Journal Article Environmental TEM at Atmospheric Pressure: An Operando View of the Materials at the Nanoscale Get access Ovidiu Ersen, Ovidiu Ersen Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS – Université de Strasbourg, 23 rue du Loess, 67034 Strasbourg Cedex 2, France Search for other works by this author on: Oxford Academic Google Scholar Georgian Melinte, Georgian Melinte Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS – Université de Strasbourg, 23 rue du Loess, 67034 Strasbourg Cedex 2, France Search for other works by this author on: Oxford Academic Google Scholar Simona Moldovan, Simona Moldovan Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS – Université de Strasbourg, 23 rue du Loess, 67034 Strasbourg Cedex 2, France Search for other works by this author on: Oxford Academic Google Scholar Kassiogé Dembélé, Kassiogé Dembélé Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS – Université de Strasbourg, 23 rue du Loess, 67034 Strasbourg Cedex 2, FranceInstitut Français de Pétrole – Energies Nouvelles (IFPEN), 69360 Solaize, France Search for other works by this author on: Oxford Academic Google Scholar Charles Hirlimann, Charles Hirlimann Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS – Université de Strasbourg, 23 rue du Loess, 67034 Strasbourg Cedex 2, France Search for other works by this author on: Oxford Academic Google Scholar Cuong Pham-Huu, Cuong Pham-Huu Institut de Chimie et Procédés pour l'Énergie, l'Environnement et la Santé (ICPEES), UMR 7515 CNRS – Université de Strasbourg, ECPM, 25 rue Becquerel, 67087 Strasbourg Cedex 2, France Search for other works by this author on: Oxford Academic Google Scholar Anne-Sophie Gay, Anne-Sophie Gay Institut Français de Pétrole – Energies Nouvelles (IFPEN), 69360 Solaize, France Search for other works by this author on: Oxford Academic Google Scholar Sylvie Maury Sylvie Maury Institut Français de Pétrole – Energies Nouvelles (IFPEN), 69360 Solaize, France Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 22, Issue S5, 1 November 2016, Pages 6–7, https://doi.org/10.1017/S1431927616012058 Published: 21 December 2016
Nous avons etudie des catalyseurs de cobalt utilises pour la synthese Fischer-Tropsch des hydrocarbures en suivant les processus d’activation, de fonctionnement et de desactivation par microscopie electronique en transmission in-situ environnementale. Une methodologie operando a ete developpee en couplant ces etudes structurales dans une cellule environnementale a la mesure de gaz residuels par spectrometrie de masse. Utilisant des nano-objets de morphologie controlee, nous avons mis en evidence des mecanismes de desactivation des catalyseurs par frittage des particules, re-oxydation, encapsulation et carburation. Pour les catalyseurs supportes, leur activation se distingue par une densification des particules. Nous avons demontre que la reduction des particules est plus facile sur silice que sur alumine ainsi qu’en presence des atomes de Pt. Durant leur fonctionnement sous gaz de synthese, nous avons detecte la formation d’hydrocarbures. Cette methodologie a donne acces aux proprietes physico-chimiques d’une serie de catalyseurs de cobalt, ouvrant ainsi la voie a des etudes approfondies de catalyseurs heterogenes par microscopie operando.
Abstract Here the thermal behaviour and the surface reactivity of cobalt catalysts supported by alumina‐silica and promoted by platinum were investigated by in situ transmission electron microscopy (in situ TEM) in a syngas environment. At the standard operating temperature of 220 °C, atomic diffusion and sintering processes onto the support are quite limited on the time scale of the TEM experiment. At temperatures between 350 and 450 °C, particles encapsulation occurred due to a higher CO dissociation and conversion into graphitic layers. Beyond 500 °C, carbon nanotubes (CNTs) growth is activated and the particles undergo (i) morphological changes through continuous elongation and contraction; and (ii) microstructural changes with the appearance of cobalt carbide. By comparing reactions under pure CO and a mixture CO−H 2 , it was shown that the addition of dihydrogen to CO increased the rate of CNTs growth and modified the structure of the nanotubes. These results clearly demonstrate the strong ability of the in situ TEM to provide the main lines of the reactivity synopsis of nanocatalysts at a nanometric scale under temperature and reactive gas.
