Biomass-derived N-doped porous carbon: an efficient metal-free catalyst for methylation of amines with CO 2

Developing green, efficient, and low-cost catalysts for methylation of N–H by using CO 2 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 CO 2 -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 CO 2 to weaken the CO 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 CO 2 and accelerate mass transfer, synergistically promoting the conversion of CO 2 . The optimized NPC (1/5) catalyst, integrating the porous structure and strong Lewis basicity, exhibits excellent catalytic activity for CO 2 -based methylation reaction under mild conditions (1 bar CO 2 , 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 CO 2 as the C1 resource.