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Carbon supported platinum catalysts for catalytic wet air oxidation of refractory carboxylic acids

Gomes, Helder; Serp, Philippe; Kalck, Philippe; Figueiredo, José; Faria, Joaquim
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.07%
Carbon supported platinum (1% wt) catalysts were prepared by the incipient wetness impregnation method and by organometallic chemical vapor deposition. Catalyst characterization was carried out by means of adsorption and thermogravimetric techniques, and by electron microscopy. The catalyst with higher metal dispersion was produced by incipient wetness impregnation. The catalysts were tested in the catalytic wet air oxidation (200 C and 6.9 bar of oxygen partial pressure) of aqueous solutions containing low molecular weight (C2 to C4) carboxylic acids. Significant conversions (greater than 60% over 2 h) and 100% selectivity towards water and non-carboxylic acid products were observed for both systems. The initial reaction rate was used to compare the performance of the two catalytic materials and direct correspondence to the metal dispersion was found. No metal leaching was observed during reaction and no significant deactivation occurred in three successive catalytic oxidation runs. A kinetic model based on the Langmuir–Hinshelwood formulation was applied and the results were analyzed in terms of a heterogeneously catalyzed free radical mechanism.

Structured catalysts for partial oxidations

Campos, Victor J. M. de; Quinta-Ferreira, Rosa M.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
Português
Relevância na Pesquisa
36.18%
The objective of the present work is centred on the analysis of the behaviour of fixed-bed reactors packed with structured catalysts when a partial oxidation takes place. The fluid flow within an element, formed by the intersection of two adjacent corrugated plates, was mathematically modelled and numerical simulations were performed in order to study possible optimising of the catalyst structure. A simple model, involving the continuous stirred tank approach, was used to simulate the performance of the catalyst in an industrial reactor. The profiles of temperature, concentration, velocity and pressure along the reactor were obtained through the global mass balance, partial molar balances, conservation of moment, energy balance and mechanical energy balance. These equations were applied to an exothermic reactional system, the selective oxidation of methanol to formaldehyde, in order to evaluate the possibility of application of these catalysts in industry. Various parameters specific to the catalyst and the reactional system were tested in order to achieve a better understanding of the behaviour of these structured packing. The comparison with the heterogeneous model predictions for a random packing and with industrial values pointed out that the choice of parameters is fundamental to the performance of the catalyst. The adjustments to the parameters allows for significant improvements in some of the more troublesome aspects of the reactional system. Lowering the hot-spot...

Synthesis of NiO-MgO-ZrO(2) catalysts and their performance in reforming of model biogas

ASENCIOS, Yvan J. O.; BELLIDO, Jorge D. A.; ASSAF, Elisabete M.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.21%
Catalysts containing NiO/MgO/ZrO(2) mixtures were synthesized by the polymerization method in a single step. They were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR) and physisorption of N(2) (BET) and then tested in the reforming of a model biogas (1.5CH4:1CO(2)) in the presence of air (1.5CH(4) + 1CO(2) + 0.25O(2)) at 750 degrees C for 6h. It was observed that the catalyst Ni20MZ performed better in catalytic processes than the well known catalysts, Ni/ZrO(2) and Ni/MgO, synthesized under the same conditions. The formation of solid solutions, MgO-ZrO(2) and NiO-MgO, increased the rate of conversion of reactants (CH(4) and CO(2)) into synthesis gas (H(2) + CO). The formation of oxygen vacancies (in samples containing ZrO(2) and MgO) seems to promote removal of the coke deposited on the nickel surface. The values of the H(2)/CO ratio were generally found to be slightly lower than stoichiometric, owing to the reverse water gas shift reaction occurring in parallel. (C) 2011 Elsevier B.V. All rights reserved.; Brazilian National Council for Scientific Development (CNPq); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Methane conversion reactions on Ni catalysts promoted with Rh: Influence of support

