Sonochemical synthesis of Ni-Based catalysts for Ethanol Steam Reforming

Increasing attention is focused on hydrogen as a clean energy vector, because its oxidation is highly exothermal and the only product is water. Despite the huge potential benefits, the use of hydrogen is currently limited by the insufficient capacity of hydrogen storage technologies and by the safety issues related with its storage and transportation under mild conditions. Furthermore, nowadays 47% of global hydrogen is produced from natural gas, 30% from oil, 19% from coal and the remaining fraction via water electrolysis; therefore, ca. 96% of hydrogen derives from the conversion of fossil resources, which means a net co-production of CO2. New sources and new processes are needed to produce hydrogen in a sustainable way. Ethanol steam reforming (ESR) has received considerable attention, because ethanol is mainly obtained by renewable sources, it is simple to store, handle and transport because of its low volatility and toxicity. This process could be industrially advantageous, ideally yielding 6 moles of H2 per mole of ethanol reacted. Several metal-based catalysts have been proposed for the steam reforming of alcohols. Nickel is particularly attractive because of its high activity and selectivity in breaking C-C bonds and its lower cost if compared with noble metals [1]. In this study, MgAl2O4 was employed as support for Ni-based catalysts. Mg–Al mixed oxide supported Ni catalysts showed high activity in terms of H2 productivity and catalyst stability compared to nickel catalysts supported on pure oxides. MgAl2O4 was chosen as the preferred choice of support due to the following factors: (i) it is a slightly basic material, (ii) it exhibits moderate acidic and basic site strength and density, (iii) it limits the promotion of collateral reactions and, thus, minimises coke formation and therefore enhances catalyst stability. Therefore, we investigated a series of Ni/MgAl2O4 catalysts with different Ni loading and prepared with an ultrasound assisted technique to achieve high surface area and higher metal dispersion. Catalysts were characterized before and after catalytic tests by different techniques: FE-SEM, EDX, TEM, XRD, BET, TPR, MicroRaman and FT-IR. Ethanol Steam Reforming (ESR) tests were carried out in a continuous bench scale reactor operated at 625 °C, 500 °C and 400 °C, especially focusing at low temperatures for this application, aiming at process intensification. The effect of metal loading on activity and hydrogen selectivity was investigated, together with possible deactivating phenomena. Finally, hypotheses on the reaction mechanism were drawn on the basis of DRIFTS analysis. References (10 pt) 1. Rossetti I., Biffi C., Bianchi C. L., Nichele V., Signoretto M., Menegazzo F., Finocchio E., Ramis G., Di Michele A. Applied catalysis B. 2012, 117-118, 384-396.