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The characterisation by luminescence spectroscopy of uranium(VI) incorporated into zeolites and aluminas

Azenha, M. E. D. G.; Miguel, Maria da Graça; Formosinho, S. J.; Burrows, H. D.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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Luminescence spectroscopy of solids at 77 K has been used to characterise the uranium(VI) species incorporated into [alpha]-alumina, [gamma]-alumina and zeolites Y and ZSM-20 by adsorption from solution and into ZSM-5 by chemical synthesis. With uranyl adsorbed from nitrate solutions onto [alpha]- and [gamma]-aluminas, the luminescence measurements show the dominant uranium species is schoepite, UO3·xH2O, in agreement with results from X-ray diffraction and Raman spectroscopy. With uranyl acetate, there are indications that a crystalline acetate species is also present. With zeolite-Y and ZSM-20, the main species is a dimer. In addition, some monomeric [UO2(H2O)5]2+ is also present. With ZSM-5, although this is not observed in X-ray diffraction, the luminescence spectrum shows the presence of a species, similar to the schoepite seen with the aluminas. It is suggested that this may be due both to closely related polymeric species, and to uranyl anions, such as [UO2(OH)4]2- and [UO2(OH)3]-.; http://www.sciencedirect.com/science/article/B6TGS-435M5SD-2D/1/1fcff58939e013c8fdee4bba2d901a3b

Remoção de Pb2+ e Cr3+ em solução por zeólitas naturais associadas a rochas eruptivas da formação serra geral, bacia sedimentar do Paraná; Removal of Pb2+ and Cr3+ from aqueous solution by natural zeolites associated with eruptive rocks from the serra geral formation, Paraná sedimentary basin

SHINZATO, Mirian Chieko; MONTANHEIRO, Tarcísio José; Janasi, Valdecir de Assis; Andrade, Sandra; Yamamoto, Jorge Kazuo
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica
POR
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The capacity of natural zeolites and its host rock (dacite) to remove Pb2+ and Cr3+ from aqueous solutions has been investigated. Results showed that both samples prefer to remove Pb2+ instead of Cr3+. Almost 100% of Pb2+ was removed from solutions with concentration until 50 mg L-1 and 100 mg L-1 of this metal, respectively by dacite and zeolite. The equilibrium of metals adsorption process was reached during the first 30 min by both materials. Na+ can be used to recover Pb2+, but not to remove Cr3+ from the treated samples. The Sips model showed a good fit for experimental data of this study.; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudos sobre a remoção de íons metálicos em água usando zeólitas sintetizadas a partir de cinzas de carvão; STUDIES ON REMOVAL OF METAL IONS IN WATER USING ZEOLITES SYNTHESIZED FROM COAL ASHES

Izidoro, Juliana de Carvalho
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 07/08/2008 PT
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As cinzas de carvão podem ser convertidas em produtos zeolíticos por tratamento hidrotérmico alcalino. No presente estudo, a capacidade de zeólitas sintetizadas a partir de cinzas de carvão brasileiras (6 amostras da cinza volante do filtro de mangas e 6 amostras da cinza leve do filtro ciclone) na remoção de Zn2+ e Cd2+ de soluções aquosas foi investigada. O tempo de equilíbrio alcançado pela maioria das zeólitas foi de 24 horas. Os dados de equilíbrio obtidos se ajustaram à isoterma de adsorção de Langmuir. As capacidades de troca catiônica máximas estavam entre 25,9 e 39,5 mg g-1 para o Zn2+ e entre 49,5 e 72,3 mg g-1 para o Cd2+. A zeólita sintética (ZM1) apresentou área superficial no valor de 66,38 m2 g-1, baixa relação Si/Al (1,65) e a formação de zeólitas sodalita e faujasita, que contribuíram para seu melhor desempenho. Estudos de adsorção de íons metálicos com a ZM1 indicaram a seguinte seqüência de seletividade: Pb2+ > Cd2+ > Cu2+ > Zn2+ > Ni2+. Para a ZM1, a maior porcentagem de remoção de Zn2+ e Cd2+ foi obtida em pH 5 e a recuperação de metais foi efetivamente realizada com solução de NaCl 2 mol L-1. Comparou-se o desempenho das zeólitas sintetizadas a partir das cinzas de carvão com as zeólitas sintéticas comerciais...