LUCREDIO, Alessandra F.; ASSAF, Jose M.; ASSAF, Elisabete M.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.11%
Ni catalysts supported on gamma-Al(2)O(3) and Mg(Al)O were prepared with and without Rh as a promoter and tested in the reforming of methane in the presence of excess methane, simulating a model biogas. The effects of adding synthetic air on the methane conversion and the formation of carbon were assessed. The catalysts were characterized by X-ray spectroscopy (EDS), surface area (BET), X-ray diffraction (XRD), Temperature-programmed reduction (TPR), X-ray absorption near-edge structure (XANES) and XPD. The results showed that in catalysts without Rh, the Ni interacts strongly with the supports, showing high reduction temperatures in TPR tests. The addition of Rh increased the amount of reducible Ni and facilitated the reduction of the species interacting strongly with the support. In the catalytic tests, the samples promoted with Rh suffered higher carbon deposition. The in situ XPD suggested that on the support gamma-Al(2)O(3), the presence of Rh probably led to a segregation of Ni species with time on stream, leading to carbon deposition. On the support MgAlO, the presence of Rh improved the dispersion of Ni, by reducing the Ni(0) crystallite size, suggesting that in this case the carbon deposition was due to a favoring of CH(4) decomposition by Rh. (C) 2011 Elsevier B.V. All rights reserved.; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq

Effects of catalyst load in Pt and Pb-based catalysts using formic acid oxidation as a model

Buzzo, G. S.; Orlandi, M. J. B.; Teixeira-Neto, E.; Homem-de-Mello, P.; Lopes, A. C. G.; Franco-Junior, E.; Suffredini, H. B.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.17%
In this paper, we discuss the effects of catalyst load with respect to carbon powder for several Pt and Pb-based catalysts, using formic acid as a model molecule. The discussion is based on electrochemical tests, a complete morphological investigation and theoretical calculations. We show that the Pt and Pb-based catalysts presented activity in formic acid oxidation at very low catalyst loads (e.g., 0.5% in respect to the carbon content). Physical characterisations demonstrate that the electrodes are composed of separated phases of Pt and lead distributed in Pt nanometric-sized islands that are heterogeneously dispersed on the carbon support and Pb ultra-small particles homogeneously distributed throughout the entire carbon surface, as demonstrated by the microscopy studies. At high catalyst loads, very large clusters of Pb(x)O(y) could be observed. Electrochemical tests indicated an increase in the apparent resistance of the system (by a factor of 19.7 Omega) when the catalyst load was increased. The effect of lead in the materials was also studied by theoretical calculations (OFT). The main conclusion is that the presence of Pb atoms in the catalyst can improve the adsorption of formic acid in the catalytic system compared with a pure Pt-based catalyst. (C) 2011 Elsevier B.V. All rights reserved.; FAPESP; FAPESP [2007/05155-1...

Reações de reforma de biogás sobre catalisadores de NiO-MgO-ZrO2 e NiO-Y2O3-ZrO2; Reforming of biogas on NiO-MgO-ZrO2 and NiO-Y2O3-ZrO2 catalysts

Asencios, Yvan Jesús Olortiga
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 29/11/2012 Português
Relevância na Pesquisa
36.24%
A fermentação anaeróbia da matéria orgânica produz uma mistura de gases chamada biogás. Este biogás contém CH4 e CO2 como componentes majoritários. Estes dois compostos são gases de efeito estufa e sua utilização é muito importante do ponto de vista ambiental e econômico. O presente trabalho teve por objetivo produzir gás de síntese (H2/CO), uma matéria prima de alto valor industrial, a partir da reforma oxidativa do biogás com adição de oxigênio (1,5CH4+1,0CO2+0,25O2) sobre catalisadores de NiO-MgO-ZrO2 e NiO-Y2O3-ZrO2. Os catalisadores foram preparados usando o método de polimerização numa única etapa e foi estudada a variação do teor de MgO e de Y2O3 contido nas amostras. Estes materiais foram caracterizados por DRX, RTP, Adsorção-dessorção de N2, XPS, XAS-XANES, MEV e EDX e foram avaliados na reação de reforma oxidativa de um biogás modelo (composição molar:1,5 CH4/1CO2) em presença de oxigênio, a 750°C e 1atm, visando à obtenção de gás de síntese. Os teores de MgO utilizados no sistema NiO/MgO/ZrO2 foram de 0%, 4%, 20%, 40% e 100% em relação ao ZrO2 (os mesmos teores foram utilizados para Y2O3 no sistema NiO/Y2O3/ZrO2) e o teor mássico de Ni foi 20%. As análises de DRX, TPR...

