Unconventional Inverse Size-Effects Enable Efficient C-N Coupling on Copper Electrocatalysts.

Area of Science:

• Heterogeneous electrocatalysis
• Organic synthesis
• Materials science

Background:

• Coordinatively unsaturated sites (CUS) on catalysts usually enhance electrocatalytic performance with decreasing size.
• This size-effect may not apply to electrocatalytic C-N coupling reactions, such as oxime synthesis.
• Understanding catalyst-intermediate interactions is crucial for optimizing reaction pathways.

Purpose of the Study:

• To investigate the size-effect of copper (Cu) nanocatalysts in the electrocatalytic synthesis of benzaldehyde oximes (BAO).
• To explore the mechanism behind the observed size-effect in C-N coupling reactions.
• To demonstrate a versatile electrosynthesis strategy for various oximes.

Main Methods:

• Electrocatalytic synthesis of BAO from nitrates and benzaldehyde using Cu nanocatalysts of varying sizes and Cu foil.
• Analysis of reaction intermediates and over-reduction pathways.
• Characterization of catalyst properties, focusing on exposed CUS.

Main Results:

• An inverse size-effect was observed: smaller Cu nanocatalysts with more CUS led to lower BAO yields due to over-reduction.
• Cu foil, possessing fewer CUS, effectively suppressed over-reduction, enabling the accumulation of key intermediates (*NH2OH and *Ph-CHO).
• A high BAO yield of 91% was achieved on Cu foil, demonstrating the efficacy of minimizing CUS for this reaction.

Conclusions:

• The conventional size-effect is unsuitable for electrocatalytic C-N coupling; an inverse size-effect is operative.
• Minimizing coordinatively unsaturated sites (CUS) on Cu catalysts is key to enhancing BAO yield by preventing over-reduction.
• This study provides insights into catalyst design for electrocatalytic C-N coupling, highlighting the potential of inverse size-effects.