Bio-waste derived Ni single-atom catalysts with Ni-pyridine-N4 active sites for efficient N-alkylation of alcohols and amines

Abstract

Due to traditional methods’ inability to synthesize N-alkylation compounds in a green and efficient manner, and the unclear catalytic mechanisms. This study employed seafood waste-derived chitin as a raw material to prepare porous chitin (PC) with a “coral cluster” morphology by means of an exfoliating–etching strategy, which was further used as a support to fabricate Ni single-atom catalysts (CPC@Ni). The chitin-derived support could provide both physical and chemical confinements to firmly anchor Ni atoms through abundant micropores and self-doped N elements, as well as regulate the coordination environment and electronic structure of Ni atoms. The CPC@Ni catalyst exhibited excellent catalytic performance in N-alkylation of alcohols and amines compared to various commercial and reported catalysts, as well as good stability and broad substrate compatibility. Notably, the results indicated that CPC@Ni presented typical Ni–N₄ coordination structures (Ni-pyridine-N₄ or Ni-pyrrole-N₄). By combining theoretical calculations, it first revealed that the Ni atoms in Ni-pyridine-N₄ with fewer electron transfer could facilitate the breakage of C–H bond in the intermediate Ph-CH₂O*, thus driving the whole reaction and proving the dominant catalytic activity sites. This study may provide new perspectives for investigating the intrinsic catalytic mechanism of the hydrogen borrowing reaction between alcohols and amines.