Análise estrutural de zeólitos pelo método de Rietveld; Structural analysis of zeolites using the Rietveld method

Silva, Maria Teresa da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 27/03/1991 PT
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A primeira parte desta dissertação consiste em uma exposição de alguns aspectos do fenômeno de difração de raios X por cristais, de vários tipos estruturais de zeólitas e de uma introdução ao Método de Rietveld (MR)para refinamento de estrutura utilizando amostras policristalinas. Apresenta-se a seguir o resultado da aplicação do MR a uma amostra conhecida: a alumina Al2O3-α (Corindo). No teste foram refinados o fator de escala, o ponto zero (2θ0), os parâmetros de rede, os parâmetros atômicos posicionais e vibracionais e os parâmetros de perfil usando-se a função pseudo-Voigt. Passa-se então à aplicação do MR ao refinamento da estrutura de uma zeólita Y sinética e de três amostras da mesma zeólita após terem sido tratadas sob ação de vapor d´água e calor com (NH4) 2SO4 e com H2SO4; The first parto f this dissertation is presented some aspects of X-ray diffraction by crystals, different kind of zeolites and an introduction to the Rietveld Method (RM) of structure refinement by polycrystalline samples. The refinement of α- Al2O3 (Corindon) is then presented as a test for the use of RM. In this test the scale factor, the zero point (2θ0), the lattice parameters, the positional, vibrational atomic parameters and the profile parameters were refined using the pseudo-Voigt profile function. Next the RM is used for the structure refinement of a synthetic Y-zeolite and of three samples of the same zeolite after treatment with water vapour...

A questão do acesso em zeólitos : os zeólitos lamelares; The accessibility problem of zeolite sites : delaminated zeolites

Mendelssolm Kister de Pietre
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 20/07/2012 PT
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O presente trabalho descreve a síntese e esfoliação dos precursores lamelares [V,Al]-PREFER e [V,Al]-Nu-6(1), onde os elementos Al e V foram inseridos diretamente na síntese. Difração de raios-X, fisissorção de N2 e Si-MAS-RMN confirmaram o sucesso da esfoliação. A manutenção da entidade zeolítica foi observada por FTIR, através da presença dos anéis duplos, enquanto que a presença de Al tetraédrico, responsáveis pelos fortes sítios ácidos de Bronsted, foi confirmado por Al-MAS-RMN. Através das técnicas espectroscópicas, V-MAS-RMN e UV-Vis, observa-se que diferentes tratamentos conduzem a formação de espécies com ambientes distintos de vanádio. Para os catalisadores obtidos a partir do tratamento em meio alcalino, observou-se somente espécies de vanádio tetracoordenado com a estrutura. Por outro lado, os materiais derivados do processo em meio ácido, geram sítios octaédricos de vanádio, localizados fora da rede. A questão do acesso foi confirmada pela reação de desidratação da xilose. Os materiais esfoliados foram mais eficientes do que os respectivos zeólitos Nu-6(2) e ferrierita, evidenciando que os sítios ácidos estão mais facilmente acessíveis a moléculas volumosas. A sondagem da bifuncionalidade dos catalisadores [V...

