Selectivity Modulation of Multistep Reduction Reactions by Gold Nanoclusters

Area of Science:

• Catalysis
• Materials Science
• Organic Chemistry

Background:

• Selective synthesis of azo- and azoxyaromatic compounds is crucial for various chemical industries.
• Traditional methods often involve multiple steps or harsh conditions.
• Controlling catalyst structure offers a promising route for targeted synthesis.

Purpose of the Study:

• To develop a direct method for selectively synthesizing azobenzene and azoxybenzene from nitroaromatic compounds.
• To investigate the effect of gold (Au) catalyst size on the selectivity of nitrobenzene reduction.
• To elucidate the structure-activity relationship governing the transfer coupling reaction.

Main Methods:

• Utilizing gold nanoclusters (NCs) and gold nanoparticles (NPs) embedded in ZIF-8 as catalysts.
• Employing X-ray photoelectron spectroscopy (XPS) and CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) for surface analysis.
• Performing Density Functional Theory (DFT) calculations to understand reaction mechanisms and adsorption energies.

Main Results:

• Au NCs/ZIF-8 selectively produced azoxybenzene, while Au NPs/ZIF-8 selectively produced azobenzene.
• Au NCs exhibited a higher valence state and lower electron density, leading to stronger adsorption of intermediates.
• DFT calculations confirmed higher adsorption energy of azoxybenzene on Au NCs, inhibiting further reduction.

Conclusions:

• The size of gold particles significantly influences the selectivity of nitrobenzene transfer coupling.
• Gold nanoclusters with controlled size and electronic properties can selectively yield azoxybenzene.
• This study provides valuable insights into catalyst design for selective organic synthesis.