1,720,958 research outputs found
Biosyngas and Derived Products from Gasification and Aqueous Phase Reforming
No full textThe production of second-generation fuels from biomass is entering a new
stage focused on large projects and industrial initiatives. However, the uncertain
scenario in terms of climate change commitment and burden share, fossil fuel
price, and renewable legislation limits does not provide the best environment
for a large-scale spread of new technologies; furthermore, this innovation still
requires a real breakthrough in order to lead to a clearly enhanced efficiency
and sustainability. There are different approaches driving the conversion of
biomass bulk or its fraction into fuel: (i) the fermentation process to bioethanol
and biomethane, (ii) the production of oxygenated liquid compounds by several
treatment (pyrolysis, liquefaction, triglyceride extraction, etc.) followed by
hydrotreating (HDT) to upgrade the bio-oil produced, and (iii) gasification or
aqueous phase reforming (APR), which produces syngas and hydrocarbons or
alcohols. Gasification uses an oxidizing agent (air, steam, oxygen, or a combination
of these) for the high-temperature transformation of a carbonaceous
feedstock into a gaseous energy carrier consisting of permanent, non condensable
gases, mainly syngas. Subsequently, in a separate stage, the syngas obtained is
transformed by Fischer–Tropsch (FT) reaction into diesel or other syngas fuel
such as methanol dimethyl ether (DME) or C2+ alcohols.
The APR reaction is an alternative pathway to gasification for the transformation
of biomass and its main components (sugars, polyols, and even proteins) into several
products such as hydrogen, hydrocarbon, and oxygenated molecules, with the
main products depending on the reaction conditions, process configuration, and
catalysts.The APR treatment is applied to a hydrolyzed biomass in water solutions
at 225–300 ∘C in subcritical conditions
H2 Production by Methane Oxy-Reforming: Effect of Catalyst Pretreatment on the Properties and Activity of Rh-Ce0.5Zr0.5O2 Synthetized by Microemulsion
Full text linkGreen hydrogen introduction in hard-to-abate processes is held back by the cost of substituting steam reforming plants with electrolyzers. However, green hydrogen can be integrated in properly modified reforming processes. The process proposed here involves the substitution of steam reforming with oxy-reforming, which is the coupling of the former with catalytic partial oxidation (CPO), exploiting the pure oxygen coproduced during electrolysis to feed CPO, which allows for better heat exchange thanks to its exothermic nature. With the aim of developing tailored catalysts for the oxy-reforming process, Ce0.5Zr0.5O2 was synthetized by microemulsion and impregnated with Rh. The Ce-based supports were calcined at different temperatures (750 and 900 °C) and the catalysts were reduced at 750 °C or 500 °C. Tuning the calcination temperature allowed for an increase in the support surface area, resulting in well-dispersed Rh species that provided a high reducibility for both the metal active phase and the Ce-based support. This allowed for an increase in methane conversion under different conditions of contact time and pressure and the outperformance of the other catalysts. The higher activity was related to well-dispersed Rh species interacting with the support that provided a high concentration of surface OH* on the Ce-based support and increased methane dissociation. This anticipated the occurrence and the extent of steam reforming over the catalytic bed, producing a smoother thermal profile
Integration of catalytic methane oxy-reforming and water gas shift membrane reactor for intensified pure hydrogen production and methanation suppression over Ce0.5Zr0.5O2 based catalysts
Full text linkThe production of pure hydrogen from methane or biomethane is a multistep process that can be intensified by the use of membrane reactors. In this study we have synthetized by microemulsion technique Rh and Pt supported over Ce0.5Zr0.5O2 to be applied to the catalytic methane oxy-reforming and water gas shift (WGS) reaction respectively. At first the reformate produced by the reforming process at 750 ◦C was purified using and hydrogen selective empty Pd-based membrane operated at 400 ◦C. This led to pure hydrogen production but it resulted also in a not-fully exploitation of the membrane performances. Thus, the Pt-based catalyst was loaded in the membrane reactor configuration leading to in situ hydrogen production that helped to increase the separation driving
force. The water gas shift reaction downstream oxy-reforming was also studied on the Pt/Ce0.5Zr0.5O2 catalyst and evidenced the consumption of hydrogen by methanation at high H2/H2O ratio. Comparing the WGS membrane reactor with a classical fixed bed demonstrated that removing hydrogen led to increased CO conversion over the equilibrium of an analogous fixed bed, higher H2 yield and suppression of the methanation reaction, even at high inlet H2/H2O ratio. Optimizing the reaction conditions allowed to reach high hydrogen recoveries (89 %) for the integrated oxy-reforming/membrane water gas shift at high GHSV and without the need of a sweep gas
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
Catalysts and processes for next-generation H2 production
No full textThe present study is focused on the development of new VIII group metal on CeO2 – ZrO2 (CZO) catalyst to be used in reforming reaction for syngas production. The catalyst are tested in the oxyreforming process, extensively studied by Barbera [44] in a new multistep process configuration, with intermediate H2 membrane separation, that can be carried out at lower temperature (750°C) with respect the reforming processes (900 – 1000°C). In spite of the milder temperatures, the oxy-reforming conditions (S/C = 0.7; O2/C = 0.21) remain critical regarding the deactivation problems mainly deriving from thermal sintering and carbon formation phenomena. The combination of the high thermal stability characterizing the ZrO2, with the CeO2 redox properties, allows the formation of stable mixed oxide system with high oxygen mobility. This feature can be exploited in order to contrast the carbon deposition on the active metal surface through the oxidation of the carbon by means of the mobile oxygen atoms available at the surface of the CZO support. Ce0.5Zr0.5O2 is the phase claimed to have the highest oxygen mobility but its formation is difficult through classical synthesis (co-precipitation), hence a water-in-oil microemulsion method is, widely studied and characterized. Two methods (IWI and bulk) for the insertion of the active metal (Rh, Ru, Ni) are followed and their effects, mainly related to the metal stability and dispersion on the support, are discussed, correlating the characterization with the catalytic activity. Different parameters (calcination and reduction temperatures) are tuned to obtain the best catalytic system both in terms of activity and stability. Interesting results are obtained with impregnated and bulk catalysts, the latter representing a new class of catalysts. The best catalysts are also tested in a low temperature (350 – 500°C) steam reforming process and preliminary tests with H2 membrane separation have been also carried out
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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