1,720,963 research outputs found
Hierarchical materials for energy and environmental applications
No full textThe research activity of the present thesis has focused on the development of carbon/inorganic hierarchical nanostructured hybrids to be employed as catalysts for two important energy processes: the water-gas shift reaction (WGSR) and the photocatalytic hydrogen production from renewable sources, such as biomass-derived oxygenated compounds (i.e. ethanol and glycerol). The design of the nanohybrids follows a specific hierarchy where a carbon component, consisting of properly functionalized multiwalled carbon nanotubes (MWCNTs) or carbon nanocones (CNCs), is used as scaffold for an inorganic phase that acts as the catalyst/cocatalyst. The inorganic phase in turns consist of noble metal nanoparticles (i.e. palladium) enclosed into a mesoporous metal oxide. The functionalization of the carbon components serves to equip the nanocarbon with anchor points for the metal phase and to enhance dispersion in liquid media. The as-prepared ternary hybrid is then subjected to specific thermal treatments, with the temperature chosen on the basis of thermogravimetric analysis, in order to crystallize the metal oxide phase and remove the organic ligands. The final catalyst package has shown remarkable catalytic features in both the investigated processes, confirming that the presence of the nanocarbon scaffold and the specific hierarchy result in a large improvement of the performance as compared to state-of-the art catalysts. Such improvement is related to the excellent electronic properties of the carbon nanostructures as well as to their ability to enhance robustness and stability of the inorganic phase. More specifically, CeO2-based catalysts display an increased activity and stability in the WGSR, while the TiO2-based photocatalysts were successfully used in the photocatalytic production of H2 with very high productivity. Characterization of the materials has been carried out through several techniques including HR-TEM, EDX mapping, XRD, microRaman, physi- and chemi-sorption analysis and TGA, which confirmed the obtainment of the desired assembly
Improved activity and stability of Pd@CeO2 core-shell catalysts hybridized with multi-walled carbon nanotubes in the water gas shift reaction
No full textAn efficient method is presented for preparing hierarchical catalysts composed of multi-walled carbon nanotubes (MWCNTs) and Pd@CeO2 core–shell nanoparticles. These materials were then examined for the water gas shift reaction (WGSR), which demonstrated intimate contact between the constituent parts. The integration of the carbonaceous support improves the stability of the nanoparticles by ordering the dispersion of the inorganic phase and increases the activity by suppressing the deactivation of the active phase that is commonly observed in conventional Pd–CeO2 under reducing conditions, e.g. WGSR conditions. An optimum MWCNTs:Pd@CeO2 ratio exists that affords totally homogeneous structures and provides the best catalytic properties
Highly efficient hydrogen production through ethanol photoreforming by a carbon nanocone/Pd@TiO2 hybrid catalyst
No full textProduction of molecular hydrogen (H2) is becoming an increasingly prominent process, due to high expectations as a new green energy carrier and key reagent for many industrial processes. Herein we report the high efficiency of H2 production via photoreforming of ethanol using a catalyst based on hierarchical carbon nanocones hybridised with an inorganic layer of nanocrystalline TiO2 containing Pd nanoparticles
Making H2from light and biomass-derived alcohols: the outstanding activity of newly designed hierarchical MWCNT/Pd@TiO2hybrid catalysts
No full textHydrogen evolution is among the most investigated catalytic processes given the importance of H2 from an industrial and an energy perspective. Achieving H2 production through green routes, such as water splitting or more realistically photoreforming of alcohols, is particularly desirable. In this work, we achieve a remarkable H2 productivity through photoreforming of either ethanol or glycerol as a sacrificial electron donor by employing a hybrid nanocatalyst where the properties of multi-walled carbon nanotubes (MWCNTs), Pd nanoparticles and crystalline TiO2 are optimally merged through appropriate engineering of the three components and an optimised synthetic protocol. Catalysts were very active both under UV (highest activity 25 mmol g−1 h−1) and simulated solar light (1.5 mmol h−1 g−1), as well as very stable. Critical to such high performance is the intimate contact of the three phases, each fulfilling a specific task synergistically with the other components
H2 production by photocatalytic reforming of oxygenated compounds using TiO2-based materials
No full textClean and efficient hydrogen production is of great interest because hydrogen is envisioned as the fuel of the future. In particular, hydrogen production from biomass-derived alcohols has attracted great attention because of the potential application in fuel cells. In this short review, the major results obtained in the last years by the Material, Environment and Energy (MEE) research group at the University of Trieste (Italy) in the photocatalytic production of hydrogen are summarized. Our attention has been devoted to the use of biomass-derived oxygenated compounds (mainly ethanol and glycerol) as sacrificial agents to improve hydrogen production. Various synthetic techniques (sol-gel, hydrothermal synthesis etc.) have been adopted to prepare nanostructured TiO2-based photocatalysts with different phase composition "and/or morphology in the form of powders. Different strategies have been adopted to improve the performances of TiO2-based materials, especially favoring the photocatalytic activity under simulated sunlight. Metal nanoparticles (Cu, Pt, Au, Pd), self-doping of TiO2 and hierarchically organized nanocomposite with carbon nanotubes strongly improve the hydrogen production. The results will highlight the role of different parameters (phase composition, morphology, doping and nanocomposite formulation) in the improvement of photocatalytic hydrogen productio
Photocatalytic H2 production by ethanol photodehydrogenation: Effect of anatase/brookite nanocomposites composition
Full text linkIn view of the sustainable H2 production, development of more efficient catalysts for photocatalytic reforming of oxygenated compounds is required. In this study, we report the preparation of TiO2 nanocomposite with anatase/brookite composition prepared by hydrothermal treatments of Na-titanate precursor. The anatase/brookite ratio can be modulated changing the synthetic parameters, i.e. precursor/water mass-to volume ratio and hydrothermal treatment duration. The obtained materials present well crystallized particles with polyhedral morphology. The anatase/brookite ratio in the nanocomposite affects the mean size of Pt nanoparticles grown by photodeposition and the photocatalytic activity in H2 production by photodehydrogenation of ethanol, with multiphasic materials presenting smaller Pt nanoparticles and higher H2 production. The present anatase/brookite nanocomposites show higher H2 production normalized to the surface area with respect a reference TiO2 prepared by conventional sol–gel synthesis, suggesting that the present materials might expose a higher fraction of highly reactive facets instead of the most thermodynamically stable
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
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