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···WSA FLP) sites are constructed for photocatalytic CO2 conversion through introducing W single-atoms into polymeric carbon nitride. In the atomically dispersed N···WSA 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···WSA FLP on photocatalytic CO2 reduction are well revealed. The N···WSA 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.