Harnessing Construction and Demolition Wood Residues and Calcium Hydroxide to Co-produce H ₂ and Composite Materials Bearing Biochar and Calcium Carbonate

Valorization of construction and demolition wood (C&DW) residues and calcium hydroxide to co - produce sustainable energy carriers such as H2 and composite materials bearing calcium carbonate and biochar is a thermodynamically favorable but less explored approach. Though C&DW residues are globally available and contain lignocellulosic biomass, which is suitable for thermochemical energy conversions, they remain underutilized. In this work, Alkaline Thermal Treatment (ATT) of C&D wood residue is achieved by reacting it with Ca(OH)2 at 500 °C under a N2 atmosphere in the presence of a Ni/ZrO2 catalyst and steam. CO2 emissions are suppressed by forming a solid product containing CaCO3 and biochar. Ni/ZrO2 as a reforming catalyst is found to enhance H2 production to 6.4 mmol/g biomass from 1.5 mmol without Ca(OH)2, steam, or the catalyst. Steam injection further promotes H2 formation to 9.4 mmol/g of biomass. In addition to capturing CO2, Ca(OH)2 enables the deconstruction of biomass by promoting decarbonylation, ring opening, and cracking reactions. Ca(OH)2 is also found to induce branching in the biochar structure, while steam improves deoxygenation. Therefore, this study unlocks sustainable pathways to deconstruct biomass to produce multiple high-value products such as H2 and composite materials bearing biochar and CaCO3 for energy and environmental security.