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Brazilian Journal of Chemical Engineering, Volume: 15, Número: 2, Publicado: 1998
  • Cardoso, Dilson
  • EFFECT OF VANADIUM ON THE DEACTIVATION OF FCC CATALYSTS

    Roncolatto, R.E; Lam, Y.L.

    Resumo em Inglês:

    This work provides concrete evidence that vanadium causes the destruction of the zeolite in the FCC catalysts by a mechanism of acid attack or solid-solid transformation, as well as additional dealumination of the zeolite framework in the presence of steam and at high temperature. While these effects resulted in the reduction in crystallinity (zeolite Y content), specific area and unit cell size of the Y zeolite as the amount of vanadium in the catalysts increased, the reduction in activity was the most pronounced. The differences in these behaviors were interpreted and the model can be used for better catalyst formulation or screening.
  • A study on the Deactivation of Usy Zeolites with Different Rare Earth Contents

    Henriques, C.A.; Santos, J.O.J.; Polato, C.M.S.; Valle, M.L. Murta; Aguiar, E.F.S.; Monteiro, J.L.F.

    Resumo em Inglês:

    The deactivation of USY zeolites with different rare earth contents due to the coke formed from n-heptane at 450oC was studied. The results show that the presence of rare earth elements decreases the cracking and coking activities, increasing catalytic stability. However, reaction selectivity was not significantly influenced. The greater the rare earth content, the lower the coking rates and the coke contents. The TPO/DSC profiles suggested that the catalytic effect of the rare earth elements promoted coke oxidation.
  • Aldol Condensation of Citral with Acetone on Basic Solid Catalysts

    NODA, C.; ALT, G. P.; WERNECK, R. M.; HENRIQUES, C. A.; MONTEIRO, J. L. F.

    Resumo em Inglês:

    The catalytic performance of solids with basic properties, such as CaO, MgO and hydrotalcites, was evaluated in the aldol condensation of citral and acetone, the first step in the synthesis of ionones from citral. The best results were obtained with CaO and hydrotalcite with high conversions (98%) and selectivities (close to 70% for the main product) observed for both of the catalyst. Such pseudoionone yields were greater than those reported in the literature for the homogeneous reaction.
  • KINETIC ANALYSIS OF THE CATALYTIC DECOMPOSITION OF HYDRAZINE

    MEDEIROS, J.E. de; VALENÇA, G.P.

    Resumo em Inglês:

    The bond-order conservation method was used to study the catalytic decomposition of N2H4. Variation in the activation energy, E, of the most relevant steps was calculated as a function of the enthalpy of adsorption of N, QN, between 0 and 1250 kJmol-1. Results suggest that below QN = 520 kJmol-1 the catalytic decomposition of N2H4 produces mostly N2 and H2. Above QN = 520 kJmol-1, NH3 and N2 are the main products. Near QN = 520 kJmol-1 N2, H2 and NH3 are obtained, in agreement with experimental results on different metals.
  • n-HEPTANE CRACKING ON USY ZEOLITE THE EFFECT OF REACTION TEMPERATURE ON ACTIVITY AND DEACTIVATION

    SANTOS, R.F. dos; URQUIETA-GONZÁLEZ, E.A.

    Resumo em Inglês:

    n-Heptane cracking on a USY commercial zeolite at 350, 400 and 450ºC was studied. XRF, XRD, 27Al and 29Si-MAS-NMR were used for USY characterization. The nature of the coke was determined by 1H-NMR and infrared spectroscopy. It was observed that temperature influenced the nature of the coke formed, and that an increase in temperature led to a reduction in the solubility of coke in CH2Cl2 and an increase in its aromaticity. Despite these characteristics and the larger amount of coke formed, higher temperatures have less effect on the deactivation process than lower temperatures. Selectivity for C1-C6 fractions was hardly influenced by temperature, and it was that expected for the cracking mechanism of n-paraffins on acid catalysts.
  • SELECTIVE HYDROGENATION OF CINNAMALDEHYDE WITH Pt AND Pt-Fe CATALYSTS: EFFECTS OF THE SUPPORT

    Silva, A.B. da; Jordão, E.; Mendes, M.J.; Fouilloux, P.

    Resumo em Inglês:

    Low-temperature reduced TiO2-supported Pt and Pt-Fe catalysts are much more active and selective for the liquid–phase hydrogenation of cinnamaldehyde to unsaturated cinnamyl alcohol than the corresponding carbon-supported catalysts. High-temperature reduced catalysts, where the SMSI effect should be present, are almost inactive for this reaction. There is at present no definitive explanation for this effect but an electronic metal-support interaction is most probably involved.
  • Epoxidation of Cyclohexene on Heterogenized Molybdenum Compounds

    Barradas, E.F.M.; Cestari, A.R.; Airoldi, C.; Buffon, R.

