<p>The Water Gas Shift (WGS) reaction can be either thermodynamically or kinetically limited, depending on process conditions. Improved catalysts are of particular interest at low temperatures where kinetic limitations dominate. In this work, density functional theory calculations were performed to calculate the binding energies, reaction energies, and activation barriers for the proposed WGS pathways on Pt and Pd(111). In addition to the previously published pathways, a new reaction involving the concerted formation of the carboxyl intermediate from water and CO is introduced. In general, binding energies and reaction energies are close on both surfaces. However, Pt has lower activation barriers. </p><p> Since CO is important for WGS, the CO-CO interactions on Pd(111) were studied by the development of a cluster expansion. A cluster expansion is a polynomial function that allows for rapid prediction of the energy if a structure is given. At low coverages, CO adsorbs in HCP Hollow sites. As the CO coverage increases, CO begins to adsorb in FCC Hollow and Atop sites until the saturation coverage of 3/4 ML. Next grand canonical Monte Carlo simulations were performed to determine the coverage-dependent binding energy and temperature programmed desorption spectrum. </p><p> Finally, a kinetic model was developed to analyze the different WGS reaction pathways, and metals. On both the Pt and Pd surfaces, WGS proceeds through the carboxyl intermediate with water dissociation being the rate determining step, but yields an unfavorably high CO coverage. Next, a coverage dependent binding energy of CO was included in the kinetic model. As the CO binding energy becomes less exothermic, WGS still proceeds through the carboxyl intermediate but carboxyl formation becomes rate determining. Also, the kinetic model shows that Pt is more active than Pd, independent of the CO binding energy. However, the calculated apparent activation barriers and rates do not agree with the experimental results of Pt and Pd supported on &gamma;-Al₂O₃, which suggest that the support plays an active role in catalyzing the WGS reaction. Since the support plays an important role in WGS catalysis, future studies should attempt to understand the promoting effect of the support and the support-metal interaction. </p>

Thesis (Ph.D.)--Lehigh University, 2007.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 3143. Adviser: Zhi Li. Includes bibliographical references (leaves 126-141). Available on microfilm from Pro Quest Information and Learning.

<p> Colloidal nanocrystals with optical properties in the near-infrared (NIR) are of interest for many applications such as photovoltaic (PV) energy conversion, bioimaging, and therapeutics. For PVs and other electronic devices, challenges in using colloidal nanomaterials often deal with the surfaces. Because of the high surface-to-volume ratio of small nanocrystals, surfaces and interfaces play an enhanced role in the properties of nanocrystal films and devices. </p><p> Organic ligand-capped CuInSe₂ (CIS) and Cu(In_XGa_1-X)Se2 (CIGS) nanocrystals were synthesized and used as the absorber layer in prototype solar cells. By fabricating devices from spray-coated CuInSe nanocrystals under ambient conditions, solar-to-electric power conversion efficiencies as high as 3.1% were achieved. Many treatments of the nanocrystal films were explored. Although some treatments increased the conductivity of the nanocrystal films, the best devices were from untreated CIS films. By modifying the reaction chemistry, quantum-confined CuInSe_XS_2-X (CISS) nanocrystals were produced. The potential of the CISS nanocrystals for targeted bioimaging was demonstrated via oral delivery to mice and imaging of nanocrystal fluorescence.</p><p> The size-dependent photoluminescence of Si nanocrystals was measured. Si nanocrystals supported on graphene were characterized by conventional transmission electron microscopy and spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM). Enhanced imaging contrast and resolution was achieved by using Cs-corrected STEM with a graphene support. In addition, clear imaging of defects and the organic-inorganic interface was enabled by utilizing this technique.</p>

