1,721,179 research outputs found
AuPd Bimetallic catalyst for Lignin-derivatives alcohols valorization
No full textLignin moieties consist in three hydroxycinnamyl alcohol derivatives (p-coumaryl, coniferyl and sinapyl alcohols), which differ in the degree of methoxylation on the aromatic ring. Their oxidation to aldehydes is one of the major methods for their valorization. Au-Pd based catalysts effectively oxidize benzyl alcohol (BA), as Wang et al. showed that the Au:Pd ratio on the surface of the particles is a key parameter that influences the catalytic performance. On the basis of these results, here we investigated the effect of the methoxy substituent on catalytic activity of Au-Pd catalysts by studying the oxidation of 4- and 3,4-Dimethoxybenzyl alcohol (4-MBA, 3,4-DMBA) to the corresponding aldehydes. Samples at different Au/Pd ratio were synthesized by sol impregnation.
The presence of the OMe group influenced the catalytic activity, depending on its position. When OMe is in para, we observed a clear difference in catalytic activity by changing the Au-Pd ratio. Contrariwise, a substantial negligible effect of the Au/Pd ratio was detected for 3,4-DMBA oxidation. A deep characterization of the NPs structure will be shown to give some insight on the reaction
Micro-Sized TiO2 for Toluene Photodegradation in Gas Phase: catalyst preparation and role of doped metal to increase the photo-activity
No full textMicro-Sized TiO2 for Toluene Photodegradation in Gas Phase: catalyst preparation and role of doped metal to increase the photo-activity. Indoor air pollution is a problem not to be underestimated because of two reasons: firstly, because the majority of the population spends about 80-90% of the time in these places and secondly, because the risk is affects almost the entire population. Pollutants are classified in three big categories: chemical, physical and biological; VOC's, formaldehyde, toluene, benzene, carbon monoxide, carbon dioxide and nitrogen dioxide fall in the category of chemical agents.
Industrial age caused an increase of indoor pollution and chemical substances like formaldehyde, xylene or toluene could making the air inside homes to 20 times more polluted than outdoor air.
In fact, toluene and xylene are in many household and educational products, well as they are emitted from the exhaust gases of cars; in particular, they are widespread because they are ubiquitous. Titanium dioxide is a semiconductor material that has good catalytic properties and is able to degrade numerous organic compounds by oxidation; its molecules exposed to light catalyse the oxidation of organic residues in water and carbon dioxide.
In this work, catalysts based on titanium dioxide were tested and improved in particular on the degradation of toluene. P25 was the sample reference for nanometric powders, and its activity was compared with Kronos 1077, which consists of micrometric particles. Kinetics are carried out in a glass Pyrex reactor with a 200 mm diameter and a 5,5 L volume. Located 50 cm above the reactor there is an UV lamp; its power is 500 W and the wavelengths of the emissions are between 100 and 400 nm. The power calculated on the catalyst surface is 30 W\m2.
A gas chromatograph tracked the toluene and carbon dioxide concentrations inside the reactor. Although micrometric sample showed a lower activity than P25, it is possible to modify it, in particular with metals, and improve its final performance. Finally, the toluene kinetic reaction pathway was studied as well, and the main by-products were analyzed and classified
TIO2 PHOTOCATALYSIS FOR IMPROVING THE AIR QUALITY: FROM MOLECULES, TO BUILDING MATERIALS DEVELOPMENT
Full text linkGeneral abstract
1. Introduction
During these last years, the innovation and development processes lead pollution to its highest level; the air pollution is one the most prominent and dangerous form of it. Causes are several, from fuel combustion to factories activity, which increase the level of organic molecules and nitrogen or sulfur oxides in atmosphere (WHO Global Urban Ambient Air Pollution Database, update 2016).
Unfortunately, effects are more than evident: from the global warming, to the acid rains, from the sudden climate changes, to the increase of diseases such as asthma and lung cancer (Ambient (outdoor) air quality and health, WHO).
