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

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.

Automated summary

The study demonstrates the synthesis of silver nanoparticles using two pyridine-based covalent organic frameworks (COFs) with rich porosity, showing outstanding catalytic activity for the carboxylative cyclization of propargylic amines with CO2. By regulating the position of pyridinic-N in the frameworks, selective confinement of silver sites to specific sizes in different pores is achieved, influencing catalytic activity and stability. The ultrasmall nanoparticles in Ag@2,6-FPP-TAPT exhibit enhanced catalytic activity due to synergistic effects among particle size, mass transfer, adsorption and activation for propargylic amines and CO2, supporting scalable preparative ability with full conversion and high TOF value in continuous-flow conditions.