1,721,111 research outputs found
Flame Spray Pyrolysis: catalysts for the Steam Reforming of bio-ethanol
No full textFlame Spray Pyrolysis (FSP) is a one step high temperature synthesis able to impart strong metal-support interaction [1], besides high thermal resistance. A set of Ni catalysts supported over ZrO2 doped with different basic oxide (CaO, MgO) were prepared by this innovative technique. Steam Reforming catalytic test were carried out for the production of hydrogen using bio-ethanol. The catalytic activity was compared with catalysts of the same composition, but prepared with a traditional precipitation/impregnation method (multistep synthesis). Very high activity has been observed at high reaction temperature (>600°C), but further kinetic studies were done under milder conditions (500-300°C), in order to lower the energy input to the process and to improve H2 productivity favoring the water gas shift reaction [2]. Two different bioethanol samples, 50 and 90 vol%, produced and supplied by Mossi&Ghisolfi, have been used for 8 h-on-stream at each temperature. Attention was paid to the catalyst resistance towards deactivation by coking, besides its activity and selectivity. The acidity of the support was tuned by doping ZrO2 with basic oxides, helping to prevent ethanol dehydration and coking by ethylene polymerization. Fresh and spent samples were characterized by XRD, TPR, TPO, TEM, FE-SEM and Raman analysis.
Figure: scheme and image of Flame Spray Pyrolysis
[1] G. Ramis, I. Rossetti, E. Finocchio, M. Compagnoni, M. Signoretto, A. Di Michele, Progress in Clean Energy, I. Dincer, Ed. Springer, in press.
[2] I. Rossetti, J. Lasso, E. Finocchio, G. Ramis, V. Nichele, M. Signoretto, A. Di Michele, Appl. Catal. B: Environmental, 150-151 (2014) 257-267
Metal modified TiO2 for CO2 photoreduction in unconventional conditions
No full textCO2 photoreduction, a growing field in green catalysis, shows great potentialities to avoid fossil fuels exploitation and to obtain C-based solar fuels through a sustainable process using water as a reductant and light irradiation as only energy input [1]. However, many efforts need to be made to have a substantial breakthrough to increase the efficiency of the whole process. To pursue this aim, different strategies can be followed, such as reaction conditions implementation and photocatalyst formulation.
Process efficiency is strictly dependent on chosen photocatalytic materials. In particular titanium dioxide, the most commonly used material, needs to be modified in order to boost light harvesting and increase photoactivity [2]. In this work, TiO2 was modified in order to increase electron mobility on photocatalytic surface. In particular, copper oxide was introduced as a co-catalyst and gold nanoparticles as surface plasmonic agents.
Some of the authors reported that unconventional conditions are able to increase solar fuels production from CO2 photoreduction in liquid phase, enhancing in particular CO2 absorption in aqueous media and tuning selectivity to desired products [3]. A novel pressurized liquid phase reactor was employed to study photocatalytic activity of these materials in liquid phase and reaction conditions were chosen in order to enhance CO2 absorption in liquid phase. In photocatalytic tests it was observed the formation of different liquid and gaseous products such as formic acid, formaldehyde, methanol, methane and hydrogen. The different materials provide a significant difference in both activity and product distribution. Photocatalytic behaviours were correlated to different physicochemical properties that were investigated though several techniques.
References
[1] O. Ola, M. Maroto-Valer, Journal of Photochemistry and Photobiology C: Photochemistry Reviews 24 (2015) 16-42
[2] A. Olivo, V. Trevisan, E. Ghedini, F. Pinna, C.L. Bianchi, A. Naldoni, M. Signoretto, Journal of CO2 Utilization 12 (2015) 86-94
[3] I. Rossetti, A. Villa, M. Compagnoni, L. Prati, G. Ramis, C. Pirola, C.L. Bianchi, W: Wang, D. Wang, Catalysis Science and Technology 5 (2015) 4481 - 448
Perovskite-based catalysts for CO2 photoreduction reaction
No full textPerovskite-based catalysts for CO2 photoreduction reaction
I. Martin1*, G. Forghieri2, E. Ghedini2, I. Rossetti3, M. Signoretto2
1Functional Nanosystems, Italian Institute of Technology, Via Morego 30, 16163 Genoa, Italy
2Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice and INSTM RU of Venice, Via Torino 155, 30172 Venice, Italy
3Chemical Plants and Industrial Chemistry Group, Chemistry Department, University of Milan, CNR-SCITEC ans INSTM RU of Milan, Via C. Golgi 19, 20133 Milan, Italy
*Corresponding Author’s E-mail address: [email protected]
Introduction. The worrying rise in greenhouse gas emissions has led to the necessity of limiting the consumption of fossil sources on one hand, and on the other to develop new technologies for capturing, storing and utilising these gases [1]. In this perspective, CO2 photoreduction, paired with water splitting, presents a great potential for the synthesis of fuels and other building block molecules of high value, e.g. methane (CH4), carbon monoxide (CO) and other C1-based products [2]. To develop an effective and selective photocatalytic system, the perovskite barium titanate (BaTiO3) was chosen as a new promising photoactive material with respect to other common photocatalysts, e.g. titanium dioxide (TiO2) and zinc oxide (ZnO). Copper (II) oxide was introduced as a co-catalysts to hinder charge recombination [3], enhacing the activity and selectivity of the perovskite.
