Enhanced Hydrogen Production from Sawdust Decomposition Using Hybrid-Functional Ni-CaO-Ca₂SiO₄ Materials

A hybrid-functional material consisting of Ni as catalyst, CaO as CO₂ sorbent, and Ca₂SiO₄ as polymorphic "active" spacer was synthesized by freeze-drying a mixed solution containing Ni, Ca and Si precursors, respectively, to be deployed during sawdust decomposition that generated gases mainly containing H₂, CO, CO₂ and CH₄. The catalytic activity showed a positive correlation to the Ni loading, but at the expense of lower porosity and surface area with Ni loading beyond 20 wt %, indicating an optimal Ni loading of 20 wt % for Ni-CaO-Ca₂SiO₄ hybrid-functional materials, which enables ∼626 mL H₂ (room temperature, 1 atm) produced from each gram of sawdust, with H₂ purity in the product gas up to 68 vol %. This performance was superior over a conventional supported catalyst Ni-Ca₂SiO₄ that produced 443 mL H₂ g-sawdust^-1 under the same operating condition with a purity of ∼61 vol %. Although the Ni-CaO bifunctional material in its fresh form generated a bit more H₂ (∼689 mL H₂ g-sawdust^-1), its cyclic performance decayed dramatically, resulting in H₂ yield reduced by 62% and purity dropped from 73 to 49 vol % after 15 cycles. The "active" Ca₂SiO₄ spacer offers porosity and mechanical strength to the Ni-CaO-Ca₂SiO₄ hybrid-functional material, corresponding to its minor loss in reactivity over cycles (H₂ yield reduced by only 7% and H₂ purity dropped from 68 to 64 vol % after 15 cycles).