Sustainable Electrosynthesis of Hexamethylenetetramine via Paired Electrolysis of Nitrate and PET Waste.

Abstract

Hexamethylenetetramine (HMTA) is a critical organonitrogen compound widely used in the defense, pharmaceutical, and polymer industries. Conventional HMTA production relies on toxic formaldehyde (HCHO) and energy-intensive Haber-Bosch-derived ammonia (NH3) as feedstocks. This study demonstrates a sustainable electrocatalytic approach for the direct synthesis of HMTA via paired electrolysis, using nitrate (NO3 -) and polyethylene terephthalate (PET) waste as nitrogen and carbon sources, respectively. With iron-doped nickel phosphide (Fe-Ni2P) as a bifunctional catalyst, the system achieves concurrent cathodic NO3 - reduction to NH3 with a Faradaic efficiency of ∼ 96.0%, and anodic oxidation of PET-derived ethylene glycol to electrophilic *HCHO intermediates. These resulting intermediates subsequently condense with nucleophilic NH3 to form HMTA with ∼75.2% carbon selectivity. Mechanistic studies reveal that Fe doping induces charge redistribution and upshifts the d-band center, thereby facilitating the adsorption and activation of reactants and lowering the energy barrier for *HCHO intermediate formation and desorption-a critical step enabling subsequent C─N coupling. This work establishes a mild and sustainable electrocatalytic route for HMTA synthesis from environmental waste, underscoring the potential of paired electrolysis in valorizing waste into valuable organonitrogen chemicals.