    Resumo em Inglês:

    Heterogenization of molybdenum species, starting either with Mo(CO)6 or MoO2(acac)2, on the surface of functionalized silicas bearing one (Si-Et1) or two (Si-Et2) ethylenediamine ligands was studied. The resulting systems are active in the catalytic epoxidation of cyclohexene by tert-butyl hydroperoxide. Using fresh catalysts, Si-Et2 results in higher selectivity, regardless of the Mo precursor. However, MoO2(acac)2-based systems are far more active. Formation of diols was never detected. Although XPS analyses point mainly to Mo(VI) species on the surface of all systems, UV-vis spectra suggest different ligands in their coordination sphere
  • Hydroisomerization of Ethylbenzene on Mordenite-Based Bifunctional Catalysts with Different Platinum Contents

    Fernandes, L.D.; Corma, A.; Martinez, A.; Aguiar, E.F.S.; Monteiro, J.L.F.

    Resumo em Inglês:

    A commercial Na-mordenite sample underwent ion exchange with HCl. The ion-exchanged sample was sequentially submitted to hydrothermal treatments at 823, 873 and 923 K, each followed by acid leaching of the extraframework alumina (EFAL) generated. Six mordenite samples, presenting different framework and extraframework compositions, were obtained. These samples were used to prepare bifunctional catalysts by mixing them with Pt/Al2O3 in different proportions. The generated samples presented distinct platinum contents and were tested in the hydroisomerization reaction of ethylbenzene. A maximum xylene selectivity at about 0.45 wt% of platinum was observed. Normally, the total activity increased as the platinum content increased; this effect was more pronounced in the samples which presented lower mesoporosity. The most dealuminated sample, which presented a high mesoporosity, did not show any change in activity with the increase in platinum content.
  • MATHEMATICAL MODELLING OF METHANE STEAM REFORMING IN A MEMBRANE REACTOR: AN ISOTHERMIC MODEL

    ASSAF, E.M.; JESUS, C.D.F.; ASSAF, J.M.

    Resumo em Inglês:

    A mathematical modelling of one-dimensional, stationary and isothermic membrane reactor for methane steam reforming was developed to compare the maximum yield for methane conversion in this reactor with that in a conventional fixed-bed reactor. Fick's first law was used to describe the mechanism of hydrogen permeation. The variables studied include: reaction temperature, hydrogen feed flow rate and membrane thickness. The results show that the membrane reactor presents a higher methane conversion yield than the conventional fixed-bed reactor.
  • The Role of the Coprecipitation Sequence of Salt Precursors on the Genesis of Cu-ZnO-Al2O3 Catalysts: Synthesis, Characterization and Activity for Low Temperature Shift Reaction

    Figueiredo, R.T.; Andrade, H.M.C.; Fierro, J.L.G.

    Resumo em Inglês:

    Cu-ZnO-Al2O3 catalysts for the low-temperature water-gas shift reaction were prepared using methods of direct and reverse coprecipitation. The catalysts obtained were characterized by DRX, TPR, XPS, N2O chemisorption, Hg-Porosimetry and BET surface area. It was observed that the precipitation sequence of the precursors led to significant differences in values of copper dispersion and consequently in the activity of the catalyst for the water-gas shift reaction.
  • THE INFLUENCE OF NIOBIUM ON THE ACIDITY AND STRUCTURE OF GAMMA-ALUMINA-SUPPORTED VANADIUM OXIDES

    Sathler, M.N.B.; Eon, J.G.

    Resumo em Inglês:

    Gamma-alumina-supported niobium oxide was used as a support for vanadium oxides. The influence of the addition of niobium oxide was studied by looking for changes in the structure and acid-base character of superficial species. Vanadium oxide was deposited using the continuous adsorption method; niobium oxide was impregnated using the incipient wetness method. The catalysts were characterized by XPS, UV-visible and IR spectroscopy. Catalytic tests were performed using propane oxidation reaction at 400oC. For coverage below the monolayer, both vanadium and niobium oxides were observed in slightly condensed superficial species. The presence of vanadium oxide on the support was found to increase the Lewis acidity and create some Bronsted acidity. Higher catalytic activity and selectivity for propene were associated with vanadium oxides. The presence of niobium did not contribute to the modification of the chemical properties of superficial vanadium but did decrease the adsorption of vanadium on the alumina.
  • Ethylbenzene Disproportionation on HZSM-5 Zeolite: The Effect of Aluminum Content and Crystal Size on the Selectivity for p-Diethylbenzene

    Velasco, N.D.; Machado, M.S.; Cardoso, D.