Catalytic behavior of biosorbents supported in zeolites

Figueiredo, Hugo; Neves, Isabel C.; Quintelas, C.; Tavares, M. T.; Taralunga, M.; Mijoin, J.; Magnoux, P.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em 05/06/2005 ENG
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The catalytic oxidation of 1,2-dichlorobenzene at 350 oC was investigated over a robust biosorption system consisting of a bacterial biofilm supported on NaY or NaX zeolites. The batch method has been employed using chromium concentrations in solution ranging from 50 to 250 mgCr/L. The results showed that the maximum removal efficiency was 20% for Cr in both systems based in NaY or NaX. The bacterial biofilm, Arthrobacter viscosus, supported on the zeolite reduces Cr(VI) to Cr(III). The Cr(III) is retained in the zeolite by ion exchange. The new biosorvents catalysts were characterized by spectroscopic methods (FTIR and ICP-AES), surface analysis (DRX) and thermal analysis (TGA). The various techniques of characterization used show that this biosorption process does not modify the morphology and structure of the FAUzeolites. These catalysts, Cr/FAU, prepared through this new procedure present good activity and selectivity for dichlorobenzene oxidation in wet air. The Cr50-Y was selected as the most active, selective and stable catalyst for oxidation of 1,2 dichlorobenzene in wet air.; Fundação para a Ciência e a Tecnologia (FCT); Departamento de Ciências da Terra of Universidade do Minho; Agence de l’Environnement et de la Maîtrise de l’Energie (ADEME) and the Région Poitou-Charentes

Preparation of catalysts from biosorbents supported on zeolites

Figueiredo, Hugo
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Tese de Doutorado
Publicado em 03/04/2012 ENG
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Tese de doutoramento em Engenharia Química e Biológica; Heavy metal contamination of aquifers by industrial effluents is a known environmental concern for which a recent effort for the development of treatment/remediation technologies has been conducted. Nevertheless, technologies that allow recuperation/reutilization of the metals are still of limited application. This work presents the development of a clean technology allowing treatment and recovery of heavy metals in industrial effluents. The proposed recovered metals will be used as catalysts in liquid-phase oxidation reactions. The proposed system consists in bridging the biosorption capacity of the Arthrobacter viscosus bacterium with the intrinsic ion-exchange capacity of synthetic zeolites. This system was tested in the treatment of Cr(VI) solutions, in batch conditions (either in single step or sequencing reactor operation). The system showed capacity for the treatment of Cr(VI) solutions. Although zeolites have natural limitation to exchanging Cr(VI) species, as they are anionic in solution, the bacterium is able to reduce Cr(VI) to Cr(III) and the last is cationic in solution and therefore has access to the zeolites. Several operational parameters were evaluated in order to increase the performance of this system in the treatment of Cr(VI) solutions up to 100 mgCr/g. The pH in each reactor was allowed to vary freely in early studies. It was observed that the chemical composition of the zeolitic support had influence on the efficiency of the bioreduction of Cr(VI) to Cr(III). H+- containing zeolites allowed higher reduction than the Na+-containing counterparts. Despite this fact...

Evaluation of ion exchange-modified Y and ZSM5 zeolites in Cr(VI) biosorption and catalytic oxidation of ethyl acetate

Silva, Bruna Andreia Nogueira Airosa; Figueiredo, Hugo; Soares, O. S. G. P.; Pereira, M. F. R.; Figueiredo, J. L.; Lewandowska, A. E.; Bañares, M. A.; Bañares, M. A.; Neves, I. C.; Tavares, M. T.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica
Publicado em //2012 ENG
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The aim of this work was the evaluation of the performance of two zeolites with different structures (FAU and MFI) and acidity properties in the biosorption of Cr(VI) and catalytic oxidation of ethyl acetate. The starting zeolites, Y (FAU) and ZSM5 (MFI), were modified by ion exchange treatments with NaNO3 in order to obtain zeolites with different acidity and sodium content. A biosorption system consisting of a bacterium, Arthrobacter viscosus, supported on the different zeolites was used for Cr(VI) reduction and removal from solution. The best removal efficiencies and uptake of chromium, above 90% and 14 mgCr/gzeolite respectively, were achieved for Y zeolites due to their higher ion exchange capacity in comparison with ZSM5 zeolites. The ion exchange treatment did not produce considerable changes on the uptake process performed by the modified zeolites. Y and ZSM5 zeolites were characterized by ICP-AES, SEM, NH3 chemisorption, XRD and N2 adsorption. Y and ZSM5 zeolites obtained after biosorption presented chromium loadings between 0.92 and 1.20%, and were successfully reused as catalysts in the oxidation of ethyl acetate. The chromium-loaded ZSM5 zeolites were considerably more active and selective towards CO2 than chromium-loaded Y zeolites...

