Transforming Inorganic Nitrate to Organic Nitriles by the pH Swing Effect in a Pickering Emulsion Electrocatalytic System

Electroreduction of nitrate to ammonia is attracting increasing attention. However, the purification and storage of low-concentration ammonia generated in electrolytes are economically inefficient. In this study, we present a novel electrochemical reduction coupling reaction that takes place within a Pickering emulsion electrocatalytic system, facilitating the transformation of NO₃ ^- and aldehydes into high-value-added nitriles. The key to this conversion lies in the pH swing effect within the catalytic system, through which hydroxylamine and NO₂ ^-, the semi-reduction products of NO₃ ^-, are generated at distinct pH levels. Hydroxylamine initially engages in a nucleophilic addition reaction with aldehydes to form aldoximes. The aldoximes were nitrated by NO₂ derived from NO₂ ^- and then spontaneously converted into nitrile oxides. The nitrile oxides ultimately undergo electrocatalytic hydrodeoxygenation to yield nitriles. Aliphatic, aromatic, and heteroaromatic aldehydes can be effectively transformed into corresponding nitriles. This research offers novel perspectives and valuable insights for the high-value utilization of nitrate.