Estudo das propriedades físico-químicas de sistemas Pd, Pd-Fe e Pd-Co suportados em CeO2/Al2O3; Study of the physico-chemical properties of the Pd, Pd-Fe and Pd-Co systems supported at CeO2/Al2O3

Eleonora Maria Pereira de Luna Freire
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 2005/08/3 Português
Relevância na Pesquisa
36.2%
Os catalisadores à base de paládio apresentam particular interesse para o tratamento de gases de exaustão automotiva, notadamente no caso da combustão do etanol. O presente trabalho tem o objetivo de estudar as propriedades físico- químicas de catalisadores Pd - Fe e Pd - Co suportados em alumina modificada pelo óxido de cério. Para tanto, catalisadores modelo foram preparados através do método de impregnação por via úmida, empregando-se sais precursores à base de nitrato dos metais, e os suportes Al2O3, CeO2 e CeO2/Al2O3. Os catalisadores obtidos tiveram seus teores metálicos determinados por meio de espectrofotometria de absorção atômica, tendo sido caracterizados através de adsorção de nitrogênio (método B.E.T), espectroscopia no infravermelho, difração de raio-X, redução à temperatura programada. Os sistemas preparados foram avaliados pela reação catalítica de oxidação do etanol em fase gasosa em um microreator tubular de leito fixo, operando a pressão atmosférica e a temperatura de 3500 C. Os catalisadores preparados apresentam frações mássicas em torno de 2 % para o Pd, e de 1% para os aditivos Fe ou Co. A adição de Pd, Pd-Fe e Pd-Co aos suportes Al2O3 e CeO2/Al2O3 não levou a modificações...

Towards an atomic level understanding of niobia based catalysts and catalysis by combining the science of catalysis with surface science

Schmal,Martin; Freund,Hans-Joachim
Fonte: Academia Brasileira de Ciências Publicador: Academia Brasileira de Ciências
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2009 Português
Relevância na Pesquisa
46.28%
The science of catalysis and surface science have developed, independently, key information for understanding catalytic processes. One might argue: is there anything fundamental to be discovered through the interplay between catalysis and surface science? Real catalysts of monometallic and bimetallic Co/Nb2O5 and Pd-Co/Nb2O5 catalysts showed interesting selectivity results on the Fischer-Tropsch synthesis (Noronha et al. 1996, Rosenir et al. 1993). The presence of a noble metal increased the C+5 selectivity and decreased the methane formation depending of the reduction temperature. Model catalyst of Co-Pd supported on niobia and alumina were prepared and characterized at the atomic level, thus forming the basis for a comparison with "real" support materials. Growth, morphology and structure of both pure metal and alloy particles were studied. It is possible to support the strong metal support interaction suggested by studies on real catalysts via the investigation of model systems for niobia in comparison to alumina support in which this effect does not occur. Formation of Co2+ penetration into the niobia lattice was suggested on the basis of powder studies and can be fully supported on the basis of model studies. It is shown for both real catalysts and model systems that oxidation state of Co plays a key role in controlling the reactivity in Fischer-Tropsch reactions systems and that the addition of Pd is a determining factor for the stability of the catalyst. It is demonstrated that the interaction with unsaturated hydrocarbons depends strongly on the state of oxidation.

