Anaerobic oxidation of ethanol over spinel mixed oxides: the first step in the steam-iron process for H2 production

The future hydrogen demand is expected to increase, both in existing industries (including upgrading of fossil fuels or ammonia production) and in new technologies, like fuel cells. Nowadays, hydrogen is obtained predominantly by steam reforming of methane, but it is well known that hydrocarbon based routes result in environmental problems and besides the market is dependent on the availability of this finite resource which is suffering of rapid depletion. Therefore, alternative processes using renewable sources like wind, solar energy and biomass, are now being considered for the production of hydrogen. One of those alternative methods is the so-called “steam-iron process” which consists in the reduction of a metal-oxide by hydrogen-containing feedstock, like ethanol for instance, and then the reduced material is reoxidized with water to produce “clean” hydrogen (water splitting). This kind of thermochemical cycles have been studied before but currently some important facts like the development of more active catalysts, the flexibility of the feedstock (including renewable bio-alcohols) and the fact that the purification of hydrogen could be avoided, have significantly increased the interest for this research topic. With the aim of increasing the understanding of the reactions that govern the steam-iron route to produce hydrogen, it is necessary to go into the molecular level. Spectroscopic methods are an important tool to extract information that could help in the development of more efficient materials and processes. In this research, ethanol was chosen as a reducing fuel and the main goal was to study its interaction with different catalysts having similar structure (spinels), to make a correlation with the composition and the mechanism of the anaerobic oxidation of the ethanol which is the first step of the steam-iron cycle. To accomplish this, diffuse reflectance spectroscopy (DRIFTS) was used to study the surface composition of the catalysts during the adsorption of ethanol and its transformation during the temperature program. Furthermore, mass spectrometry was used to monitor the desorbed products. The set of studied materials include Cu, Co and Ni ferrites which were also characterized by means of X-ray diffraction, surface area measurements, Raman spectroscopy, and temperature programmed reduction.

Oxidation and pyrolysis of methane and methyl formate in a plug flow reactor: computational and experimenal studies

Biodiesel represents a possible substitute to the fossil fuels; for this reason a good comprehension of the kinetics involved is important. Due to the complexity of the biodiesel mixture a common practice is the use of surrogate molecules to study its reactivity. In this work are presented the experimental and computational results obtained for the oxidation and pyrolysis of methane and methyl formate conducted in a plug flow reactor. The work was divided into two parts: the first one was the setup assembly whilst, in the second one, was realized a comparison between the experimental and model results; these last was obtained using models available in literature. It was started studying the methane since, a validate model was available, in this way was possible to verify the reliability of the experimental results. After this first study the attention was focused on the methyl formate investigation. All the analysis were conducted at different temperatures, pressures and, for the oxidation, at different equivalence ratios. The results shown that, a good comprehension of the kinetics is reach but efforts are necessary to better evaluate kinetics parameters such as activation energy. The results even point out that the realized setup is adapt to study the oxidation and pyrolysis and, for this reason, it will be employed to study a longer chain esters with the aim to better understand the kinetic of the molecules that are part of the biodiesel mixture.

Selective photo-oxidation of cellobiose with tio2-supported metal nanoparticles

Upgrade of biomass to valuable chemicals is a central topic in modern research due to the high availability and low price of this feedstock. For the difficulties in biomass treatment, different pathways are still under investigation. A promising way is in the photodegradation, because it can lead to greener transformation processes with the use of solar light as a renewable resource. The aim of my work was the research of a photocatalyst for the hydrolysis of cellobiose under visible irradiation. Cellobiose was selected because it is a model molecule for biomass depolymerisation studies. Different titania crystalline structures were studied to find the most active phase. Furthermore, to enhance the absorption of this semiconductor in the visible range, noble metal nanoparticles were immobilized on titania. Gold and silver were chosen because they present a Surface Plasmon Resonance band and they are active metals in several photocatalytic reactions. The immobilized catalysts were synthesized following different methods to optimize the synthetic steps and to achieve better performances. For the same purpose the alloying effect between gold and silver nanoparticles was examined.

