(582b) A DFT Study of Desulfurization and Tar Cracking of Gasifier Effluents Over Ceria-Based Rare-Earth Oxides
AIChE Annual Meeting
2010
2010 Annual Meeting
Sustainable Engineering Forum
Catalytic Conversion of Renewable Resources to Synthesis Gases and Pyrolysis Oils
Thursday, November 11, 2010 - 8:55am to 9:20am
Cleanup of biomass gasifier effluents involves both the removal of sulfur-containing compounds such as H2S and the cracking of tars. Mixed rare earth oxides of ceria containing lanthanides or transition metal additives are effective H2S sorbents and tar cracking catalysts. We report density functional theory (DFT+U) results used to evaluate the H2S adsorption capacity and tar cracking activity of pure ceria and ceria doped with a series of lanthanides and group VIIB-VIIIB transition metals. We use ab initio thermodynamics to construct phase diagrams for the surface layers of these rare earth oxides as well their corresponding sulfides and oxysulfides as a function of H2S and O2 partial pressures. Our results illustrate the relationship between oxide reducibility and H2S sorbent capacity, and quantify changes in the surface activity for sulfur adsorption as a result of doping. We also evaluate the effects of transition metal additives on C-H and C-C bond activation, and discuss our results in the context of designing improved rare earth oxide catalysts for simultaneous desulfurization and tar cracking of gasifier effluents.