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Qiubin Kan - One of the best experts on this subject based on the ideXlab platform.

Jingqi Guan - One of the best experts on this subject based on the ideXlab platform.

Bernard Delmon - One of the best experts on this subject based on the ideXlab platform.

  • Catalytic behaviour of multiphasic oxide catalysts containing lanthanides (La, Ce, Pr, Sm, Tb) in the selective oxidation of isobutene to Methacrolein
    Catalysis Letters, 1996
    Co-Authors: F. Desmet, Patricio Ruiz, Bernard Delmon, M. Devillers
    Abstract:

    The catalytic performances of five lanthanide oxides (La2O3, Sm2O3, CeO2, Pr6O11 and Tb4O7) for the selective oxidation of isobutene to Methacrolein are evaluated within the framework of the remote control mechanism. Mechanical mixtures of these oxides with typical donor (Sb2O4) or acceptor (MoO3) phases of spill-over oxygen were prepared and tested for their activity in the isobutene-to-Methacrolein oxidation at 400 degrees C. Amongst the five lanthanide oxides tested, only CeO2 and Pr6O11 were found to display significant cooperation effects for the investigated reaction, with enhanced yields and selectivity for partial oxidation and concomitant decrease of CO2 production. The fresh and used catalysts were characterized by X-ray diffractometry, and the occurrence of solid state reactions between the partner oxides outside the reaction conditions was investigated in parallel in the temperature range 400-500 degrees C. No new phase was observed in the case of the mixtures with La2O3, Sm(2)O3, CeO2 and Tb4O7. Account taken of the absence of any new phase in the CeO2-MoO3 system, it can be concluded that CeO2 is a potential donor of spill-over oxygen. The situation in the MoO3-Pr6O11 mixtures is more complex, owing to the generation of various praseodymium molybdates, together with the oxocarbonate Pr2CO5. The latter phase was shown to have no intrinsic tendency to produce Methacrolein, but it seems that some of the praseodymium molybdates present in the working catalysts may exhibit noticeable catalytic properties.

  • Inhibition of Formation and Removal of Adsorbed Species, in the Isobutene Methacrolein Sno2-sb2o4 System
    Journal of Molecular Catalysis, 1992
    Co-Authors: Qin Xin, Patricio Ruiz, Xiexian Guo, Bernard Delmon
    Abstract:

    FT-IR measurements show that Methacrolein adsorbs on SnO2, and transforms to strongly held precursors of complete oxidation products at 300-400-degrees-C. In SnO2-Sb2O4 mechanical mixtures in the presence of oxygen however, where the remote control has been shown to operate, no such effect is observed. An identical effect is observed when the adsorbed species produced by the contact of isobutene and oxygen with the catalysts are studied. This suggests that the remote control modifies SnO2 surface sites in such a way that the adsorption strength of intermediate oxidation products of Methacrolein is depressed. This could be the reason for the increased selectivity in isobutene oxidation observed when Sb2O4 is mixed with SnO2.

  • phase cooperation between tin and antimony oxides in selective oxidation of isobutene to Methacrolein 1 mechanical mixtures of sno2 and alpha sb2o4
    Journal of Catalysis, 1991
    Co-Authors: Lt Weng, Patricio Ruiz, N Spitaels, B Yasse, Jean Ladriere, Bernard Delmon
    Abstract:

    Results are reported concerning the cooperation between SnO2 and α-Sb2O4 particles in the selective oxidation of isobutene to Methacrolein. The catalysts were prepared by mechanically mixing the corresponding powders. A conspicuous catalytic synergy was observed when Methacrolein production and selectivity to Methacrolein formation were considered. The catalysts, both fresh and used, were characterized by XRD, 119Sn Mossbauer spectroscopy, XPS, analytical electron microscopy (AEM), and ESR in order to investigate the origin of the synergy observed. The joint use of these techniques yielded no indication that a new phase (or solid solution) formed or that mutual surface contamination during either the preparation of the mixture or the catalytic test took place. Within the sensitivity limits of the techniques used, the mechanical mixtures can be considered as composed of two pure separate phases in good contact. The origin of the observed synergy and the other experimental observations is explained in a satisfactory manner by the existence of a “remote control” mechanism, i.e., that α-Sb2O4 produces a mobile oxygen species, namely spillover oxygen, which, by flowing onto the surface of SnO2, creates on the surface of the latter new selective sites and/or regenerates those which have become deactivated. Spillover oxygen produced by α-Sb2O4 seems to control the selective catalytic sites on SnO2 by inhibiting their transformation to reduced, nonselective sites. Spillover oxygen also inhibits the formation of carbonaceous deposits.

