1,720,983 research outputs found
Catalytic Hydrogen Generation and Use for Production of Fuels
Full text linkThis book focuses on catalytic hydrogen generation from formic acid, ammonia borane, and ethanol as well as on the production of fuels from tar using formic acid as a hydrogen source. The list of discussed catalysts includes single-atom catalysts, metallic/bimetallic catalysts, and supported metal complexes. These catalysts were thoroughly characterized using different methods. Optimized catalyst compositions are proposed
Advanced Catalysis in Hydrogen Production from Formic Acid and Methanol
Full text linkThis Special Issue is related to studies of the hydrogen production from formic acid decomposition. It is based on five research papers and two reviews. The reviews discuss the liquid phase formic acid decomposition over bimetallic (PdAg), molecular (Ru, Ir, Fe, Co), and heterogenized molecular catalysts. The gas-phase reaction is studied over highly dispersed Pd, Pt, Au, Cu, and Ni supported catalysts. It is shown that the nature of the catalyst’s support plays an important role for the reaction. Thus, N-doping of the carbon support provides a significant promotional effect. One of the reasons for the high activity of the N-doped catalysts is the formation of single-atom active sites stabilized by pyridinic N species present in the support. It is demonstrated that carbon materials can be N-doped in different ways. It can be performed either directly from N-containing compounds during the carbon synthesis or by a post-synthetic deposition of N-containing compounds on the carbon support with known properties. The Issue could be useful for specialists in catalysis and nanomaterials as well as for graduate students studying chemistry and chemical engineering. The reported results can be applied for development of catalysts for the hydrogen production from different liquid organic hydrogen carriers
A study of the production of hydrogen by the decomposition of formic acid over Pd-based and Pt-based catalysts
No full textAs one of main products of acid hydrolysis procedure from biomass, formic acid is a promising hydrogen carrier that has recently been earning more and more attention. CO-free hydrogen production and mild reaction conditions have recently been the two main targets in the production of hydrogen by the catalytic decomposition of formic acid. This thesis reports investigations of the catalytic performance of modified Pd-based and Pt-based catalysts for this reaction. The doping by alkali metal ions of a C-supported Pd catalyst promotes both its activity and hydrogen selectivity, the effect being in the order: K≥Cs>Na>Li. The reaction rate is increased by 1-2 order of magnitude using the optimum modified catalyst, 10 wt.% K-Pd/C, and the content of CO in the product is limited TO 30 ppm. The apparent activation energy for the reaction increases from a value around 60 kJ mol-1 to 100 kJ mol-1 upon K-doping for both the Pd/C catalyst and a Pd powder catalyst, this showing that the reaction mechanism changes on doping. Based on the activity measurements under both steady state and unsteady state conditions as well as on catalyst characterization results (TEM/EDS, STEM/HAADF, XPS, XRD and TOF-SIMS) and DRIFTS measurements, a reaction mechanism is proposed to explain the results with the K-doped Pd/C catalysts. Pt-based catalysts supported on N-doped carbon nanofibers (CNFs) have also been studied in formic acid decomposition. The use of CNFs as catalyst supports gives the possibility of controlling the structure of the catalysts during preparation. Nitrogen doping of the CNFs changes the electronic properties and gives more structural defects in the CNFs. Sub-nano-sized Pt particles stabilized by the N-doped CNFs supports have been found to have improved activity in formic acid decomposition and to be inactive in ethylene hydrogenation
Development of heterogeneous catalysts for hydrogen production from biomass derived formic acid
No full textHydrogen is increasingly used in a variety of applications and holds promise as a replacement for fossil fuels. Biomass derived formic acid represents an excellent renewable material for hydrogen storage. This thesis is devoted to an investigation of different catalysts aiming ultrapure hydrogen production from formic acid decomposition.
Two research directions were considered: (I) decomposition of formic acid over Au catalysts supported on a selection of metal oxides, and (II) decomposition of formic acid over Ru, Pd and Pt catalysts supported on a variety of N-free and N-doped carbon materials. A series of characterization methods were applied to understand the promotion of the catalysts with the nitrogen incorporated into the carbon structure, which should be taken into the account when designing a catalyst for particular use.
A study of ~2.5 wt.% Au catalysts supported on different metal oxides (Al2O3, ZrO2, CeO2, La2O3 and MgO) with the same mean Au particle sizes showed that alumina is the most efficient support for stabilization of Au species providing almost CO free hydrogen production for at least 16 h. High activity of Au catalysts was associated with acid–base properties of the support.
N-doping of Ru catalysts supported carbon nanofibers (CNFs) demonstrated an increase of the rate of the formic acid dehydrogenation reaction and lead to an increase of the selectivity to hydrogen from 83 to 92%. The increase in activity was explained by coordination of the Ru species by pyridinic nitrogen located on the open edge of graphene layers of the herringbone type CNFs used.
The effects of preparation variables, structure of the carbon supports (carbon nanofibers and porous carbon network), and surface functional composition on catalytic properties of the Pd and Pt catalysts were studied. Single Pd atoms and single Pt atoms on nitrogen-functionalized carbon materials, observed by aberration-corrected scanning transmission electron microscopy were found to contribute considerably to the catalytic activity, selectivity and did not affect the stability of the catalysts at least for 30 h in hydrogen production. XPS analysis proved the presence of Pd2+ ions in significant concentration even after treatment of the catalyst with H2 and interaction of Pd atoms with pyridinic nitrogen of the support was recognized
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
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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