Flash Pyrolysis of Oleic Acid as a Model Compound Adsorbed on Supported Nickel Catalysts for Biofuel Production

Fréty,Roger; Santos,Marilia R.; Sales,Renan F.; Silva,Antonio O. S.; Barbosa,Celmy B. M.; Pacheco,Jose G. A.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2014 Português
Relevância na Pesquisa
36.17%
Flash pyrolysis of oleic acid was studied over 10 wt.% nickel catalysts supported on silica and alumina. The catalysts were impregnated with 10 wt.% oleic acid. The dried precursors and the catalysts containing oleic acid were characterized by thermogravimetric analysis. The calcined catalysts were analyzed by X-ray diffraction (XRD) and temperature programmed reduction (TPR). Samples containing adsorbed oleic acid were submitted to flash pyrolysis up to 650 °C. Whereas pyrolysis of oleic acid without catalyst converted only about 10%, the pyrolysis of oleic acid adsorbed on catalysts allowed practically a complete conversion. NiO/alumina yielded a higher amount of liquid hydrocarbons than NiO/silica. The main products obtained with NiO/silica were 1-alkenes, whereas the main products obtained with NiO/alumina were alkene isomers and aromatics. Small amounts of oxygenated compounds were also observed, principally alcohols. The flash pyrolysis of oleic acid adsorbed on different catalyst surfaces appears as a useful way to distinguish activity trends of different catalyst samples.

EFFECT OF VANADIUM ON THE DEACTIVATION OF FCC CATALYSTS

Roncolatto,R.E; Lam,Y.L.
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 Português
Relevância na Pesquisa
36.07%
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.

Surface science of single-site heterogeneous olefin polymerization catalysts

Kim, Seong H.; Somorjai, Gabor A.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.29%
This article reviews the surface science of the heterogeneous olefin polymerization catalysts. The specific focus is on how to prepare and characterize stereochemically specific heterogeneous model catalysts for the Ziegler–Natta polymerization. Under clean, ultra-high vacuum conditions, low-energy electron irradiation during the chemical vapor deposition of model Ziegler–Natta catalysts can be used to create a “single-site” catalyst film with a surface structure that produces only isotactic polypropylene. The polymerization activities of the ultra-high vacuum-prepared model heterogeneous catalysts compare well with those of conventional Ziegler–Natta catalysts. X-ray photoelectron spectroscopic analyses identify the oxidation states of the Ti ions at the active sites. Temperature-programmed desorption distinguishes the binding strength of a probe molecule to the active sites that produce polypropylenes having different tacticities. These findings demonstrate that a surface science approach to the preparation and characterization of model heterogeneous catalysts can improve the catalyst design and provide fundamental understanding of the single-site olefin polymerization process.

Nanostructured, mesoporous Au/TiO2 model catalysts – structure, stability and catalytic properties

Roos, Matthias; Böcking, Dominique; Gyimah, Kwabena Offeh; Kucerova, Gabriela; Bansmann, Joachim; Biskupek, Johannes; Kaiser, Ute; Hüsing, Nicola; Behm, R Jürgen
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 15/09/2011 Português
Relevância na Pesquisa
46.21%
Aiming at model systems with close-to-realistic transport properties, we have prepared and studied planar Au/TiO2 thin-film model catalysts consisting of a thin mesoporous TiO2 film of 200–400 nm thickness with Au nanoparticles, with a mean particle size of ~2 nm diameter, homogeneously distributed therein. The systems were prepared by spin-coating of a mesoporous TiO2 film from solutions of ethanolic titanium tetraisopropoxide and Pluronic P123 on planar Si(100) substrates, calcination at 350 °C and subsequent Au loading by a deposition–precipitation procedure, followed by a final calcination step for catalyst activation. The structural and chemical properties of these model systems were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption, inductively coupled plasma ionization spectroscopy (ICP–OES) and X-ray photoelectron spectroscopy (XPS). The catalytic properties were evaluated through the oxidation of CO as a test reaction, and reactivities were measured directly above the film with a scanning mass spectrometer. We can demonstrate that the thin-film model catalysts closely resemble dispersed Au/TiO2 supported catalysts in their characteristic structural and catalytic properties...

