Mixed Rare Earth Oxides (REOs) for Desulfurization and Tar Removal From Gasifier Effluents

The removal of H₂S, NH₃ and tars from syngas generated in biomass or coal/biomass gasification plays an important role in further processing of syngas. We have developed materials capable of both H₂S adsorption and tar reforming at high temperatures (~600-650ºC). These are mixed rare earth oxides (REOs) such as CeO₂/La₂O₃, prepared by templated sol-gel methods, and then impregnated with transition metals (Mn, Fe, etc.). Desulfurization tests have been carried out using model syngas mixtures. Successive desulfurization-regeneration cycles some of these materials (e.g., Mn/Ce/LaO_x) demonstrated reasonable sulfur capacities in the presence of water and CO₂, along with regenerability. Naphthalene and propane have been used as models for tar reforming/cracking, and the effects of H₂S, CO and CO₂ on the model reactions were examined. H₂S and CO₂ are strong inhibitors, while CO is not. Fresh, used and regenerated sorbents and catalysts have been characterized by BET, TPR, XRD, XANES and EXAFS.