Sr-enriched R-P type layered perovskite for biomass to syngas conversion with exceptional efficiency and selectivity...

Biomass chemical looping gasification (BCLG) demonstrates great potential to help address global environmental issues and green energy demands. Yet it remains a challenge to develop novel oxygen carriers (OCs) in BCLG to break the trade-off between the biomass conversion and syngas selectivity with high syngas yield. In this study, Sr-Fe OCs labelled as S3F2, S4F2, and S5F2, containing primarily of Ruddlesden-Popper (R-P) layered perovskite structured Sr₃Fe₂O_7-x, were synthesized. Sr₃Fe₂O_7-x thermodynamically favors the selective formation of CO over CO₂, conferring its inherently high CO selectivity. Both the interstitial oxygen and lattice oxygen were found to contribute to the gasification process, which presented enhanced activity and oxygen uncoupling characteristic. The excessive Sr incorporation in S4F2 and S5F2 further increased the oxygen vacancies of Sr₃Fe₂O_7-x, and caused a much higher oxygen mobility and oxygen release capacity (S5F2 > S4F2 > S3F2). Additional Sr in S5F2 formed Sr(OH)₂·H₂O on Sr₃Fe₂O_7-x surface, which acted as additional oxygen source for gasification and also suppressed the overoxidation of syngas product on the surface. These combined features enabled the most favorable performance of S5F2 with a carbon conversion of 91%, CO selectivity of 94%, and syngas yield of 1208 mL/g at 900 °C, much higher than the Fe₂O₃ benchmark (77.8%, 59.8%, and 557.9 mL/g, respectively).