NiCo bimetallic catalysts supported on activated carbon/CaAl layered double hydroxide nanosheets for boosting hydrogen production via supercritical water gasification of spruce hydrochar pellets

Aiming to convert hydrothermal carbonization (HTC)-derived hydrochar pellets along with HTC-aqueous phase (HTC-AP) into renewable hydrogen via supercritical water gasification, a series of NiCo supported catalysts were prepared. A novel composite was devised as the support material for NiCo-catalysts. To this, activated carbon (AC) obtained by chemical activation of the hydrochar was modified using CaAl-layered double hydroxide (CaAl-LDH). The synthesized NiCo-catalysts (C0.5, C1, and C1.5) with different Co/Ni mass ratios (0.5, 1, and 1.5 wt/wt) were examined under various operating conditions. 10Ni5Co/AC@CaAl-LDH nanosheet catalyst (C0.5) presented highest hydrogen yield of 2.42 ± 0.05 mol/kg at 550 °C, with maximized hydrogen selectivity. Moreover, the impacts of Co/Ni mass ratio on the physicochemical properties of NiCo bimetallic supported catalysts were analyzed. The better performance of the C0.5 catalyst could originate from smaller particle size, higher specific surface area, and more reduced Ni and Co species compared with other catalyst formulations. Compared with 10Ni5Co/AC catalyst, C0.5 catalyst improved hydrogen yield by 30 % due to CaAl-LDH nanosheets, which provides a highly uniform NiCo distribution. Additionally, HTC-AP as the supercritical water gasification medium exhibited a 50 % increase in hydrogen yield compared to the ultrapure water in a noncatalytic reference test.