Ossidazione parziale catalitica di i-C8H18 e n-C8H18 su catalizzatori Rh/α-Al2O3

Catalytic partial oxidation (CPO) is a promising technology used in the small-scale production of synthesis gas, commonly known as syngas, from a hydrocarbon and oxygen. Overall, the process is an exothermic reaction, and can therefore be conducted in adiabatic reactors that enable high levels of selectivity and yield. The experiments were performed on honeycomb monoliths, which were coated with Rh/α-Al2O3-based catalysts using the dip-coating preparation method. Such catalysts are very active and lead to thermodynamic equilibrium within milliseconds. This feature allows one to work with highly reduced reaction volumes. A new interest lies in applying the CPO technology to the automotive industry by producing syngas on-board from liquid hydrocarbons. More specifically, this thesis focuses on two isomers that were chosen as gasoline surrogates, iso-octane and n-octane. In order to increase the catalyst’s stability, experiments were carried out with cordierite, typically used for the CPO process, and silicon carbide catalyst supports; the reactor’s performance was evaluated as the severity of the operating conditions was increased. The experiments were performed by using air in slightly higher quantities compared to partial oxidation stoichiometry (the oxygen-to-carbon ratio was 0.56). The reactivity levels of both hydrocarbon fuels were also carefully compared to each other. Homogenous reactions were present due to high temperatures in the gas phase of the reaction. The spatially resolved sampling technique was applied to analyze changes in the reactor’s composition profile and temperature along the reactor axis, which provided details on the reaction mechanism and the indirect reaction path. The CPO process consists of a series of both exothermic and endothermic reactions. As a matter of fact, the hydrocarbon fuel is initially oxidized to CO2 and H2O, and is only later converted to synthesis gas through steam reforming. The results clearly demonstrate that, under the experiment’s operating conditions, iso-octane has greater reactivity in the gas phase compared to n-octane. Challenges that emerged include catalyst deactivation, given the high temperatures reached on its surface, which can result in sintering of rhodium particles. Therefore, new strategies need to be developed to improve the catalyst’s stability.