Atomically Dispersed Iron Metal Site in a Porphyrin-Based Metal–Organic Framework for Photocatalytic Nitrogen Fixation

Abstract

The rational design of photocatalysts for efficient nitrogen (N 2 ) fixation at ambient conditions is important for revolutionizing ammonia production and quite challenging because the great difficulty lies in the adsorption and activation of the inert N 2 . Inspired by a biological molecule, chlorophyll, featuring a porphyrin structure as the photosensitizer and enzyme nitrogenase featuring an iron (Fe) atom as a favorable binding site for N 2 via π-backbonding, here we developed a porphyrin-based metal−organic framework (PMOF) with Fe as the active center as an artificial photocatalyst for N 2 reduction reaction (NRR) under ambient conditions. The PMOF features aluminum (Al) as metal node imparting high stability and Fe incorporated and atomically dispersed by residing at each porphyrin ring promoting the adsorption and the activation of N 2 , termed Al-PMOF(Fe). Compared with the pristine Al-PMOF, Al-PMOF(Fe) exhibits a substantial enhancement in NH 3 yield (635 μg g −1 cat. ) and production rate (127 μg h −1 g −1 cat. ) of 82% and 50%, respectively, on par with the best-performing MOF-based NRR catalysts. Three cycles of photocatalytic NRR experimental results corroborate a stable photocatalytic activity of Al-PMOF(Fe). The combined experimental and theoretical results reveal that the Fe−N site in Al-PMOF(Fe) is the active photocatalytic center that can mitigate the difficulty of the rate-determining step in photocatalytic NRR. The possible reaction pathways of NRR on Al-PMOF(Fe) were established. Our study of porphyrin-based MOF for the photocatalytic NRR will provide insight into the rational design of catalysts for artificial photosynthesis.

Ferric Porphyrin-Based Porous Organic Polymers for CO2 Photocatalytic Reduction to Syngas with Selectivity Control

“…Notably, according to the EIS analysis (Figure S11), POP2-Fe possesses a smaller impedance radius than POP2, indicating that the coordination facilitates the photoinduced electron transportation of POP2-Fe; this is beneficial to the subsequent reduction. 61 Based on the above Results and Discussion, a possible mechanism is proposed in Figure 7b. Ru(bpy) 3…”

“…According to the electron orbitals of molecular monomers, i.e., 1-Fe and 2-Fe, the electrons are located on the porphyrin ring (Figure S14). Notably, according to the EIS analysis (Figure S11), POP2-Fe possesses a smaller impedance radius than POP2, indicating that the coordination facilitates the photoinduced electron transportation of POP2-Fe; this is beneficial to the subsequent reduction …”

The curious saga of dehydrogenation/hydrogenation for chemical hydrogen storage: a mechanistic perspective

“…Recently, electrochemical N 2 conversion to N 2 H 4 has been achieved. 64–66 Thus, one can foresee on the horizon a path for the development of solar electrochemical plants for hydrazine production collocated along with an AB fueling plant for vehicles running on hydrogen.…”

Recent Advances on Porous Materials for Synergetic Adsorption and Photocatalysis

“…The insertion of Fe into the porphyrin ring of a porphyrin‐based metal–organic framework (PMOF) enabled this PMOF for photocatalytically reducing N 2 to NH 3 . [ 49 ] UiO‐66 MOF exhibited extended wavelength absorption once the linker was changed from terephthalate to aminoterephthalate, leading to the enhanced photocatalytic H 2 production performance. [ 50 ] The amine group (NH 2 )‐modified NH 2 ‐MIL‐125(Ti) MOF showed visible‐light‐induced photocatalytic CO 2 reduction.…”