Constructing Atomic Tungsten-Based Solid Frustrated-Lewis-Pair Sites with d-p Interactions for Selective CO₂ Photoreduction

Solid frustrated Lewis pair (FLP) shows remarkable advantages in the activation of small molecules such as CO₂, owing to the strong orbital interactions between FLP sites and reactant molecules. However, most of the currently constructed FLP sites are randomly distributed and easily reunited on the surface of catalysts, resulting in a low utilization rate of FLP sites. Herein, atomic tungsten-based FLP (N···W_SA FLP) sites are constructed for photocatalytic CO₂ conversion through introducing W single-atoms into polymeric carbon nitride. In the atomically dispersed N···W_SA FLP, the electron-deficient W single-atom acts as the Lewis acid (LA), and the adjacent electron-rich N atom acts as the Lewis base. Through the combination of various characterizations, including pyridine-IR, in situ diffuse reflectance infrared Fourier transform spectroscopy, CO₂-temperature programmed desorption, and theoretical calculations, the positive effects of N···W_SA FLP on photocatalytic CO₂ reduction are well revealed. The N···W_SA FLP can effectively adsorb CO₂ to form an unusual W-O-C-N structure with significant d-p orbital interactions, which leads to an interesting "push-push" electron transfer effect. The π back-donation from W 5d to the antibonding orbital (2π) of CO₂ realizes reverse electron transfer from the W single-atom to the O site, while the electrons are transferred from the electron-rich N site to the electropositive C site via Lewis acid-base interactions, therefore effectively breaking the C═O bond to activate CO₂ molecules and boost CO₂-to-CO performance. This work provides a brand new route for the research on high-efficiency activation of small molecules based on single-atom-based FLP catalysts.