Synergistic catalysis of ZIF-67/ZIF-74 and Al in hydrogen production from tobacco straw pyrolysis: Co/Ni site regulation and mechanism analysis

Tobacco stalks are abundant, hydrogen-rich, and cost-effective. However, the generation of hydrogen through pyrolysis remains limited by incomplete tar cracking and the tendency of catalysts to sinter and deactivate. Our work proposes an in-situ catalytic strategy employing ZIF-67/ZIF-74 coupled with metallic aluminum (Al). The effects of pyrolysis temperature and the catalyst/biomass mass ratio on product distribution are investigated in a fluidized bed, and the structural evolution is elucidated through characterization techniques including SEM, XRD, and XPS. The results revealed that higher temperatures significantly promoted H 2 production. The H 2 yields for the ZIF-67/Al and ZIF-74/Al systems increased from the 773 K yields of 35.9 vol% and 31.3–43.5 vol% and 44.3 vol% at 973 K, respectively, while the CO 2 yields decreased significantly. The appropriate increase in the catalyst ratio enhances the exposure of more active sites. As the catalyst/biomass mass ratio increased from 1:6–1:2, the H 2 yields reached 51.06 vol% and 49.96 vol%, which corresponding to increases of 15.60% and 17.56% compared to the 1:6 ratio. ZIF-74 tends to promote deep deoxygenation to form CO 2 , while ZIF-67 maintains high CO selectivity, which reflects the intrinsic differences between Co and Ni sites. The Al is converted into an Al 2 O 3 carrier during the pyrolysis process, which effectively suppresses metal sintering. The MOF-derived Co/Ni species promote the lightening of tar and the ordering of the carbon structure, thereby enhancing H 2 production. These findings elucidate the synergistic catalytic mechanism of ZIF-67/ZIF-74 with Al, providing a theoretical basis for the design of catalysts for the efficient and directed hydrogen production from biomass.