CO2 as Carbon Source for Fuel Synthesis

Abstract The growing use of fossil fuels (solid, liquid and gas) as the main primary energy sources, inevitably leads to an increasing amount of carbon dioxide released into the atmosphere. On the other hand, the increasing CO2 concentration in the atmosphere is indicated as the main cause of the greenhouse effect on the planet with consequent climate change. These reasons motivated in recent years growing efforts, from both technical-scientific and political communities, to control the accumulation of the atmospheric CO2. Carbon capture technologies are a well stabilized route to reduce the concentration of the greenhouse gas (CO2) from the atmosphere. However, the introduction of these capture processes always requires additional costs regardless of the adopted technology (post-combustion capture, pre-combustion capture or oxy-combustion). Despite higher costs, the adoption of efficient technologies for capturing CO2 is essential for the preservation of the environment. Besides the capture of CO2, its final sequestration in geologically stable sites is currently proposed for storing enormous quantities of gas involved. However, the geological storage of a given amount of CO2 avoids the possible use of C for about 27% wt. Therefore it seems reasonable to question if we can take advantage of this huge amount of carbon. As a matter of fact, the CO2 could become an important source of carbon for the synthesis of organic and inorganic compounds. In particular, there is a growing interest around the possibility to treat the CO2 in a reducing environment to convert it to methanol or methane. This option is an alternative to the well documented reduction of CO2 to carbon monoxide. Our interest is focused on the conversion to methane by hydrogen reduction. When the hydrogen is obtained by renewable energy, the method is a good way to store the electricity generated from renewable sources such as chemical energy; it is easily accessible and transportable thanks to the widespread presence of methane distribution network. We investigate the hydrogenation of CO2 on various Ni based catalysts. The conversion yield, the time stability and the poison sensitivity has been studied up to the temperature of 723 K and at atmospheric pressure

Sintesi e caratterizzazione di nanostrutture di carbonio e loro applicazione nel campo delle celle a combustibile

