Microwave-assisted pyrolysis of biomass for efficient H2-rich syngas production promoted by calcium oxide

H2-rich syngas production via microwave-assisted pyrolysis (MAP) of lignocellulosic biomass has recently gained significant attention in biorefineries. Herein, a novel pearl-like calcium oxide (P-CaO) was developed to investigate the dual roles of CaO in H2 enhancement and CO2 absorption during MAP of lignocellulosic biomass, dedicated to achieving high production of H2-rich syngas. Utilizing a self-constructed MAP system, the different catalytic performance between P-CaO and other metal oxides were examined, revealing that our P-CaO produced the highest H2 yield (257 NmL/gcorn stover, 7.6 times higher than no-catalyst group and 2.2 times higher than commercial CaO group), and lowest CO2 production (44 NmL/gfeedstock), with syngas purity exceeding 72 vol% at 600°C. This increase in H2-rich syngas production demonstrated universal applicability across other biomass feedstocks. Finally, the study delved into the microstructural changes and phase transition mechanisms of P-CaO, shedding insights into gas formation pathways. The P-CaO nanoparticles, with abundant alkaline sites, excellent adsorption capacity and large specific surface area due to aggregate, facilitate the secondary cracking of organic intermediates like phenols, thus promoting the production of H2, while CO2 adsorption derives a favorable shift in the water–gas shift equilibrium. These findings are expected to offer critical insights and serve as a reference for the development of efficient catalysts in the next-generation hydrogen industry. © 2025