Outdoor air pollution is the major environmental health problem affecting everyone in developed and developing countries alike, however, unlike one might usually think, indoor levels of organic pollutants are often higher than outdoor (Viegi et al., 2004). The problem is even more important because people live mainly indoors, constantly exposed to all the pollutants present in these close environments (Chen et al., 2016; Allen et al., 2016).
For this reason, demands to improve the air quality situation have been largely extended, finding new strategies for waste reduction or for the oxidation and degradation of pollutants (Ambient (outdoor) air quality and health, WHO).
Among several processes, considering that very important factors are saving energy and reducing emissions, photocatalysis has been exploited as very suitable technique to reduce pollution.
In a photocatalytic reaction (eq. 1), a semiconductor material, the photocatalyst, is activated by light and, thanks to the formation of some electron-hole couples between his valence and conduction bands, it is able to reduce or oxidize molecules that adsorb on his surface (J.M. Herrmann, 2005).
In heterogeneous photocatalysis, the reaction implies the previous formation of an interface between the semiconductor and the reactants of the reaction (K. Demeestere et al., 2007; M. Schiavello, 1997).
(Ox1)ads + (Red2)ads Red1 + Ox2 (1)
Among a large variety of semiconductor materials, which are mainly metal oxides, only few of them are considered to be applicable photocatalysts, in relation with their specific photocatalytic properties. Titanium dioxide (TiO2) induced photocatalysis is an example of AOP processes and it has been demonstrated its efficiency in the decomposition of various organic contaminants. TiO2 is a very well known and well-researched material due to the stability of its chemical structure, biocompatibility, physical, optical, and electrical properties (M. Serpone et al., 1989).
The crystalline forms of TiO2 are anatase, rutile and brookite (A. Linsebigler et al., 1995). In general, TiO2 is preferred in anatase form because of its high photocatalytic activity, however the major drawbacks of TiO2-based photocatalysts is related to the rapid charge recombination of the electron−hole pairs, and the wide band gap, which restricts light absorption to only ultraviolet region (wavelength <390 nm), restraining the practical applications of TiO2-based photocatalysts under solar light or visible light.
TiO2-based photocatalysts are used for a variety of applications such as degradation of volatile organic compounds (VOCs) and decomposition of nitrogen pollutants (NOx) or also organic dyes, like Methylene Blue (K. Demeestere et al., 2007; P.K.J. Robertson et al., 2005).
When TiO2 is irradiated with energies equal to or higher than its band gap (>3.0 eV), electrons are excited from the valence band into the conduction band, leading to excited electrons in the conduction band and positive holes in the valence band. This fundamental process can be expressed by the following reaction equations (eq. 2):
TiO2 + hv → e- + h+ (2)
As electrons have a reducing potential, holes can oxidize water and lead to the formation of more oxidant species such as hydroxyl radicals, able to oxidize organics.
As mentioned above, the field of practical applications of TiO2-based photocatalysts becomes less expanded under solar light or visible light.
In this sense, different strategies have been developed (X. Li et al., 2011; S. Afzal et al., 2013; S. Wu et al., 2013; Y. Cho et al., 2001), starting from the chemical modification of TiO2 lattice using non-metals, particularly carbon, nitrogen and sulfur (S. Khan et al., 2002; J. Gole et al., 2003; T. Umebayashi et al., 2003).
The presence of metal nanoparticles on TiO2 surface can promote charge transfer process in the composite systems (N. Chandrasekharan et al., 2000; A. Dawson et al., 2001), because of the electron injection that occurs from the nanosurface to the conduction band of TiO2 and the metal particle.
In recent years, formation of photocatalytic heterostructures based on TiO2 with other semiconductor/noble metal has emerged as an important strategy to increase the separation of charge carriers and suppress the recombination rate of photoinduced electron−hole pairs, resulting in improved photocatalytic efficiency (F.X. Xiao et al., 2012; B. Liu et al., 2011; V. Etacheri et al., 2013; V. Etacheri et al., 2010; V. Etacheri et al., 2012; Y. Wang et al., 2013).