Nella tesi di dottorato viene descritta la sintesi di nano strutture di carbonio, in particolare “MWNT: Multi-wall carbon Nanotubes”, nanotubi a parete multipla e “SWNH: Single-Wall carbon Nanohorns”, strutture a parete singola, mediante la tecnica di scarica ad arco in ambiente liquido e gassoso. E’ stato messo a punto un sistema per la produzione sia in corrente continua (DC), convenzionale, che corrente alternata (AC), di nuova concezione, per la sintesi di queste nano strutture di carbonio. I materiali prodotti sono stati caratterizzati con diffrattometro ai raggi X e analisi termo gravimetrica. In particolare è stato messa a punto una metodologia per la misura quantitativa del contenuto di nanotubi di carbonio in una polvere di materiale appena prodotto che utilizza entrambe le tecniche. Le nano strutture di carbonio sono state utilizzate come supporto per il platino per poter realizzare elettrodi per celle a combustibile a elettrolita polimerico (PEM) o a metanolo diretto (DMFC). Il platino è stato depositato mediante un processo chimico di impregnazione a partire da un precursore del platino, acido esacloroplatinico, e successiva riduzione. La resa di deposizione del platino sulle due nano strutture di carbonio prodotte e sul Vulcan XC 72 commerciale è stata valutata. Inoltre un’analisi approfondita con il SEM, il TEM e il diffrattometro per polveri ha permesso di conoscere le caratteristiche delle particelle di catalizzatore depositate. Per concludere il lavoro della tesi di dottorato il composito Platino-Carbonio sintetizzato è stato utilizzato per produrre elettrodi mediante un processo a inchiostro. Misure elettrochimiche, voltammetria ciclica, ha permesso di valutare l’area specifica superficiale del catalizzatore depositato e di valutare l’attività catalitica di questo materiale verso il processo di ossidazione del metanolo.Carbon has been under deep investigation since half part of the 20th century. In particular the branches of micro and nanotechnology received a great attention due to the discovery of new allotropes form of carbon: fullerenes and carbon nanotubes. Carbon is used under different forms which have peculiar properties: graphite is a lubrificant and electrical conductor, diamond is the hardest material known, carbon black is used as filler in rubber, in plastic composites and as support material in the electrodes for fuel cells, carbon fibres exhibit very high tensile and compressive strength and they are widely used in automotive and aerospace industries, fullerenes are thought to be useful as vehicle for pharms, carbon nanotubes have extraordinary electrical, mechanical and thermal properties and some laboratory applications have just been realized, single-walled nanohorns are known to have very high reactive surface. These different forms of carbon reported introduce us to the world of nanometric objects. Only to have an idea, the diameter of a fullerene is of 0.71 nm. Nanomaterials show unexpected features and properties. These aspects represent one of the most important subject of investigation for the future. Materials with typical dimensions of tens of nanometers have just been synthesised and studied during the 19th century, i.e. colloids, but new methods of characterization and a systematic approach gave a great development to the knowledge of nanometric materials. The synthesis and characterization of these new forms of carbon have been under deep study since 1985 (discovery date of fullerene). Some theses are reported in literature about the mechanism of growth of carbon nanostructures, but this is far from being completely understood. Many techniques are used to characterize these carbon nanostructures: electron microscopy, AFM, STM, X-ray diffraction, Raman, NMR. Moreover in the last few years the possibility of manipulating nanostructures, in particular carbon nanostructures, has been exploited. Contemporary to the study of the properties of these nanostructures, their possible applications have been investigated by many authors. The topics of this PhD thesis concern the synthesis of carbon nanostructures by arc discharge, with the purpose of exploring new approaches respect to those reported in literature. Multi wall carbon nanotubes and single wall carbon nanohorns have been synthesised by an arc discharge powered respectively by direct current (DC)alternating current (AC). The quantitative evaluation of multi wall carbon nanotubes in the raw material produced by arc discharge has been carried out by X-ray diffraction and thermo-gravimetric analysis supported by transmission electron microscopy. A suitable application of these carbon nanostructures has been exploited. In particular the feasible use of these carbon nanostructures as supports for catalysts for fuel cells application has been carried out by the mean of cyclic voltammetry. Pt nano-particles have been successfully deposited on three different carbon supports, multi wall carbon nanotubes, single wall nanohorn and Vulcan XC-72, by the mean of an impregnation process, in order to compare their performances as anodes in PEFC (polymer electrolyte fuel cell) and DMFC (direct methanol fuel cell). The relationship between the structure of the different carbon supports and their electrochemical behaviour is discussed

Effect of Ti-Based Additives on the Hydrogen Storage Properties of MgH₂: A Review

For the few past decades, study of new hydrogen storage materials has been captivating scientists worldwide. Magnesium hydride, MgH2, is considered one of the most promising materials due to its low cost, high hydrogen capacity, reversibility and the abundance of Mg. However, it requires further research to improve its hydrogen storage performance as it has some drawbacks such as poor dehydrogenation kinetic, high operational temperature, which limit its practical application. In this study, we introduce an overview of recent progress in improving the hydrogen storage performance of MgH2 by the addition of titanium-based additives, which are one of the important groups of additives. The role of Ti-based additive hydrides, oxides, halides, carbides and carbonitrides are overviewed. In addition, the existing challenges and future perspectives of Mg-based hydrides are also discussed

Microstructural and Kinetic Evolution of Fe Doped MgH2 during H2 Cycling

The effect of extended H2 sorption cycles on the structure and on the hydrogen storage performances of MgH2 powders with 5 wt% of Fe particle catalyst is reported. MgH2 powders with and without Fe have been ball milled under Argon, the doped MgH2 nanocomposite has been cycled under hydrogen pressure up to a maximum of 47 desorption and absorption cycles at 300 °C. After acceleration during the first 10 cycles, the kinetics behavior of doped MgH2 is constant after extended cycling, in terms of maximum storage capacity and rate of sorption. The major effect of cycling on particle morphology is the progressive extraction of Mg from the MgO shell surrounding the powder particles. The Mg extraction from the MgO shell leaves the catalyst particles inside the hydride particles. Many empty MgO shells are observed in the pure ball milled MgH2 upon cycling at higher temperature, suggesting that this enhancement of the extraction efficiency is related to the higher operating temperature which favors Mg diffusivity with respect to the H ion one