<p> Abstract not available.</p>

No description available.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6426. Advisers: Paul J.A. Kenis; Andrzej Wieckowski. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Made available in DSpace on 2014-06-11T19:23:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-02-27Bitstream added on 2014-06-13T20:30:04Z : No. of bitstreams: 1 silvajunior_jf_me_jabo.pdf: 787738 bytes, checksum: 7b3e41cb53972e8468ad03ecb64cfbe1 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os óxidos de ferro são importantes indicadores ambientais e possuem grande influência nos atributos físicos e químicos do solo. Entretanto, para o melhor entendimento de sua formação e ocorrência são necessários estudos de variabilidade espacial. A geoestatística é a melhor ferramenta para este estudo, sendo que a Krigagem ordinária (KO) é um interpolador de mínimos quadrados, mais utilizado em ciência do solo. Porém, ela suaviza os detalhes locais da variação espacial, superestimando pequenos valores e subestimando altos valores. Por isso, ela revela-se inadequada na avaliação da verdadeira variabilidade espacial dos óxidos de ferro. Embora a krigagem mostre a melhor estimativa de um atributo Z, ele não representa bem a variação. Deste modo, a alternativa é simulação geoestatística que avalia e quantifica a incerteza de um atributo, de maneira mais realista. A técnica de simulação estocástica mais utilizada é a simulação sequencial gaussiana (SSG), por ser, rápida e direta na construção da função de densidade de probabilidade acumulada condicional (f.d.p.a.c), sendo, portanto preferível à estimação pela KO. Desta forma, é importante testar outros métodos para caracterizar espacial dos óxidos de ferro. Objetivando avaliar o desempenho da (KO), krigagem ordinária dos dados padronizados (KOP) e da simulação seqüencial gaussiana (SSG) da variabilidade espacial dos óxidos de ferro em uma área com pedoformas: côncava e convexa foram coletados 121 amostras de duas malhas nos dois relevos classificados como: côncavo e convexo com espaçamento de 10 metros. O erro médio, o erro quadrático médio e o erro quadrático médio padronizado foram os critérios de avaliação da acurácia da predição. Os valores altos dos coeficientes de variação dos óxidos de ferro afetaram o desempenho dos métodos... / Iron oxides are important environmental indicators and have great influence on the physical and chemical properties of soil. However, for a better understanding of their formation and occurrence studies are necessary spatial variability. Geostatistics is a tool for this study, ordinary kriging (OK) is a least squares interpolator, is the most widely used in soil science. However smooths out local details of spatial, small values overestimating and underestimating high values. Therefore, is inadequate in the evaluation of iron oxides. Although the kriging show the best estimate of an attribute Z, it does not represent well the variation. Thus, the alternative is geroestatisctical simulation that evaluates and quantify the uncertainty of an attribute, more realistically. Since the most widely used is the sequential Gaussian simulation (SGS), to be quickly and directly in the construction of the density function of cumulative probability (fdpac), and are preferred to the estimation. Thus, is important to test other methods to characterize spatially of iron oxides. In order to evaluate the performance of (OK), ordinary kriging of standardized data (OKS) and sequential Gaussian simulation (SGS) of the spatial variability of iron oxides in an area with landform: concave and convex 121 samples were collected data in two loops with two reliefs classified as concave and convex with spacing of 10 meters. The average error, the mean square error and root mean square error were standardized criteria for evaluating the accuracy of prediction. High values of coefficient of variation of iron oxides harmed the performance of the methods. The landforms showed variable differentiated by SGS. The maps of OKS and E-type had higher accuracy and greater detail in relation to landforms in the OK. It is recommended that E-type maps instead of maps OK... (Complete abstract click electronic access below)

