Ding Mengning of Nanjing University and William of the California Institute of TechnologyGoddard et alA simple, green, and safe electrocatalytic pathway for the selective oxidation of amines to nitrile under mild conditions is reported on a metal-doped -Ni(OH)2, a typical catalyst for oxygen evolution reactions, and requires the assistance of anode H2O oxidation. By controlling the co-adsorption of amine molecules and the balance between hydroxyl groups on the surface of the catalyst, it was proved that the doping of MN significantly promoted the subsequent chemical oxidation of amines, and the Faraday efficiency of nitrile was 96% at 99% conversion rate.
Density functional theory (DFT) calculations elucidate the reaction mechanisms and pathways of amine and water oxidation. Considering the relatively large molecular size of benzylamine (Ba) and the similar R-CH2-NH2 structure, ethylamine was used as the model substrate in the calculations. The rate-determining step (RDS) in NIOOH-catalyzed OER is the formation of M-O bonds with radical characteristics on oxygen. For Mn-doped Niooh catalysts, the Mn-NiOH surface covered with 2 3 mLo and 1 3 MLO is the most stable equilibrium surface.
Similar to the case of NiOOH, for MN-doped NIOOH, the RDS of OER is the O radical formation step at the Ni site on the surface. Co, Ir, Rh, and Mn doping does not promote O radical properties, resulting in a reaction free energy (ΔGRDS) of RDS from 087EV increased to 130ev。
The introduction of amines into the system alters the reaction pathway due to the significantly greater adsorption energy of amine molecules (compared to water molecules) on Niooh or Mn-Niooh surfaces. Therefore, the δg for each step of the amine oxidation process is calculated, and RDS is the third deprotonation-oxidation step of NioOh.
The ΔG of the deprotonation step on the surface of the Mn-NiOH catalyst is significantly reduced due to the change in the amine adsorption site (from Ni to Mn), where the surface adsorption of OH (derived from part of the OER) on the adjacent Ni site contributes to and facilitates the amine oxidation process。As a result, RDS becomes the second H rearrangement step, which is thermodynamically more achievable. These results confirm that MN doping significantly promotes amine oxidation. Therefore, the presence of amine molecules on the surface inhibits the OER process and favors amine oxidation, and MN doping in NiOOH is an ideal catalyst for this process to inhibit OER activity while promoting amine oxidation.
yuxia sun, hyeyoung shin, et al. highly selective electrocatalytic oxidation of amines to nitriles assisted by water oxidation on metal-doped α‑ni(oh)2. j. am. chem. soc. (2022)