strong redox character upon room temperature interaction with NO as well as a strong affinity for C2H2 adsorption. However, Fe-HFER shows a higher NOX reduction efficiency when submitted to SCR conditions. Indeed, iron ions enhance the NO oxidation into NO2 that seems to be more reactive with C2H2. The reaction mechanism was revealed by an FT-IR operando study coupled with 15NO isotopic labelling that proved the formation of hydrocyanic acid and isocyanate species as key intermediate species.
Heterogeneous single-site catalysts consist of isolated, well-defined, active sites that are spatially separated in a given solid and, ideally, structurally identical. In this review, the potential of metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) as platforms for the development of heterogeneous single-site catalysts is reviewed thoroughly. In the first part of this article, synthetic strategies and progress in the implementation of such sites in these two classes of materials are discussed. Because these solids are excellent playgrounds to allow a better understanding of catalytic functions, we highlight the most important recent advances in the modelling and spectroscopic characterization of single-site catalysts based on these materials. Finally, we discuss the potential of MOFs as materials in which several single-site catalytic functions can be combined within one framework along with their potential as powerful enzyme-mimicking materials. The review is wrapped up with our personal vision on future research directions.
Structure-activity relationships in heterogeneous catalysis demand the development of original preparation routes to create catalyst sets with extended surface properties. Pure zirconia is a bifunctional catalyst which shows a high versatility in acid-base catalysis. The present work aims to synthesize a set of zirconia catalysts with various acid-base reactivities. It proposes a new route to prepare pure zirconia using sodium alginate, a low-cost biosourced polymer. This zirconia phase is compared to samples obtained from two more conventional preparation routes, namely precipitation and sol-gel. Upon calcination (500 – 900°C), the alginate-derived zirconia maintains a high specific area, which can be explained by the high dispersion of the zirconyl species in the ionogel precursor. Moreover, the three types of catalysts have distinct acid-base properties, as shown by CO2 adsorption and catalysis (methylbutynol model reaction). The alginate-derived ZrO2 has a higher and more stable amphoteric reactivity than the phases obtained by precipitation and sol-gel, which can be rationalized by a higher level of Lewis acid-base pairs.
The evolution of Ba sites in two distinct NOx storage and reduction (NSR) catalysts that are based on alumina or zirconia-titania mixed oxide (ZrO2-TiO2 or ZT) during NOx adsorption/desorption was investigated by in situ and operando IR spectroscopy. Based on various evidences from the in situ study, medium sized Ba sites on alumina supported fresh catalysts are proposed to experience sintering under NOx adsorption to form bigger particles, while for ZT, initially possessing smaller sized Ba particles, the formation of a thin layer or very fine particles of Ba would proceed under the same condition. This evolution can also be affirmed by observations from the operando IR study showing that NOx adsorption on ZT supported catalyst is initially faster than on alumina supported catalyst (time on stream lower than 300 sec), but after long adsorption time (about 50 min) the two catalysts show similar storage capacity. This new mechanistic insight suggests that NOx ad/desorption rate, which is critical for optimizing NSR performance, needs to be controlled by support materials whose interaction with the Ba particles not only determines their initial size (fresh catalyst) but also their resistance towards sintering during the NOx adsorption.
Stable luminescent silver clusters in nanosized EMT zeolite suspension were prepared and directly observed with high-resolution transmission electron microscopy (HRTEM). The luminescence of the Ag clusters remains stable in time due to their stabilization within the sodalite cages (0.7 nm) of the EMT zeolite nanocrystals. In addition to the experimental results, the first principle Density Functional Theory (DFT) computations showed that hydrated neutral clusters up to octamer (Ag8) with a diameter of 0.47 nm were stabilized in the sodalite cages of the EMT zeolite, trough binding of silver atom(s) to the zeolite oxygen(s). The silver clusters exhibit molecular-like emission properties (lem = 395 nm and t1/2 ≤ 1 ns) that are in a good agreement with the HRTEM and DFT results. The stabilization of charge silver species in the form of weakly interacting dimer or trimer was observed too, which was based on the microsecond lifetime of the emission band measured at 545 nm. The high stability combined with the luminescence properties of silver clusters in the EMT zeolite nanocrystals will be of great advantage for applications such as bio imaging and bio sensing.
by M. Denoual , D. Robbes, S. Inoue, Y. Mita, J. Grand, H. Awala, S. Mintova New concept of microfabricated thermal resonant gas sensor comprising of a cantilever-like thermal device covered with a selective zeolite layer associated to heat feedback electronics is presented. Sensing principle exploits the thermal resonant frequency shift caused by mass variations upon gas adsorption in the zeolite layer; […]
Jacob a été accueilli au Laboratoire Catalyse et Spectrochimie en 1990. Il avait été recommandé par San de Beer de l’Université Technologique d’Eindhoven pour travailler à Caen sur un contrat de recherche soutenu par un partenaire industriel. Pur produit de l’Ecole hollandaise, il s’est d’emblée imposé par ses compétences en catalyse. De plus il possédait […]
C’est avec une grande tristesse que nous annonçons que Jacob van Gestel est décédé ce dimanche après une longue maladie. Jacob a joué un rôle important en tant que maître de conférence et chercheur à l’ Université de Caen et plus particulièrement au Laboratoire Catalyse et Spectrochimie (LCS). Jacob était un spécialiste en cinétique pour la catalyse hétérogène. Il […]
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Paris, 13 janvier 2017 Cristallographie : la diffraction des électrons localise les atomes d’hydrogène Les méthodes d’analyse par diffraction sont très utilisées dans les laboratoires, mais elles peinent à étudier des échantillons de taille inférieure au micromètre. Des chercheurs du Laboratoire de cristallographie et sciences des matériaux (CNRS/Ensicaen/Unicaen), du Laboratoire catalyse et spectrochimie (CNRS/Ensicaen/Unicaen)1 et de […]
Position de l’hydrogène dans des nanocristaux isolés révélés par diffraction électronique.
Hydrogen positions in single nanocrystals revealed by electron diffraction.
L. Palatinus*, P. Brázda, P. Boullay*, O. Perez, M. Klementová, S. Petit, V. Eigner, M. Zaarour and S. Mintova, Science 355, 166-169 (2017).
The formation of colloidal AlPO-5 nanocrystals were studied under hydrothermal and microwave conditions in the presence of a new templating agent, 1-ethyl-2,3-dimethylimidazolium hydroxide ([edmim]OH).