Advances in the application of active metal-based sorbents and oxygen carriers in chemical looping biomass steam gasification for H2 production

Active metal-based materials (AMMs) as CO2 sorbents or oxygen carriers (OCs) have been investigated to enhance hydrogen production during various biomass-based chemical looping processes. CaO-based sorbents and Fe-based OCs are widely used in this field; therefore, these two types of materials will be the focus of this review. CaO-based sorbents can promote the water-gas shift reaction towards H2 generation with in-situ CO2 removal. OCs partly oxidise biomass, releasing CO – a reactant in the water-gas shift reaction. The use of Fe-based OCs boosts H2 yield via iron-steam reactions. AMMs possess catalytic activity for tar cracking, generating more H2. However, these AMMs suffer from sintering over cycles, which hinders their utilisation at industrial scales. The addition of support materials aims to overcome this issue. This review first assesses the impacts of CaO sorbents and OCs on H2 production, and then examines the material behaviour, cyclic performance and applications in biomass-based chemical looping processes. The mechanism of support materials as a reactivity enhancer and sintering inhibitor is proposed in the review. The effects of operating conditions on H2 yield are summarised and provided in the Supplementary materials.