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Preparation of nano-structured catalysts
Get PDFgold catalysts have been found to be effective for many oxidation reactions and it is
known that the performance of these catalysts depends strongly on the particle size of
Au nanoparticles. However, other factors have strong influence on the catalytic activity
such as the preparation methods, choice of support, the structure and morphology of
supports. The effect of support morphology and structure on the activity of Au catalysts
was investigated using two hydrothermally prepared supports, CeO2 and MnO2.
Ceria foams as a support for nano-clusters of gold were synthesised hydrothermally at
160 °C by the reaction of L-Asparagine and CeCl3.7H2O at different crystallisation
times. The effect of the reaction time on the morphology of prepared CeO2 was
investigated. The morphology varied remarkably and it was found to change from
spherical particles to foam and eventually to a collapsed foam as the crystallisation time
increased. Gold catalysts were prepared by sol-immobilisation, supported on the foam
ceria and examined for solvent free oxidation of benzyl alcohol using molecular O2 as
an oxidant and the effect of the support was compared with commercial ceria. Au/CeO2
foam catalysts were more active than the Au/commercialCeO2 although the Au
nanoparticles were larger in ceria foam supports. This was due to the greater lability of
surface oxygen in the foam support compared with commercial CeO2 materials. The
Au/CeO2 foam catalyst was found to be reusable over three experiments. The effect of
catalyst loading, oxygen pressure and reaction time-online were also studied. It was
found that there was no mass transfer limitation when the mass of catalyst varied from 5
to 40 mg under the reaction conditions. The conversion of benzyl alcohol decreased as
the oxygen pressure decreased which shows that oxygen was involved in the oxidation
process. For time-online study, the conversion increased as the reaction time increased
with slightly increase.
MnO2 supports were synthesised by reacting MnSO4.H2O with (NH4)2S2O8
hydrothermally at 160 °C. Two different phases and morphologies of MnO2 were
formed and as the reaction time increased the morphology changed from microspheres
to nanowires and the MnO2 phase changed from α- to β-. Gold was deposited on all
prepared MnO2 materials and the catalysts were examined for solvent free benzyl
alcohol and CO oxidation. The influence of the preparation method on the catalytic
activity was studied and sol-immobilisation was found to be the best for benzyl alcohol
VII
oxidation whereas the deposition-precipitation was found to be the best for CO
oxidation. Impregnation method exhibited poor activity for both reactions. The effect of
the morphology and phase on the catalyst activity for both reactions was researched and
Au/α-MnO2 microspheres catalysts were best for benzyl alcohol oxidation while Au/β-
MnO2 nanowires catalysts exhibited better performance for CO oxidation due to their
smaller Au nanoparticles and easier surface reduction. The catalysts reusability, timeonline
and the effect of catalyst loading were also studied of an Au/MnO2 microsphere
catalyst for benzyl alcohol oxidation reaction.
Vanadium phosphate catalysts have been extensively studied for the selective oxidation
of butane to maleic anhydride. The catalytic activity of vanadium phosphates is greatly
dependant on the preparation method of the catalyst precursor VOHPO4·0.5H2O. Poly
(acrylic acid-co-maleic acid) copolymer, PAAMA, was employed as a structure
directing agent in the preparation of VOHPO4.0.5H2O via two routes. The effect of
PAAMA concentration on the structure morphology of VOHPO4·0.5H2O was studied in
both preparation routes. As the concentration of PAAMA increased the morphology
changed from rosette like for the standard precursors to rosette-like agglomerates with
isolated rhomboidal platelets and eventually to isolated rhomboidal platelets at highest
concentration of PAAMA. The XRD confirmed that all precursors were
VOHPO4·0.5H2O but as the concentration of PAAMA increased the (001) reflection
increased and the (220) reflection decreased. When these precursors were tested for
butane selective oxidation, the standard precursors that contain rosettes VPO0 and
VPD0 activated to the active phase ((VO)2P2O7) over typically observed time (> 100 h).
While the precursors that had rosette-like agglomerates with isolated rhomboidal
platelets and a relative intensity ratio of the (001)/(220) reflections of around 1.4, VPO5
and VPD15, activated much faster, less than 20 h with a comparable conversion and
selectivity. The isolated rhomboidal platelets precursors which had a high relative
intensity ratio of the (001)/(220) reflections, VPO15, VPO25 and VPD25, displayed
very poor activity because the thin platelets were rapidly oxidised to αII-VOPO4 phase
as confirmed by the XRD and Laser Raman Spectroscopy
Oxidation of benzyl alcohol and carbon monoxide using gold nanoparticles supported on MnO2 nanowire microspheres
Get PDFMnO2 was synthesised as a catalyst support material using a hydrothermal method. This involved reacting MnSO4×H 2O and (NH4)2S2O8 at 120 °C for a range of crystallisation times, which affords control over the morphology and phase composition of the MnO2 formed. Gold was deposited on these supports using sol-immobilisation, impregnation and deposition precipitation methods, and the resultant materials were used for the oxidation of benzyl alcohol and carbon monoxide. The effect of the support morphology on the dispersion of the gold nanoparticles and the consequent effect on the catalytic performance is described and discussed. Shape selectivity: Different nanostructured MnO2 materials were prepared by adjusting the synthesis conditions. When used as a support for gold oxidation catalysts, it was found that α-MnO2 spherical agglomerates performed the best in the liquid phase oxidation of benzyl alcohol, whereas β-MnO 2 nanowires performed better for gas-phase CO oxidation (see figure). Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Oxidation of benzyl alcohol by using gold nanoparticles supported on ceria foam
No full textThe efficacy of using cerium oxide foams as a support for Au nanoparticles and subsequent use as oxidation catalysts have been investigated. These were synthesized using L-asparagine to produce a cerium coordination polymer foam, which was calcined to give the oxide foam. Au nanoparticles were supported on the CeO2 foams using a sol-immobilization method. The activity of the Au/foamCeO2 for solvent-free benzyl alcohol oxidation was superior to standard Au/CeO2 catalysts, and the activity was found to be dependent on the crystallization time of the precursor foam. A crystallization time of 4 h was found to produce the most active catalyst, which retained activity and a high selectivity to benzaldehyde (ca. 96 %) when re-used and this is related to the structure of the material. The high activity is attributed to the greater lability of surface oxygen in the support compared with commercial CeO2 materials. Tailored foam bed: Cerium oxide with a foam morphology is used as a support for gold nanoparticles. The foams are synthesized using L-asparagine to produce a cerium coordination polymer foam, which is calcined to give the oxide foam. The activity of the Au/foamCeO 2 for solvent-free benzyl alcohol oxidation is superior to standard Au/CeO2 catalysts. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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
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
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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