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

A hybrid-functional material consisting of Ni as catalyst, CaO as CO sorbent, and CaSiO 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 H, CO, CO and CH. 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-CaSiO hybrid-functional materials, which enables ∼626 mL H (room temperature, 1 atm) produced from each gram of sawdust, with H purity in the product gas up to 68 vol %. This performance was superior over a conventional supported catalyst Ni-CaSiO that produced 443 mL H g-sawdust 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 H (∼689 mL H g-sawdust), its cyclic performance decayed dramatically, resulting in H yield reduced by 62% and purity dropped from 73 to 49 vol % after 15 cycles. The "active" CaSiO spacer offers porosity and mechanical strength to the Ni-CaO-CaSiO hybrid-functional material, corresponding to its minor loss in reactivity over cycles (H yield reduced by only 7% and H purity dropped from 68 to 64 vol % after 15 cycles).