Catalytic Hydrogenations for Energy Applications and Chemical Productions (Processi di Idrogenazione per Applicazioni Energetiche e Produzione di Chemicals)

Catalytic hydrogenation is one of the most important classes of reactions in industrial chemistry. Generally, these reactions are limited by the equilibrium thermodynamics and, especially when using H2 as a hydrogenation agent, the use of catalysts and heterogeneous catalysts is of paramount importance. Generally, hydrogenations are conducted in the gas phase or in the liquid phase, depending on the substrate to be hydrogenated. In this thesis, the focus was on liquid phase hydrogenations. Specifically, the thesis was divided into four main chapters: 1) a general introduction to hydrogenation reactions, reactors, thermodynamics, kinetics, catalysis and safety; 2) the direct synthesis of H2O2 by using membrane reactors; 3) the hydrodeoxygenation/hydrocracking of microalgae oils by using Ni/BEA (hierarchical) zeolites; 4) The hydrodeoxygenation of furfural to 2-methylfuran. All these products are of relevant industrial interest. Regarding the first research topic, about the direct synthesis of H2O2, three families of catalytic membranes have been prepared by dispersing Pd on asymmetric alumina membranes. By using 1) reduction with hydrazine in an ultrasonic bath, 2) impregnation-decomposition and 3) sol-immobilisation techniques, Pd nanoparticles (NPs) with different particle size distributions were prepared. The prepared catalytic membranes were tested for the direct synthesis of H2O2 in a membrane reactor operating in semi-batch in the presence of H2SO4 and, eventually, KBr as promoters. All the catalytic membranes were tested in the fully reduced state and/or after pre-oxidative treatments (calcination). The catalytic membranes have been characterised before, and after testing by using transmission electron microscopy (TEM), Temperature-programmed reduction (TPR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). Sol-immobilisation and impregnation-decomposition have been identified as promising preparation techniques. Compared to other reported procedures, catalytic membranes prepared by using the sol-immobilisation technique have shown the greatest selectivities and productivities in their reduced form. This was related to promotion effects active in the presence of polyvinyl alcohol, the capping agent used for obtaining colloidal Pd NPs in the case of the sol-immobilisation. However, during the tests, by using this technique, extensive deactivation phenomena were observed. In line with the extensive literature about the direct synthesis of H2O2, the calcination pretreatment led to improved selectivity and productivity. However, the results have shown a marked dependence on the Pd NPs size. The experimental results have been analysed by using several kinetic models in order to understand the origin of the deactivation phenomena observed for SI membranes, obtaining insights on the promotion effect of PVA and analysing the nature of the active sites for pre-oxidised catalytic membranes. For studying the HDO/HC of microalgae oils to Green Jet Fuel, four catalysts were prepared by using two commercial Bea zeolites supplied by Zeolyst (CP811E-75, CP814E) and a homemade SBA-15. The deposition of 8%wt of the Ni active metal was performed by incipient wetness. To minimise diffusional problems inside the pore of zeolites, the desilication treatment was performed on the commercial BETA zeolite CP811E-75 determining an increase of both, surface area and volume in the mesopore range. The prepared Ni-based catalysts were tested for methyl palmitate conversion in a batch autoclave reactor. Analysis of the results revealed the role of the surface acidity of the catalysts for the hydrogenolysis of methyl palmitate to palmitic acid, further evidencing the role of the greater available surface area and mesoporosity by the desilicated Ni/CP811E-75 in directing the selectivity toward the production of the C12 fraction. The third topic, the hydrodeoxygenation of furfural to 2-methylfuran was developed in collaboration with Avantium, The Netherlands. The hydrogenation of furfural is a very versatile reaction which can be used for obtaining a variety of high-value chemicals and potential biofuels. Between these potential biofuels, 2-methylfuran has been recently identified as high-value fuel/octane booster and has triggered an increasing the interest by the scientific community toward this reaction. The hydrogenation of furfural has been studied by many research groups, producing a large number of publications. However, the variation in the conditions used for this synthesis is huge, and a comparison with commercial catalysts is missing. Furthermore, the effect of the solvent has been only scarcely analysed. In this study, a large number of commercially available catalysts, comprising Cu, Ni, Pd, Pt, Ru, Rh dispersed on common supports or used as Raney catalysts were analysed using a high-throughput approach. The effect of the solvent and temperature was further analysed and discussed.