Two-stage structured catalysts of eggshell-derived CaO@SiC foam and HZSM-5@SiC foam for catalytic pyrolysis of corn cob into aromatics: reuse modes of two-stage catalysts

A two-stage structured catalytic system consisting of eggshell-derived CaO@SiC foam and HZSM-5@SiC foam was constructed for ex-situ upgrading of corn cob pyrolysis vapor to aromatics. Compared to single-stage or non-structured catalytic systems, the two-stage structured catalytic system exhibited superior activity for aromatics production, obtaining the highest aromatics content of 80.14% and BTX content of 29.59% at an optimal catalyst ratio of 1:1. The effects of different reuse modes of the two-stage structured catalysts (regenerating only one or both) on product selectivity and catalyst intrinsic structure were further investigated. The mode of regenerating both catalysts showed the highest overall activity and stability. In terms of product distribution, the peak content of aromatics in liquid product was higher and remained relatively stable across multiple runs. Regarding changes in catalyst properties, this mode alleviated the degradation of morphology, crystal structure, active sites, and pore structure of the catalysts. The enhanced performance in this mode stemmed from synergistic interactions between regeneration-induced oxygen vacancies formation in CaO and acidity moderation in HZSM-5. This study provides fundamental data to support the scale-up and industrial application of two-stage structured catalytic systems.