Evaluation of ion exchange-modified Y and ZSM5 zeolites in Cr(VI) biosorption and catalytic oxidation of ethyl acetate

Silva, Bruna Andreia Nogueira Airosa; Figueiredo, Hugo; Soares, O. S. G. P.; Pereira, M. F. R.; Figueiredo, J. L.; Lewandowska, A. E.; Bañares, M. A.; Neves, Isabel C.; Tavares, M. T.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2012 ENG
Relevância na Pesquisa
27.77%
The aim of this work is the evaluation of the performance of two zeolites with different structures (FAU and MFI) and acidity properties in the biosorption of Cr(VI) and catalytic oxidation of ethyl acetate. The starting zeolites, Y (FAU) and ZSM5 (MFI), were modified by ion exchange treatments with NaNO3 in order to obtain zeolites with different acidity and sodium content. A biosorption system consisting of a bacterium, Arthrobacter viscosus, supported on the different zeolites was used for Cr(VI) reduction and removal from solution [1]. The best removal efficiencies and uptake of chromium, above 90% and 14 mgCr/gzeolite respectively, were achieved for Y zeolites due to their higher ion exchange capacity in comparison with ZSM5 zeolites. The ion exchange treatment did not produce considerable changes on the uptake process performed by the modified zeolites. Y and ZSM5 zeolites were characterized by ICPAES, SEM, NH3 chemisorption, XRD and N2 adsorption. Y and ZSM5 zeolites obtained after biosorption presented chromium loadings between 0.92 and 1.20%, and were successfully reused as catalysts in the oxidation of ethyl acetate [2]. The chromium-loaded ZSM5 zeolites were considerably more active and selective towards CO2 than chromium-loaded Y zeolites...

Selective catalytic reduction of NO to N2 with copper and cobalt exchanged ZSM-5 zeolites: the effect of calcium addition

Martins,Leandro; Peguin,Robson Pablo S.; Wallau,Martin; Urquieta-González,Ernesto Antonio
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2005 EN
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ZSM-5 catalysts containing either Cu or Co cations individually or Cu/Ca or Co/Ca cation combinations were prepared by ion exchange. These materials were tested as catalysts for the reduction of NO to N2 in the presence of propane or methane. Cu2+ and [Cu-O-Cu]2+ species were identified in ion exchangeable sites in the copper-containing catalysts. The amount of the latter cation increased with increasing copper content and in the presence of Ca2+ and was the most active in the reduction of NO. However, at temperatures higher than 400 ºC its activity decreased markedly. For cobalt-exchanged zeolites, Co2+ in charge-compensation sites or Co3+ in extra-framework precipitates were present in the catalysts. It was verified that the amount of Co3+ diminished with the presence of Ca2+. For the catalysts prepared in this study no significant differences in specific activity for the reduction of NO or for methane oxidation were observed in the presence of calcium.

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.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/1998 EN
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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.

