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