Characterization of Pd nanoparticles and of silica-supported Pd-catalysts for the Suzuki-Miyaura reaction.

HANIF, MOHAMMAD ABU
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
36.26%
The importance of palladium (Pd) as a catalyst in organic coupling reactions is undeniable. Mesoporous silica is widely used as the support of Pd catalysts. But the porous structure of the mesoporous silica limits complete characterization. As a result, heterogeneous Pd catalysts are not fully understood. Model Suzuki-Miyaura reaction catalysts have been made by immobilizing Pd on a mercaptopropyltrimethoxysilane (MPTMS) functionalized Si substrate. Two types of Pd species were found on the fresh catalysts that may be attributed to a S-bound Pd (II) species and Pd nanoparticles. A sulfur species that has not been previously reported on this class of catalysts has also been observed. A systematic study of various palladium/sulfur complexes using XPS was carried out to identify this species, which may be assigned to high oxidation state sulfur formed by oxidation of thiol during the reduction of the Pd(OAc)2 used to load the catalyst with Pd. Shifts in binding energy observed for both Pd and S spectra of the used catalysts were examined in order to probe the change of electronic environment of reactive palladium center and the thiol ligand during the reaction. Electron and atomic force microscopic imaging of the surfaces demonstrates the formation of Pd nanoparticles on fresh catalysts and subsequent size reduction of the Pd nano-particles following reaction. Nanoparticles have gained increased attention due to their unique properties different from the bulk materials. Polyvinyl pyrrolidone (PVP) and dodecyl sulfide stabilized palladium nanoparticles have been synthesized with a size range of 3 to 10 nm and 2 to 5 nm respectively. XPS confirmed the conversion of Pd (II) to Pd (0) and presence of stabilizing agent on nanoparticles surface by observing Pd 3d...

The role of Ni on the performance of automotive catalysts: evaluating the ethanol oxidation reaction

Noronha, Fábio Bellot; Durão, Marcelo C; Batista, Marcelo S; Appel, Lúcia Gorenstin
Fonte: Instituto Nacional de Tecnologia Publicador: Instituto Nacional de Tecnologia
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
46.21%
Catalysis today, 85(1): 13-21 Set 30, 2003.; The role of the nickel oxide on the ethanol oxidation reaction over different model catalysts and commercial catalyst was studied. At 473 K, the catalytic activity followed the order: Pd/Al2O3≈Pd/CeO2/Al2O3≈Pd/Al2O3+NiO/Al2O3 physical mixture>Pd/NiO/Al2O3≈Pd/NiO/CeO2/Al2O3≈commercial catalyst. NiO/Al2O3 and CeO2/Al2O3 catalysts were not active at this temperature. Nickel addition strongly decreased the catalytic activity of Pd/Al2O3 and Pd/CeO2/Al2O3 catalysts. Temperature-programmed reduction (TPR) and oxygen storage capacity (OSC) measurements showed that palladium promoted the nickel oxide reduction. This strong interaction between both metals was destroyed under the reaction conditions leading to a nickel oxide surface segregation. The decrease of ethanol conversion in the presence of nickel was due to the coverage of palladium particles by nickel oxide, as demonstrated by IR analysis. The catalytic behavior of commercial catalyst was well represented by the Pd/NiO/CeO2/Al2O3 model catalyst. The main products of ethanol oxidation were acetaldehyde, acetic acid, carbon oxides and ethyl acetate. Ethanol oxidation proceeds through parallel and series reactions. The nickel addition shifted all the reaction system towards high temperature due to the decrease of activity.

