Cerium Oxide-Based Sorbents for Regenerative Hot Reformate Gas Desulfurization

Abstract

The activity and stability of lanthanum- or copper-containing cerium oxide sorbents for hot reformate gas desulfurization were investigated in this work. Reformate gas, derived from the catalytic partial oxidation or autothermal reforming of heavy fuels such as JP-8, is rich in hydrogen and CO and may also contain up to 500 ppmv H2S. Desulfurization at temperatures in the range of 650-800°C is required before using the fuel gas in solid oxide fuel cells. In this work, regenerable cerium oxide-based sorbents were used in desulfurization. The sorbents were prepared with high surface area by the urea coprecipitation/gelation method, followed by slow heating and calcination in air at 650 °C for 4 h. Lanthanum doping (up to 50 at. %) was determined to be effective in moderating the surface area loss of cerium oxide (ceria) in H2S-free reformate gas at 800 °C. On the other hand, severe sintering occurred when copper was used as an additive, even in amounts as low as 10 at. % copper in ceria. However, the copper-containing ceria had the best sulfidation kinetics among the ceria-based sorbents. Sorbents were evaluated in cyclic sulfidation/regeneration tests at 650 and 800 °C, using a simulated reformate gas mixture in sulfidation, and a 3% O2-He gas mixture for regeneration. Using very high space velocities, we determined that sulfidation could be limited to the sorbent surface. The surface sulfur capacity of the sorbents was stable in cyclic sulfidation/regeneration under these conditions.