Highly efficient and reusable nanostructured porous Ni/La₂O₂CO₃ tandem catalyst for hydrogen and methane production from subcritical hydrothermal treatment of nitrocellulose

Chemical conversion of biomass into fuel gas under subcritical water conditions is a crucial step towards a sustainable and carbon–neutral route for energy storage. However, generation of highly selective gas, such as hydrogen and methane, remains a challenge under such conditions. We present here a reusable tandem catalyst, porous nanostructured nickel-exsolved lanthanum oxycarbonate (Ni/La₂O₂CO₃) for nitrocellulose gasification. Hydrogen (H₂) and methane (CH₄) production achieves 45.5 % (13.6 mmol) and 9.4 % (2.8 mmol) selectivity, respectively, at 350 ℃, which overwhelms the activity of Raney nickel (41 %,10 mmol and 2.8 %, 0.7 mmol for H₂ and CH₄, respectively). The study of temperature-dependent structure and the electron paramagnetic resonance spectroscopy further elucidated the origin of its high catalytic efficacy together with the phase change of the catalyst. The reused catalyst after regeneration retains 55 % of its initial activity after five consecutive tests. This study highlights the Ni/La₂O₂CO₃ catalyst that holds significant potential for selective fuel gas generation from various biomass sources.