1,720,959 research outputs found
Development of sulfonic supported acids and their application in power to gas systems
Full text linkDimethyl ether (DME) is an environmentally friendly fuel that is being widely considered as an alternative fuel to replace petroleum fuels. DME can be produced by dehydration reaction of methanol by using solid catalysts in catalytic reactions. This study shows the influence of catalyst's surface acidity on the catalytic activity in the dehydration of methanol to DME. In this work, the conversion of methanol to dimethyl ether has been investigated using a continuous flow fixed-bed reactor at temperatures between 60°C and 350°C and 1 bar. Sulfonated catalysts with-SO3H acid function were tested and compared with conventional catalysts as γ-Al2O3. SiO2, MCM-41 and fluoropolymer were used as inorganic and organic supports for sulfonic groups. The experimental results demonstrate a good catalytic activity for the functionalized MCM-41 and the fluoropolymeric material. Effects of H2O on the activity and deactivation of these catalysts were also studied
Effect of acidic MCM-41 mesoporous silica functionalized with sulfonic acid groups catalyst in conversion of methanol to dimethyl ether
No full textThe global issue of contamination and power reserves has given dimethyl ether (DME) considerable attention. It is an encouraging and clean green material for the future resulting from its clean combustion properties. In this paper, a novel MCM-41-propyl-SO3H catalyst was successfully prepared with tethering of the active sulfonic acid groups onto the support via covalent bonds. This material was investigated as catalyst for DME synthesis via methanol dehydration in a fixed bed flow reactor at different experimental settings. TGA, NH3-TPD, SEM, XRD and BET techniques were utilized to characterize the synthesized material. MCM-41 sulfonated catalyst showed great thermal stability, high surface area and significant acid loading. The catalytic tests also demonstrated that the maximum methanol conversion was observed at 350 °C and catalyst contact time of 8 s. In addition, the catalyst showed a total selectivity to DME; light hydrocarbons and higher oxygenated compounds were not formed at temperatures above 300° C
Engineering modified mesoporous silica catalysts through porosity and surface acidity control for selective production of dme
No full textDME has been received the attention as a renewable energy due to its thermal efficiencies equivalent to diesel fuel, lower NOx emission, near-zero smoke and non-toxic. DME can be obtained by methanol dehydration over solid acid catalysts or directly from syngas over bifunctional catalysts. The catalytic dehydration of methanol to DME has been widely studied in the literature over pure or modified γ-aluminas (γ-Al2O3) and zeolites. Mesoporous silica has obtained much consideration due to its well-defined structural order, high surface area, and tunable pore diameter. In this work, sulfonic acid and aluminium modified mesoporous silica were synthesized and tested as catalysts for production of dimethyl ether from methanol. The modified silicas were studied utilizing XRD, N2 physisorption, pyridine adsorption, and scanning electronic microscopy. The effects of reaction temperature and water deactivation on the methanol selectivity and conversion to dimethyl ether were investigated. Sulfonic acid modified mesoporous silica showed higher selectivity and stability of DME than that of aluminosilicate. The grafting of mesoporous silica with sulfonic groups displayed much more enhanced hydrothermal stability than Al-MCM-41 and γ-Al2O3
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
Effect of surface acidity on the catalytic activity and deactivation of supported sulfonic acids during dehydration of methanol to DME
No full textThe influence of a catalyst's surface acidity on the catalytic activity and deactivation in the dehydration of methanol to DME was investigated. Different materials including propylsulfonic acid functionalized silica with different Brønsted acidities, silica-alumina, and propyl and phenylsulfonic acid functionalized silica-alumina catalysts were prepared. All the samples were characterized by XRD, TGA, XPS, N2-sorption, ICP-OES and SEM analysis. It was found that the Brønsted and Lewis acidity of the SiO2/Al2O3-PhSO3H catalyst played a critical role in the performance of methanol to DME transformation. The grafting of sulfonic acid groups on silica-alumina enhanced the surface Brønsted acidity and also the reaction activity and selectivity for the dehydration of methanol to DME. In addition, the phenylsulfonic acid functionalized silica-alumina catalyst exhibited the highest activity and stability for the dehydration reaction at relatively low temperatures at which the γ-Al2O3 catalyst, commercial reference, displayed low dehydration activity. The effect of water was also investigated because in the indirect process to produce DME using acidic γ-alumina, it had the most important effect on catalyst deactivation. As a result, water had a positive effect on methanol dehydration over the SiO2/Al2O3-PhSO3H catalyst in contrast to γ-Al2O3 which was rapidly deactivated. Thus, Brønsted and Lewis acid sites with suitable strength may be responsible for the effective conversion of methanol to DME with high stability and selectivity. This journal i
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
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