27 research outputs found
Valorisation of vegetable oils by heterogeneous catalysis via metathesis reactions
No full textThe metathesis of unsaturated fatty acid methyl esters (FAME) to obtain value-added chemicals is becoming increasingly attractive in oleochemistry. Nevertheless, there is a need to develop efficient solid catalysts for FAME metathesis that would allow straightforward catalyst separation and recovery. In this work, the main advances achieved lately using novel heterogeneous catalysts for the homo-metathesis of methyl oleate and the cross-metathesis of methyl oleate with lower olefins are analyzed.Fil: Nieres, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Zelin, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Trasarti, Andres Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Apesteguia, Carlos Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentin
Structure sensitivity and in-situ activation of benzene combustion on Pt/Al2O3 catalysts
No full textThe structure sensitivity and in situ activation of benzene combustion on Pt/Al2O3 catalysts of different platinum and chlorine loadings were studied. The catalyst activities were evaluated through both conversion versus temperature (light-off curves) and conversion versus time catalytic tests. The light-off curves shifted to lower temperature with increasing Pt particle size, thereby suggesting that benzene combustion is a structure sensitive reaction. Kinetically-controlled catalytic tests confirmed that benzene oxidation turnover rates are preferentially promoted by larger Pt crystallites. Kinetic studies showed that the reaction orders and the apparent activation energy are not changed by changing the metallic dispersion. Results are explained by considering that benzene oxidation proceeds via a Langmuir–Hinshelwood mechanism which involves the rapid and strong adsorption of benzene on metallic platinum and assumes that the rate constant of oxygen adsorption is very low compared to the rate constant of the surface reaction. The number of PtO bonds of lower binding energy, i.e. the site density of more reactive surface oxygen, increases on larger Pt particles. Low-conversion catalytic tests performed at constant temperature showed that on well-dispersed Pt/Al2O3 catalysts the benzene conversion increases with time, irrespective of the chlorine content on the sample. TEM examination and hydrogen chemisorption measurements suggested that the activity increase parallels a concomitant increase in the platinum particle size. In contrast, sintered samples (platinum dispersions lower than 10%) did not exhibit initial activation periods. It is proposed that the initial in situ activation of well-dispersed Pt catalysts is caused by the sintering of the metallic phase. Hot-spots on the metallic particles together with the presence of gaseous water cause the formation of larger Pt crystallites, even at mild reaction conditions. As a result, the benzene conversion increases with time until the formation of larger steady state Pt particles is completed.Fil: Garetto, Teresita Francisca. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Apesteguia, Carlos Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentin
Imitation - Theory and Experimental Evidence
No full textWe introduce a generalized theoretical approach to study imitation models and subject the models to rigorous experimental testing. In our theoretical analysis we find that the different predictions of previous imitation models are due to different informational assumptions, not to different behavioral rules. It is more important whom one imitates rather than how. In a laboratory experiment we test the different theories by systematically varying information conditions. We find that the generalized imitation model predicts the differences between treatments well. The data also provide support for imitation on the individual level, both in terms of choice and in terms of perception. But imitation is not unconditional. Rather individuals' propensity to imitate more successful actions is increasing in payoff differences.Evolutionary game theory; Stochastic stability; Imitation; Cournot markets; Experiments
Determination of the accessible metal fraction and the metal particle size on coked Pt/Al2O3-Cl catalysts
No full textBio-hydrogen production by APR of C 2 -C 6 polyols on Pt/Al 2 O 3 : Dependence of H 2 productivity on metal content
No full textThe effect of the platinum loading on the production of hydrogen by aqueous-phase reforming of ethylene glycol, glycerol, xylitol and sorbitol was studied on Pt/Al2O3 catalysts containing 0.30, 0.57, 1.50 and 2.77 Pt%. Catalytic runs were performed at a space velocity of 1.2h-1, 498K, 29.3bar and using a polyol(1.0%)/water feed. The total polyol conversion and the polyol conversion to gaseous products increased with surface Pt concentration (Pts, μmol Pt/gcat). Similarly, the yield and the productivity to hydrogen (Pr, molH2/gh) increased continuously with Pts in all the cases, but the Pr values diminished with the polyol chain length. Coke formation depended on Pts and the polyol size; the amount of carbon formed on the catalyst increased indeed with Pts and diminished with the polyol chain length. The metal fraction was severely sintered during the APR reaction, irrespective of the reactant size. Nevertheless, the magnitude of the Pt dispersion drop was not dependent on the amount of platinum on Pt/Al2O3 catalysts.Fil: Duarte, Hernán Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Sad, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Apesteguia, Carlos Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentin
