Tar Reforming in Model Gasifier Effluents: Transition Metal/Rare Earth Oxide Catalysts

The removal of tars from syngas generated in biomass or coal/biomass gasifiers plays an important role in syngas cleanup. Rare earth oxides (REOs, e.g., Ce/LaOx) mixed with transition metals (e.g., Mn, Fe) were synthesized by various methods and in some cases supported on a thermally stable alumina. These catalysts were applied to tar removal in the temperature range <1100 K using synthetic syngas mixtures with C₁₀H₈ as a tar model compound, both with and without H₂S. Some commercial Ni reforming catalyst formulations were examined comparatively. Fresh and used catalysts were characterized by XANES, XAFS, XRD, TPO, and BET. We found that the C₁₀H₈ is reformed to at least methane, although further reforming to CO and H₂ is not always achieved. While CO₂, H₂S, and coke formation all inhibited or deactivated the catalysts at certain temperatures and to different extents, it was determined that Fe- or Mn-doped supported REOs are promising tar cleanup catalysts. They exhibited higher sulfur tolerance, less coking, and less methanation than typical Ni-based high temperature reforming catalysts. This behavior is in part attributed to enhanced generation of oxygen vacancies in the doped REOs