Here we report on the use of formic acid as a green and safe reagent for the N-methylation of primary amides in the presence of a Pd/In2O3 solid catalyst. No additive is needed and primary amides are selectively N-methylated in good to excellent yields. The reaction operates through a formylation/reduction pathway, leaving the amide carbonyl untouched.
Superconducting qubits have arisen as a leading technology platform for quantum computing, which is on the verge of revolutionizing the world's calculation capacities. Nonetheless, the fabrication of computationally reliable qubit circuits requires increasing the quantum coherence lifetimes, which are predominantly limited by the dissipations of two-level system defects present in the thin superconducting film and the adjacent dielectric regions. In this paper, we demonstrate the reduction of two-level system losses in three-dimensional superconducting radio frequency niobium resonators by atomic layer deposition of a 10 nm aluminum oxide Al2O3 thin films, followed by a high vacuum heat treatment at 650 °C for few hours. By probing the effect of several heat treatments on Al2O3-coated niobium samples by x-ray photoelectron spectroscopy plus scanning and conventional high resolution transmission electron microscopy coupled with electron energy loss spectroscopy and energy dispersive spectroscopy, we witness a dissolution of niobium native oxides and the modification of the Al2O3-Nb interface, which correlates with the enhancement of the quality factor at low fields of two 1.3 GHz niobium cavities coated with 10 nm of Al2O3.
A large signal of gas-phase CO overlapping with those of adsorbates is often present when investigating catalysts by operando diffuse reflectance FT-IR spectroscopy. Physically removing CO(g) from the IR cell may lead to a fast decay of adsorbate signals. Our work shows that carbonyls adsorbed on metallic Pt sites fully vanished in less than 10 min at 30 °C upon removing CO(g) when redox supports were used. In contrast, a broad band assigned to CO adsorbed on oxidized Pt sites was stable. It was concluded that physically removing CO(g) at room temperature during IR analyses will most likely lead to changes in the distribution of CO(ads) and a misrepresentation of the Pt site speciation, misguiding the development of efficient low-temperature CO oxidation catalysts. A tentative representation of the nature of the Pt phases present depending on the feed composition is also proposed.
In this Research Article which reported the unexpected simultaneous presence of both oxidized and metallic Pt species during CO oxidation over a 5 wt % Pt/CeO 2 , the work of Safonova and co-workers [32] was misquoted by stating that these authors had not considered the possibility of the presence of oxidized Pt species on their 1.5 wt % Pt/ CeO 2 catalyst used under similar conditions.In fact, Safonova and co-workers exclusively observed the presence of metallic Pt species by Pt L3 XAS measurements carried out over their catalyst placed in a plug flow reactor cell when exposed to 1 % CO or 1 % CO + 4 % O 2 (see figure S2.b in the Supporting Information of reference [32]).
Abstract Pt‐basierte Materialien sind weitverbreitet in der heterogenen Katalyse für die katalytische Entfernung von Schadstoffen. Oft wird der Zustand des aktiven Platins als abhängig von den experimentellen Bedingungen beschrieben: bei niedrigen Temperaturen unterhalb der Light‐off‐Temperatur liegt mit CO vergiftetes metallisches Pt vor, bei höheren Temperaturen oberhalb der Light‐off‐Temperatur oxidiertes Pt. Im Gegensatz zu vorherigen Studien zeigen wir hier, dass metallisches wie auch oxidiertes Pt in ähnlichen Proportionen an der Oberfläche von hoch aktiven, ca. 1 nm großen Nanopartikeln unter Reaktionsbedingungen bei 30 °C vorliegen. Die simultane Gegenwart von metallischem und oxidiertem Pt ermöglicht eine Synergie zwischen den beiden Phasen. Dabei bietet das metallische Pt Adsorptionsstellen für CO, während das oxidierte Pt vermutlich reaktiven Sauerstoff zuführt. Unsere Ergebnisse zeigen die Komplexität von dualen oxidischen‐metallischen Pt‐Katalysatoren und ihre leicht veränderliche Natur unter den jeweiligen Reaktionsbedingungen.