Orientador: Gener Tadeu Pereira / Coorientador: José Marques Júnior / Banca: Ednaldo Carvalho Guimarães / Banca: Marcílio Vieira Martins Filho / Resumo: Os óxidos de ferro são importantes indicadores ambientais e possuem grande influência nos atributos físicos e químicos do solo. Entretanto, para o melhor entendimento de sua formação e ocorrência são necessários estudos de variabilidade espacial. A geoestatística é a melhor ferramenta para este estudo, sendo que a Krigagem ordinária (KO) é um interpolador de mínimos quadrados, mais utilizado em ciência do solo. Porém, ela suaviza os detalhes locais da variação espacial, superestimando pequenos valores e subestimando altos valores. Por isso, ela revela-se inadequada na avaliação da verdadeira variabilidade espacial dos óxidos de ferro. Embora a krigagem mostre a melhor estimativa de um atributo Z, ele não representa bem a variação. Deste modo, a alternativa é simulação geoestatística que avalia e quantifica a incerteza de um atributo, de maneira mais realista. A técnica de simulação estocástica mais utilizada é a simulação sequencial gaussiana (SSG), por ser, rápida e direta na construção da função de densidade de probabilidade acumulada condicional (f.d.p.a.c), sendo, portanto preferível à estimação pela KO. Desta forma, é importante testar outros métodos para caracterizar espacial dos óxidos de ferro. Objetivando avaliar o desempenho da (KO), krigagem ordinária dos dados padronizados (KOP) e da simulação seqüencial gaussiana (SSG) da variabilidade espacial dos óxidos de ferro em uma área com pedoformas: côncava e convexa foram coletados 121 amostras de duas malhas nos dois relevos classificados como: côncavo e convexo com espaçamento de 10 metros. O erro médio, o erro quadrático médio e o erro quadrático médio padronizado foram os critérios de avaliação da acurácia da predição. Os valores altos dos coeficientes de variação dos óxidos de ferro afetaram o desempenho dos métodos... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Iron oxides are important environmental indicators and have great influence on the physical and chemical properties of soil. However, for a better understanding of their formation and occurrence studies are necessary spatial variability. Geostatistics is a tool for this study, ordinary kriging (OK) is a least squares interpolator, is the most widely used in soil science. However smooths out local details of spatial, small values overestimating and underestimating high values. Therefore, is inadequate in the evaluation of iron oxides. Although the kriging show the best estimate of an attribute Z, it does not represent well the variation. Thus, the alternative is geroestatisctical simulation that evaluates and quantify the uncertainty of an attribute, more realistically. Since the most widely used is the sequential Gaussian simulation (SGS), to be quickly and directly in the construction of the density function of cumulative probability (fdpac), and are preferred to the estimation. Thus, is important to test other methods to characterize spatially of iron oxides. In order to evaluate the performance of (OK), ordinary kriging of standardized data (OKS) and sequential Gaussian simulation (SGS) of the spatial variability of iron oxides in an area with landform: concave and convex 121 samples were collected data in two loops with two reliefs classified as concave and convex with spacing of 10 meters. The average error, the mean square error and root mean square error were standardized criteria for evaluating the accuracy of prediction. High values of coefficient of variation of iron oxides harmed the performance of the methods. The landforms showed variable differentiated by SGS. The maps of OKS and E-type had higher accuracy and greater detail in relation to landforms in the OK. It is recommended that E-type maps instead of maps OK... (Complete abstract click electronic access below) / Mestre

Zeolites are crystalline aluminosilicates that are frequently used as catalysts to transform chemical feedstocks into more useful materials in a size- or shape-selective fashion; they are one of the earliest forms of nanotechnology. Zeolites can also be used, especially in the form of zeolite membranes (layers of zeolite on a support), to separate mixtures based on the size of the molecules. Recent advances have also created the possibility of using zeolites as alkaline catalysts, in addition to their traditional applications as acid catalysts and catalytic supports. Transport and catalysis in zeolites are greatly affected by physical and chemical defects. Such defects can be undesirable (in the case of zeolite membranes), or desirable (in the case of nitrogen-doped alkaline zeolites). Studying zeolites at the relevant length scales requires indirect experimental methods such as vapor adsorption or atomic-scale modeling such as electronic structure calculations. This dissertation explores both experimental and theoretical characterization of zeolites and zeolite membranes. Physical defects, important in membrane permeation, are studied using physical adsorption experiments and models of membrane transport. The results indicate that zeolite membranes can be modeled as a zeolite powder on top of a support—a “supported powder,” so to speak—for the purposes of adsorption. Mesoporosity that might be expected based on permeation and confocal microscopy measurements is not observed. Chemical defects—substitutions of nitrogen for oxygen—are studied using quantum mechanical models that predict spectroscopic properties. These models provide a method for simulating the 29Si NMR spectra of nitrogendefected zeolites. They also demonstrate that nitrogen substitutes into the zeolite framework (not just on the surface) under the proper reaction conditions. The results of these studies will be valuable to experimentalists and theorists alike in our efforts to understand the versatile and complicated materials that are zeolites.