Stability and activity maintenance of Al₂O₃- and carbon nanotube-supported Ni catalysts during continuous gasification of glycerol in supercritical water

We have evaluated the long-term stability of activities and physicochemical properties for nickel nanoparticles supported on Mg-promoted γ-Al₂O₃ (MgAl₂O₄-Al₂O₃), α-Al₂O₃, and multi-wall carbon nanotubes (CNTs) for supercritical water gasification (SCWG) in a continuous flow reactor at 425 °C, 25.2 MPa, using 9 wt.% glycerol as the feed. Ni/CNT achieved the lowest H₂ yields but produced consistent carbon gasification efficiencies (CGEs) ∼80% during 48 h of operation at steady state, whereas the CGEs from Ni/α-Al₂O₃ and Ni/MgAl₂O₄-Al₂O₃ decreased to <80% when the gasification was extended to 48 h. Characterization results indicated that CNTs showed stable pore structures and Ni/CNT showed the best dissolution resistance of Ni in SCW. Persistent loss of Al into SCW probably contributed to the deactivation of Al₂O₃-supported Ni catalyst beds. Results also suggest that enhanced interaction of Ni and the supports may be beneficial for reducing dissolution of Ni in SCW.