Characterization of Graphite-Supported Palladium-Cobalt Catalysts by Temperature-Programmed Reduction and Magnetic Measurements

Noronha, Fábio Bellot; Schmal, Martin; Nicot, C.; Moraweck, B.; Fréty, R.
Fonte: Instituto Nacional de Tecnologia Publicador: Instituto Nacional de Tecnologia
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36%
Journal of catalysis, 168(1): 42-50, Maio 1997.; Graphite-supported cobalt, palladium, and cobalt-palladium systems were prepared by a simple impregnation technique and submitted to hydrogen reduction in a temperature-programmed mode. Using X-ray diffraction to define the structure of the calcined precursors, magnetic measurements to determine the amount of metallic cobalt formed after reduction, and analysis of the gaseous medium during the reduction, a general model for the reduction of the graphite supported catalysts has been suggested. At room temperature, both pure Pd~ and Pd~ associated with C0304 are reduced to the metallic state. In the case of bimetallic systems, a fraction of C0304 in close proximity or interfaced with Pd~ can be reduced to the metallic state and to CoO species, demonstrating a strong catalytic effect of palladium on the reduction of cobalt oxides. At temperatures between 298 and 500 K, depending on the catalyst formulation, the presence of metallic palladium promotes the reduction of a large fraction of oxidized cobalt. At higher reduction temperature, at least two competitive phenomena were detected: direct reduction of the residual oxidized cobalt by the graphite, leading to carbon monoxide and dioxide formation...

The role of Ni on the performance of automotive catalysts: evaluation the ethanol oxidation reaction

Noronha, Fábio Bellot; Durão, Marcelo C; Batista, Marcelo S; Appel, Lúcia Gorenstin
Fonte: Instituto Nacional de Tecnologia Publicador: Instituto Nacional de Tecnologia
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
46.21%
Catalysis Today 85 (2003) 13-21; The role of the nickel oxide on the ethanol oxidation reaction over different model catalysts and commercial catalyst was studied. At 473 K, the catalytic activity followed the order: Pd/ Al203 ~ Pd/Ce021 Ab03 ~ Pd/ Ab03 +NiOI Ab03 physical mixture> Pd/NiO / AI203 ~ Pd/NiO /Ce02 / AI203 commercial catalyst. NiOI Al203 and Ce021 Al203 catalysts were not active at this temperature. Nickel addition strongly decreased the catalytic activity of PdlAb03 and Pd/Ce02/Ab03 catalysts. Temperature-programmed reduction (TPR) and oxygen storage capacity (OSC) measurements showed that palladium promoted the nickel oxide reduction. This strong interaction between both metals was destroyed under the reaction conditions leading to a nickel oxide surface segregation. The decrease of ethanol conversion in the presence of nickel was due to the coverage of palladium particles by nickel oxide, as demonstrated by IR analysis. The catalytic behavior of commercial catalyst was well represented by the PdINiOlCe021 AI203 model catalyst. The main products of ethanol oxidation were acetaldehyde, acetic acid, carbon oxides and ethyl acetate. Ethanol oxidation proceeds through parallel and series reactions. The nickel addition shifted all the reaction system towards high temperature due to the decrease of activity.

Model catalysts for high-pressure spectroscopic investigations

Bedenbaugh, John
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
46.2%
Lauterbach, Jochen; In molecular-level catalytic investigations, discrepancies that exist between surface science observations under ultra-high vacuum (UHV) conditions and industrial catalytic performance at higher pressures are referred to as the “pressure gap.” For example, changes in the population of adsorption sites and variation in reaction mechanisms on catalyst surfaces have been observed as pressure increases above UHV conditions. This work addresses this pressure issue through the investigation of surface adsorption behavior of model catalytic systems over the range from UHV to atmospheric pressures using polarization modulation infrared reflection absorption spectroscopy (PM-IRAS). Likewise, a “materials gap” exists between single crystal surfaces and the supported nanoparticle catalysts used industrially. This work also includes preliminary investigations exploring the use of the reverse micelle technique for catalyst synthesis in order to produce nanoparticles with well-controlled dispersion. Adsorption of CO on Pt(100) was investigated at elevated pressures using PM-IRAS measurements. At sample temperatures of 325 K, a linear C-O stretch (~2090 cm-1) was observed. Peak sharpening and a frequency shift were observed for this CO adsorption band at higher pressures. At 325 K...

