Synthesis, characterization and catalytic performances of ruthenium-based catalysts for the acceptorless dehydrogenative coupling of butanol

A growing interest towards new sources of energy has led in recent years to the development of a new generation of catalysts for alcohol dehydrogenative coupling (ADC). This green, atom-efficient reaction is capable of turning alcohol derivatives into higher value and chemically more attractive ester molecules, and it finds interesting applications in the transformation of the large variety of products deriving from biomass. In the present work, a new series of ruthenium-PNP pincer complexes are investigated for the transformation of 1-butanol, one of the most challenging substrates for this type of reactions, into butyl butyrate, a short-chain symmetrical ester widely used in flavor industries. Since the reaction kinetics depends on hydrogen diffusion, the study aimed at identifying proper reactor type and right catalyst concentration to avoid mass transfer interferences and to get dependable data. A comparison between catalytic activities and productivities has been made to establish the role of the different ligands bonded both to the PNP binder and to the ruthenium metal center, and hence to find the best catalyst for this type of reaction.

New catalysts for the water gas shift reaction at middle-temperature

H2 demand is continuously increasing since its many relevant applications, for example, in the ammonia production, refinery processes or fuel cells. The Water Gas Shift (WGS) reaction (CO + H2O = CO2 + H2 DeltaH = -41.1 kJ.mol-1) is a step in the H2 production, reducing significantly the CO content and increasing the H2 one in the gas mixtures obtained from steam reforming. Industrially, the reaction is carried out in two stages with different temperature: the first stage operates at high temperature (350-450 °C) using Fe-based catalysts, while the second one is performed at lower temperature (190-250 °C) over Cu-based catalysts. However, recently, an increasing interest emerges to develop new catalytic formulations, operating in a single-stage at middle temperature (MTS), while maintaining optimum characteristics of activity and stability. These formulations may be obtained by improving activity and selectivity of Fe-based catalysts or increasing thermal stability of Cu-based catalysts. In the present work, Cu-based catalysts (Cu/ZnO/Al2O3) prepared starting from hydrotalcite-type precursors show good homogeneity and very interesting physical properties, which worsen by increasing the Cu content. Among the catalysts with different Cu contents, the catalyst with 20 wt.% of Cu represents the best compromise to obtain high catalytic activity and stability. On these bases, the catalytic performances seem to depend on both metallic Cu surface area and synergetic interactions between Cu and ZnO. The increase of the Al content enhances the homogeneity of the precursors, leading to a higher Cu dispersion and consequent better catalytic performances. The catalyst with 20 wt.% of Cu and a molar ratio M(II)/M(III) of 2 shows a high activity also at 250 °C and a good stability at middle temperature. Thus, it may be considered an optimum catalyst for the WGS reaction at middle temperature (about 300 °C). Finally, by replacing 50 % (as at. ratio) of Zn by Mg (which is not active in the WGS reaction), better physical properties were observed, although associate with poor catalytic performances. This result confirms the important role of ZnO on the catalytic performances, favoring synergetic interactions with metallic Cu.

Produzione di alcol furfurilico da furfurale in fase gas con catalizzatori a base di CaO

The hydrogenation of biomass-derived molecules is a key reaction in upgrading these compounds into chemicals and fuels. The use of catalytic transfer hydrogenation, employing alcohols as hydrogen sources, offers an alternative approach to this process, avoiding the use of H2 under high pressure and precious metal catalysts. In this work, the gas-phase conversion of biomass-derived furfural into furfuryl alcohol and 2-methylfuran was studied, using methanol as the H-transfer agent and CaO-based catalysts. The results obtained with this catalyst were compared with those obtained by using MgO, which due to its basic properties and to its high surface area, at present appears to be among the best basic catalysts used for the conversion of biomass-derived molecules. Pure CaO, despite having a very low surface area, compared to MgO catalyst (5 m2/g vs. 172 m2/g), was shown to reduce furfural into its corresponding unsaturated alcohol at 350°C, thus allowing selective H-transfer from methanol to the substrate. These results highlight the potential application of the H-transfer reaction over CaO based catalysts as an efficient process for the selective reduction of biomass-derived molecules.

Study of Co-based hydrotalcite-derived mixed metal oxides partially modified with silver as potential catalysts for N2O decomposition

Co-Al-Ox mixed metal oxides partially modified with Cu or Mg, as well as Ag were successfully prepared, characterized and evaluated as potential catalysts for the N2O decomposition. The materials were characterized by the following techniques: X-Ray Diffraction, Thermogravimetric Analysis (TGA), N2 Physisorption, Hydrogen Temperature-Programmed Reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). Ag-modified HT-derived mixed oxides showed enhanced activity compared to the undoped materials, the optimum composition was found for (1 wt.% Ag)CHT-Co3Al. The catalyst characterization studies suggested that the improved catalytic activity of Ag-promoted catalysts were mainly because of the altered redox properties of the materials.

Synthesis of novel cobalt and iron complexes for sustainable catalytic hydrogenations

Aim of the present work of thesis is to synthesize new non-noble metal based complexes to be employ in redox reactions by a metal-ligand cooperative mechanism. The need of replacing toxic and expensive precious metal complexes with more available and benign metals, has led to the development of new compounds based on cobalt and iron, which are the metals investigated in this study. A carbonyl-tetrahydroborato-bis[(2-diisopropylphosphino)ethyl]amine-cobalt complex bearing a PNP-type ligand is synthesized by a three-step route. Optimization attempt of reaction route were assessed in order to lowering reaction times and solvent waste. New cobalt complex has been tested in esters hydrogenation as well as in acceptorless dehydrogenative coupling of ethanol. Other varieties of substrates were also tested in order to evaluate any possible applications. Concerning iron complex, dicarbonyl-(η4-3,4-bis(4-methoxyphenyl)-2,5-diphenylcyclopenta-2,4-dienone)(1,3-dimethyl-ilidene)iron is synthesized by a three steps route, involving transmetallation of a silver complex, derived from an imidazolium salt, to iron complex. In order to avoid solvent waste, optimization is assessed. Studies were performed to assess activity of triscarbonyl iron precursor toward imidazolium salt and silver complexes.

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.