Supercritical Water Gasification of Lignin and Cellulose Catalyzed with Co-precipitated CeO₂-ZrO₂

Lignin and cellulose were gasified at 500 and 600 °C in supercritical water over co-precipitated CeO2-ZrO2 catalyst. The addition of CeO2-ZrO2 improved the gasification efficiency and hydrogen production, and the catalytic effect was more significant at lower temperatures. The H2 yield from cellulose gasification at 500 °C increased by over 2.5 times to 8.50 mol/kg with the presence of CeO2-ZrO2. The gas chromatography-mass spectrometry (GC-MS) analysis showed that the catalyst reduced the content of cyclopentenone and furan derivatives in the aqueous product but increased the content of refractory phenols. We characterized the fresh and the used catalysts with H2-temperature-programmed reduction (H2-TPR), X-ray diffraction (XRD), and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) analysis, showing that CeO2 was the main active component, which catalyzed gasification through redox reactions. ZrO2 enhanced the catalytic activity of CeO2 by lowering the reduction temperature in hydrogen, increasing the dispersion of CeO2, and facilitating H2 adsorption on the catalyst surface.