Etude infra-rouge des propriétés superficielles d'oxyde de fer γ Fe

L'analyse des spectres I.R de la pyridine (py) adsorbée sur γ Fe203 indique l'existence de sites Fen+ dont la coordinence est suffisamment perturbée pour intéragir fortement avec l'adsorbat en formant des liaisons σΝ → Fen+. Les sites anioniques superficiels sont plus basiques que la py, et empêchent la formation d'ions pyH+ même en présence de vapeur d'eau. Les groupes OH libres n'exhibent pas d'acidité de Bronsted, mais interagissent différemment avec la py

Selective catalytic reduction of NOx by NH3 on V-Mo-zeolite prepared by solid-state ion exchange method

International audienceV-Mo-Zeolite catalysts prepared by solid-state ion exchange were studied in the selective catalytic reduction of NOx by ammonia. The catalysts were characterized by chemical analysis, X-ray powder diffraction, N2 adsorption (BET), DRIFT, UV-Vis and Raman, spectroscopy and H2 TPR. Catalytic results show that upon addition of Mo to V-ZSM-5, catalytic performance was enhanced compared to V-ZSM-5

Influence of the V + Mo/Al ratio on vanadium and molybdenum speciation and catalytic properties of V–Mo–ZSM-5 prepared by solid-state reaction

International audienceV–Mo–ZSM-5 catalysts with various composition prepared by solid-state ion exchange were investigated with respect to their physico-chemical characteristics using chemical analysis, XRD, BET, DRIFT, UV–vis, 27Al MAS-NMR spectroscopy, H2 TPR and TPD of NH3. It was found that all the preparations leads to either metal ions sitting at the bridging oxygen of Si–OH–Al or anchored at Si–OH groups or deposited as oxide. These different solids were tested in the selective catalytic reduction of NOx by ammonia. The main result is that upon addition of small amount of Mo to V–ZSM-5, catalytic performances were enhanced

Catalytic activity of copper-bis(oxazoline) grafted on mesoporous silica in enantioselective cyclopropanation

Chiral phenyl substituted bis(oxazoline) (PhBox) was covalently immobilized through carbamate linkers onto mesoporous silica materials. These supports were previously prepared by the sol–gel method and they exhibit different textural properties. The presence and the integrity of the bis(oxazoline) ligand was checked by 13C-CP-MAS-NMR. These chiral mesoporous materials were complexed with copper(II) triflate. In spite of the different textural properties of these supports, the copper loading, determined by ICP-AES, was nearly the same (0.041–0.044 mmol Cu/g of solid). The supported Cu(II) complexes were tested as catalysts in the enantioselective cyclopropanation of styrene with ethyl diazoacetate. Enantioselectivities are consistently lower than those obtained in homogeneous phase. Different analyses point to a difficulty in the formation of the expected chelate, due to the presence of a coordinating functional group in the linker, as responsible for the loss in enantioselectivity. The textural properties of the materials do significantly affect the behavior upon recovery.This work was made possible by the generous financial support from the Spanish Ministerio de Economía y Competitividad (Project CTQ2011-28124), the Diputación General de Aragón (E11 Group co-financed by the European Regional Development Funds) and the AECI (Agencia Española de Cooperación International project A/8491/07).Peer Reviewe

Influence of zirconia addition in TiO₂ and TiO₂–CeO₂ aerogels on the textural, structural and catalytic properties of supported vanadia in chlorobenzene oxidation

This paper studies the effect of the direct incorporation of ZrO2 in TiO2 and TiO2–CeO2 aerogel supports prepared by sol–gel route on the physico–chemical and catalytic properties of supported vanadia catalysts in the total oxidation of chlorobenzene. The obtained catalysts have been characterized by means of ICP-AES, N2 adsorption–desorption at 77 K, XRD, XPS, H2-TPR and NH3-TPD. The results revealed that Zr-doped V2O5 based catalyst is beneficial for the improvement of catalytic properties in chlorobenzene total oxidation. In particular, in the absence of cerium groups, this beneficial effect is correlated with the better acidic properties or/and the stabilization of the V2O5 active phase in a higher oxidation state. However, in the case of cerium rich catalyst, this positive effect is much stronger thanks to the enhanced redox properties of V2O5/TiO2–CeO2–ZrO2

Effect of acidic components (SO42- and WO3) on the surface acidity, redox ability and NH3-SCR activity of new CeO2-TiO2 nanoporous aerogel catalysts: A comparative study

International audienceSelective catalytic reduction (SCR) of nitrogen oxide (NO) by ammonia (NH 3) was studied in this work over new sulfate (SO 4 2-) or tungsta (WO 3) modified CeO 2-TiO 2 aerogel catalysts. The catalytic systems were elaborated via sol gel method then characterized by: XRD, N 2-Physisorption at 77 K, DRUV-vis, NH 3-TPD and H 2-TPR. It was revealed that the nature of acidic components influences differently the texture, surface oxygen concentration, acidity, reducibility and NH 3-SCR activity of new Ce-based catalysts. Hence, the incorporation of sulfate modifies the nature of Ce species, improves their dispersion through the Ce-SO 4 2interactions and, particularly, generates new strong acid sites which display superior catalytic performance at high temperature NO reduction (NO conversion into N 2 > 90 % between 450 and 500 °C over CeO 2-TiO 2-SO 4 2catalyst). However, the addition of tungsta affects slightly the surface acidity of CeO 2-TiO 2 catalyst but it induces the creation of more reactive surface oxygen and new redox sites at its surface (mainly due to the existence of W-Ce interactions) leading to highly active WO 3-CeO 2-TiO 2 system for the low temperature NH 3-SCR reaction with above 90 % NO conversion into N 2 between 320 and 400 °C