Experimental/methodology. BaTiO3 was synthesized by hydrothermal method, modified from literature [4], and was compared with commercial TiO2 (Degussa P25, Evonik) and a lab-synthesized ZnO (synthesized by precipitation [5]). CuO was synthesized by hydrothermal method [6] and introduced as a co-catalyst by impregnation (2.5 wt%) on BaTiO3, TiO2 and ZnO. The photocatalysts were tested in a gas and liquid phase.
Results and discussion. Experiments performed in gas phase resulted in the production of methane and hydrogen, in accordance with the proposed reaction mechanism [7]. Pristine BaTiO3 was less active with respect to TiO2 (79 vs 104 μmol gcat-1 h-1 of CH4, respectively), but the presence of CuO both improved both its activty and resulted in a minor H2 production with respect to CuO/TiO2 (221 vs 169 μmol gcat-1 h-1 of CH4 and 239 vs 414 μmol gcat-1 h-1 of H2, repectively). Experiments performed in liquid phase under neutral pH resulted in the production of formic acid and methanol [7], whereas under basic pH only HCOOH was detected. The basic enviroment also provided a ten-fold total productivity in C-based molecules with respect to pH 7. Under these reaction conditions, the materials showed similar activity and the introduction of CuO did not lead to significant improvements. Thus it is possible to argue that CO2 photoreduction performed in liquid phase is driven by reaction conditions, whilst in gas phase the choice of the appropriate photocatalyst can redirect the activity and selectivity of the reaction.
References
[1] Riahi, K. et al. IPCC, 2022: Mitigation of Climate Change, Contribution of Working Group III to the Sixth Assessment Report of Intergovernmental Panel on Climate Change, Cambridge, UK and New York, NY, USA 2022.
[2] Gür, T.M. Progress in Energy and Combustion Science 2022, 89, 1009657.
[3] Nogueira, A.E. Catalyis Communications 2020, 137, 105929.
[4] Kwak, B.S. and Kang, M. Journal of Nanoscience and Nanotechnology 2017, 17, 7351-7357.
[5] Thompson, W.A. et al. RSC Advances 2019, 9, 21660.
[6] Chandrasekar, M. et al. Journal of Kind Saud University – Science 2022, 34, 101831.
[7] Olivo, A. et al. Energies 2017, 10, 1394
Photocatalytic production of hydrogen from carbohydrates
No full textThe photocatalytic production of H2 from water is seen as a promising way for the storage of solar light into a clean energy vector. The direct water splitting is poorly efficient and a common solution to improve hydrogen productivity is to add an organic sacrificial agent, which may be oxidised more effectively than water. In this work we have selected as organic sacrificial agents some model carbohydrates that can be obtained by hydrolysis of cellulose or lignocellulosic material.
The process conditions have been at first optimised using a 1.3 L photoreactor and changing the operating conditions, including pressure, temperature, catalyst amount and pH using glucose as model reactant and commercial TiO2 (P25 by Evonik) as catalyst. The temperature showed an important effect on hydrogen productivity, since at T 60°C high glucose conversion was observed, but with negligible hydrogen yield. By contrast, at higher temperature (80°C), the consecutive reaction paths to hydrogen were fulfilled leading to appreciable productivity of H2, CO and CO2 in gas phase. In some cases, also some ethane and ethylene were observed.
Then, the screening of different catalytic materials was carried out under the best reaction conditions (P = 4 bar, T = 80°C, 0.25 g/L catalyst, 5 g/L glucose, pH = 5.5). The commercial titania was compared with one prepared by precipitation (TiO2) and one prepared by flame pyrolysis (FP). The samples were added with CuO in different loading (0.2 or 1 wt%), added by impregnation (I), deposition precipitation (D) or using citrate ions as complexing agents (C). The highest hydrogen productivity was achieved with 0.2 wt% CuO prepared by impregnation over the FP-prepared titania, which led to 5 mol H2 per hour per kg of catalyst. By looking at the performance during time, a constant productivity was observed for the whole duration of the test, without any evidence of deactivation.
