Tailoring d-Band Center of Single-Atom Nickel Sites for Boosted Photocatalytic Reduction of Diluted CO from Flue Gas.

Photocatalytic reduction of diluted CO from anthropogenic sources holds tremendous potential for achieving carbon neutrality, while the huge barrier to forming *COOH key intermediate considerably limits catalytic effectiveness. Herein, via coordination engineering of atomically scattered Ni sites in conductive metal-organic frameworks (CMOFs), we propose a facile strategy for tailoring the d-band center of metal active sites towards high-efficiency photoreduction of diluted CO. Under visible-light irradiation in pure CO, CMOFs with Ni-O sites (Ni-O CMOFs) exhibits an outstanding rate for CO generation of 13.3 μmol h with a selectivity of 94.5 %, which is almost double that of its isostructural counterpart with traditional Ni-N sites (Ni-N CMOFs), outperforming most reported systems under comparable conditions. Interestingly, in simulated flue gas, the CO selectivity of Ni-N CMOFs decreases significantly while that of Ni-O CMOFs is mostly unchanged, signifying the supremacy for Ni-O CMOFs in leveraging anthropogenic diluted CO. In situ spectroscopy and density functional theory (DFT) investigations demonstrate that O coordination can move the center of the Ni sites' d-band closer to the Fermi level, benefiting the generation of *COOH key intermediate as well as the desorption of *CO and hence leading to significantly boosted activity and selectivity for CO-to-CO photoreduction.