Reverse micelle synthesis and characterization of supported bimetallic catalysts

Cheney, Beth
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
36.35%
Lauterbach, Jochen A.; Chen, Jingguang G.; Synthesis of supported nanoparticles with consistent particle size is a bridge between what researchers refer to as the “materials gap,” the gap in structure complexity between single crystals and supported catalysts. Controlling particle size during supported catalyst synthesis allows researchers to investigate optimal conditions for desired activity and/or selectivity toward specific chemical reactions. This information can lead to the possibility to tune catalyst synthesis to optimize efficiency and cost while minimizing the waste of precious, nonrenewable resources. This thesis investigates a procedure potentially capable of synthesizing supported catalysts with uniformly-sized nanoparticles. This combines the idealized environment of a model system with the increased complexity associated with nanoparticle size and support effects. To bridge the materials gap, extensive work has been performed to determine how metallic structures affect adsorbate interactions. Chapter 1 discusses density functional theory (DFT) calculations used to predict adsorbate binding energies on metal monolayer bimetallic surfaces and the correlation to single crystal surfaces and polycrystalline foils. Recently...

Experimental and computational analysis of acid catalysts for biomass conversion

Courtney, Timothy D.
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
35.9%
Vlachos, Dionisios G.; Chen, Jingguang G.; The Earth's growing population and limited supply of fossil fuels implore us to develop alternatives in order to maintain our quality of life far into the future. This need is only exacerbated by mounting evidence that sustained fossil fuel use is changing our climate with trillions of dollars in potential damage. Wind, solar, and nuclear power can help to address our energy need, but fossil fuels are also an invaluable feedstock for commodity chemicals and the production of consumer goods. A future driven by renewable energy therefore requires renewable routes to replace these chemicals. Biomass feedstocks are highly oxygenated, enabling a rich and diverse chemistry with immense potential, but also making it difficult to control reaction selectivity. Chemical engineers have spent 100 years learning to control the reaction network of fossil fuels, and must now extend that control to biomass. Catalysis is critical to the economic feasibility of these processes not only to accelerate reactions, but to selectively accelerate only those reactions most desirable. In this thesis, Density Functional Theory (DFT) calculations, experimental reactor kinetics, and catalyst characterization are collectively employed to investigate a survey of open questions in biomass processing. Particular emphasis is placed on understanding the catalytic systems holistically and developing models that include other salient features of the system beyond the simple catalyst that fits on an organic chemistry reaction arrow. Glycerol is an immensely promising biomass feedstock available in surplus as a waste product of biodiesel formation. With these depressed feedstock costs...

Formulation and numeric calculation of non-isothermal effectiveness factor for finite cylindrical catalysts with bi-dimensional diffusion

Hoyos,Bibian; Cadavid,Juan Guillermo; Rangel,Hermes
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2004 Português
Relevância na Pesquisa
36%
A model for calculating the effectiveness factor and the concentration and temperature profiles for finite cylindrical either hollow or solid catalyst particles is presented. The model accounts for dispersion in both radial and axial directions and non-isothermal behavior. The resulting differential partial equations system is discretized by a centered finite difference method and a program written for the Excel™ electronic sheet solves the highly nonlinear algebraic system. The numerical technique can be extended for any kinetic expression; for illustration, some results for n-th order reactions rate expressions are shown.