Simultaneous deactivation by coke and sulfur of Pt-Re(Ge,Sn)/Al2O3 catalysts for n-hexane reforming
No full textThe simultaneous deactivation by coke and sulfur of monometallic Pt/Al2O3 and bimetallic Pt–Re(Ge, Sn)/Al2O3 catalysts was studied using n-hexane reforming as bifunctional test reaction and thiophene as poisoning molecule. The residual activities in the activity decay curves were used for measuring the catalyst sensitivity to coke formation and sulfur poisoning. Sulfur and carbonaceous deposits accumulated essentially on the metallic fraction and affected the catalyst activity for both monofunctional metallic and bifunctional metal–acid catalyzed reactions. The overall deactivation rate for n-hexane conversion increased in the order Pt–Ge<Pt⪡Pt–Sn≤Pt–Re. This deactivation trend resulted from the combination of the catalyst resistance to each individual deactivation process. Pt–Ge/Al2O3 was the most stable catalyst essentially because of its high thiotolerance for n-hexane transformation reactions and also because it showed low activity for dehydrogenation reactions leading to the formation of coke precursors. Sulfur poisoning on Pt/Al2O3 decreased monofunctional metal-catalyzed reactions but concomitantly increased the activity for acid-controlled skeletal rearrangement reactions; as a result, n-hexane conversion was only slightly diminished by the addition of sulfur. Pt–Sn/Al2O3 showed high resistance to coke deactivation but was severely poisoned by the addition of sulfur. The Pt–Re/Al2O3 activity was significantly decreased by both deactivation processes. Changes in catalyst selectivity are interpreted in terms of selective deactivation by coke and sulfur of individual reaction pathways involved in the n-hexane reforming mechanism.Fil: Borgna, Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Garetto, Teresita Francisca. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Apesteguia, Carlos Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentin
Deep oxidation of propane on Pt-supported catalysts: Drastic turnover rate enhancement using zeolite supports
No full textThe combustion of propane was studied on Pt supported on MgO, alumina, and zeolites KL, HY, ZSM5 and Beta. Samples contained a similar amount of Pt, between 0.32 and 0.44%, and were characterized by employing a variety of physical and spectroscopic techniques. The catalyst activities were evaluated through both conversion versus temperature (light-off curves) and conversion versus time catalytic tests. Kinetic studies showed that the reaction is first order in propane, and zero (Pt/Al2O3, Pt/MgO) or negative (Pt/zeolites) orders in oxygen. Apparent activation energies (Ea) and pre-exponential factors (A) were determined and it was verified that the experimental data obey a Constable relation (ln A = mEa + c). Pt/Al2O3 catalysts of different metallic dispersions were prepared for investigating the effect of Pt crystallite size on combustion activity. It was found that propane oxidation is a structure insensitive reaction on Pt/Al2O3. Propane oxidation turnover rates (TOF) followed the order: Pt/MgO < Pt/Al2O3 Pt/KL < Pt/HY ≤ Pt/ZSM5 < Pt/Beta. The TOF values on Pt/acid zeolites were more than two orders of magnitude higher than on Pt/Al2O3. Propane oxidation activity was also significantly higher on Pt/KL
as compared to Pt/Al2O3, despite that Al2O3 and zeolite KL supports exhibited similar acid sites density and strength. This result showed that the support acid strength did not have a major influence on propane combustion activity. Areal propane uptake was more than one order of magnitude higher on Pt/zeolites than on Pt/Al2O3 and this drastic increase in the density of propane adsorbed species may promote the alkane oxidation rate. It is proposed that the enhanced combustion activity obtained on Pt/zeolites is associated with an additional oxidation pathway from propane adsorbing on the metal-oxide interface region and reacting with oxygen spilled-over from the metal surface.Fil: Garetto, Teresita Francisca. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Rincon, Eduardo Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Apesteguia, Carlos Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentin
Influence of The Chemical Composition on the Preparation of Cu-Co-Zn-Al Mixed Oxide Catalysts with A High Metal Dispersion
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Modeling of Simultaneous Deactivation Processes: Thioresistance and Coking on Pt Based Catalysts
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