Alumina-Supported Porphyrin Zinc as a Carbonic Anhydrase Mimic: Enhanced CO₂ Hydration Catalysis

Zinc porphyrin is a promising carbonic anhydrase (CA) mimic for promoting CO₂ absorption, but its application is hindered by poor dispersibility in absorption solutions. To address these challenges, we developed a strategy to impregnate zinc porphyrin on an γ-Al₂O₃ carrier. The hydrophilic surface groups and porous structure of γ-Al₂O₃ were expected to enhance both the hydrophilicity and stability of zinc porphyrin. To verify its feasibility, zinc tetraphenylporphyrin (ZnTPP) was chosen as the representative to synthesize ZnTPP/Al₂O₃. Characterizations showed that ZnTPP could be loaded into the pores of γ-Al₂O₃ in a highly dispersed state. Also, ZnTPP/Al₂O₃ could be uniformly dispersed in the absorption liquid, effectively exposing the Zn²⁺ active sites and reducing diffusion resistance. CO₂ absorption experiments revealed that ZnTPP/Al₂O₃ significantly enhanced CO₂ absorption in water, 20 wt % K₂CO₃, and 20 wt % monoethanolamine (MEA) solutions, far outperforming original ZnTPP. Density functional theory (DFT) calculations further elucidated the interaction mechanisms, showing that oxygen atoms on γ-Al₂O₃ stabilize ZnTPP by forming van der Waals and coordination bonds with Zn²⁺ active sites. Additionally, these oxygen atoms donate electrons to Zn²⁺, enhancing its catalytic activity. These findings highlight the effectiveness of this strategy and provide a promising pathway for optimizing other CA-mimics for CO₂ capture applications.