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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.

Supercritical water gasification technology has bright prospects because it can convert biomass into hydrogen-rich gaseous products in an effective and clean way. The devolatilization process is relatively fast, and char conversion is the rate-determining step in the whole gasification process. To discuss the kinetic model of char gasification in supercritical water, the quartz tube reactor was adopted as the reactor to omit the undesired catalytic effect of the reactor wall and bamboo charcoal was selected as typical char as a result of the low volatile content. The experiments were investigated within the operating range of temperatures of 700–900 °C and residence times of 5–20 min. The experimental results were analyzed within the framework of homogeneous, non-reacted core, and random pore models. Dependences of the carbon gasification rate, residence time, and temperature were described in an assumption of the first-order reaction and the Arrhenius dependence. The calculation results showed that the r...

Char conversion is the rate-determining step for coal gasification in supercritical water, because the main components of char are polycyclic aromatic hydrocarbons (PAHs) with chemical stability. Anthracene was selected as the model PAH compound to explore the gasification mechanism of coal in supercritical water. The experimental parameters investigated with autoclaves were within the following ranges: temperature, 600–750 °C; residence time, 5–30 min; and pressure, 23–25 MPa. The main gas products were H2 and CO2. The liquid intermediates were analyzed by gas chromatography–mass-selective detection (GC-MSD) for qualitative analysis and quantitative analysis, respectively. Benzene and naphthalene were found to be relatively stable compounds in the liquid products. Effective catalyst and appropriate temperature were obtained to enhance the gasification process.