Migration: A Neglected Potential Contribution of HCl-Oxidized Au(0)

Area of Science:

• Catalysis
• Surface Chemistry
• Materials Science

Background:

• Gold (Au) catalysts are crucial in various chemical reactions.
• Understanding the stability and reactivity of Au/C catalysts in acidic media like hydrochloric acid (HCl) is important.
• Standard electrode potentials do not fully explain the observed oxidation behavior of Au in HCl.

Purpose of the Study:

• To investigate the oxidation process of Au/C catalysts when exposed to HCl.
• To analyze the

Main Methods:

• X-ray Photoelectron Spectroscopy (XPS) for surface analysis.
• Controlled exposure of Au/C catalysts to HCl.
• Analysis of gold species and their migration within the carbon matrix.

Main Results:

• The observed oxidation of Au(0) species in Au/C catalysts by HCl is not a direct oxidation.
• Surface chlorination does not facilitate the oxidation of Au(0) or Au(I) to Au(III).
• The phenomenon is largely attributed to the migration of pre-existing Au(III) species from the carbon bulk to the surface.

Conclusions:

• The migration of gold species within the carbon support plays a significant role in the apparent oxidation of Au/C catalysts by HCl.
• This migration mechanism offers a new perspective on the reactivity of noble metals in acidic environments.
• The study challenges the direct oxidation model and highlights the importance of bulk-surface transport phenomena.