Electrochemical and chemical cascade catalysis for efficient hexamethylenetetramine synthesis over mesoporous copper nanotips.

Abstract

Catalytic carbon-nitrogen (C-N) coupling reactions offer a sustainable and environmentally friendly route for the production of high value-added hexamethylenetetramine (HMTA). However, it still suffers from limited chemisorption, low activation kinetics, and unfavorable thermodynamics, resulting in low HMTA Faradaic efficiency (FE_HMTA) and yield rate. Here, by physically constructing hierarchically tip and mesoporous structure, copper mesoporous nanotips (Cu MNTs) realize efficient HMTA synthesis by an electrochemical-chemical cascade catalysis. Unlike traditional catalysts, tip-enhanced site of Cu MNTs electrochemically favors NO₃^- chemisorption and further electroreduction into *NH₃ radicals, while its confined mesoporous nanoreactor ensures cascade chemical C-N coupling and subsequent cyclization to HMTA. With minor byproducts, Cu MNTs deliver a FE_HMTA of 94.2% and a yield rate of 0.227 mmol h^-1 cm^-2. Moreover, this route enables efficient HMTA synthesis in a flow cell electrolyzer with high economic feasibility and market potential for industrial application. This work thus deepens the physical design strategies of hierarchically structural catalysts that promote electrochemical-chemical cascade C-N coupling reactions for efficient synthesis of various important chemicals and feedstocks.