Raman identification of corrosion products on automotive galvanized steel sheets

Iron oxides (haematite, maghemite, magnetite), (oxy)hydroxides (lepidocrocite), carbonates, as well as zinc carbonate and oxide, have been identified on corroded galvanized steel samples after corrosion accelerating tests in the laboratory and compared with those observed on samples taken from vehicles that have been in circulation for five years in severe weather conditions. Spectra recorded on the corroded parts are compared with synthesized compounds. (Hydroxy)carbonates are clearly evidenced on galvanized and phosphated steel sheets. Corrosion layers beneath the paint could be detected. White regions always correspond to a ZnO‐rich phase but maghemite (γ‐Fe₂O₃) and sometimes akaganite (β‐FeOOHCl) are observed at the centre (maroon) of very corroded spots. Maghemite is observed in strongly corroded regions. Goethite (α‐) and lepidocrocite (γ‐FeOOH) (and akaganite) are observed at the surface of less corroded regions of phosphate‐free galvanized steel and are absent for phosphate‐coated steel. Green rust is observed only on galvanized samples corroded in the laboratory. Copyright © 2008 John Wiley & Sons, Ltd.     

Etude De L'acidité De Zéolithes Y Modifiées Par Différents Cations. Application à la réaction de reformage sec du méthane

A series of modified zeolite catalysts (HYM) was prepared by ion-exchange of a commercial faujasite Y by various cations (M=Ni, Cr, Fe, Li, Ce). The exchange level was calculated from the chemical analysis results. The acidity of the samples was determined by ammonia adsorption calorimetry which allowed the simultaneous determination of the number and strength of the acid sites. The order of acidity obtained was the following: HYCr>HY>HYNi>HYLi>HYFe>HYCe. These catalysts were tested in the dry reforming reaction of methane by carbon dioxide in the 400–700°C domain, under atmospheric pressure. The best catalytic performances were observed with the HYNi sample which displayed methane and dioxide conversions of 74,1 and 78,5% respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Catalytic properties of antimony-SBA-15 materials in the benzylation of aromatics reactions

Antimony-containing mesoporous SBA-15 with different Si/Sb ratio has been synthesized using a post-treatment procedure with an aqueous solution of SbCl₃ and characterized by elemental analysis, XRD method, N₂ adsorption measurements (BET and BJH theory) and FTIR spectroscopy. The benzylation of aromatics by benzyl chloride has been investigated over these solids. Indeed, the antimony-containing mesoporous SBA-15 showed both high activity and high selectivity for this reaction. More interesting is the observation that Sb-SBA-15 (35) catalyst is active and selective for large molecules like naphthenic compounds such as 2-methylnaphthalene and it can also be reused in the benzylation of benzene for several times. Kinetics of the benzene benzylation over these catalysts have also been investigated. Published in Russian in Kinetika i Kataliz, 2009, vol. 50, no. 3, pp. 428–433. The article is published in the original.     

Catalytic reforming of methane by carbon dioxide over nickel-exchanged zeolite catalysts

A series of nickel-exchanged catalysts based on ZSM-5, USY, and Mordenite zeolites has been prepared by the ionic exchange method. The NiZeol catalysts have been characterized by XRD and BET. The exchange levels and nickel contents of the catalysts have been determined by chemical analysis. The acidity of the zeolite supports has been investigated using NH₃ adsorption microcalorimetry. The number of acidic sites was found to decrease according to the following sequence: HUSY > HZSM-5 > HMOR. The temperature programmed reduction studies showed that the most reducible catalyst is NiZSM-5. The Ni-exchanged zeolites presented good catalytic performance in the methane reforming by CO₂. At a temperature of 650°C, CH₄ conversions of 71 and 54% were achieved on NiUSY and NiZSM-5 respectively. At 400°C, CO₂ FTIR adsorption has shown that CO₂ decomposes into CO and oxygen on NiZSM-5 which explains its reactivity at such a low temperature, while no decomposition of this probe molecule was observed on the NiUSY catalyst. The catalytic performance was found to vary in the following sequence at 650°C: NiUSY > NiZSM-5 > NiMOR. Moreover, the catalytic performances were found to depend strongly on the CO₂/CH₄ ratio in the feed and were markedly improved for CO₂/CH₄ greater than 1.     

