Support effects in heterogenized Fe(II) molecular catalysts for formic acid dehydrogenation: Silica versus oxidized activated carbon

Formic acid dehydrogenation (FADH) is a promising approach for reversible hydrogen storage in liquid organic hydrogen carrier systems. Herein, Fe II –Schiff base and reduced Schiff-base catalysts were covalently immobilized onto SiO 2 and oxidized activated carbon (Acox) via organosilane grafting, to investigate support effects on catalytic activity and stability. SiO 2 -supported catalysts, under continuous formic acid feeding conditions, exhibited higher initial activity and lower apparent activation energies (47–53 kJ mol −1 ), indicating favorable kinetics for hydride formation and transfer. Conversely, ACox-supported systems demonstrated superior durability, preserving activity over four cycles and achieving turnover numbers above 80,000 without detectable CO formation. Post-catalytic analyses revealed distinct support-dependent redox environments and deactivation pathways. SiO 2 -supported catalysts mainly underwent ligand degradation, whereas ACox-supported systems showed partial support reorganization with gradual Fe leaching. Overall, the results established a clear structure–support–performance relationship, while ACox emerged as a cost-effective and robust support for durable Fe-based FADH catalysts.