Surface chlorination of IrO2(110) by HCl

Area of Science:

• Surface Science
• Catalysis
• Materials Chemistry

Background:

• Controllable surface chlorination of metal oxides is key for designing selective oxidation catalysts.
• Iridium dioxide (IrO2) is a promising material for catalytic applications.

Purpose of the Study:

• To investigate the surface chlorination of IrO2(110) using hydrochloric acid (HCl).
• To understand the resulting surface species, reaction pathways, and coverage limits.
• To explore the potential for modifying IrO2 surface reactivity for enhanced catalysis.

Main Methods:

• Temperature Programmed Reaction Spectroscopy (TPRS) to analyze desorption products.
• X-ray Photoelectron Spectroscopy (XPS) to determine surface composition and chemical states.
• Density Functional Theory (DFT) calculations to predict reaction barriers and energetics.

Main Results:

• HCl exposure and heating to 650 K on IrO2(110) yields both on-top (Clt) and bridging (Clbr) chlorine atoms.
• Bridging chlorine atoms replace surface oxygen atoms, forming water (H2O).
• Saturation chlorine coverage is limited to 1 monolayer (ML) due to competing HCl and H2O desorption, below the thermodynamic maximum.
• Chlorine partitioning between Clt and Clbr states is tunable via reductive/oxidative treatments.

Conclusions:

• Surface chlorination of IrO2(110) by HCl results in a dynamic Cl site population.
• Understanding these chlorination dynamics is crucial for tailoring IrO2 reactivity.
• This work provides foundational insights for developing IrO2-based catalysts for selective partial oxidation chemistry.