Zinc-containing mesoporous silicas as a catalyst for the benzylation of benzene and other aromatics by benzyl chloride

The benzylation of benzene and the substituted benzenes reaction employing benzyl chloride as the alkylating agent over a series of zinc-containing mesoporous silicas with different Zn contents have been investigated. These materials (Zn-HMS-n) have been characterized by chemical analysis, BET, and XRD. The mesoporous zinc-containing materials showed both high activity and high selectivity for benzylation of benzene. The activity of these catalysts for the benzylation of different aromatic compounds is in the following order: benzene > toluene > p-xylene > anisole. The kinetics of the benzene benzylation over these catalysts has also been investigated. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 3, pp. 421–425.     

Study of the benzylation of benzene and other aromatics by benzyl chloride over transition metal chloride supported mesoporous SBA-15 catalysts

The benzylation of benzene by benzyl chloride to diphenylmethane over FeCl₃, InCl₃, GaCl₃, ZnCl₂, CuCl₂ and NiCl₂ supported on mesoporous SBA-15 at 353 K has been investigated. The redox property due to the impregnation of the SBA-15 by transition metal chloride seems to play a very important role in the benzene benzylation process. Among the catalysts, the FeCl₃/SBA-15 showed both high conversation and high selectivity for the benzylation of benzene. The activity of these catalysts for the benzylation of different aromatic compounds is in the following order: benzene > toluene > p-xylene > anisole. More interesting is the observation that this catalyst is always active and selective for large molecules like naphthenic compounds such as methoxynaphthalene and he can also be reused in the benzylation of benzene for several times. Kinetics of the benzene benzylation over these catalysts have also been investigated.     

Effects of support and metal loading on the characteristics of Co based catalysts for selective hydrogenation of citral

Silica-, alumina- and titania-supported Co catalysts with different metal loadings were tested for selective citral hydrogenation in liquid phase. Temperature programmed desorption of hydrogen (H₂-TPD) indicated that the catalysts with the highest unsaturated alcohols selectivities present particular H-Co species. Electron diffraction and XRD measurements revealed that these species would be linked to the presence of Co⁰ hexagonal phase. According to the results obtained by TEM and cyclohexane dehydrogenation, these two properties would be present on large Co particles.     

Hydrogen production on iron–magnesium oxide in the high-temperature water-gas shift reaction

The effect of the structure of the achiral primary amine additive on the enantioselective heterogeneous catalytic hydrogenation of (E)-2-methyl-2-butenoic acid over cinchonidine modified Pd/Al₂O₃ was studied. It was found that a variety of amines increase the enantioselectivity, which was always accompanied by decrease in the initial rate of the hydrogenations. Based on these results, the participation of the amine additive in the formation of the intermediate complex responsible for enantioselection was suggested. A decrease in the reaction temperature resulted in further increase in the optical purity of the product up to 67%, the highest value reported in the hydrogenation of unsaturated aliphatic acids in this heterogeneous catalytic system so far.     

Investigation of magnetically coupled ferromagnetic stripe arrays

We studied the magnetic coupling of ferromagnetic, submicron-sized stripes in the material system MnAs on GaAs. A specific coupling state, determined by stripe period and stripe width, can be tuned via film thickness and temperature, respectively. Micromagnetic imaging – in combination with micromagnetic simulations – reveals two coupling regimes. Strong magnetic coupling between the stripes creates micromagnetic domains extending across several stripes, whereas weak coupling allows for demagnetization within individual stripes. This behavior is observed for all investigatedfilm thicknesses, since a stripe geometry leading to a given coupling scenario is a function of temperature. PACS 68.37.Rt; 68.35.Rh; 75.70.-i; 75.70.Kw