    Resumo em Inglês:

    The aim of this work was to verify the effect of MFI aluminum content and crystal size on the selectivity for para-diethylbenzene during ethylbenzene disproportionation. It was observed that the para-diethylbenzene selectivity increased as MFI crystal size increased. The increase in aluminum content caused a decrease in the selectivity for para-diethylbenzene. However, for crystals larger than 8 <FONT FACE="Symbol">m</FONT> m, the decrease in aluminum content had little influence on the selectivity for para-diethylbenzene. The results can be explained by the number of active aluminum sites on the external surface of the crystals.
  • The Effect of Preparation Method on Pt/Nb2O5 Catalysts

    Eleutério, A.; Santos, J.F.; Passos, F.B.; Aranda, D.A.G.; Schmal, M.

    Resumo em Inglês:

    The use of the ion-exchange method and the addition of lithium to Pt/Nb2O5 catalysts were investigated in this work, using techniques of temperature-programmed reduction, H2 and CO chemisorption, UV-Vis diffuse reflectance spectroscopy and the conversion of n-heptane as a catalytic test. The superficial precursor present after the calcination step is platinum oxide, as previously observed for Pt/Nb2O5 catalysts prepared by the incipient wetness method. For some of the samples, autoreduction was observed during the calcination step, with the formation of low dispersion metallic platinum. The Pt/Nb2O5 catalysts prepared by ion exchange showed a high yield of olefins, as compared to aromatics, in the conversion of n-heptane. However, a high yield of hydrogenolysis products was also observed. For some of the lithium-containing samples, there was a suppression of dehydrogenation and aromatization reactions, with an increase in central C-C bond hydrogenolysis.
  • Pt-Rh/<FONT FACE=Symbol>g</FONT> Al2O3 Influence of Catalyst Preparation Methods on Metallic Particle Dispersion and Size Distribution

    Fonseca, N.M. da; Djega-Mariadassou, G.; Manoli, J.M.; Felcman, J.; Cunha, D.S.; Cruz, G.M. da

    Resumo em Inglês:

    - Pt-Rh/Al2O3 catalysts were prepared by successive incipient impregnations or coimpregnation. Characterization was achieved by H2 chemisorption and transmission electron microscopy. It was verified that method of preparation, ratio of metal weights and sequence of deposition are factors that result in very distinct catalysts.
  • Pt-Rh/<FONT FACE=Symbol>g</FONT> Al2O3 Benzene Hydrogenation Reaction as a Characterization Technique

    Fonseca, N.M. da; Neto, T.G.S.; Roma, M.N.S.C.; Felcman, J.; Cunha, D.S.; Cruz, G.M. da

    Resumo em Inglês:

    Pt-Rh/Al2O3 catalysts prepared by successive incipient impregnations and coimpregnation were characterized by H2 chemisorption, temperature programmed reduction and benzene hydrogenation reaction in the vapor phase. The results showed that Rh plays the role of Pt reducting agent, which is very different from the effects of metal-metal interaction which appear mainly in solids with the highest metal contents. The most important parameter that results in bimetallic particles in the catalyst prepared by successive impregnation is the sequence of metal addition.
  • Characterization and Catalytic Activity for the Oxidation of Ethane and Propane on Platinum and Copper Supported on CeO2/Al2O3

    Cataluña, R.; Marcilio, N.R.; Soria, J.; Cortés Corberán, V.; Martínez-Arias, A.

    Resumo em Inglês:

    Ethane and propane oxidation on platinum and copper supported on Al2O3 and CeO2/Al2O3 catalysts were studied comparatively by examining reaction rates as a function of temperature. Results show that the addition of cerium oxide shifts the catalytic activity to higher temperatures. This negative influence is less pronounced in the case of supported copper samples, which on the basis of EPR and FTIR of adsorbed CO results is attributed to the low relative amount of this metal is in contact with ceria. The decrease in activity the presence of ceria might be due to changes in metal particle size or to the stabilization of the oxidized states of the metals, induced by their interactions with cerium oxide. The higher activity of platinum, in comparison with copper, is attributed to its higher reducibility along with an easier hydrocarbon activation on that metal.
  • Metylcyclohexane conversion to light olefins

    SCOFIELD, C.F.; BENAZZI, E.; CAUFFRIEZ, H.; MARCILLY, C.

    Resumo em Inglês:

    This study consists in the evaluation of the catalytic properties of zeolites with different structures in the conversion of methylcyclohexane to light olefins. Results obtained suggest that the steric constrictions of the catalysts used play an important role in hydrogen transfer reactions. Higher selectivities for light olefins (C3= and C4=) were observed for zeolites having more closed structures, like MFI and ferrerite, when compared to those having more open ones, like beta, omega and faujasite.
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