30 research outputs found

    Mechanism of NO-SCR by methane over Co,H-ZSM-5 and Co,H-mordenite catalysts

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    Results of X-ray photoelectron spectroscopic (XPS) examination and temperatureprogrammed reduction measurements by H2 (H2-TPR) showed that the Co-zeolite catalysts, which were found most active in the selective catalytic reduction of NO by methane to N2 in the presence of excess O2 (NO-SCR), contain both Co2+/[Co-OH]+/H+ exchange cations, Cooxo species and cobalt oxide clusters. Using operando Diffuse Reflectance Infrared Fourier Transform Spectroscopic method (DRIFTS method) the NO-SCR reaction was shown to proceed in consecutive steps via bifunctional mechanism over active sites (i) promoting the oxidation of NO by O2 to NO2 (NO-COX reaction), and sites (ii) whereon disproportionation and charge separation of 2NO2 generates activated surface intermediate NO3 -/NO+ ion pair. Latter process was found to require Co2+ zeolite cations. The NO-COX reaction was shown to proceed over Co-oxo species and cobalt oxide, if present, and also over Brønsted acid sites but at a significantly lower rate. In the reaction of methane and the NO3 -/NO+ ion pair CO2, H2O, and N2 was formed and the active Co2+ sites were recovered (CH4/NO-SCR reaction). The surface concentration of the NO3 -/NO+ ion pair must have been controlled by the relative magnitude of the apparent rate constants of the consecutive NO-COX and CH4/NO-SCR reactions. Below about 700 K reaction temperature latter reaction governed the rate of the consecutive NO reduction process. Above about 700 K combustion became the main reaction of methane. Because of the low equilibrium NO2 concentration at these high temperatures the NO-COX reaction took over the control over the rate of the NO-SCR process. Under steady state reaction conditions a temperature-dependent fraction of the Co2+ active sites was always poisoned by adsorbed H2O formed in the CH4 oxidation reaction

    Selective hydroconversion of levulinic acid to γ-valerolactone or 2 methyltetrahydrofuran over silica-supported cobalt catalyst

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    Solvent-free hydroconversion of levulinic acid (LA) was studied over Co/silica catalysts applying flow-through fixed-bed microreactor. Consecutive hydrogenation/hydrogenolysis and dehydration reactions proceeded over the catalyst having Co0 metal and CoOx Lewis acid active sites. As a first step, LA was dehydrated to form angelica lactone (AL) intermediate. Because dehydration of LA is a facile reaction, the selectivity was controlled by the hydrogenation/hydrogenolysis activity of the catalyst. At 200 °C and 30 bar total pressure in the steady state, the catalyst could only saturate the double bond of AL ring. Thus, γ-valerolactone (GVL) was obtained with 98 mol% yield at full LA conversion. However, at temperature 225 °C the hydrogenation activity was high enough to cleave the GVL ring and obtain 2-methyltetrahydrofuran (2-MTHF) with a stable yield of about 70 mol %. FT-IR spectroscopic examination of the adsorbed LA showed the formation of H-bound LA and also surface carboxylate. 4-Hydroxy-3-pentenoate and 4-hydroxypentanoate were substantiated as surface intermediates of lactone formation by dehydration

    Ion beam surface engineering for highly active nanocatalysts

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    Interface science is at the forefront in the development of new materials for advanced technological applications. In particular, surface properties strongly influence catalysis which is essentially a surface phenomenon. One of the novel applications of ion beam irradiation includes the modification of the catalytic activity of solid catalysts. In this study we evaluated the effect of ion irradiation on the catalytic properties of Ce0.7Zr0.3O2 and the supported noble metal catalyst Pt/Ce0.7Zr0.3O2, which plays an important role in automotive exhaust control applications, among others. The effect on the catalytic properties is discussed from Temperature Programmed Oxidation (TPO) and Reduction (TPR) measurement, together with the results of microstructural (TEM) and IR spectrometric analyses

    Multifunkcionális polimer gélek és kompozitok kifejlesztése = Development of multifunctional smart polymer gels and composites

