Developing Oxygen Carriers for Chemical Looping Biomass Processing: Challenges and Opportunities

Among the various thermochemical biomass conversion pathways, chemical looping gasification and chemical looping reforming, collectively known as chemical looping biomass processing (CLBP), offers numerous advantages, including the generation of renewable hydrogen, high exergy efficiency, inherent carbon capture, and process intensification. Like all other chemical looping applications, oxygen carriers play key roles in determining the effectiveness and efficiency of CLBP. In addition to the requirement for high oxygen transfer capacity, the chemical activity of the lattice oxygen also needs to be modulated to steer the selectivity of CLBP toward syngas. Furthermore, it is desirable for the CLBP oxygen carriers to possess catalytic activities that accelerate the conversion of biomass-based feedstocks. However, despite the large volume of relevant research publications, the diversity in oxygen carrier formulations, biomass compositions, and test conditions used leads to mixed views regarding the structural–functional relationships between oxygen carriers and their performance during CLBP. To address the above knowledge gap, this review presents a systematic, but non-exhaustive summary of the development and evaluation of oxygen carriers for CLBP applications, with an aim to elucidate the rational design principles and operation parameters toward optimal process efficiency.