Fred C. Fehsenfeld - One of the best experts on this subject based on the ideXlab platform.

  • Measurements of 3‐methyl furan, methyl vinyl ketone, and Methacrolein at a rural forested site in the southeastern United States
    Journal of Geophysical Research, 1995
    Co-Authors: Stephen A. Montzka, Michael Trainer, Wayne M. Angevine, Fred C. Fehsenfeld
    Abstract:

    Three oxygenated hydrocarbons were measured in ambient air above a rural forested site in western Alabama. Mixing ratios of methyl vinyl ketone (MVK), Methacrolein (MACR), and 3-methyl furan were determined during a 3-week period in the summer of 1992. While the mean mixing ratio for methyl vinyl ketone was determined to be 740 parts per 1012 (ppt), the mean mixing ratio for Methacrolein was 480 ppt. The results for methyl vinyl ketone and Methacrolein are compared to previously reported measurements from this same location during the summer of 1990. Although isoprene levels were lower by ∼50% in 1992, mixing ratios of the carbonyls were reduced by only ∼25%. These differences are discussed in light of the changes that had occurred to the forest canopy in the time elapsed between the two measurement campaigns. Despite the differences observed during the 2 years, a consistent diurnal variability is observed for methyl vinyl ketone, relative to Methacrolein, during both years. In addition to a weak correlation observed between the carbonyls and temperature, levels of MVK and MACR in air sampled from just above the forest canopy are influenced by the depth of the mixed layer. A third oxidation product of isoprene, 3-methyl furan, was identified and measured in ambient air. Mean daytime mixing ratios were estimated at 60 ppt. Nighttime levels were lower, averaging 40 ppt. Mixing ratios of 3-methyl furan were highly correlated with isoprene (R2 = 0.82), and during the day, were typically ∼2% of levels measured for isoprene.

  • Isoprene and its oxidation products, methyl vinyl ketone and Methacrolein, in the rural troposphere
    Journal of Geophysical Research: Atmospheres, 1993
    Co-Authors: Stephen A. Montzka, Michael Trainer, Paul D. Goldan, William C. Kuster, Fred C. Fehsenfeld
    Abstract:

    The mixing ratios of methyl vinyl ketone (CH2=CHCOCH3) and Methacrolein (CH2=C(CH3)COH) were measured at a site located in the Kinterbish Wildlife Management Area in western Alabama. The measurements were made between June 15 and July 20, 1990. Considering all the data over the whole measurement period, the concentrations of these two carbonyls were approximately equal at this isolated rural site. The average mixing ratios for methyl vinyl ketone and Methacrolein were 0.98 parts per billion by volume (ppbv) and 0.66 ppbv, respectively, while the medians were 0.87 ppbv and 0.57 ppbv. The methyl vinyl ketone mixing ratio varied from 3.4 ppbv to the detection limit of the instrument, ≈0.01 ppbv, while the Methacrolein mixing ratio varied from 2.6 ppbv to 0.027 ppbv. These carbonyls constituted a significant fraction of the volatile organic compounds observed at the site: their mixing ratios, measured 2 m above the top of the forest canopy, were less than that of the dominant compound isoprene but were considerably greater than the mixing ratios of anthropogenic compounds (e.g., benzene). The mixing ratios of methyl vinyl ketone and Methacrolein were found to be highly correlated and exhibited a systematic variation with respect to each other. On average, during the day, methyl vinyl ketone was larger than Methacrolein, while Methacrolein tended to be slightly larger during the night. The systematic behavior of these compounds with respect to each other and other compounds measured at the site were simulated using a one-dimensional photochemical model. These observations were consistent with the production and loss of isoprene, methyl vinyl ketone, and Methacrolein by photochemical oxidation reactions.

Lihong Xing - One of the best experts on this subject based on the ideXlab platform.