Enhanced activity and stability in microwave steam reforming of tar with TiO2-coated zeolitic imidazole framework-67 derived Co/C

Microwave steam reforming using carbon-based catalyst presents a promising solution for tar elimination in biomass gasification, crucial for renewable syngas production toward heating, electricity, and value-added chemicals. However, activated-steam-induced catalyst deactivation remains challenging. Herein, a ZIF-67-derived core-shell Co/C-TiO2 catalyst was engineered via tailored TiO2 hydrophilicity and structural protection. Catalytic performance exhibited a volcano-type trend versus TiO2 shell thickness. The optimal catalyst (Co/C-T2) achieves a 96.62 % toluene conversion rate and a 72.17 % carbon conversion rate at 550 °C, sustaining >87.61 % efficiency over 6 h. Structural characterizations revealed the core-shell architecture transformed carbon-supported Co(111) structure into anatase TiO2(101)-stabilized Co3O4(311) configuration, significantly enhancing surface basicity and oxygen species density. DFT-based molecular dynamics simulations further elucidated the mechanism by demonstrating reduced adsorption and dissociation energy barriers for H2O molecules, which facilitate steam activation in the reforming process. However, excessive TiO2 coating induces diffusion limitations at the reactant/metal active site interface, coupled with coking-induced pore occlusion, consequently triggering significant deterioration in catalytic activity and stability. This work establishes a facile modification paradigm for developing microwave-responsive carbon catalysts while providing fundamental insights into the structure-activity relationships of core-shell systems in heterogeneous catalysis. These findings offer practical guidance for designing advanced catalysts in sustainable energy conversion applications.