1,721,022 research outputs found
The ultra-selective hydrogenation of Furfural on PtCu supported bimetallic nanoparticles and on Pt(111) under ultra-high vacuum
No full textThe selective transformation of furfural, a biomass platform molecule, was studied on Pt based heterogeneous catalysts and model single crystal surfaces. Hydrogenation reactions were carried out at pressures ranging from ultra-high vacuum to 20 bar. Temperature Programmed Desorption data in conjunction with Scanning Tunnelling Microscopy suggest that the decarbonylation of furfural on clean Pt(111) and the hydrogenation of furfural on hydrogen pre-covered Pt(111) is governed by surface crowding, molecular orientation and hydrogen bonding networks of the adsorbed molecules. Liquid phase experimentation on Pt nanoparticles, dispersed on a wide range of oxide supports, show that Pt is a very active hydrogenation catalyst even at very mild temperature and pressure conditions. The reaction was found to be highly dependent on the solvent used, while catalyst support is critical for maintaining thermally stable, monodisperse nanoparticles. The addition of Cu into Pt nanoparticles was investigated in a range of Pt:Cu metal molar ratios varying from pure Pt to pure Cu¬. This was achieved by using a modified polyol synthesis to generate colloidal nanoparticles, followed by thermal processing. Bimetallic particles synthesized using a sulphur free Cu precursor, were found to be beneficial for the suppression of CO adsorption, normally a poison for this reaction, which is formed from the decarbonylation of furfural. The alloying of these two metals had a profound effect on the overall catalytic activity by providing superior initial rates of reaction and catalytic turnover, as well as achieving high selectivities towards furfuryl alcohol, surpassing the behaviour of pure Pt catalyst across 3 different pressures. Finally, Single Atom Alloys (SAA), formed via the galvanic replacement of dispersed host Cu nanoparticles by Pt was investigated. Pt:Cu nanoparticles with atomic ratios ranging from 1:20 to 0.5:250 were synthesized and tested. After overcoming a brief induction period due to the reduction of surface CuO and possibly the reordering of the surface atoms, SAAs exhibit extremely high rates of hydrogenation, surpassing the catalytic turnover for monometallic and bimetallic catalysts. These cutting edge materials are at the frontier of catalyst research, proving to be ideal materials for the future of green chemistry due to both their activity and economic viability
The ultra-selective hydrogenation of Furfural on PtCu supported bimetallic nanoparticles and on Pt(111) under ultra-high vacuum
No full textThe selective transformation of furfural, a biomass platform molecule, was studied on Pt based heterogeneous catalysts and model single crystal surfaces. Hydrogenation reactions were carried out at pressures ranging from ultra-high vacuum to 20 bar. Temperature Programmed Desorption data in conjunction with Scanning Tunnelling Microscopy suggest that the decarbonylation of furfural on clean Pt(111) and the hydrogenation of furfural on hydrogen pre-covered Pt(111) is governed by surface crowding, molecular orientation and hydrogen bonding networks of the adsorbed molecules. Liquid phase experimentation on Pt nanoparticles, dispersed on a wide range of oxide supports, show that Pt is a very active hydrogenation catalyst even at very mild temperature and pressure conditions. The reaction was found to be highly dependent on the solvent used, while catalyst support is critical for maintaining thermally stable, monodisperse nanoparticles. The addition of Cu into Pt nanoparticles was investigated in a range of Pt:Cu metal molar ratios varying from pure Pt to pure Cu¬. This was achieved by using a modified polyol synthesis to generate colloidal nanoparticles, followed by thermal processing. Bimetallic particles synthesized using a sulphur free Cu precursor, were found to be beneficial for the suppression of CO adsorption, normally a poison for this reaction, which is formed from the decarbonylation of furfural. The alloying of these two metals had a profound effect on the overall catalytic activity by providing superior initial rates of reaction and catalytic turnover, as well as achieving high selectivities towards furfuryl alcohol, surpassing the behaviour of pure Pt catalyst across 3 different pressures. Finally, Single Atom Alloys (SAA), formed via the galvanic replacement of dispersed host Cu nanoparticles by Pt was investigated. Pt:Cu nanoparticles with atomic ratios ranging from 1:20 to 0.5:250 were synthesized and tested. After overcoming a brief induction period due to the reduction of surface CuO and possibly the reordering of the surface atoms, SAAs exhibit extremely high rates of hydrogenation, surpassing the catalytic turnover for monometallic and bimetallic catalysts. These cutting edge materials are at the frontier of catalyst research, proving to be ideal materials for the future of green chemistry due to both their activity and economic viability
The Ultra-Selective Hydrogenation of Furfural on PtCu Supported Bimetallic Nanoparticles and on Pt(111) under Ultra-High Vacuum
Full text linkThe selective transformation of furfural, a biomass platform molecule, was studied on Pt based heterogeneous catalysts and model single crystal surfaces. Hydrogenation reactions were carried out at pressures ranging from ultra-high vacuum to 20 bar. Temperature Programmed Desorption data in conjunction with Scanning Tunnelling Microscopy suggest that the decarbonylation of furfural on clean Pt(111) and the hydrogenation of furfural on hydrogen pre-covered Pt(111) is governed by surface crowding, molecular orientation and hydrogen bonding networks of the adsorbed molecules. Liquid phase experimentation on Pt nanoparticles, dispersed on a wide range of oxide supports, show that Pt is a very active hydrogenation catalyst even at very mild temperature and pressure conditions. The reaction was found to be highly dependent on the solvent used, while catalyst support is critical for maintaining thermally stable, monodisperse nanoparticles. The addition of Cu into Pt nanoparticles was investigated in a range of Pt:Cu metal molar ratios varying from pure Pt to pure Cu. This was achieved by using a modified polyol synthesis to generate colloidal nanoparticles, followed by thermal processing. Bimetallic particles