Nanostructured catalysts for the bio-ethanol conversion to acetaldehyde: development and optimization

Heterogeneous catalysts, especially when nanostructured, can play a crucial role to minimize byproducts and to stabilize the catalyst itself, thanks to its tailored properties. The efforts of my PhD have been focused to synthetize new nanostructured catalysts for the acetaldehyde production from ethanol via oxidative and non-oxidative dehydrogenation reactions. For oxidative dehydrogenation process Mo-based catalysts, supported on alumina, silica-alumina or silica, have been synthesized and tested. High acetaldehyde yield was obtained in the temperature range 573-673 K even if at higher temperatures dehydration products are formed. Catalytic activity was enhanced when a small amount of silica was introduced in the alumina support, thus obtaining more stable catalysts. Thus, other two different catalytic systems have been tested: Nb-P-Si oxides and copper-based catalysts, but the first presents low selectivity to acetaldehyde while the second catalyses the total oxidation to CO2. For non-oxidative dehydrogenation, the research activity started with the synthesis of copper supported (Al2O3, Mg2Al2O4 and ZnAl2O4 as supports) catalysts by means of conventional impregnation method. Even if these materials are active to produce acetaldehyde they suffer of deactivation and several by products were detected. To improve the catalytic performances of the best catalyst identified, the CuO-ZnAl2O4 one, new synthetic procedures were investigated and optimized. Moreover, during the period abroad, another innovative technique based on Aerosol Assisted Sol Gel process, was employed to synthesize CuO-SiO2 catalysts. All the synthetized catalysts were tested on a laboratory plant and deeply morphologically and structurally characterized. Particular attention was also dedicated to the characterization of exhaust catalysts to enlighten deactivation causes and regeneration possibilities.