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    Ferromágneses vagy szuperparamágneses CoO és Co3O4 nanoporok oldatfázisú szintetizálása felületaktív anyagok jelenlétében történt vagy termikus bontással kombinált lecsapásos vagy szol-gél módszerrel. A szol-gél módszer etil-acetát és 1-propanol keverékében eredményezte a legkisebb méretű (átlagosan 85 nm-es) és polidiszperzitású (70-100 nm), egységes alakú, gömbszerű részecskéket. Vizes és organikus közegű stabil mágneses és elektroreológiai folyadékokat is előállítottunk. Vizsgáltuk a reológiai tulajdonságaikat: annak ellenére, hogy az elektro- és magnetosztatika törvényei alapján homogén sztatikus térben hasonló reológiai viselkedés várható, mégis található olyan jelenség, amely – jelenlegi ismereteink szerint - csak az elektroreológia folyadékoknál lép fel. Ilyen például az elektrokonvekció, vagy az általunk részletesen tanulmányozott részecske elektrorotáció. Mágneses- és elektromos térre érzékeny kolloid részecskéket rugalmas polimerbe és polimer gélbe építettük be. Izotróp és anizotróp géleket egyaránt szintetizáltunk, és vizsgáltuk ezek mechanikai és termodinamikai tulajdonságait. Poliszukcinimid- és poliaszparaginsav alapú géleket szintén készítettünk és tanulmányoztuk ezek gélkollapszuson alapuló nyitó-záró mechanizmusát. Vizsgáltuk a duzzadásfok változásának nagyságát, valamint a folyamat kinetikáját. A hálóláncok hidrofil/hidrofób jellegét különböző polaritású molekulák főlánchoz történő ojtásával multifunkcionális polimer géleket lehetett szintetizálni. | In the present work, CoO and Co3O4 nanoparticles were synthesized by various liquid-phase methods, namely, coprecipitation and sol-gel techniques combined with thermal decomposition. The best result (130-230 nm) could be achieved by application of cobalt nitrate, a carbonate agent and PDMS of 550 g mol-1. In the sol-gel procedures, the use of ethyl acetate yielded the finest particles with mean diameter of 85 nm and a narrow polydispersity (70-100 nm). The sol-gel method results in more spherical shaped and uniform particles, than those produced by coprecipitation. We have prepared magnetorheological and electrorheological fluids and studied the rheological behaviour as a function of external applied field. Isotropic and highly anisotropic magnetic field responsive gels were prepared and the deformation and the swelling under external fields were investigated on the basis of thermodynamic arguments. Chemically cross-linked poly(aspartic acid) (PASP) gels were prepared by the hydrolysis of poly(succinimide) (PSI). The PSI chains were cross-linked by natural amines and amino acid derivatives to obtain biodegradable, biocompatible hydrogels. The gels show a volume phase transition around the pK values of PASP. The most important network parameters were determined by a modified version of the Brannon–Peppas–Peppas theory. Kinetics of hydrolysis induced swelling as well as pure swelling of PSI and PASP gels were studied

    Technical Market Indicators: An Overview

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    The purpose of this study is to review the evidence in the scientiic literature on technical analysis applications in financial markets. In the empirical literature are the irst studies to analyze the usefulness of technical analysis, more recent studies applied to the international market and finally, studies developed for the Colombian market. Some of these studies provide important implications for market eficiency.El propósito de este estudio es revisar las evidencias en la literatura cientíica sobre las aplicaciones del análisis técnico en los mercados financieros. En la literatura empírica se encuentran los primeros estudios que analizan la utilidad del análisis técnico, estudios más recientes aplicados al mercado internacional, y por último, estudios desarrollados para el mercado colombiano. Algunos de estos estudios proporcionan implicaciones importantes sobre la eiciencia del mercado.Le but de cette étude est d’examiner les éléments de preuve dans la littérature scientiique sur les applications d’analyse technique des marchés financiers. Dans la littérature empirique sont les premières études pour analyser l’utilité de l’analyse technique, des études plus récentes appliquées sur le marché international et, enin, les études développées pour le marché colombien. Certaines de ces études fournissent des implications importantes pour l’eficacité du marché.O objetivo deste estudo é revisar as evidências na literatura cientíica sobre a aplicação da análise técnica nos mercados inanceiros. Na literatura empírica são os primeiros estudos que analisam o utilitário de análise técnica, estudos mais recentes aplicadas ao mercado internacional e por último, estudos desenvolvidos para o mercado colombiano. Alguns desses estudos fornecem importantes implicações sobre a eiciência do mercado
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