synthesized using a sulphur free Cu precursor, were found to be beneficial for the suppression of CO adsorption, normally a poison for this reaction, which is formed from the decarbonylation of furfural. The alloying of these two metals had a profound effect on the overall catalytic activity by providing superior initial rates of reaction and catalytic turnover, as well as achieving high selectivities towards furfuryl alcohol, surpassing the behaviour of pure Pt catalyst across 3 different pressures. Finally, Single Atom Alloys (SAA), formed via the galvanic replacement of dispersed host Cu nanoparticles by Pt was investigated. Pt:Cu nanoparticles with atomic ratios ranging from 1:20 to 0.5:250 were synthesized and tested. After overcoming a brief induction period due to the reduction of surface CuO and possibly the reordering of the surface atoms, SAAs exhibit extremely high rates of hydrogenation, surpassing the catalytic turnover for monometallic and bimetallic catalysts. These cutting edge materials are at the frontier of catalyst research, proving to be ideal materials for the future of green chemistry due to both their activity and economic viabilit
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
Smart design of solid base catalysts with different pore architecture, properties and functional groups for the transesterification of triglycerides and the selective oxidation cascade of benzyl alcohol with benzyl amine
Full text linkInternal diffusion limitations within a heterogeneous catalytic material can prove problematic for industrially relevant chemical reactions, especially when using large reagent molecules. This work explores the use of a smart pore system design through a dual templated silica support for biodiesel synthesis and oxidation reactions. One-pot MgO/SBA-15 was synthesised, with selective functionalisation within the mesopores to allow for excellent dispersion. These materials were further improved by adding a macroporous network, resulting in a hierarchical pore system. When screened for the transesterification of triglycerides, the hierarchal materials outperformed the diffusion-limited mesoporous materials. In addition, the incorporation of a macroporous template improved the materials pore integrity and structure. Through manipulation of the pH during synthesis, MgO/SBA-15 was further functionalised with gold to be screened in selective oxidation reactions. Again, hierarchical materials were superior to mesoporous materials. In addition, chemometrics was used to assess key variables related to performance and selectivity. The heat-treatment temperature proved to be crucial for the activity, with 400 °C being optimum to increase activity and prolong catalyst life-time. Additionally, the addition of potassium carbonate mitigated substantially the deactivation of the catalyst produced by the reaction products. Subsequently, gold supported on MgO, CaO and SiO2 materials were synthesised and screened for the selective oxidation of benzyl alcohol, with the aim to compare their performance against Au/MgO/SBA-15 synthesised materials. Initial activity was found to relate to the gold loading of each material. However, deactivation was correlated to the basic nature of the support, as predicted. The most basic supports Au/CaO and Au/MgO deactivated slower and were unaffected by the addition of potassium carbonate. Finally, all materials were screened for the oxidative coupling of alcohols and amines. Au/CaO and Au/MgO hindered the oxidative coupling. Upon addition of potassium carbonate, the Au/MgO/SBA-15 hierarchical material proved to be the superior material tested
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
Platinum catalysts for the sustainable oxidation of biomass related compounds
Full text linkThe project described in this thesis is concerned with the platinum catalysed aerobic oxidation of biomass related model compounds, to explore new clean catalytic routes for the production of relevant intermediates in the field of fine chemicals and materials. This work started with the optimisation of mesoporous and hierarchical TLCT SBA-15 structures through systematic variation of their textural properties, including pore diameter, surface area and metal loading. The successful synthesis has been validated via extensive characterisation of the materials. Pore-expanded mesoporous and macro-mesoporous Pt-TLCT SBA-15 materials have been subsequently applied to the aerobic oxidation of dodecanal. The attentive choice of the type of support architecture conferred significant advantages in terms of internal diffusion and catalytic activity, evidencing the elimination of mass-transport barriers inherent to SBA-15 materials. Furthermore, a green and sustainable alternative for the selective synthesis of cinnamic acid from cinnamaldehyde has been investigated, as cinnamic acid is a promising compound to be developed in the medical field. The complex reaction mechanism has been studied, to identify the optimal conditions that favour the formation of cinnamic acid while minimising the production of benzaldehyde, the main by-product of this reaction. Air as oxidative agent together with a Pt-SiO2 catalyst decreased the activity of the oxidative cleavage mechanism that promotes the formation of benzaldehyde, rendering the reaction more selective towards cinnamic acid. Finally, the aerobic oxidation of 5-hydroxymethylfurfural has been explored with platinum nanoparticles dispersed over fumed silica, a non-porous acidic support that has not been extensively investigated in previous scientific literature, to assess the importance of the solid support in this reaction. A comprehensive study to investigate the catalytic abilities of Pt-SiO2 has been conducted, exploring the effect of different temperatures, pressures and amount of base. The employed catalysts have been prepared with two platinum precursors, in order to examine if different precursors had a remarkable impact on the catalysis. The obtained results led to the conclusion that, between the two precursors used, hydrogen hexachloroplatinate (IV) hexahydrate represents the most suitable one for HMF aerobic oxidation, since it allowed smaller nanoparticle size, which in turn afforded higher platinum content located on the surface of the catalyst, where the reaction occurred
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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