Biomass-derived N-doped porous carbon: an efficient metal-free catalyst for methylation of amines with CO2

Abstract

Developing green, efficient, and low-cost catalysts for methylation of N–H by using CO₂ as the C1 resource is highly desired yet remains a significant challenge. Herein, N-doped porous carbons (NPCs) were designed, synthesized, and proved to be an excellent metal-free catalyst for CO₂-participated methylation conversion. NPCs were prepared via the pyrolysis of a mixture of tannic acid and urea. Both theoretical calculation and experiment demonstrate that the N species especially pyridinic N and pyrrolic N within NPCs can work as Lewis basic sites for attacking CO₂ to weaken the CO bonds and lower the molecule conversion barrier, facilitating the subsequent methylation of N–H to produce, for example, N,N-dimethylaniline. Besides, the unique porous structure can enrich CO₂ and accelerate mass transfer, synergistically promoting the conversion of CO₂. The optimized NPC_(1/5) catalyst, integrating the porous structure and strong Lewis basicity, exhibits excellent catalytic activity for CO₂-based methylation reaction under mild conditions (1 bar CO₂, 75 °C). Our work, for the first time, demonstrates the feasibility of using NPCs to catalyze the methylation of amino compounds to produce N,N-dimethylamine by exploiting CO₂ as the C1 resource.