Photocatalytic Formamide Synthesis via Coupling of Electrophilic and Nucleophilic Radicals over Atomically Dispersed Bi Sites.

Abstract

Formamide (HCONH2) plays a pivotal role in the manufacture of a diverse array of chemicals, fertilizers, and pharmaceuticals. Photocatalysis holds great promise for green fabrication of carbon-nitrogen (C-N) compounds owing to its environmental friendliness and mild redox capability. However, the selective formation of the C-N bond presents a significant challenge in the photocatalytic synthesis of C-N compounds. This work developed a photocatalytic radical coupling method for the formamide synthesis from co-oxidation of ammonia (NH3) and methanol (CH3OH). An exceptional formamide yield rate of 5.47±0.03 mmol ⋅ gcat -1 ⋅ h-1 (911.87±5 mmol ⋅ gBi -1 ⋅ h-1) was achieved over atomically dispersed Bi sites (BiSAs) on TiO2. An accumulation of 45.68 mmol ⋅ gcat -1 (2.0 g ⋅ gcat -1) of formamide was achieved after long-term illumination, representing the highest level of photocatalytic C-N compounds synthesis. The critical C-N coupling for formamide formation originated from the "σ-σ" interaction between electrophilic ⋅CH2OH with nucleophilic ⋅NH2 radical. The BiSAs sites facilitated the electron transfer between reactants and photocatalysts and enhanced the nucleophilic attack of ⋅NH2 radical on the ⋅CH2OH radical, thereby advancing the selective C-N bond formation. This work deepens the understanding of the C-N coupling mechanism and offers an intriguing photocatalytic approach for the efficient and sustainable production of C-N compounds.