Acnowledgements
The financial contribution of MIUR through the PRIN2015 grant (20153T4REF) is gratefully acknowledged.
I. Rossetti and E. Bahadori are grateful to Fondazione Cariplo and Regione Lombardia for financial support (2016-0858 – “Up-Unconventional Photoreactors”)
The acid-catalysed dehydration of glycerol into acrolein: the control of selectivity with sulphated zirconia catalysts
No full textSystemC: A Homogenous Environment to Test Embedded Systems
No full textThe SystemC language is becoming a new standard in the EDA field and many designers are starting to use it to model complex systems. SystemC has been mainly adopted to define abstract models of hardware/software components, since they can be easily integrated for rapid prototyping. However, it can also be used to describe modules at a higher level of detail, e.g., RT-level hardware descriptions and assembly software modules. Thus, it would be possible to imagine a SystemC-based design flow, where the system description is translated from one abstraction level to the following one by always using SystemC representations. The adoption of a SystemC-based design flow would be particularly efficient for testing purpose as shown in this paper. In fact, it allows the definition of a homogeneous testing procedure, applicable to all design phases, based on the same error model end on the same test generation strategy. Moreover, test patterns are indifferently applied to hardware and software components, thus making the proposed testing methodology particularly suitable for embedded systems. Test patterns are generated on the SystemC description modeling the system at one abstraction level, theta, they are used to validate the translation of the system to a lower abstraction level. New test patterns are then generated for the lower abstraction level to improve the quality of the test set and this process is iterated for each translation (synthesis) ste
“Ni-, Co- and Cu-TiO2 catalysts for the steam reforming of ethanol: how the preparation method affects catalytic performance”
Full text linkConcept
A set of Ni-, Co-, Cu-based catalysts supported over TiO2 for the steam reforming of ethanol were prepared by different procedures. For most of them the support was prepared by precipitation and calcined at 500°C or 800°C. Other samples were prepared by flame pyrolysis (FP), aiming at high metal dispersion coupled with synthesis at high temperature, to impart a strong metal-support interaction, besides high thermal resistance. The samples were characterised by AAS, XRD, N2 adsorption-desorption, TPR, SEM, TEM and FT-IR. Activity testing for the steam reforming of ethanol was performed after activation at 500°C or 800°C in H2 flow on a continuous micropilot plant, by feeding a 3:1 (mol/mol) mixture of water/ethanol at 500°C for 8 h-on-stream.
Motivations and Objectives
Ni-based catalysts raised much interest for the present application [1-3]. Very high activity has been observed at high reaction temperature (>600°C), but it would be interesting to operate under milder conditions, in order to lower the energy input to the process and to improve H2 productivity by favoring the water gas shift reaction. The major inconvenient for Ni-based samples is usually ascribed to coking, often due to the formation of carbon filaments over the active phase. This phenomenon is correlated to catalyst deactivation and appearance of by-products. Indeed, if at high reaction temperature with excess steam carbon may be gasified, at operation at 500°C the C balance, often much lower than 100% evidences coke accumulation.
Results and Discussion
H2 productivity at 500°C seemed firmly dependent on the calcination and on activation temperature of the catalyst when Ni was supported over TiO2 prepared by impregnation. When the sample was calcined and activated at 500°C, no H2 production was observed due to poor ethanol conversion, with selectivity mostly to acetaldehyde and poor carbon balance. By contrast, calcination of the sample at 800°C induced very high H2 productivity, higher C balance and negligible byproducts formation except some CH4 These results were attributed to the formation of a mixed oxide between Ni and the support during synthesis at high temperature (both for Impregnation and FP), which keeps the metal well dispersed in spite of the high activation temperature. This leads to very small Ni particles after activation, which demonstrated to be more active and, most of all, more stable towards coking. C balance was in general much higher for the Co- and Cu-containing samples than for the Ni-based ones. One may conclude that for most of these samples there is no additional coking on the catalyst due to the active phase. However, they proved in general less active than Ni-based ones when tested at 500°C.
References
[1] I. Rossetti, A. Gallo, V. Dal Santo, C.L. Bianchi, V. Nichele, M. Signoretto, E. Finocchio, G. Ramis, G. Garbarino, A. Di Michele, ChemCatChem, 5 (2013) 294.
[2] I. Rossetti, C. Biffi, C. Bianchi, V. Nichele, M. Signoretto, F. Menegazzo, E. Finocchio, G. Ramis, A. Di Michele, Appl. Catal. B, 117-118 (2012) 384.
[3] E. Finocchio, I. Rossetti, G. Ramis, Int. J. Hydrogen Energy, 38 (2013) 3213
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
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