Deep insight into CO adsorption on Ni-USY zeolite catalyst by FTIR spectroscopy. Evidence for isotopic isomerism

International audienc

IR Study of the Adsorption and Isotopic Scrambling of Thiophene on CaO

International audienceThiophene, thiophene-2,5-d 2 , and thiophene-d 4 adsorption on CaO activated at 723-973 K has been investigated at 170-300 K by means of IR spectroscopy and IR analysis of desorbed gas. Molecular adsorption of thiophene occurs on surface oxygen ions and basic OH groups by weak H-bonding of CH groups with the lone electron pairs of oxygen. On the most basic oxygen ions of CaO activated at 973 K, thiophene dissociates already at 200 K with the formation of surface OH groups and thiophenide C 4 H 3 S-anions. This reversible dissociation accounts for the catalytic reaction of isotopic scrambling of thiophene-2,5-d 2 that takes place already at 220 K and leads to the appearance of all 10 possible thiophene isotopomers in the desorbed gas. Experiments with thiophene coadsorption with CO enable one to associate the sites of thiophene dissociation with those oxygen ions that bound CO giving carbonite CO 2 2-ions. Three kinds of such sites could be distinguished, which differ in the band positions of the resulting OH groups and in thermal stability of corresponding thiophenide anions

Modifications of the AgMo3P2O14 Catalyst in the Oxidation of Propane

The catalytic performances in the oxidation of propane of the AgMo3P2O14 catalyst are quite good, leading to 70% of propene selectivity at 7% of propane conversion. We have checked that, before reaction, results of XANES and EXAFS obtained at the Mo K-edge (19999 eV) confirm those obtained by X-ray spectroscopy (oxidation state and Mo number of oxygen neighbour of 5.66, Mo=O bond length=1.72Å). After reaction, we have shown that the catalyst is partially reduced [5.66 → 5.2], the number of oxygen atoms increases to 6 and the mean molybdenyl bond length decreases (1.68Å) which is in agreement with the variation of this bond length with the oxidation state of the molybdenum in molybdenum phosphates. XPS measurements also confirmed a partial reduction of molybdenum species and showed a migration of the silver cation to the surface, certainly participating to the surface stabilization. Moreover, a correlation between the catalytic activity and the modification of the catalyst is made showing that an equilibrium between MoV and MoVI species in the catalyst leading to the avrerage oxidation state of molybdenum of 5.2 seems to be very important

An infrared and solid-state NMR study of the H2S adsorption on basic zeolite

International audienceThe modification of surface properties resulting from H2S adsorption on a fully sodium-exchanged Y zeolite was studied in situ using a combination of Infrared and Solid-State NMR spectroscopy. In order to perform in situ measurement in the same conditions with both techniques, a homebuilt device for preparing the NMR samples under vacuum or controlled atmosphere was used. Double-resonance NMR methods were achieved for a complete assignment of the different lines in proton NMR spectra. A small fraction of H2S is shown to adsorb dissociatively on NaY whereas the main part of H2S interacts non-dissociatively, either by coordination with the Na+ cations or by H-bonding

Essai de fertilisation minérale sur pin maritime à Mimizan(Landes). Résultats après la 6è année

