1,720,980 research outputs found
CuO/La0.5Sr0.5CoO3: Precursor of efficient NO reduction catalyst studied by: Operando high energy X-ray diffraction under three-way catalytic conditions
Full text linkSubstitution of critical raw materials such as platinum group metals in automotive catalysts is challenging. In this work we prepared a nanocomposite in which CuO nanoparticles are highly dispersed on a La0.5Sr0.5CoO3 perovskite-type oxide. The behaviour and reactivity under three way catalyst conditions was monitored by operando time-resolved high-energy X-ray diffraction under oscillating rich/lean feed. The reducing environment converted CuO into Cu(0) in a two step process: Cu(ii) to Cu(i) and to Cu(0), while the perovskite evolved to an oxygen deficient brownmillerite phase. These structural transformations are shown to be crucial for catalytic activity. The in situ generated Cu(0)/Cu(i)/brownmillerite nanocomposite is active for NO reduction above 300 °C, reaching 90% NO conversion at 450 °C. The effect of feed composition on the diffraction patterns was studied by Rietveld refinement in order to rationalize the experimental observations under TWC conditions
SrTiO3-based perovskites: developing economic and robust materials for sustainable development
No full textCuO/La0.5Sr0.5CoO3 nanocomposites in TWC
No full textIn this contribution several La0.5Sr0.5CoO3 based nanocomposites have been prepared and tested for application as Three-Ways Catalysts (TWC), aiming to develop Platinum Group Metal (PGM)-free catalysts. To reach this objective we designed and realized nanocomposites in which active CuO nanoparticles are deposited on La0.5Sr0.5CoO3. This perovskite is active in oxidation and is characterized by high oxygen anion mobility; copper is active in reduction: catalytic bifunctionality is thus built-in via a tailor-made and controlled nano-composition. The supporting perovskite was prepared following the "citrate" route. The deposition was carried out by means of the Ammonium-Driving-Deposition precipitation (ADP) to highly disperse CuO on La0.5Sr0.5CoO3. In a precedent paper we focused on nanocomposites obtained using LaCoO3 as a support because this perovskite is active in oxidation. Sr-doped LaCoO3, in addition, is characterized by a more relevant presence of oxygen vacancies and mobility and the desire of comparing these systems is to better investigate the different role played by all these aspects on the interaction between highly dispersed CuO nanoparticles and perovskite and on the catalytic activity. The copper amount on the nanocomposite surface does not increase linearly with the nominal composition reaching a plateau: migration below the surface is observed for the nanocomposite with 30 wt.% of Cu. The surface composition of the perovskite is modified by the copper deposition which causes the decrease of A-cations surface segregation and enhances the presence of cobalt suggesting a certain synergy; the reducibility of the perovskite is also greatly favored by deposition. Both model reactions (CO oxidation and CO assisted NO reduction) and reactions with a synthetic automotive exhaust mixture, including 10% steam, and oxygen, were carried out. We compared the results with the ones obtained in similar reactions with CuO/LaCoO3. Different interaction and synergy were observed with respect to CuO/La0.5Sr0.5CoO3. Sr-doping, in fact, enhances oxygen mobility affecting the reducing character of the nanodispersed CuO and thus the reactivity under different conditions. The deposition of copper oxide significantly increases the activity of the nanocomposites in CO oxidation (about 100% conversion at 200 degrees C) and in CO + NO (50% conversion at 250 degrees C, more than 80% at 400 degrees C) reactions. When compared with the corresponding CuO/LaCoO3, the more significant difference has been observed in nanocomposites poorer in CuO, which became highly active at lower temperature. On simulated gasoline engine exhaust the nanocomposites always improve the oxidation activity compared to the parent perovskite, while the NO reduction is quantitative in the absence of O-2. The activity on a mixture simulating actual gasoline-engine exhaust proves that ADP synthesis provides materials with a higher activity compared to wet impregnation (WI), thanks to a higher dispersion of copper. NO reduction in fuel-rich conditions is activated at approx. 300 degrees C, (400 degrees C on WI sample), when significant amount of O-2 is still in the mixture. This feature completes the good performance in absence of noble critical metals that are promising facts to develop PGM-free catalysts for the automotive industry
Is fighting against pollutants possible with critical raw material free perovskites?
No full textPerovskites free of critical raw materials (noble metals and rare earths) of the type Ba1-ySryMn1−0.2-xMg0.2CuxO3 (y = 0.1, 0.5; x = 0.1, 0.2, 0.3) are developed for the abatement of pollutants in automotive exhaust, both gaseous (CO, NOx and HCs) and solid (carbon soot). The reactivity in oxidation and reduction is tuned through ad-hoc induced surface segregation phenomena and the promotion of specific Mn(III)/Mn(IV) and Cu/Mn atomic ratios. The insertion of Cu into the perovskitic cell, moves the crystalline structure from 2H-type toward a Mn-deficient one, in which Mn(III) is prevalent. The catalytic capability in abatement of pollutants was studied comparing the activity in the following reactions: CO oxidation, CO assisted NO reduction, and with a complex mixture simulating the composition of automotive exhausts in stoichiometric and rich conditions. CO oxidation is favored by surface segregation of Mn, Mg may play a role in CO coordination. Copper enhances the NO reduction activity of the catalysts in the CO + NO reaction and Ba0.9Sr0.1Mn0.5Mg0.2Cu0.3O3 is the more active, whereas in the complex mixture Ba0.9Sr0.1Mn0.7Mg0.2Cu0.1O3 and Ba0.9Sr0.1Mn0.6Mg0.2Cu0.2O3 are the more active suggesting a less relevant role of surface composition and a more active contribution of bulk ion mobility
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
Critical Raw Materials-free Ba, Mn-based perovskites for sustainable development: building functionalities through doping
No full text
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
- …
