"Wet Technique" Metal Deposition for SEM Observation

"Wet technique" metal deposition for the metallization of non conducting surfaces and especially 3D substrates in order to perform SEM observation is an attractive method. The deposition of a 300-500 Å  thin "wet" metallic film needs a two-step procedure: an activation step, followed by an electroless deposition step. This metallization technique gives good results. Nevertheless the authors show in this work that a one-step process is sufficient to obtain a good SEM observation. The use of a Sn-Pd colloidal solution allows to prepare nonconductive surfaces in order to get SEM observation; this method is cheap and quick. This paper describes the conditions and properties of this "wet" preparation.La technique de métallisation chimique par voie liquide est une alternative aux méthodes classiques de métallisation pour l'observation d'échantillons non conducteurs. Simple, rapide, économique, cette technique apporte dans certains cas, en particulier pour les substrats tridimensionels, la solution aux problèmes des charges parasites. Une première technique consiste à métalliser les échantillons en deux étapes ; une étape d'activation de la surface non conductrice suivie par un dépôt autocatalytique permettant d'obtenir un film continu et conducteur de 300 à 500 A d'épaisseur. La deuxième technique qui met en œuvre une solution colloidale Sn-Pd, permet en une seule étape d'obtenir des échantillons pouvant être observés au MEB dans d'excellentes conditions. Cet article décrit les conditions et propriétés de ces techniques "humides" de préparation

Polyethylene glycol Gold-Nanoparticles: Facile Nanostructuration of Doxorubicin and its complex with DNA molecules for SERS detection

International audienceWe report the synthesis of dicarboxylic acid-terminated polyethylene-glycol (PEG)-gold nanoparticles by a simple one-step method, and their further use to form nanostructured surfaces for biomolecule immobilization. The synthesized nano-scale particles were conjugated with probe/target oligonucleotides in order to evaluate intercalation phenomenon in the presence of doxorubicin drug via Surface Enhanced Raman Spectroscopy (SERS) analysis

Lewis acido-basic interactions between CO2 and MgO surface: DFT and DRIFT approaches

International audienceCombined experimental infrared (IR) and theoretical approaches have been carried out in an attempt to specify the actual structure of the CO2 species adsorbed on the magnesium oxide surface. The interaction of CO2 with regular sites of the MgO(100), (111) and (110) surfaces as well as MgO(100) defect sites (steps, corners, kinks and di-vacancies) has been investigated by mean of Density Functional Theory study. Theoretical IR frequencies compared with IR experiments show distinguishable carbonate species, adsorbed on different planes and defects, vibrating in different IR-frequency ranges. In addition, by mean of thermodynamic model, the stability of carbonates as a function of temperature have been calculated and compared to the experiment. Analyzing the nature of basic sites, the results show that the most active site versus CO2, which is a Lewis acid, is not the same that the strongest site for the deprotonating adsorption of Brønsted acids. The present work revisits and improves the understanding of carbonate species that could exist on the magnesium oxide surface and gives a picture of the accessible planes of magnesium oxide as well as their surface Lewis basicity

Influence of the nature and environment of cobalt on the catalytic activity of Co-BEA zeolites in selective catalytic reduction of NO with ammonia

International audienceThe influence of cobalt environment on the catalytic properties of CoxSiBEA zeolite in selective catalytic reduction of NO with ammonia was studied. Catalysts were prepared by a two-step postsynthesis method which consists, in the first step, of dealumination of parent BEA zeolite to obtain aluminum-free SiBEA support and then, in the second step, of contacting the obtained material with an aqueous solution of cobalt nitrate. DR UV–Vis and XPS results showed that cobalt was successfully incorporated into zeolite beta framework as isolated mononuclear Co(II). The presence of only isolated framework mononuclear Co(II) was evidenced in CoxSiBEA with cobalt content lower than 2 wt % and both isolated framework mononuclear Co(II) and extra-framework octahedral Co(II) for Co3.0SiBEA catalyst. FTIR investigation of pyridine adsorption revealed that the incorporation of cobalt into zeolite framework led to a creation of new Lewis acidic sites which are responsible for high activity in SCR of NO with ammonia. The catalytic activity of CoxSiBEA in selective catalytic reduction of NO with ammonia as reducing agent strongly depends on the nature and environment of cobalt in BEA structure. The single-site Co2.0SiBEA zeolite catalyst was the most active among tested, with maximum NO conversion about 80% at 673 K. In contrast, Co3.0SiBEA catalyst containing a mixture of framework and extra-framework Co(II) had lower activity in SCR of NO process than Co2.0SiBEA at higher temperature due to a competitive reaction of ammonia oxidation to NO

On the relationship between the basicity of a surface and its ability to catalyze transesterification in liquid and gas phases: the case of MgO

International audienceGas or liquid phase transesterification reactions are used in the field of biomass valorization to transform some platform molecules into valuable products. Basic heterogeneous catalysts are often claimed for these applications but the role of basicity in the reaction mechanism depending on the operating conditions is still under debate. In order to compare the catalyst properties necessary to perform a transesterification reaction both in liquid and gas phases, ethyl acetate and methanol, which can be easily processed both in these two phases, were chosen as reactants. The catalyst studied is MgO, known for its basic properties and its ability to perform the reaction. By means of appropriate thermal treatments, different kinds of MgO surfaces, with different coverages of natural adsorbates (carbonates and hydroxyls groups), can be prepared and characterized by means of CO2 adsorption followed by IR spectroscopy and hept-1-ene isomerization model reaction. New results on the basicity of the natural MgO surface (covered by carbonate and hydroxyl groups) are first given and discussed. The catalytic behavior in the transesterification reaction is then determined as a function of the adsorbate coverage. It is shown that the transesterification activity in the liquid phase is directly correlated with the kinetic basicity of the surface in agreement with the mechanism already proposed in the literature. On the reverse, no direct correlation with the basicity of the surface was established with the transesterification activity in the gas phase. A very high activity, in the gas phase, was observed and discussed for the natural surface pre-treated at 623 K. Preliminary DFT modeling of ester adsorption and methanol adsorption capacity determination were performed to investigate plausible reaction routes

Comparing Al-SBA-15 Support and Pt/Al-SBA-15 Catalyst: Changes in Al Speciation and Acidic Properties Induced by the Introduction of Pt via Aqueous Medium

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Importance of the Nature of the Active Acid/Base Pairs of Hydroxyapatite Involved in the Catalytic Transformation of Ethanol to n ‐Butanol Revealed by Operando DRIFTS

International audienceOperando DRIFTS is used to identify the nature and the role of the surface sites of hydroxyapatites (HAps) involved in the catalytic transformation of ethanol to n‐butanol. The surface processes occurring upon a first reaction step followed by a step under He flow greatly influence the reactivity of HAps in a subsequent second reaction step. Ethanol is found to be mostly activated by the basic OH− groups of HAps, as indicated by the concomitant recovery of ethanol conversion and OH− groups under He flow. The drastic changes in selectivity observed during the second reaction step reveal the key role of acidic sites cooperatively acting with basic sites for basic reaction steps. Once the POH groups are poisoned by extensive formation of polymeric carbon species and the Ca2+ sites are available, the production of acetaldehyde is drastically promoted at the expense of that of n‐butanol. It is concluded that i) acetaldehyde acts as an intermediate in the formation of n‐butanol, and ii) various active sites are involved in the key basic reaction steps such as Ca2+−OH− and POH−OH− acid‐base pairs in the dehydrogenation of ethanol to acetaldehyde and the aldol condensation for n‐butanol formation, respectively