Enhanced hydrogen production via in-situ chemical looping reforming of fast pyrolysis volatiles from microalgae

Hydrogen production via in-situ chemical looping reforming of rapidly pyrolyzed volatiles from microalgae was investigated using a NiFe₂O₄@SBA-15 oxygen carrier (OC). A two-stage fixed-bed reactor system was first employed to identify optimal pyrolysis conditions for chlorella and then to systematically optimise key reforming process parameters, including the confinement strategy, temperature, OC loading, and steam addition. The reaction pathway was further clarified using ex-situ characterisation techniques, providing detailed insight into intermediate species and structural changes during the process. Results showed that hydrogen and carbon yields in the pyrolysis products increased progressively with temperature. Therefore, 600 °C was identified as the optimal condition, attributed to the abundance of hydrogen-rich volatile precursors, including hydrocarbons and light volatile species. During the reforming stage, the highest hydrogen production performance was achieved at 850 °C, with an oxygen carrier to biomass ratio of 1 g·g_microalgae⁻¹, and a steam injection volume of 0.4 mL, maintaining excellent stability over ten redox cycles. Ex-situ characterisation revealed that the controlled lattice oxygen transfer in nickel ferrite effectively promoted the selective conversion of volatiles. However, the accumulation of aldehyde intermediates and the extensive removal of oxygenated species were identified as rate-limiting steps. This study elucidates the reaction mechanism of hydrogen production via chemical looping reforming of fast microalgae pyrolysis. It provides an important theoretical basis and technical reference for green and low-carbon production of hydrogen from algal biomass.