Les auteurs décrivent en détail les études préalables à l'implantationde l'essai (climat, sol, plan d'eau, végétation).Les engrais ont été appliqués, avant le labour et le semis, surdes bandes de 2 mètres représentant la moitié de la surface, dansUn sol podzolique et selon un dispositif en blocs à cinq répétitions.Les closes employées à l'hectare sont respectivement': N: 78 kgs,P2O5: 125 kgs, K2O : 130 kgs, sous forme d'urée formol, de scoriesde déphosphoration et de chlorure de potassium.L'action de certains engrais a été très forte sur la croissance dèsla deuxième année et se poursuit après la sixième où le phosphoreseul procure un gain de 56 %, porté à 76 % pour NPK. L'azote etla potasse n'ont pas agi seuls et ont marqué surtout au début.L'action des engrais a été favorable pour la régularité des hauteursainsi que sur la composition de la couverture vivante, la floraison,la persistance des feuilles, la composition chimique des feuilles, lamy corhization. Ils sont sans effet actuellement sur la présence desparasites et ont une action difficile à interpréter sur la levée dessemis.Cet essai sera poursuivi pendant plusieurs dizaines d'années etdevrait fournir de nombreux autres renseignements.The authors give a detailed account of their studies previousto the establishment of the experiment (climate, soil, water-table,vegetation).Fertilizers have been applied before ploughing and sowing, ontwo-meter-wide strips covering half the area, in a podzolic soil andaccording to a block design with five replications. Rates per hawere respectively : N 78 kg, P2O5 125 kg, K2O 130 kg in theform of formol urea, basic slag and potassium chloride.Some fertilizers greatly influenced growth as soon as the secondyear and lasts after the sixth year when phosphorus aloneimproved it by 56 % and NPK by 76 %. N and P have not actedalone and influenced mainly at the start.Fertilizers had a favourable effect in regard to height uniformityas well as to ground cover composition, flowering, leaf persistance,chemical composition of leaves, mycorhizal development. Theyare now without effect on pests and it is difficult to analyze theirinfluence on seedling emergence.This trial will be carried on for twenty years and more andshould give many further results

Nature, structure and strength of the acidic sites of amorphous silica alumina: An IR and NMR study

International audienc

Combined Aging Processes during Bio-Syngas Methanation for SNG Production

SSCI-VIDE+ING+FRM:CMI:YSCInternational audienceThis study focuses on the conversion of bio-syngas obtained from biomass gasification to synthetic natural gas (SNG). It evaluates the kinetic sensitivity of Ni based catalysts to various poisons, in parallel with metal particle sintering occurring under SNG conditions. From a combination of state-of-the-art DRIFT/SSITKA operando techniques, a rationale of these aging processes is proposed on the basis of a direct evaluation of active reacting intermediates nature and concentration. The reversible poisoning of N and Cl containing species affects essentially surface controlling steps such as hydrogenation of CHx intermediates deriving from carbonyls decomposition, via a reversible electronic transfer from Ni to the electrophilic additives. A reverse effect would characterize the promoting effect of alkali addition. For tar-type hydrocarbons, the absence of electronic effects explain their negligible toxicity, unless surface coking and diffusion limitation. S containing molecules neutralize part of the catalytic bed without changing the reactivity of the unpoisoned metal

Bipyramidal anatase TiO₂ nanoparticles, a highly efficient photocatalyst? Towards a better understanding of the reactivity

International audienceAnatase nanoparticles with shape controlled bipyramidal morphology (TiO2-A-bipy) exhibited mainly {101} facets were synthesized through the sol–gel method and then used for the photodegradation of three model pollutants – Rhodamine B, phenol and formic acid – under UV-A radiation exposure. These titania samples exhibit better photocatalytic efficiency than the commercial TiO2-P25 reference for the dye degradation while this one demonstrates a higher activity for both phenol and formic acid. Moreover, supplementary washings of the particles significantly enhanced their photocatalytic efficiency in any case. To better understand these differences in term of photoactivity and the role of the TiO2 surface according to the nature of the targeted organic pollutant, various characterization techniques such as XRD, TEM and N2-sorption were used. Their surface properties were studied by FT-IR, TRMC and EPR. The presence of more acidic sites on TiO2-A-bipy surface could explain the faster degradation of the dye molecule through surface-mediated reactions. On the other side, a better generation and separation dynamic of photogenerated charges for TiO2-P25 could account for its higher photocatalytic efficiency for both formic acid and phenol degradation. This study shows that even if a quick test of dye degradation is mostly used in literature to confirm the efficiency of a photocatalyst, further investigation is often needed