1,720,967 research outputs found
Synthesis, Characterization and Catalytic Performance of Dedicated Ceria-Zirconia Catalysts for HCl Oxidation Reaction
No full textThe heterogeneously catalyzed oxidation of HCl to Cl2 (Deacon process) represents a sustainable route to the recovery of chlorine from HCl-containing streams in the chemical chemistry. It has been demonstrated that CeO2-based materials have the potential to act as effective catalysts for the HCl oxidation reaction, offering an economically viable alternative to those based on RuO2 commercial materials. The thesis continues to focus on CexZr1-xO2 mixed oxides and supported CeO2 on ZrO2 (CeO2@ZrO2) catalysts, with the aim of elucidating the relationship between structure, oxygen storage capacity and catalytic HCl oxidation activity and durability. Moreover, rapid and sensitive in situ deactivation and reactivation experiments are devised to gain insight into the “chlorination-dechlorination” process.
Although the enhanced Deacon activity can be achieved by combining CeO2 with ZrO2 in solid solution reported by numerous studies, a clear-cut relationship between OSC and the activity may be obscured due to the fact that previous studies have suffered from the limitation that CexZr1-xO2 differ in several key parameters, such as specific surface area. Accordingly, in this thesis, we initially developed CexZr1-xO2 solid solutions as a function of the composition x through the co-precipitation method, maintaining a constant specific surface area at 46 ± 2 m2/g. It can therefore be stated that the OSCc value is an appropriate descriptor of the catalytic HCl and CO oxidation reaction. From the linear relationship between the oxidation activity of HCl and OSCc, which in turn is linearly related to the activity of CO oxidation, it can be concluded that the HCl oxidation reaction over the CexZr1-xO2 catalysts proceeds via the Mars-van Krevelen mechanism.
Furthermore, the effect of calcination process on the structural properties and catalytic performance of CeO2@ZrO2 catalysts was systematically investigated. CeO2 with varying concentrations were loaded onto the surface of ZrO2 particles using the incipient wetness impregnation method and calcined at different temperatures. The catalyst, which was calcined at 600 °C for a period of 5 h, resulted in the formation of a highly dispersed CeO2 layer, which exhibited an enrichment of Ce3+ species. The observed 1-2 nm thick CeO2 wetting layer is responsible for the high specific activity observed in the catalytic oxidation of HCl. Moreover, enhanced stability of the CeO2 layer calcined at 600 °C can be attributed to the formation of a sharp interface with the ZrO2 support.
Lastly, we applied two “deactivation-reactivation” cycles at 430 °C over fresh CeO2 and 20CeO2@ZrO2 catalyst respectively by switching the reaction gas mixture. It was unexpected that the activity of the 20CeO2@ZrO2 catalyst can be fully restored by oxygen exposure at 430 °C after the second deactivation/reactivation cycle, whereas the activity of the pure CeO2 catalyst decreases gradually after each cycle. Apparently, 20CeO2@ZrO2 catalyst exhibits superior regeneration performance to that of the CeO2 catalyst. Furthermore, a straightforward model is devised based on the Johnson-Mehl-Avrami-Kolmogorov approach to elucidate the reoxidation process of the catalyst. This observation is modelled by a faster nucleation rate in the supported 20CeO2@ZrO2 catalysts compared to the pure CeO2 catalyst. This can be explained by the abundant nucleation sites provided by the high surface area of ZrO2
Understanding Ru Exsolution Process from LaFe0.9Ru0.1O3 and its Impact on Catalytic Propane Oxidation Reaction
Get PDFThe catalytic transformation of hydrocarbons, particularly light alkanes such as propane, is of critical importance for both environmental and industrial applications. Catalysts that support precious metal nanoparticles (NPs) on oxides have shown significant promise due to their high surface area. However, these systems often face challenges such as NP sintering under reaction conditions, which can diminish catalytic performance over time. To address this, the development of catalysts that present high activity and improved stability is essential. Reductive exsolution is a facile way to produce homogenously distributed nanoparticles through the extraction of uniformly incorporated precious metal ions from a solid oxide solution. Nanoparticles originated via exsolution anchor in the surface of the parent backbone, delivering improved thermal stability, which makes it an ideal catalyst for reactions conducted at elevated temperatures, such as hydrocarbons total oxidations.
The material studied in this work is the perovskite LaFe0.9Ru0.1O3 (LFRO), in which 10% Fe in the B site is replaced by Ru. Reduction in hydrogen at 800 ℃ (a typical temperature for the exsolution) leads to the formation of socketed nanoparticles (LFRO-800R). These particles are revealed to be a core-shell structure in which the active Ru is alloyed with a slight amount of Fe, encapsulated by an inert LaOx coating, thus exhibiting a lower catalytic activity compared with the pristine LFRO for the propane oxidation. However, LFRO_800R can be activated by an oxidative treatment at 400 ℃, leading to an improved activity which is five times higher than the activity of LFRO at 210 ℃. Detailed characterizations including TEM and CODRIFTS indicate that the inert LaOx can be selectively removed by oxidative treatment at 400 ℃. Meanwhile, the exposed RuFe alloy particle transforms into catalytically active oxidic Ru species, without any indication of a separate FeOx phase. The structure evolution of LFRO in each reduction temperature is systematically investigated to uncover the RuFe-LaOx formation process. When heating LFRO in the reducing atmosphere, Ru exsolves to the surface processing through Ru3+ → Ruβ → Ru0 and Ru is likely to diffuse in the form of Ruβ which serves as the intermediate species during this process. The transformation of Ru3+ initiates already at 300 °C while subsequent reduction to Ru0 which is the sign for the exsolution requires 400 °C. When the reduction temperature is higher than 500 ℃, Ru in the bulk starts to be exsolved and accompanied by the co-segregation of LaOx. Further enhancing of the reduction temperature leads to the continuous growth of Ru particles while the segregated LaOx eventually encapsulates the exsolved Ru, forming the core-shell structured nanoparticles.The information on structure evolution during Ru exsolution from LFRO and following change in reaction condition provides insights into the rational design of precious metal-based catalysts via the exsolution strategy for various application scenarios
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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