Sulfonated catalysts for methanol dehydration to dimethyl ether (DME)

Sulfonic acids grafted on inorganic support such as SiO 2 and MCM41 was used as catalysts for conversion of methanol to dimethyl ether. In this experimental work the catalysts were compared for their catalytic properties in a continuous flow fixed-bed reactor at temperatures between 180 and 320 °C and 1 bar. It was found that all SO 3 H-functionalized materials in this study were active, selective and stable for DME synthesis. According to the experimental results MCM-41-(CH 2 ) 3 -SO 3 H exhibited the best performance, related to its higher surface area and acidity

Quantitative evaluation of nanotube content in the raw material produced by arc discharge

International audienceThe amount of carbon nanotube in the raw material grown by electric arc discharge ignited in different liquid environments has been evaluated by the combined use of X-Ray diffraction, electron microscopy and TG-DTA in reactive environment. In particular, X-ray diffraction is used to discriminate among the different carbon microstructures owing to the difference in the lattice parameter between curved and planar graphite structures. The results are repeatable and in good agreement with TG-DTA measurements carried out in reactive environment where the relative amount of carbon nanostructures is evaluated on the basis of the difference in the reaction kinetics with atmospheric oxygen. In the analysed specimens, SEM and TEM show the presence of just two allotropic form of carbon, namely nanotubes and globular particles, which relative amount results to depend on the nature of the liquid surrounding the discharge and on the voltage applied to the electric arc

Effect of surface acidity on the catalytic activity and deactivation of supported sulfonic acids during dehydration of methanol to DME

The influence of catalyst's surface acidity on the catalytic activity and deactivation in the dehydration of methanol to DME was investigated. Different materials including propylsulfonic acid functionalized silica at different Bronsted acidity, silica-alumina, propyl and phenylsulfonic acid functionalized silica-alumina catalysts were prepared. All samples were characterized by XRD, TGA, XPS, N2-sorption, ICP-OES and SEM analysis. It was found that the Bronsted and Lewis acidity of SiO2/Al2O3-PhSO3H catalyst played a critical role in the performance of methanol to DME catalyst. The grafting of sulfonic acid groups on the silica-alumina enhanced the surface Brønsted acidity and also the reaction activity and selectivity for the dehydration of methanol to DME. In addition, phenylsulfonic acid functionalized silica-alumina catalyst exhibited the highest activity and stability for the dehydration reaction at relatively low temperatures at which the γ-Al2O3, commercial reference, displayed the low dehydration activity. The water effect was also investigated because in the indirect process to produce DME using acidic -alumina, has the most important effect on catalyst deactivation. As a result, the water had a positive effect on methanol dehydration over SiO2/Al2O3-PhSO3H catalyst contrary to of γ-Al2O3 that was rapidly deactivated. Thus, the Brønsted and Lewis acid sites with suitable strength may be responsible for the effective conversion of methanol to DME with high stability and selectivit

Thermoplastic Starch Films Added with Dry Nopal (Opuntia Ficus Indica) Fibers

Dry fibers coming from garden waste, originating from Opuntia ficus indica, were introduced in amounts of either 8 or 16 wt % into a self-produced thermoplastic starch (TPS) based on potato starch and glycerol. Thermal (differential scanning calorimetry, DSC), mechanical (tensile tests), and morphological characterization with scanning electron microscopy (SEM) and performing energy-dispersive X-ray spectrometry (microanalysis) were carried out. The results indicated that the uneven distribution and variable geometry of fibers introduced led to a reduction of tensile stress and strain with respect to pure TPS. However, the positive effects of prolonged mixing and increased thickness were highlighted, which suggest the fabrication of the composite could be improved in the future by controlling the manufacturing procedure