1,721,001 research outputs found
Design of bifunctional 1D nanostructures for the catalytic conversion of carbon dioxide into cyclic carbonates
No full textOne dimensional silica-based nanotubes represent an innovative and promising morphology in the context of heterogeneous catalysis. Here these nanostructures were prepared for the first time as bifunctional materials, with hafnium or tin atoms inserted as single sites in the silica structure and imidazolium moieties anchored at the surface. The low dimensional solids thus present both acid sites owing to the presence of metal cations in tetrahedral coordination (co-catalyst) and nucleophilic species coming from the counterion of the imidazolium moieties (catalyst). The design of the catalysts consisted of two main steps. The Hf- or Sn-doped silica solids were initially prepared using a straightforward sol-gel method including a pH adjustment step allowing a quantitative insertion of the metal cations in the silica framework. These materials were post-functionalized with imidazolium moieties. The solids were extensively characterized thus confirming the presence of well-defined and open tubular structure, high specific surface area, successful insertion of Hf and Sn in the silica framework, and a correct functionalization with imidazolium salts. The different catalysts were tested in the valorization of CO2 with styrene oxide to give the corresponding cyclic carbonate. The bifunctional solids were stable and recyclable. The versatility of the best catalyst, represented by the Hf-based material, was confirmed using different epoxides. Finally, by tuning the reaction conditions or changing the imidazolium salt, a further boost of the catalytic performances was achieved
Modes of interaction of simazine with the surface of amorphous silica in water. Part II: adsorption at temperatures higher than ambien
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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
Sacrificial Oxidants as a Means to Study the Catalytic Activity of Water Oxidation Catalysts
No full textAn overview of the different sacrificial oxidants used in literature is reported, paying particular attention to the “sacrificial pair”, a photosystem made of a Ru-dye (Tris(bipyridine)ruthenium(II) dichloride, working as “antenna” for visible light) and a final electron acceptor (i.e. the persulfate ion). Such sacrificial oxidant is one of the most common in the literature and it was used in all the experiments described in Chap. 4. Different configurations of batch reactors can be used in the sacrificial-oxidant-driven water oxidation (WO) reaction, and three of them (i.e. the Clark-electrode Cell, the Stripping Flow Reactor and the Bubbling Reactor) are described in detail. The effects of both mass transfer limitations and side reactions on the determination of the two parameters describing the activity of water oxidation catalysts (i.e. the O2 production rate and the total evolved O2) are discussed, evidencing how such undesired phenomena occur to a different extent with the three reactor configurations
Steps Towards a Sustainable Hydrogen Production from Sunlight and Water
No full textThis chapter focuses on some aspects concerning the realization of an actually sustainable H2 production, and especially the need for earth abundant, environmental friendly, solar driven heterogeneous catalysis for the Water Oxidation reaction: the catalyst shall be thermodynamically and mechanically stable to allow cyclic long-term operations. The focus will be mainly on Mn- and Co-compounds, though reference will be made to other compounds, when appropriate
Use of the Bubbling Reactor with the Ru(bpy)23/S2O28 Photosystem for Measuring the Rate of Water Oxidation as Promoted by Different Manganese Oxides
No full textIn the current chapter, the use of a bubbling reactor for investigating the activity of different manganese oxides (i.e. Mn2O3, Mn3O4 and MnO2) is described. The most important aspects of water oxidation reaction considered are the role of the catalyst specific surface area (SSA), and the effect of the irradiance on the system. The former was investigated by preparing and testing samples with the same crystal structure, but with different SSA values. Notably, water oxidation catalyst activity does not strictly increase with SSA, but rather depends on the preparation route, which affects the nature of the surface. The effect of the irradiance was studied by using three irradiances conditions (i.e. 0.3, 0.5 and 1.0 sun) and three different catalyst contents (i.e. 10, 20 and 40 mg), evidencing how the increase in irradiance enhances the degradation processes rather than the O2 evolution. On this basis, a kinetic model imposing steady state conditions on transient species was developed, yielding a simple linear combination of two exponentials as expression of. The results show that the ratio between the kinetic constants of the desired (i.e. O2 formation) and undesired path (i.e. dye degradation) decreases at increasing irradiance, evidencing how the role of parasitic reactions, far from being negligible, tends to be overwhelming
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
Electrochemical Measurements as Screening Method for Water Oxidation Catalyst
No full textIn actual water splitting devices, the WOC will be deposited on an anode surface. Therefore, whatever the results obtained with WOC particles suspended in stirrer tank reactors, it becomes necessary to study WOC performances by means of electrochemical experimental setups. The WOCs deposition on an anode will depend on their physico-chemical nature, therefore several deposition methods, including wet and dry approaches, are found in literature. This Chapter reviews the available electrochemical techniques that can be adopted to study WOCs that are deposited on an electrode. In addition, the parameters used in literature to compare the different WOC materials will be explained. At the end of the Chapter, an example of the performance of different MnOx films will be reported. The water oxidation activity of three MnOx crystalline phases prepared by two deposition techniques will be compared. The aim of the comparison is to determine whether two electrodes having the same crystalline phase behave differently or not when they are deposited by two different techniques
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