On the acidity and/or basicity of USY zeolites after basic and acid treatment

Calsavara,V.; Machado,N. R. C. F.; Bernardi Jr,J. L.; Sousa-Aguiar,E. F.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2000 EN
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The isopropanol decomposition reaction was used to evaluate the catalytic activity of ultrastable (USY) zeolites with different degrees of dealumination, treated in strongly alkaline medium at various temperatures and contact times. This treatment resulted in the reinsertion of non-framework aluminium, a result of the ultrastabilization process. The samples obtained were also submitted to an acid treatment, leaching the non-framework aluminium that had not been reinserted. The results obtained at 723K showed a large reduction in the acidic activity of the alkaline-treated zeolite, as the treatment conditions became more severe (the longer the treatment time or the higher the temperature, the higher the degree of dealumination). On the other hand, treated samples displayed some isopropanol dehydrogenation activity (basic sites). However, this activity was not very significant and did not depend on the alkaline treatment or ultrastabilization conditions used. The effect of reaction temperature and acid leaching on activity is also shown.

Characterization of three natural zeolites.

SOARES, F. S. C.; BERNARDI, A. C. de C.; NOGUEIRA, A. R. de A.
Fonte: In: INTERNATIONAL CONFERENCE ON FOOD AND AGRICULTURE APPLICATIONS OF NANOTECHNOLOGIES, 2010, São pedro, São Pedro: Aptor Software, 2010. Publicador: In: INTERNATIONAL CONFERENCE ON FOOD AND AGRICULTURE APPLICATIONS OF NANOTECHNOLOGIES, 2010, São pedro, São Pedro: Aptor Software, 2010.
Tipo: Resumo em anais de congresso (ALICE) Formato: p. 179
PT_BR
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In recent years, great attention has been paid to the application of nano structure materials. Since zeolites have primary particles with at least one dimension in the nanometer scale, they may be regarded as nanomaterials of geological and pedological origins. Zeolites are hydrated aluminosilicates, crystalline, with a wide variety of technological applications. Its structure consists of a skeleton with three-dimensional tetrahedral of AlO4 and SiO4, linked via oxygen atoms, and having channels and cavities in which it is possible to settle ions, water molecules or other adsorbates and salts. The Si and Al are at the center of the tetrahedron, the structural frame includes cavities occupied by relatively large sizes cations (Na+, K+, Ca2+, Mg2+) and water molecules, both having considerable freedom of movement, allowing ion exchange and reversible dehydration. High degree of hydration, low density, stability of the crystal structure, cation exchange properties, electrical conductivity, adsorption of gases and catalytic properties are the main properties of zeolites. About forty species of natural zeolites have been identified and over one hundred and fifty species have been synthesized. The synthetic zeolites have a high degree of purity and are widely used as catalysts for the petrochemical industry. In contrast...

Selective catalytic reduction of NO over copper ion-exchanged zeolites / by Kylie Headon.

Headon, Kylie
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado Formato: 333677 bytes; application/pdf
Publicado em //1999 EN
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Copper loaded Australian natural zeolites and ZSM-5 zeolites were investigated for the selective catalytic reduction of nitrogen oxides using CH4 and C3h6 with the specific aims of investigating natural zeolite as an alternative support to ZSM-5, determining a rate law for the selective catalytic reduction of nitrogen oxides using C3h6 over Cu-ZSM-5; and, investigating the molecular scale interactions of the reaction gases with Cu-ZSM-5.; Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1999; Bibliography: leaves 244-259.; xxii, 259 leaves : ill. ; 30 cm.; Title page, contents and abstract only. The complete thesis in print form is available from the University Library.

