Redox reactivity evaluation of cement chemically and physically bonded hematite oxygen carrier during biomass chemical looping gasification

• Al-enriched calcium ferrites are promising for biomass gasification. • Multi-stage oxygen release from novel OCs enhances selective syngas production. • Sufficient oxygen vacancies contribute to solid–solid reaction. • Fe segregation hardly affects OC reactivity due to high ionic conductivity. • The activation energy of OC reduction by char significantly declines after cycling. The utilization of oxygen carrier (OC) with redox durability is crucial for scaling up biomass chemical looping gasification (BCLG) systems. In the present work, two novel OCs were synthesized by chemically and physically incorporating two cements with hematite and tested in a TGA and batch fluidized-bed reactor for BCLG. These OCs exhibited multi-stage release of oxygen at an internally controlled rate, leading to the dominant char partial oxidation followed by combustion of remnant char. This redox behavior significantly enhanced selective syngas production and reduced carbon deposition with or without steam. The characterization results from XRD, XPS, H 2 -TPR and SEM/EDS techniques reveal that active solid solution containing Fe and inert species (Al and Ca) was retained in the particle interior as Fe dispersity was improved over cycling, thereby preserving sufficient oxygen vacancies. This chemical durability conferred high oxygen anion conductivity on recycled OCs, contributing to the stable solid–solid reaction between OC and char. As a result, the reactivity loss caused by Fe segregation was mitigated. The constant presence of inert phases provided physical framework for active phases within reduction–oxidation cycles. Non-isothermal TGA tests for the solid–solid reaction show that the corresponding activation energy decreased from 801.37 kJ·mol −1 (fresh OC) to 542.04 kJ·mol −1 (used OC), indicating smoother oxygen mobility after cycling. This study proves that the dissolution of hematite into inert phases such as Ca-Al oxides is a promising approach for OC structure modification to achieve enhanced selectivity and reactivity for syngas production.