Controllable encapsulation of silver nanoparticles by porous pyridine-based covalent organic frameworks for efficient CO2 conversion using propargylic amines

Abstract

The conversion of CO₂ into value-added chemicals is an attractive alternative to produce valuable fuels and chemicals. In this work, we demonstrate two pyridine-based covalent organic frameworks (COFs) with rich porosity for the size-controlled synthesis of silver nanoparticles, showing outstanding catalytic activity for the carboxylative cyclization of propargylic amines with CO₂ under mild conditions. Experimental characterization methods elucidate that pyridinic-N in the frameworks can not only anchor silver sites in the pores by their interaction, but selectively confine them to specific sizes in different pores by regulating the position of pyridinic-N, which exerts a strong influence on the catalytic activity and stability. Importantly, Ag@2,6-FPP-TAPT with ultrasmall nanoparticles exhibits a record-level catalytic activity with an unexpectedly high turnover frequency (TOF) of 964 h⁻¹, which far exceeds that of previously reported catalysts. The enhanced activity of Ag@2,6-FPP-TAPT is attributed to the synergistic effects among its ultrasmall particle size, enhanced mass transfer, adsorption and activation for propargylic amines and CO₂. Most importantly, the continuous-flow supports a scalable preparative ability with a full conversion and a high TOF value.