(106b) Deep SO2 Adsorption at Parts per Billion Level By Alumina-Based Mn/Ce Mixed Oxides for SOFC Cathode Protection

Authors: 
Cheng, P., Auburn University
Tatarchuk, B., Auburn University

Gas phase contaminant removal is a critical process for current and future power supply systems including fuel cells, gas turbines (GT), or a combination on ships. Because of high energy efficiency, low emissions, and fuel flexibility, Solid Oxide Fuel Cells (SOFCs) are promising energy converting devices. Recently, however, researchers have shown a significant degradation caused by SO2 reacts with cathode side materials and thus hinders the active sites available for oxygen reduction. The major SO2 source is the emission from marine fuels such as JP-5 and JP-8 whose sulfur content can be up to 1200 ppmw. The cell exposed to as low as 100 ppbv of SO2 can result in a current loss during the test. Therefore, it is necessary to remove SOfrom cathode side. In this work, alumina-supported/alumina-ceria supported manganese oxides were used as adsorbents operated at high space velocity. Breakthrough capacity and saturation capacity were evaluated by varying Mn loadings, namely 2.5, 5.0, 7.5, 10, and 15 wt %. The structural and surface properties of the adsorbents were further characterized by XRD, N2 physisorption, H2-TPR, CO2-TPD, and TEM. The SO2 adsorption capacity of the mixed oxides correlated closely with their metallic dispersion, surface basicity, and average oxidation state. Mn (5 wt %)/CeO2-Al2O3 was found to be an optimum adsorbent in a wide temperature range of 20-500°C. H2-TPR technique revealed that the average oxidation state for 5 wt % Mn was around +3.8; while Mn loading (<2.5 wt % or >15 wt %) upon impregnation of nitrate precursor solution was likely to lower the oxidation state to around +3.3, which was related to catalytic activity for S4+ oxidation. Furthermore, the reducibility of mixed oxides can be enhanced by introducing Ce into Al2O3, facilitating the regeneration of spent Mn/CeO2-Al2O3.