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 H-2, 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 similar to 626 mL H-2 (room temperature, 1 atm) produced from each gram of sawdust, with H-2 purity in the product gas up to 68 vol %. This performance was superior over a conventional supported catalyst Ni-Ca2SiO4 that produced 443 mL H-2 g-sawdust(-1) under the same operating condition with a purity of similar to 61 vol %. Although the Ni-CaO bifunctional material in its fresh form generated a bit more H-2 (similar to 689 mL H-2 g-sawdust(-1), its cyclic performance decayed dramatically, resulting in H-2 yield reduced by 62% and purity dropped from 73 to 49-vol % after 15 cydes. 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 (H-2 yield reduced by only 7% and H-2 purity dropped from 68 to 64 vol % after 15 cycles).