In Situ Investigation of Charge Performance in Anatase TiO₂ Powder for Methane Conversion by Vis-NIR Spectroscopy

Area of Science:

• Photocatalysis
• Materials Science
• Chemical Kinetics

Background:

• Understanding the behavior of photogenerated charges and their reactions is crucial for optimizing photocatalytic processes.
• Observing these fundamental steps is essential for advancing photocatalysis research.

Purpose of the Study:

• To present a reliable system for monitoring basic steps in powder photocatalysts.
• To elucidate the key issues in photocatalytic methane conversion using titanium dioxide (TiO2).

Main Methods:

• Developed a robust system to monitor photoexcited charges and chemical reactions in powder photocatalysts.
• Utilized photoinduced absorption spectroscopy to analyze charge carrier behavior under excitation.
• Performed in situ measurements to investigate the initial steps of methane activation.

Main Results:

• Photoexcited electrons dominate absorption in the NIR region; photoexcited holes increase absorption towards shorter visible wavelengths.
• Direct evidence shows methane activation over TiO2 initiates with oxidation by photoexcited holes.
• Oxygen scavenges 90% of photoexcited electrons, while methane scavenges 61% of photoexcited holes, indicating higher oxygen reactivity.

Conclusions:

• Oxygen is more readily activated than methane on anatase TiO2, explaining the high methane/oxygen ratios used in practice.
• Methanol, a methane oxidation product, is more susceptible to oxidation than methane itself.
• The developed system provides insights into reaction mechanisms and catalyst efficiency.