1,720,986 research outputs found
ZIF’s como soporte catalítico y fuente primaria de carbono en la síntesis de materiales nanoestructurados de carbono y su aplicación en el almacenamiento de hidrógeno
Get PDF113 páginas. Maestría en Ciencias e Ingeniería de Materiales.En la actualidad, el uso desmedido de los combustibles fósiles, debido al crecimiento de la población, ha provocado problemas ambientales severos, como lo es el calentamiento global. Por ello, la búsqueda de nuevos combustibles limpios como el metanol e hidrógeno ha tenido un gran crecimiento, principalmente en el almacenamiento de este último. En el presente trabajo se planteó la síntesis verde de diferentes materiales ZIFs (ZIF-67, basados en Co y Ni); estos materiales, debido a sus propiedades, son competentes para el almacenamiento de hidrógeno y, además, como catalizadores en la síntesis de nanotubos de carbono. Se estudiaron tres tipos de síntesis verdes, con la finalidad de disminuir los contaminantes que se pueden generar en el proceso; el método hidrotermal, método ionotermal (usando un solvente eutéctico profundo) y el método mecanoquímico (solamente el método hidrotermal está reportado en la literatura para la síntesis de este material). Posteriormente, a estos materiales sintetizados se les realizaron pruebas para evaluar su eficiencia en el almacenamiento de hidrógeno. Por último, los ZIFs sintetizados se emplearon en el crecimiento de nanotubos de carbono por el método CVD, donde estos ZIFs se usaron como una fuente primaria de carbono. Finalmente, todos los materiales sintetizados (ZIFs y NTCs) fueron caracterizados por diferentes técnicas analíticas tales como: Difracción de rayos-X, espectroscopia FT-IR, espectroscopia Raman, microscopia electrónica de barrido, espectroscopia de rayos-X dispersivos y por fisisorción de nitrógeno. Para el caso del almacenamiento de hidrógeno los ZIF-67(Co) sintetizados por los métodos hidrotermal e ionotermal obtuvieron los mejores resultados (4.74% y 3.04%, respectivamente).Investigación realizada con el apoyo del Consejo Nacional de Ciencia y Tecnología (México). CONACYT
Identifying the active sites in catalytic hydrodesulfuration
Get PDFEste artículo analiza las evidencias de estudios experimentales para deducir un nuevo mecanismo de reacción de hidrodesulfuración (HDS), donde el sitio activo es similar a un carbono sulfurado (¨CS¨) unido a un metal. Además, en base a la ecuación de Chianelli (MoS₂-ₓCₓ), se comprobó que la estructura con composición MoCS es el sitio activo. Esta investigación identifica el mecanismo de reacción (después de la activación inicial) y modifica la ecuación química que tradicionalmente se ha utilizado en la hidrodesulfuración. El artículo ayuda a entender que la presencia de compuestos carbonosos en los catalizadores de HDS desarrolla nuevos sitios catalíticos mejorados. Este trabajo, también ayuda a poner fin a la controversia sobre la naturaleza de la fase activa en HDS, al proponer un nuevo mecanismo nunca antes propuesto.This article analyzes the evidences of experimental studies to deduce a new reaction mechanism of Hydrodesulfurization (HDS), where the active site is similar to a sulphided carbon (¨CS¨) bonded to a metal. In addition, based on the Chianelli equation (MoS₂-ₓCₓ), the structure with MoCS composition was found to be the active site. This research identifies the reaction mechanism (after the initial activation) and modifies the chemical equation that traditionally has been used in Hydrodesulfurization. The article helps to understand that the presence of carbonaceous compounds in the HDS catalysts develops new improved catalytic sites. This work also helps to end the controversy on the nature of the active phase in HDS, by proposing a new mechanism never before proposed
Study of the photocatalytic degradation of the Orange II dye, when titania is doped with Ag and graphene
Get PDFEn este estudio se prepararon catalizadores como TiO₂, Ag/TiO₂, óxido de grafeno/TiO₂, fueron sintetizados por el método sol-gel y calcinados a 450°C. Los catalizadores fueron estudiados analizado la difracción de rayos X, espectroscopia Raman y MEB. Se probaron las propiedades fotocatalíticas en la degradación del colorante Naranja II, usando luz visible. Las muestras tienen estructuras cristalinas con la fase anatasa, y son materiales mesoporosos. En el estudio de MEB se identificaron las láminas de óxido de grafeno y la existencia de partículas de plata sobre las partículas del TiO₂. Además, se propusieron los mecanismos que explican los pasos de la activación de los sitios fotocatalíticos de la titania y se aclaró como la plata y el grafeno evitan la recombinación del hueco-electrón.In this study, catalysts such as TiO₂, Ag/TiO₂, graphene oxide/TiO₂ were prepared, synthesized by the sol-gel method and calcined at 450°C. The catalysts were studied by analyzing X-ray diffraction, Raman spectroscopy and SEM. The photocatalytic properties in the degradation of Orange II dye was tested using visible light. The samples have crystalline structures with the anatase phase, and are mesoporous materials. In the SEM study, the graphene oxide sheets and the existence of silver particles on the TiO₂ particles were identified. In addition, the mechanisms that explain the activation steps of the photocatalytic sites of titania were proposed and it was clarified how silver and graphene prevent hole-electron recombination
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Tratamiento de un agua de manantial proveniente de Coatepec Harinas, Estado de México mediante fotocatálisis para la eliminación de contaminantes provenientes de plaguicidas
No full text73 páginas. Ingeniería Ambiental
Degradación de colorantes azo mediante sonocatálisis y sono-fotocatálisis
No full text53 páginas. Ingeniería Ambiental
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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