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Microwave heating for the synthesis of precious metal-based nanoparticles for gas- and liquid-phase reduction reactions
Full text linkMain goal of this overall research is the design and synthesis of highly active precious-metal based heterogeneous catalysts. The underlying strategy is to attain cost effectiveness and better catalytic performance by nanoscale dilution of expensive metals such as Rh, Pd, Pt, & Au using readily available and cheaper metals (Cu, Ag, etc.). Such hetero-metal mixing usually lead in advantageous synergy effects and yield superior nanoparticle (NP)-catalysts. A crucial aspect of this research is microwave irradiation (μwI) which unlike conventional heating (CvH), strongly couples to polar solvents, ionic metal precursors and therefore may provide access to classically immiscible bimetallic systems. Surface reactivities of our hetero-metallic NPs have been successfully used as vapor-phase probes to derive reactivity and kinetic information which in turn is directly compared with collaborative DFT calculations. Specifically, synthesis of PdₓAu₁₀₀₋ₓ alloy NPs in wide range of compositions have been carried out to distinguish efficacy of the two heating methods (μwI & CvH). Composition dependent catalytic tunability was experimentally observed in both gas-phase hydrogenation reaction, and aqueous-phase nitrite reduction using PdₓAu₁₀₀₋ₓ alloy NPs. This observation matched reasonably well with theoretical calculations. In a separate project, scalability issues associated with small-scale batch reactions are addressed using flow methods to synthesize Rh NPs under μwI. Mechanistic insight into distinct morphologies of Rh NPs obtained using single-, and two-phase flow methods is attained and structural differences are probed by model hydrogenation catalysis. In another study, Cu-containing bimetallic NP systems (PdCu & RhCu) are currently being investigated to further address the cost factor while retaining superior catalytic activity. Moreover, highly atom-efficient Ag-based nanocages are also synthesized under μwI. Detailed investigation into the formation mechanism of such exciting and unique nanostructures are currently underway. Several characterization techniques such as PXRD, UV-vis, FTIR, XPS, TEM, STEM-EDX, ICP (-MS & -OES), etc. are routinely employed to fully delineate research described herein.Chemistr
MSN supported single site Pt and Pd complexes for catalytic C-H activation reactions
No full text2013 Summer.Includes illustrations (some color).Includes bibliographical references.Mesoporous materials have several advantages like high surface area, high pore volumes, easily controllable, and relatively uniform and narrow pore size distributions, and convenient ways of attachment of desired organic or organometallic species lead to multi use organic-inorganic hybrid materials which have been effectively utilized for various applications such as drug delivery, enzyme encapsulation, catalysis, sensors, and nanoelectronics etc. Single site Pt (II) complexes were covalently tethered on mesoporous silica nanoparticles (MSNs) using co-condensation and grafting methods and the resulting catalysts were studies for olefin hydroarylation reaction of unactivated olefins. A comprehensive study was carried out towards understanding the different structural aspects of the catalysts and catalysis. A comparison was made between heterogeneous catalysts and homogeneous catalysts reported in previous studies. Single site Pd (II) complexes were covalently tethered on mesoporous silica nanoparticles (MSNs) using co-condensation and grafting methods and the resulting catalysts were studies for allylic acetoxylation reaction of alkenes. Various novel approaches were tried to understand the various aspects of this catalysis in detail
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Optimized synthesis of PdAu bimetallic nanoparticles using microwave irradiation as heterogeneous catalysts for compositional dependent hydrogenation reaction
Full text linkSynthesis of atom-efficient, cost-effective, and recyclable catalysts is quintessential for large scale production of chemicals of strategic importance. Expertise of Humphrey research group in microwave assisted synthesis of noble metal nanoparticles (NPs) has been implemented for synthesis of PdAu NPs, and a thorough investigation of their catalytic performance for cyclohexene hydrogenation was completed. Different reaction times were evaluated for their effects on extent of alloying and size distributions of NPs. Varying concentration of metal precursors used during the synthesis of Pd₅₀Au₅₀ alloy NPs led to appreciable size tunability. Microwave heating (μWI) was also effective in rapidly exchanging organic functionalization of the synthesized Pd₅₀Au₅₀ alloy NPs from a polymeric to monomeric capping agent. A comparison of μWI and conventional heating (CvH) methods showed that μWI led to superior PdAu alloy NPs with better monodispersity and size control. Using optimized reaction conditions, relative compositions of the two metals were controlled over a wide range. Synthesized PdAu alloy NPs of different compositions were thoroughly characterized using a variety of techniques and then tested for catalytic hydrogenation of cyclohexene using a continuous flow gas phase reactor. Pd59Au41 alloy NPs showed the best catalytic performance among all the catalysts studied. Continuing efforts towards further improving Pd-containing bimetallic NPs systems are currently made with the future goal of comparing catalytic performances of PdAu NPs with PdAg NPs in order to develop more economical and versatile catalysts.Chemistr
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
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