NO2 disproportionation for the IR characterisation of basic zeolites

Area of Science:

• Heterogeneous catalysis
• Surface chemistry
• Zeolite science

Background:

• Alkaline zeolites are crucial catalysts in various chemical reactions.
• Understanding surface species formed during NO2 interactions is vital for catalytic processes.
• Nitrogen dioxide (NO2) disproportionation is a key reaction pathway in NOx chemistry.

Purpose of the Study:

• To investigate the disproportionation of NO2 on alkaline zeolites.
• To identify the surface species generated, specifically nitrosonium (NO+) and nitrate ions.
• To correlate observed infrared vibrations with zeolite properties like cation hardness and oxygen basicity.

Main Methods:

• Exposure of alkaline zeolites to NO2 gas.
• In-situ infrared spectroscopy to monitor surface species.
• Analysis of vibrational frequencies to characterize nitrosonium and nitrate ions.

Main Results:

• Successful generation of nitrosonium (NO+) and nitrate ions on the zeolite surface via NO2 disproportionation.
• Observed infrared vibrations are highly sensitive to the chemical hardness of the cations within the zeolite.
• Infrared spectra demonstrate a clear correlation with the basicity of the zeolitic oxygen atoms.

Conclusions:

• Alkaline zeolites effectively mediate NO2 disproportionation to form NO+ and nitrate.
• Cation chemical hardness and zeolite oxygen basicity are critical factors influencing the surface species and their vibrational characteristics.
• Infrared spectroscopy provides a powerful tool for probing the electronic and structural properties of zeolite-surface interactions.