Application of natural zeolites in anaerobic digestion processes: A review

Guerrero, Lorna; Cortés, Isel; de la la Rubia, M. Angeles; Milán, Zhenia; Borja, Rafael; Sánchez, Enrique; Montalvo, Silvio
Fonte: Universidade do Chile Publicador: Universidade do Chile
Tipo: Artículo de revista
EN_US
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Artículo de publicación ISI; This paper reviews the most relevant uses and applications of zeolites in anaerobic digestion processes. The feasibility of using natural zeolites as support media for the immobilization of microorganisms in different high-rate reactor configurations (fixed bed, fluidized bed, etc.) is also reviewed. Zeolite, with its favorable characteristics for microorganism adhesion, has also been widely used as an ion exchanger for the removal of ammonium in anaerobic digestion due to the presence of Na+, Ca2+ and Mg2+ cations in its crystalline structure. This property is also useful for improving the anaerobic process performances in the treatment of wastewaters with high concentrations of nitrogen compounds, such as cattle, pig and chicken wastes, as it prevents process inhibition. The influence of zeolite particle size and doses in batch mesophilic and thermophilic processes when referring to synthetic or different wastewaters is also reviewed. Finally, the role of zeolite in granulation processes, in anaerobic oxidation processes (Anammox) for promoting the retention of the biomass involved (given its low growth rate), and in hybrid and sequencing reactors such as the moving bed biofilm reactors (MBBR) are also discussed.

A computational study of CO2, N2, and CH4 adsorption in zeolites

García-Pérez, E.; Parra Soto, José Bernardo; Ovín Ania, María Concepción; García-Sánchez, A.; Van Baten, J. M.; Krishna, R.; Dubbeldam, D.; Calero, S.
Fonte: Springer Publicador: Springer
Tipo: Artículo Formato: 918459 bytes; application/pdf
ENG
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8 pages, 8 figures.-- Printed version published Dec 2007.; The adsorption properties of CO2, N2 and CH4 in all-silica zeolites were studied using molecular simulations. Adsorption isotherms for single components in MFI were both measured and computed showing good agreement. In addition simulations in other all silica structures were performed for a wide range of pressures and temperatures and for single components as well as binary and ternary mixtures with varying bulk compositions. The adsorption selectivity was analyzed for mixtures with bulk composition of 50:50 CO2/CH4, 50:50 CO2/N2, 10:90 CO2/N2 and 5:90:5 CO2/N2/CH4 in MFI, MOR, ISV, ITE, CHA and DDR showing high selectivity of adsorption of CO2 over N2 and CH4 that varies with the type of crystal and with the mixture bulk composition.; This work is supported by the Spanish “Ministerio de Educación y Ciencia” (CTQ2007-63229/BQU), by the National Science Foundation (CTS-0507013), and by the resources, technical expertise and assistance provided by BSC-CNS. E. García-Pérez wishes to thank the MEC for a predoctoral fellowship. RK acknowledges the grant of a TOP subsidy from the Netherlands Foundation for Fundamental Research (NWO-CW) for intensification of reactors and NWO/NCF for provision of high performance computing resources. JBP thanks ITQ-CSIC for kindly supplying the silicalite.; Peer reviewed

Titanium-Containing Zeolites and Microporous Molecular Sieves as Photovoltaic Solar Cells

Atienzar Corvillo, Pedro; Valencia, Susana; Corma, Avelino; García Gómez, Hermenegildo
Fonte: John Wiley & Sons Publicador: John Wiley & Sons
Tipo: Artículo Formato: 22092 bytes; application/pdf
ENG
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Final edited full-text version of the paper available at: http://dx.doi.org/10.1002/cphc.200700019; Four titanium-containing zeolites and microporous molecular sieves differing on the crystal structure and particle size (Ti/Beta, Ti/Beta-60, TS-1 and ETS-10) are prepared, and their activity for solar cells after incorporating N3 (a commercially available ruthenium polypyridyl dye) is tested. All the zeolites exhibit photovoltaic activity, and the photoresponse is quite independent of the zeolite pore dimensions or particle size. The photoresponse increases with titanium content in the range 1-7% wt. In this way, cells are obtained that have open-circuit voltage Voc=560 mV and maximum short-circuit photocurrent density Isc=100 μA, measured for 1×1 cm2 surfaces with a solar simulator at 1000 W through and AM 1.5 filter. These values are promising and comparable to those obtained for current dye-sensitized titania solar cells.; Financial support by the Spanish Ministry of Science and Education (CTQ 2006–06 875) is gratefully acknowledged. P.A. thanks the Ministry of Science and Education and the Universidad Politécnica for two post-graduate scholarships.; Peer reviewed

