1,720,953 research outputs found
Development of MnOx base catalysts for the PROX process. Theoretical insights and practical application
No full textThe growing demand for sustainable energy carriers has positioned hydrogen at the center of the global energy transition. However, hydrogen produced by conventional hydrocarbon-reforming processes typically contains residual carbon monoxide (CO) hindering its direct use in proton exchange membrane fuel cells (PEM) due to the poisoning of Pt electrodes. Therefore, the abatement of CO represents a crucial purification step in hydrogen processing for PEM applications.
Among the available H2 purification strategies, apart from methanation and membrane separation, the Preferential Oxidation of CO (PROX) has emerged over the past decades as a highly promising alternative, although the development of efficient, selective and low-cost catalysts represents the main scientific and technological challenge for the practical deployment of PEM technology.
Therefore, aiming at bringing contribution in the field of H2 purification processes, this study offers a comprehensive investigation of the H2 and CO oxidation functionalities of a nanocomposite MnCeOx catalyst by a combined computational and experimental approach documenting its potential PROX behavior for PEM technology exploitation.
The catalyst, synthesized by the redox-precipitation route, was extensively characterized, revealing the dominant role of surface Mn(IV) sites in governing a distinctive PROX behavior in the range of 293-423 K. In fact, catalytic tests reveal that this depends on the high CO oxidation activity of the MnCeOx catalyst at low temperature (∼293 K) and a substantial inactivity towards hydrogen oxidation at T<373 K.
Complementary Density Functional Theory (DFT) calculations performed on a model Mn4O8 cluster provided theoretical support for the experimental observations, revealing different interaction pathways of Mn(IV) sites with CO and H2. These give rise to two separate oxidation cycles, characterized by a significant activation energy gap, which explains the observed selectivity toward CO oxidation.
The experimental and theoretical insights were integrated into two simplified reaction mechanisms involving direct lattice oxygen abstraction and diatomic oxygen species respectively. The validity of these mechanistic interpretations was confirmed through the development of two kinetic models able to predict the CO and H2 oxidation activity of the MnCeOx catalyst in the range of 293-533K.
Overall, this work contributes to the fundamental understanding of MnCeOx catalysts, elucidating the interplay between surface redox chemistry, oxygen mobility and catalytic selectivity.
Beyond elucidating the molecular basis of PROX activity, the integration of computational and experimental insights establishes a robust methodological framework for the rational design of next-generation mixed-oxide catalysts for energy and environmental applications.
Chapter 1 provides an overview of the global energy context highlighting the role of hydrogen as a sustainable energy carrier. It addresses the main hydrogen production routes, including Steam Methane Reforming (SMR), Partial Oxidation (POX) and Autothermal Reforming (ATR) of hydrocarbons and outlines the key purification strategies, namely Pressure Swing Adsorption (PSA), membrane separation and methanation required to meet hydrogen purity standards for hydrogen application. The chapter concludes with a review of recent advances in the preferential oxidation of CO describing the main classes of catalysts, their reaction mechanisms and the technological limitations that motivate further research.
Chapter 2 focuses on materials and methods employed in this study. It describes the preparation of the MnCeOx catalyst and the suite of physico-chemical characterization techniques used to assess its properties, including X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), N2 physisorption, Laser Raman Spectroscopy (LRS), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), Temperature Programmed Reduction (TPR) and Temperature Programmed Desorption (TPD). The chapter also outlines the catalyst testing protocols, such as Temperature Programmed Catalytic Reaction (TPCR) experiments, and describes the computational approach adopted for Density Functional Theory (DFT) analysis.
Chapter 3, devoted to results and discussion, begins with a detailed interpretation of the main physicochemical characterization data, providing a detailed interpretation of the structural, surface properties and redox behavior of the catalyst. Then, the second part of the chapter highlights the PROX performance of the catalyst under various conditions, in terms of activity, selectivity and stability under both kinetic regime and under real process conditions. Mechanistic insights from Density Functional Theory (DFT) calculations on a model Mn4O8 cluster and kinetic data of CO and H2 oxidation are then used to obtain simplified reaction mechanisms. Based on these evidences, finally, the chapter describes the development of suitable macrokinetic models able to predict the CO and H2 oxidation functionality of MnO2-based catalysts under a wide range of conditions, establishing quantitative correlations between structure, mechanism and reactivity and offering a rational basis for the interpretation and optimization of PROX performance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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