(538e) Spectroscopic Characterization of Sulfur Poisoning and Regeneration for Ni-Based Biomass Conditioning Catalysts

Direct evidence of transformation of sulfur species from sulfides to sulfates was observed on a a Ni-Mg-K/Al₂O₃ catalyst used in a pilot-scale study to condition biomass-derived syngas created from oak gasification.  This catalyst was tested over multiple reaction/regeneration cycles.  Catalyst samples were collected throughout the study at various conditions and were characterized by sulfur K-edge XANES, TPR, and XRD.  The pilot-scale regeneration consisted of steaming + air followed by H₂ reduction and, for comparison, a bench-scale regeneration process of steaming followed by H₂ reduction was performed.  Post-reaction samples showed the presence of sulfides arising from H₂S poisoning of metallic nickel sites.  Although gaseous sulfur species were observed to leave the catalyst bed during regeneration,  the regeneration of the post-reaction catalysts using both the steam and steam + air procedures led to a transformation of sulfur species from sulfides to sulfates.  The subsequent H₂ reduction led to a partial reduction of sulfates back to sulfides.  A proposed reaction sequence is presented.  This demonstrates the importance of regeneration protocol to effectively regenerate catalysts to recovery activity and recommended strategies are discussed.