Structure and reactivity of dehydroxylated bronsted acid sites in H-ZSM-5 zeolite: generation of stable organic radical cation and catalytic activity for isobutane conversion

Yun, Jang Ho
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
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Lobo, Raul F.; Zeolites are crystalline aluminosilicate materials that have wide application in industry as solid acid catalyst. Since zeolites have high acidity, high surface area as well as the ability to do shape selectivity, they are used primarily as a solid catalyst in oil refining and petrochemical industries, in processes such as hydrocracking, fluid catalytic cracking (FCC). Bronsted acid sites are described as a hydroxyl group bridged between Al and Si (Al-OH-Si). It is well known that Bronsted acid sites are significant in a number of hydrocarbon processes, such as alkane cracking and isomerization and many other. The Bronsted acid sites of zeolites are decomposed at high temperatures, usually above 600 ̊C. This high temperature condition is commonly found in the fluidized catalytic cracking where catalyst is recycled forth and back between the riser and the regenerator under an oxidative atmosphere. The process of decomposition of hydroxyl group from the initial structure is called dehydroxylation. The dehydroxylation is believed to proceed via a dehydration mechanism of the acid sites. This heterolytic pathway of Bronsted acid site decomposition has been the accepted dehydroxylation path for low-silica zeolites for decades...

Experimental investigations of the structure-property relations of CO2-selective zeolite adsorbents

Pham, Trong D.
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
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Lobo, Raul F.; Due to the increase in the anthropogenic CO2 emissions, the development of carbon capture and storage technology is of profound importance to minimizing global climate change and preserving our environment. In this thesis, I have investigated the adsorption properties of cation-exchanged high silica zeolites chabazite (CHA, Si/Al=6 and 12) and ZK-5 (KFI, Si/Al=3.7) due to their high surface area, large pore volume, and moderate hydrophilic properties compared to commercial faujasite and Linde type A zeolites. For zeolite materials to be practical and useful as adsorbents for CO 2 capture from flue gas, a number of aspects need to be carefully evaluated including adsorption and working capacities, selectivity, and adsorbent regeneration. We found that Li-, and Na-zeolites having high heats of adsorption (40-50 kJ/mol) performed better in the vacuum swing adsorption process and H- and K-zeolites or zeolites with higher Si/Al ratio (CHA, Si/Al=12) having lower heats of adsorption (30-40 kJ/mol) display properties more suited to pressure swing adsorption. The in situ FTIR CO 2 adsorption spectra show that physisorption accounts for the largest fraction of the total CO 2 adsorbed. A shift to higher frequency of the asymmetric stretching vibration compared to CO2 gas phase (2349 cm-1) indicated the direct coordination of cations with oxygens of CO2 molecules. To improve zeolite adsorbents for CO2 capture...

Isosteric Heats of Adsorption of N2O and NO on Natural Zeolites

Domínguez,Gerardo; Hernández-Huesca,Rosario; Aguilar-Armenta,Gelacio
Fonte: Sociedad Química de México A.C. Publicador: Sociedad Química de México A.C.
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2010 EN
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We studied the capacities of three natural zeolites to adsorb N2O or NO using a glass high-vacuum volumetric system that permitted characterization of the energetics of the adsorption process. Adsorption equilibrium data were analyzed using the classical Freundlich equation and the Dual-Langmuir model. We employed the Clausius-Clapeyron relationship to calculate the isosteric heats of adsorption using the equilibrium data of the isotherms measured at 273.15 K and 293.15 K. The isosteric heats of reversible adsorption of both gases were smaller than the heats of total adsorption. The interaction energy of N2O with mordenite was larger than the interaction energies of N2O with either erionite or clinoptilolite. The interaction energy of NO was found to be largest with erionite.