Electrocatalytic amino acid synthesis from biomass-derivable keto acids over ball milled carbon nanotubes

Electrocatalytic reductive amination (ERA) offers an attractive way to synthesise organonitrogen chemicals from renewable feedstocks. Here, we report carbon nanotubes (CNTs) as an effective catalyst for the ERA of biomass-derivable alpha-keto acids into amino acids using NH3 as the nitrogen source. Through a facile ball milling (BM) treatment, the intrinsic defects in the CNTs were increased while the electrocatalytic activity of CNTs converting 2-ketoglutaric acid into glutamic acid was enhanced by approximately seven times. A high faradaic efficiency (FE) of similar to 90% with a corresponding glutamic acid formation rate of up to 180.9 mmol g(cat)(-1) h(-1) was achieved, and similar to 60% molar yield of glutamic acid was obtained after 8 h of electrolysis. Electrokinetic analyses indicated that the BM-CNT catalysed ERA exhibits a first-order dependence on the substrate and NH3, with a rate-determining step (RDS) involving the first electron transfer. Following this protocol, a number of amino acids were prepared with moderate to high FEs and formation rates. Significantly, we synthesised long carbon chain amino acids, which are typically obtained in lower yields using the existing methods.

Automated summary

Electrocatalytic reductive amination (ERA) is a promising method for synthesizing organonitrogen chemicals from renewable feedstocks. In this study, carbon nanotubes (CNTs) were used as an efficient catalyst for converting α-keto acids derived from biomass into amino acids using NH3 as the nitrogen source. The catalytic activity of CNTs for the conversion of 2-ketoglutaric acid into glutamic acid was significantly enhanced by increasing the intrinsic defects through ball milling treatment. The ERA process exhibited high faradaic efficiency and molar yield of glutamic acid.