Aims of the work
The aims of the work regard different points of the TiO2 study and improvement. Starting from the choice of the best commercial powder of TiO2 to replace the titanium oxide nano-powders, through its modification to make it useful in visible light, until the application on ceramic supports to prepare building materials appropriate for outdoor and indoor pollution abatement, to improve the air quality and the quality of our life as well.
The purposes of this research project can be therefore summarized as follows:
• Study in depth the real potential of a micrometer TiO2, finding the best candidate among several commercial samples to obtain benefits such as economic saving, safety, ease in product handling in industry;
• Improve the use and application of micro-TiO2 on building materials to optimize their performances in pollution abatement, with particular attention to realistic settings; in this sense, find innovative methods to test materials and assesses the photocatalytic potentials;
• Make micro-TiO2 active under visible light, modifying it with noble metals and in particular combining the process with the use of high-energy ultrasound (US).
2. Experimental details
2.1 Commercial samples of TiO2
In this work, the starting point was the study of different commercial powders of TiO2.
Five commercial TiO2 materials by Kronos, Hundsman, Sachtleben (two different powders) and Cristal (respectively quoted with the B–E letters) have been selected. They are all available in the market as pigmentary powders, and they have the following key features: pure anatase phase, uncoated surface, undoped material, not sold as photocatalytic material. P25 by Evonik is the nanometric commercial TiO2 reference for photocatalytic applications, and it is the most used and studied. All commercial powders were used as received without any further treatment or activation process (C.L. Bianchi et al., 2015).
The crystallographic phase composition have been valued by XRD patterns and all the samples are pure anatase, except for P25. Crystallite size of 1077 by Kronos endorses its micro-sized nature, always connects to a low surface area. As expected, P25 is a nano-sized powder. Studying more thoroughly the morphological characteristics particularly by TEM analysis, it can be notice that the reference P25 powder is made up of well-crystallized particles of rather roundish shape, closely packed and with an average size of 20–30 nm. XPS results give information about the surface states of TiO2 and there are not differences among all the present samples concerning binding energy (BE). Even the band gap values, evaluated by means of diffuse reflectance UV–Vis analysis, do not exhibit large differences among the various samples.
2.2 Selected pollutants
Photocatalysts, whether commercial as such or modified as explained in the next sections, have been tested on VOCs molecules referring to indoor pollution, and on nitrogen oxides (NOx) in reference to outdoor pollution. Some reagents are liquid, other are gaseous and stored in cylinders under pressure. All substances were used as purchased without any particular pre-treatments or purification.
2.3 Photocatalytic reactors
VOCs degradation
Photocatalytic degradations were conducted in a Pyrex glass cylindrical reactor with diameter of 200 mm and effective volume of 5 L. The catalyst in powder form has been deposited on a flat glass sheet (100cm2) as thin film, from a suspension in 2-propanol. The catalyst amount used in each tests was 0.05 g. The atmosphere in the reactor was obtained by mixing hot chromatographic air humidified at 40%, and a fixed amount of volatilized pollutant, in order to avoid condensation. Photon sources were provided by a 500 W iron halogenide lamp (Jelosil, model HG 500) emitting in the 315–400nm wavelength range (UV-A) at 30Wm-2, or by a LED (MW mean well, 350 mA rated current, 9–48 V DC voltage range, 16.8 W rated power) with an emission between 400 and 700 nm. The actual concentrations of pollutant in the reactor were determined directly by micro-GC sampling or by Proton transfer reaction mass spectrometry (PTR-MS) (detailed description is reported in the next sections).