Experimental and computational study of methane and methyl formate pyrolysis and oxidation in a flow reactor

A study of the pyrolysis and oxidation (phi 0.5-1-2) of methane and methyl formate (phi 0.5) in a laboratory flow reactor (Length = 50 cm, inner diameter = 2.5 cm) has been carried out at 1-4 atm and 300-1300 K temperature range. Exhaust gaseous species analysis was realized using a gas chromatographic system, Varian CP-4900 PRO Mirco-GC, with a TCD detector and using helium as carrier for a Molecular Sieve 5Å column and nitrogen for a COX column, whose temperatures and pressures were respectively of 65°C and 150kPa. Model simulations using NTUA [1], Fisher et al. [12], Grana [13] and Dooley [14] kinetic mechanisms have been performed with CHEMKIN. The work provides a basis for further development and optimization of existing detailed chemical kinetic schemes.

Organic/inorganic polyoxometalate-based hybrids for oxidation catalysis and energy conversion

This thesis work has been carried out during the Erasmus exchange period at the “Université Paris 6 – Pierre et Marie Curie”, in the “Edifices PolyMétalliques – EPOM” team, leaded by Prof. Anna Proust, belonging to the “Institut Parisien de Chimie Moléculaire”, under the supervision of Dr. Guillaume Izzet and Dr. Geoffroy Guillemot. The redox properties of functionalized Keggin and Dawson POMs have been exploited in photochemical, catalytic and reactivity tests. For the photochemical purposes, the selected POMs have been functionalized with different photoactive FGs, and the resulting products have been characterized by CV analyses, luminescence tests and UV-Vis analyses. In future, these materials will be tested for hydrogen photoproduction and polymerization of photoactive films. For the catalytic purposes, POMs have been firstly functionalized with silanol moieties, to obtain original coordination sites, and then post-functionalized with TMs such as V, Ti and Zr in their highest oxidation states. In this way, the catalytic properties of TMs were coupled to the redox properties of POM frameworks. The redox behavior of some of these hybrids has been studied by spectro-electrochemical and EPR methods. Catalytic epoxidation tests have been carried out on allylic alcohols and n-olefins, employing different catalysts and variable amounts of them. The performances of POM-V hybrids have been compared to those of VO(iPrO)3. Finally, reactivity of POM-VIII hybrids has been studied, using styrene oxide and ethyl-2-diazoacetate as substrates. All the obtained products have been analyzed via NMR techniques. Cyclovoltammetric analyses have been carried out in order to determine the redox behavior of selected hybrids.

Selective photo-oxidation of glucose

Biomass transformation into high-value chemicals has attracted attention according to the “green chemistry” principles. Low price and high availability make biomass one of the most interesting renewable resources as it provides the means to create sustainable alternatives to the oil-derived building blocks of the chemical industry In recent year, the need for alternative environmentally friendly routes to drive chemical reactions has in photocatalytic processes an interesting way to obtain valuable chemicals from various sources using the solar light as energy source. The purpose of this work was to use supported noble metal nanoparticles in the selective photo-oxidation of glucose through using visible light. Glucose was chosen as model molecule because it is the cheapest and the most common monosaccharide. Few studies about glucose photo oxidation have been conducted so far, and reaction mechanism is still not totally explained. The aim of this work was to systematically analyze and assess the impact of several parameters (eg. catalyst/substrate ratio, reaction time, effect of the solvent and light source) on the reaction pathway and to monitor the product distribution in order to draw a general reaction scheme for the photo oxidation of glucose under visible light. This study regards the reaction mechanism and the influence of several parameters, such as solvent, light power and substrate concentration. Furthermore, the work focuses on the influence of gold and silver nanoparticles and on the influence of metal loading. The glucose oxidation was monitored through the mass balance and the products selectivity. Reactions were evaluated in terms of glucose conversion, mass balance and selectivities towards arabinose and gluconic acid. In conclusion, this study is able to demonstrate that the photo oxidation of glucose under visible light is feasible; the full identification of the main products allows, for the first time, a comprehensive reaction mechanism scheme.