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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; […]
Sorry, this entry is only available in French. For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language. Jacob a été accueilli au Laboratoire Catalyse et Spectrochimie en 1990. Il avait été recommandé par San de Beer de l’Université Technologique […]
It is with a great sorrow that we announce that Jacob van Gestel passed away this Sunday after a long illness. Jacob has played an important role as a teacher and researcher at the University of Caen and particularly at the Catalysis and Spectrochemistry Laboratory (LCS). Jacob was a specialist in kinetic for heterogeneous catalysis. […]
Technopôle du Madrillet – 675, Avenue de l’Université / 76801 Saint-Etienne-du-Rouvray cedex http://www.carnot-esp.fr Type de recrutement : Type de contrat : CDD 6 mois évolutif CDI Niveau d’expérience : niveau Bac +5 Rémunération : 38k€ bruts/annuel, selon profil et expérience, incl.3ème mois + mutuelle, Lieu : Seine-Maritime, Saint Etienne du Rouvray Prise de fonction : […]
Crystallography : Electron diffraction locates hydrogen atoms Diffraction-based analytical methods are widely used in laboratories, but they struggle to study samples that are smaller than a micrometer in size. Researchers from the Laboratoire de cristallographie et sciences des matériaux (CNRS/Ensicaen/Unicaen), the Laboratoire catalyse et spectrochimie (CNRS/Ensicaen/Unicaen)1, and the Academy of Sciences of the Czech Republic have […]
Position of hydrogen in isolated nanocrystals revealed by electron diffraction
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).
Pr. Marco Daturi: The synergy between four laboratories (the LCS of Caen, the ILV / IMAP of Versailles / Paris, the ICGM of Montpellier and the Korean KRICT) with unique skills in synthesis, advanced characterization and modeling of materials, to design an ordered organic-inorganic porous hybrid system, commonly called the Metal Organic Framework (MOF), capable of preferentially fixing nitrogen gas, even in the presence of other gases.
Genuine sponges of the infinitely small, nanoporous materials make it possible to selectively capture molecules of gas, vapor or liquid, a phenomenon that is of major interest in many industrial processes. A French-Korean consortium comprising researchers from the Institut Charles Gerhardt Montpellier (CNRS / Montpellier University / ENSCM), the Paris Institute of Pore Materials (CNRS / ENS / ESPCI) and the Catalysis and Spectrochemistry Laboratory (CNRS / Normandie University / ENSICAEN) has identified a crystallized porous hybrid material which, once dehydrated, is able to purify natural gas and air by selectively fixing nitrogen gas in the presence of methane or oxygen. Published in the journal Nature Materials, this work makes it possible to envisage more efficient industrial processes of gas separation.
We report mesoporous metal–organic framework materials containing accessible Cr(III) sites, able to thermodynamically capture N2 over CH4 and O2.
Membre Distingué Junior de la SCF Le titre de « Membre Distingué Junior » peut être décerné à une personne de moins de 45 ans ayant été membre de la SCF les trois années précédentes sans discontinuité, et étant à l’origine de travaux représentant une avancée notable dans un des domaines de la chimie, ou […]
Sorry, this entry is only available in French. For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language. En chimie : La synthèse efficace et moins polluante des cristaux de zéolithes La publication : Hussein Awala et al., Nature Materials, 14, 47, 2015. Le résultat : Cet […]
Study by in situ and operando spectroscopy of the relationships between the adsorption sites properties of MOFs (Metal Organic Frameworks) and their catalytic properties for model reactions CNRT conference room, 2nd floor, Tuesday December 20, 2016 10:00 AM Jury members for this public thesis : Mme Nathalie Steunou, Professeur, Université de Versailles M. Carlo Lamberti, […]
Selective Catalytic Reduction study of NOX using Acetylene as a reducing agent over zeolite catalysts loaded with transition metal ions Among NOX emission sources, the automotive industry and more specifically Diesel engines are the main pollutants. A technology already commercialized to reduce NOX to N2, consists in the dosage of an additive AdBlue® which acts […]
La cérémonie de remise des Prix 2016 aura lieu le mercredi 30 novembre à 19h30 dans le grand amphithéâtre du Muséum national d’histoire naturelle. Svetlana Mintova et les coauteurs (notamment de nos collaborateurs du CRISMAT) de l’article primé cette année dans la mention Chimie seront présents. L’article : “Template-free nanosized faujasite-type zeolites” paru dans Nature materials en […]