Nitrogen oxides degradation
➢ NOx photocatalytic degradations were conducted in a Pyrex glass cylindrical reactor with an effective volume of 20 L in batch mode. The catalyst in the form of powder has been deposited from 2-propanol suspension on a flat glass sheet (40cm2), and the amount used in each tests was 0.05 g. The gaseous mixture in the reactor was obtained by mixing NOx (mixture of NO and NO2 in air) with air humidified at 40%. The initial concentrations of NOx in the reactor were 1000 ppb in order to follow the same pollutant concentration requested by the ISO 22197-1 rules (www.iso.org) and 200 ppb that is very close to the alert threshold set by the EU Directive 2008/50/CE for NO2 (http://eur-lex.europa.eu). Photon source was provided by a 500 W iron halogenide lamp (Jelosil, model HG 500) emitting in the 320–400 nm wavelength range (UV-A). The specific UV power on the surface of the samples was 10 Wm-2. The concentration of pollutants in the reactor was determined directly by chemiluminescence (Teledyne, Mod. 200E).
➢ The continuous flow reactor has been used only for testing photocatalytic building materials; it has got walls of 10 mm in thickness, and an internal size of 625 × 625 × 115 mm3, with four inlets and one opposite outlet and can house a sample of 600 × 600 × 10 mm3. It is equipped with a thermo-hygrometer model HT- 3006A to measure the temperature and humidity during the tests. The relative humidity inside the reactor is maintained constant around a value between 40 and 50%. The experiments were carried out either using UV lamps (UV-A region, 20 Wm−2) or using sunlight from July to September. The degradation was performed at different initial NOx concentrations ranging from 100 ± 10 ppb to 200 ± 10 ppb, at room temperature and working with total gas flow rates of 140 and 180 NL h−1. Even for these tests, the concentration values were chosen in order to work closely to the limit values reported on Directive 2008/50/EC, in particular, 106 ppb (equal to 200 μg m−3) and 213 ppb (400 μg m−3, alert threshold). The duration of each continuous run was set at 6, 12 or 24 h. The final design of the reactor was selected among several possibilities by considering the good homogeneity of the reactant in the gas phase and a contact between the reactant and the photocatalytic material that effectively reproduce the real working conditions.
2.4 Samples characterization
The morphology of TiO2 in form of powder, both commercial and synthesized or modified, was inspected by means of high-resolution transmission microscopy (HR-TEM) (Jeol JEM 3010 instrument, equipped with LaB6 filament and operating at 300 kV), and the surface area of all the catalysts was determined by conventional N2 adsorption (BET) at 77 K using a Sorptometer (Costech Mod. 1042). XRD spectra were collected using a PW 3830/3020 X’ Pert Diffractometer from PANalytical working Bragg-Brentano, using the Cu Kα1 radiation (k = 1.5406 Å). X-ray photoelectron spectra (XPS) were taken in an M-probe apparatus (Surface Science Instruments). Diffuse reflectance spectroscopy (DRS) of the ground powders was performed with a Thermo Scientific Evolution 600 spectrophotometer, equipped with a diffuse reflectance accessory Praying-Mantis sampling kit (Harrick Scientific Products, USA). A Spectralon1 disk was used as reference material, and the experimental absorption versus lambda plot was elaborated using the Kubelka–Munk function. Absorption/transmission IR spectra were obtained on a Perkin-Elmer FT-IR System 2000 spectrophotometer equipped with a Hg–Cd–Te cryo-detector. Particularly for metals-modified TiO2, ICP/OES analysis has been performed using a Perkin Elmer Optima 8300 instrument. HR-SEM-EDX analysis was performed particularly on photocatalytic building materials (tiles) (Field Emission Gun Electron Scanning Microscopy LEO 1525, metallization with Cr. Elemental composition was determined using Bruker Quantax EDS). The surface wettability was evaluated by static contact angle (CA) measurements performed with an OCA20 instrument (DataPhysics Co., Germany) equipped with a CCD camera and a 500μL-Hamilton syringe to dispense liquid droplets.
