Unveiling the role of inherent biomass moisture in chemical looping gasification using NiO-Fe2O3/Al2O3 oxygen carrier for enhanced high-quality Syngas

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Abstract
Biomass chemical looping gasification (BCLG) is an emerging and efficient technology for converting biomass into high-quality syngas by employing metal-oxide oxygen carriers (OCs) to indirectly supply oxygen, thereby eliminating the need for air separation units and simplifying downstream gas-cleaning processes. This study proposes a mechanistic framework for active site evolution in a NiO-Fe2O3/Al2O3 OC system to elucidate its role in enhanced syngas production via BCLG. The physicochemical properties of the composite OC were systematically characterized using X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). Both dry biomass (DB) and biomass with inherent moisture (BIM) were investigated as feedstocks to assess the influence of moisture on gasification performance. As the reaction temperature increased from 800 to 900 °C, the tar composition shifted toward more thermally stable aromatic compounds—including toluene, naphthalene, and pyrene—reflecting enhanced secondary cracking of aliphatic chains and accelerated deoxygenation of oxygenated intermediates. Inherent moisture in biomass was found to promote char gasification, improve carbon conversion efficiency, increase H2 yield, and facilitate adjustment of the H2/CO ratio in the syngas. At 900 0C, the DB achieved an effective gas yield of 1.31 m3 kg-1 and a syngas fraction of 94.61%, while the BIM showed values of 1.44 m3 kg-1 dry biomass and 94.64% with an H2/CO ratio of 0.97, confirming that the inherent CO2 and H2O, along with CH4 and tar species, were efficiently reformed into H2 and CO via oxidation-reforming reactions. The NiO-Fe2O3/Al2O3 OC composite demonstrated excellent redox stability over 20 successive cycles, with no significant deterioration in reactivity or structural integrity.

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