Sol–gel derived mesoporous Cr/Al2O3 catalysts for SCR of NO by ammonia

International audienceCatalytic performances of Cr/Al2O3 catalysts were investigated in Selective Catalytic Reduction (SCR) of NO by NH3 in the presence of oxygen. Solids were prepared either by sol–gel method or by impregnation and were characterized by different techniques such as chemical analysis, N2 physisorption, XRD, 27Al MAS NMR, DRIFT, UV–Vis Diffuse Reflectance (DRS), Raman Spectroscopy and Temperature Programmed Reduction by H2 (H2-TPR). The physisorption of N2 at 77 K reveals that solids are mesoporous. On the other hand, XRD shows that xerogels are amorphous but supercritical drying leads to a nanosized crystallite state. No crystalline α-Cr2O3 was found which indicate that metal species reside essentially on the surface of Al2O3 and their size measured less than 4 nm. Furthermore, 27Al MAS NMR reveals that part of chromium ions occupies sites on/in Al2O3 in close vicinity of tetrahedral 27Al. This, apparently, is not the case for aerogels. DRIFT results show that there is a consumption of hydroxyl groups of alumina after calcination. The esterification reaction between hydroxyl groups and chromium oxide during calcination leads to the formation of anchored (poly-)chromates according to DRS, Raman, and H2-TPR results. The catalysts are active in the studied reaction by NH3 and the activity is principally governed by preparation method and operating conditions. When compared to xerogels, aerogels are more active in NO reduction and less selective toward N2O. Preparation method and drying mode seem to involve the predominance of active species which are essentially mono and polychromates but Cr3+ ions incorporated inside alumina seem to be inactive

Characterization and performance of over-exchanged Cu-ZSM-5 catalysts prepared by solid-state ion exchange for the selective catalytic reduction of NO by n-decane.

National audienceCu-ZSM-5 catalysts have been prepared by solid-state ion exchange at 500°C using CuCl and NH4- ZSM-5 mixture in presence of nitrogen flux. X-ray diffraction technique indicates that zeolite lattice is slightly modified for high copper loadings. The nature of copper species depends on copper exchange levels. For under exchanged catalyst, copper is mainly present as isolated Cu2+. For higher loadings, Cu+ and dispersed CuO-like species with different sizes and environments were detected besides Cu2+ ions. CuO-like species are located in the zeolite channels such as Cu2+-O-Cu2+ dimers or on the surface of zeolite crystals. Copper oxide clusters are not detectable by XRD technique, which indicates that they are amorphous and/or well dispersed on the external surface of the zeolite. The prepared catalysts show good activity in the selective catalytic reduction of NO by n-decane in oxidizing atmosphere independently of copper exchange level. The increase of copper content has an effect on the operating temperature window by decreasing the temperature of maximum NO conversion and total n-C10H22 oxidation. The presence of 25 ppm of SO2 in the reaction feed has a slight inhibiting effect for all catalysts excepting Cu(136)-Z for which NO conversion was enhanced in the temperature range of 320-425 °C

Promotional effect of ceria on the catalytic behaviour of new V2O5–WO3–TiO2 aerogel solids for the DeNOx process

International audienceNew cerium and/or tungsten modified V2O5–TiO2 aerogel catalysts (V2O5–TiO2,V2O5–WO3–TiO2, V2O5–CeO2–TiO2 and V2O5–WO3–CeO2–TiO2) were successfully developed, by associating the sol gel procedure and supercritical drying approach. A combination of various analytical techniques, including XRD, N2-Physisorption at 77 ​K, DRUV-Vis spectroscopy, NH3-TPD and H2-TPR, was used to characterize the obtained solids. Their catalytic performances were evaluated in the low temperature NO-SCR by NH3. The results reveal that all the materials exhibit high cristallinity of TiO2 anatase phase and developed mesoporous texture. The addition of tungsten (W) increases the surface acidity of V2O5–TiO2 and thereby enhances its reactivity at high temperatures (>420 ​°C). However, the addition of cerium (Ce) improves the redox properties of the latter catalyst and increases significantly its NO-SCR reactivity, especially at low temperatures. The NO-SCR activity increases over the aerogel systems, in the 200–400 ​°C temperature range, following this order: V2O5–WO3–TiO2 ​< ​V2O5–TiO2 ​< ​V2O5–CeO2–TiO2 ​< ​V2O5–WO3–CeO2–TiO2. The new V2O5–WO3–CeO2–TiO2 system was found to be the most active catalyst for converting NO into N2 (with 60% and 90% NO conversions at 250 ​°C and between 320 and 420 ​°C, respectively). The highest SCR activity of this new aerogel solid if compared to the other samples was essentially correlated with a good reactivity of its acidic and redox sites which in turn was related to the existence of strong interactions between cerium and the other active elements (mostly Ce↔ V and Ce ↔ W)