2.5 Metal NPs modified TiO2: synthesis procedure
To obtain the surface modification of the commercial powder of TiO2, in this work we performed a synthesis by means of high-energy US. Procedure steps are slightly different from a metal to another, but in general they follow the same scheme, described in the next lines. The precursor materials are organic or inorganic salts of different metals, selected in accordance with characteristics that will be detailed in the following chapters. For the US generation, we used A Bandelin SONOPLUS HD 3200 utilizing a 200W U/S generator and a sonication extension horn of 13mm diameter. Generally, the metal precursor and the commercial powder of TiO2 have been put together in a 100 ml glass flask, and they have been solved with the preferred solvent (aqueous or organic). The solution is then sonicated at constant temperature with a specific amplitude and intensity (Wcm-2). At the end the solution is centrifuged many times to remove all the solvent and the final powder is washed before evaporation and/or calcination steps.
2.6 Building materials production: ACTIVE® photocatalytic tiles (by GranitiFiandre S.p.A)
Airless spray classic preparation
Industrial porcelain grés tiles are manufactured under high pressure by dry-pressing fine processed ceramic raw materials with large proportions of quartz, feldspar, and other fluxes and finally fired at high temperatures (1200–1300°C) in a kiln.
To obtain photoactive porcelain grés tiles, they were subsequently covered by airless spray with a mixture of micro-TiO2 (specifically, 1077 by Kronos has been selected as best commercial powder) mixed with an aqueous suspension of a commercial SiO2-based compound (process developed by GranitiFiandre S.p.A, patent n. EP2443076). At the end of the preparation procedure, tiles were fired at high temperature (min 680°C) for 80 min. Finally, the powder present at the sample surface and not completely stuck was brushed and removed.
Digital Printing technology: DigitaLife Project
The digital printing technology is based on suitably designed print heads using a tailored solvent-based ink, micro-sized TiO2 and additives (process developed by GranitiFiandre S.p.A, DigitaLife project). Specific and more detailed information will be given in the various chapters dedicated.
3. Results and discussion
3.1 Characterization of the TiO2 powders and materials
Among the starting selected commercial samples, 1077 by Kronos has been chosen as best micrometer candidate to replace the nanometric reference P25. For this reason, all the results that will be presented in this thesis refers to P25 or 1077 as commercial references, nano and micro-sized respectively, and, all the structural modification studies, synthesis, tests, have been performed using 1077 as TiO2 support on which make changes.
HR-TEM images confirm the nanometric nature of P25 and the micrometric dimension of the TiO2 particles of 1077 commercial sample. Results are absolutely completely in line with the results about the surface area (gm-2), which is very low in case of bigger TiO2 particles. From the same characterization analysis performed on the various modified samples, it is shown that this structure composition has not been changed by thermic treatments (calcination steps) or modification steps of the original sample with metals, or by classical impregnation methods either by using ultrasound as will be described in the dedicated chapters. XRD spectra give particularly information about the crystallographic phase composition. As presented in the table above, 1077 consists completely of anatase, which is a very good feature in term of photocatalytic activity. Any modification steps have not altered even this composition. All the samples presented in this work, except P25, consist of anatase. Useful in term of photocatalytic activity is also the distribution on the TiO2 surface of the OH groups, which are measurable in relation to the total oxygen (OTOT), particularly by means of XPS analysis; 1077 by Kronos presents a higher OH/OTOT ratio (0.14 and 0.32 for P25 and 1077 respectively) than P25, and this value, ascertainable even more accurately using the IR spectra, increases modifying 1077 TiO2 by metals.
When TiO2 is decorated on surface with noble metal or metal-oxides nanoparticles (for every modified-metals-TiO2 sample presented in this work, we have usually a mixture of metal and metal-oxides NPs) the UV-VIS spectra show that the absorption shifts to the visible wavelengths, more or less depending on the metal species and its amount deposited on TiO2. UV-VIS spectra collected on the references, P25 and 1077 respectively, confirm the slight absorption in the visible of P25, because of the presence of rutile, and the absence of absorption in visible of 1077 by Kronos, which can be activated only by UV irradiation, even because its band gap, typical of anatase TiO2 (3.2 eV). Referring to the surface area, presented above for the references commercial powders, deposition of NPs on TiO2 surface can have slights effects on the final surface area, which increases, even if the value is very small and almost negligible.
