Hydrogen Production from Supercritical Water Gasification of Lignin and Cellulose with Coprecipitated CuO-ZnO and Fe₂O₃-Cr₂O₃

In this study, CuO-ZnO and Fe2O3-Cr2O3 were prepared by coprecipitation and their catalytic activity in supercritical water gasification (SCWG) was evaluated at 500 and 600 °C. Both catalysts improved the gasification efficiency and hydrogen production from cellulose and lignin. CuO-ZnO showed a higher catalytic activity in SCWG of lignin, while Fe2O3-Cr2O3 showed a higher impact on cellulose gasification. With CuO-ZnO, the highest H2 yield of 29.62 mol/kg was obtained in lignin gasification at 600 °C. The catalysts were characterized using X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), and scanning electron microscopy-energy-dispersive spectrometer (SEM-EDS), showing that Fe2O3 was reduced to Fe3O4 at 500 and 600 °C, while Cr2O3 was only reduced at 600 °C. In CuO-ZnO, the component CuO was reduced to Cu at both temperatures, while ZnO was not reduced, but it varied CuO performance in SCWG. The reduction of the oxides can release active oxygen species to promote the decomposition of organics, and the formed Cu can further promote the water-gas shift reaction and carbon conversion.