1,720,961 research outputs found
FeMo-based catalysts for H2 production by NH3 decomposition
No full textActive and stable catalysts for ammonia decomposition were obtained by deposition of Fe(5 wt%)–Mo(5 wt%) on commercial stabilized zirconia and modified aluminas. The adopted preparation methodology, combined with a severe reduction treatment, allowed obtaining highly dispersed nanoparticles of Fe–Mo alloy, as revealed by powder XRD. The bimetallic catalysts demonstrated a higher activity with respect to the monometallic ones with the same metal loading (10 wt%). The best performances were obtained for a bimetallic Fe5Mo5/La2O3-modified Al2O3 sample. During ammonia decomposition reaction, the Fe–Mo alloy was progressively converted into a mixture of Fe/Mo nitrides, while good catalytic activity was maintained. The performances of the present catalysts well fit with the requirements of catalysts for application in ammonia-fueled SOFCs or for internal combustion engines
Embedded Ru@ZrO2 catalysts for H2 production by ammonia decomposition
No full textAmmonia can be used as fuel in internal combustion engines (ICEs). In this case, a flame accelerator, such as hydrogen, is needed. H2 can be produced on-board by partial decomposition of ammonia. In this work, ruthenium nanoparticles were embedded into a lanthanum-stabilized zirconia (LSZ) support to obtain active and stable heterogeneous catalysts for NH3 decomposition. The effects of the preparation of both Ru nanoparticles and LSZ support were investigated. The embedded catalysts present high metal dispersion and good metal accessibility. Despite the relatively low metal loading (3 wt %), activity was very high in the temperature range 400–600 °C. The activity of the reference catalysts prepared by using classical impregnation was significantly lower under the same working conditions. Although many factors contribute to the final catalyst performances, the data reported confirm that the embedding strategy minimizes the undesirable sintering of the Ru nanoparticles, leading to promising and stable catalytic activity
Hydrogen production from ethanol steam reforming on M/CeO2/YSZ (M = Ru, Pd, Ag) nanocomposites
No full textM/CeO2/YSZ nanocomposites (M = Ru, Pd, Ag) were prepared by successive impregnation and tested in the ethanol steam reforming (ESR). Ru/CeO2/YSZ demonstrated good activity and stability under reaction conditions. Pd/CeO2/YSZ shows good initial activity but suffers of significant deactivation while the performances of the Ag-based sample were rather poor. A plethora of different structural (Powder XRD), microstructural (HR-TEM), morphological (surface area, CO chemisorption) and thermal analysis characterization techniques were used to evidence the modification of the samples induced by prolonged exposure to the reaction mixture. The promising performances of Ru/CeO2/YSZ were associated to the combination of the positive action of the metal selectivity to syn-gas and of CeO2 in metal dispersion stabilization and coke deactivation prevention
Embedded phases: a way to active and stable catalysts
No full textIndustrial catalysts are typically made of nanosized metal particles, carried by a solid support. The extremely small size of the particles maximizes the surface area exposed to the reactant, leading to higher reactivity. Moreover, the higher the number of metal atoms in contact with the support, the better the catalyst performance. In addition, peculiar properties have been observed for some metal/metal oxide particles of critical sizes. However, thermal stability of these nanostructures is limited by their size; smaller the particle size, the lower the thermal stability. The ability to fabricate and control the structure of nanoparticles allows to influence the resulting properties and, ultimately, to design stable catalysts with the desired characteristics. Tuning particle sizes provides the possibility to modulate the catalytic activity. Unique and unexpected properties have been observed by confining/embedding metal nanoparticles in inorganic channels or cavities, which indeed offers new opportunities for the design of advanced catalytic systems. Innovation in catalyst design is a powerful tool in realizing the goals of more green, efficient and sustainable industrial processes. The present Review focuses on the catalytic performance of noble metal- and non precious metal-based embedded catalysts with respect to traditional impregnated systems. Emphasis is dedicated to the improved thermal stability of these nanostructures compared to conventional systems
Effect of the Catalyst Load on Syngas Production in Short Contact Time Catalytic Partial Oxidation Reactors
No full textShort contact time catalytic partial oxidation (SCT-CPO) of natural gas is a promising technology for syngas production, representing ail appealing alternative to existing processes. This process is likely to become more important in the future due to its advantages in thermodynamics, mildly exothermic overall reaction, and H(2)/CO ratio of 2, ideal for downstream processes. Rh catalysts are preferred among those based on noble metals because they avoid coke deposition. However, Rh is very expensive. Thus, the design of nanocomposite catalysts with the minimum Rh load for a feasible industrial process is the aim of the present work: 0.25, 0.5, and 1% Rh load were considered. The catalytic reactor is made of a fixed bed of Rh deposited on both Al(2)O(3) spheres in ail egg-shell Configuration and Al(2)O(3) irregular particles in an egg-yolk configuration. The weight hourly space velocity (WHSV) was varied from 130 to 460 N L h(-1) g(cat)(-1). The 0.5% Rh in the egg-yolk configuration allowed the highest CH(4) Conversion (>90%) and H(2) selectivity (>98%) values at my tested WHSV
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
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