Finally, SEM characterization is very useful to study the ceramic surfaces when TiO2 is deposited in them. In particular, the main points in case of the two photoactive grés ceramic tiles samples are a) the fact that 1077 TiO2 does not change its nature so remains anatase and micrometer; b) changing the deposition method the distribution of the TiO2 particles completely changes.
3.2 Pollutants photodegradation: Nitrogen Oxides
The use of a pigmentary powder of TiO2 as 1077 by Kronos, consisting in micrometer particles with a lower surface area, is absolutely effective in case of NOx abatement. The comparison between 1077 and P25 (as reported in Table 4) shows that the degradation percentage obtained after 120 minutes of photocatalytic reaction is very slight and almost negligible, if we consider the advantages in term of economic saving (2/Kg for 1077) and safety. The main reasons why 1077 shows to be a very good candidate between various pigmentary and commercial TiO2 in photocatalysis, are firstly its phase composition, i.e. anatase, without rutile. Moreover we have to consider that 1077 surface present a wide population of OH groups, which both for the adsorption of pollutant molecules and for them degradation are crucial. Therefore, especially for NOx abatement, micro-TiO2 as it is proves to be efficient. Thus, a modification of the material with metals, which increase the final cost, is unnecessary. 1077 however presents a very low activity if irradiated only by visible wavelengths, as confirmed by the UV-VIS spectra, which do not show absorption peaks after 400nm (visible spectrum from 400nm to 700nm). In this case, the surface modification of TiO2 with metal NPs is a key factor to have effective samples in nitrogen oxides abatement. Preparation methods are different and they will be deeply described in the dedicated chapters. To summarize the most important results, as can be seen from the presented graphs (Fig. 4-6), the presence of silver nanoparticles clearly improve the photocatalytic activity of the sample, and the key factor related to a better NOx degradation are particularly the metal-NPs amount and dimension. Finally, after showing that 1077 by Kronos is effective, it has been deposited on ceramic grés tiles as already mentioned. The borderline between samples Z23 and S24 is the method with which the deposition is obtained. Digital printing technology leads to a better and more uniform distribution of the TiO2 powder, as well as to a lower loss of it during the process, with the final results clear presented in the kinetics graphs (see Fig. 4).
3.3 Pollutants degradation: VOCs
Commercial powders of TiO2 have been already exploited in VOCs photodegradation (C.L. Bianchi et al., 2014; S.B. Kim et al., 2002; G.M. Zuo et al., 2006), showing very good results against various molecules (see tab.5). However, and it is more evidently tha
MULTICOMPONENT APPROACHES TO THE SYNTHESIS OF SMALL BIOACTIVE MOLECULES
Full text linkIn this PhD thesis, we exploited the potentialities of four different multicomponent reactions (MCRs), namely Ugi four-component reaction (U-4CR), N-split Ugi reaction (N-split U-4CR), van Leusen three-component reaction (vl-3CR) and Biginelli reaction (Bg-3CR), developing five different approaches to the synthesis of small bioactive molecules.
In particular, we successfully applied the build/couple/pair strategy obtaining a small library of ketopiperazine-based minimalist peptidomimetics, by means of diastereoselective U-4CR/post-cyclization sequences, employing optically pure amino acid-derived α-amino aldehydes and α-isocyanoacetates as starting materials. Computer-assisted NMR NOE analysis allowed us to determine the configuration of the newly formed stereocenters, while molecular dynamics simulation and biological evaluation clearly underlined the potentiality of selected compounds to interfere with protein-protein interactions (PPIs).
We also focused our attention on another class of peptide-like compounds, namely diamine-based peptidomimetics, by carefully optimizing the N-split U-4CR conditions for the introduction of N-protected amino acids and α-isocyanoacetates components, in a stereoconservative way. This methodology largely simplifies the synthesis of such compounds, opening the way to the use of more complex secondary diamines, able to induce well-defined secondary structures in the related peptidomimetic and hopefully targeting novel PPIs.
