Formic Acid Dehydrogenation over a Recyclable and Self-Reconstructing Fe/Activated Carbon Catalyst

A novel catalyst, denoted as ACox@ImFe, was synthesized using matrix-activated oxidized carbon (ACox) featuring a [Fe2+-imidazole]-based complex covalently bonded to the carbon surface through Si–O–C bonding. The catalytic system, distinguished by its innovative hybrid structure that includes Fe2+ and imidazole on an oxidized carbon matrix in the presence of a polydentate phosphine, demonstrated remarkable turnover numbers (TONs), reaching 428,880 and effectively decomposed 53 mL of formic acid (FA) over 8 cycles. This sustained performance underscores the effectiveness, stability, and durability of the catalyst, which was further evidenced by a cumulative H2 production of 22.1 L over the same period. Structural analysis using Raman, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and electron paramagnetic resonance (EPR) spectroscopy revealed structural changes in the used catalyst compared to the pristine material. Despite the observed structural changes, such as Fe-site aggregation and matrix restructuring, the catalyst maintained a high efficiency, with enhanced activity noted with each reuse. The stability of the carbon-based radicals from the matrix was confirmed, which is crucial for the sustained performance of the catalyst. Notably, upon repeated use, the catalyst underwent a self-reconstruction process, which is linked to alterations in the hydrophobicity of the catalyst and the overall structure, resulting in enhanced water durability and improved performance, making ACox@ImFe a robust and effective system for sustainable H2 production.