Furthermore, by combining the same N-split U-4CR with common transformations, a library of dopamine receptor agonists was rapidly obtained, with biological activities in the nanomolar range. Although the desired D2/D3 selectivity was not achieved, structure-activity relationship (SAR) and docking studies allowed us to understand the key pharmacophoric elements in these novel structures, leading the way to the design of improved molecular scaffolds.
By employing the vL-3CR in an iterative way, we designed a novel C2-C5’ linked polyimidazole-based minimalist framework, able to mimic the i, i+1, i+2 and i+3 amino acid residues of a β-strand motif. Its conformational behaviour was investigated through solution-phase NMR and molecular dynamics studies, allowing to demonstrate its ability to mimic a poly-alanine β-strand.
Finally, we explored the possibility to combine MCRs with organocatalysis, developing the first BINOL-derived phosphoric acid catalysed Biginelli-like reaction on a ketone. In particular, employing N-substituted isatins as carbonyl substrates, we achieved the synthesis of a small library of biologically relevant enantioenriched spiro[indoline-pyrimidine]-diones derivatives. The assignment of the configuration at the new oxindole C-3 stereocenter was assessed through quantum-mechanical methods and NMR spectroscopy, while computational studies on the reaction transition state allowed us to explain the enantioselectivity and the stereochemical outcome
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
Post-synthesis modification of goldsilver nanoparticles: a way to tune catalytic activity and selectivity
No full textCarbon supported gold catalysts are highly active in the liquid phase oxidation of glycerol. In particular, bimetallic particles show enhanced activity, diverse selectivity and higher stability. Au–Ag catalysts supported on TiO2 by sequential deposition–precipitation method showed higher conversion than monometallic Au/TiO2 in CO oxidation, confirming the synergistic effect between Au and Ag. Moreover, the catalyst activation temperature influenced both the catalytic activity and nanoparticles composition. Theoretical studies investigating the segregation of Ag in Au-Ag NPs, reporting that segregation behaviors are composition, size and temperature dependent. Based on these facts and considering the already proven efficiency of Au-Ag bimetallic catalysts in glycerol oxidation, here we compared the catalytic activity and selectivity of differently synthesized and post-treated Au-Ag/TiO2 catalysts for glycerol oxidation. The same post-treatment had a different outcome on the nanoparticles features, and this reflected on the catalytic activity and selectivity
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
Tomography Analysis of Ru Supported on Micro and Mesoporous Carbon: A Correlation Between Morphology and Catalytic Activity
No full textRuthenium (Ru) based catalysts effectively hydrogenate aromatic compounds, olefins, aldehydes, ketones and other carbonyl compounds. Ru/C reached conversion and selectivity over 90 % for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). However, solvents and supports greatly affect activity and selectivity. Ru/graphite, Ru/zeolite, or a mixture of Ru/graphite and zeolite showed very different GVL yields. Depositing Ru on four graphitized carbon materials differing in their surface area, different Ru dispersion has been produced which lead to different catalytic activities in CO methanation, as reported by Truszkiewicz et al. However, even if the control of selectivity has been roughly achieved, the stability of Ru-based catalysts is still insufficient. Villa et al. studied the hydrogenation of levulinic acid at 70°C by Ru supported on functionalized mesoporous carbons, showing a good stability. On the contrary the same catalysts showed a decreased activity after three consecutive cycles when the reaction was performed at higher temperature (200°C). Deactivation mainly has been addressed to Ru leaching, Ru particle aggregation or carbon deposition on them. Therefore, characterization analyses of the support morphology and surface, as well as of the metal particle size, shape and dispersion, are critical to understand how certain factors can modulate the catalytic properties.
Here, we synthesized Ru nanoparticles supported on two different types of carbon, i.e. ordered mesoporous carbon (OMC) and activated carbon (AC). STEM tomography analyzed Ru particles size and distribution, showing different NPs confinement inside the pores. HAADF STEM electron tomography sets the material 3D structure and improved the identification of the preferential NPs allocation which strongly affects catalytic activity
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