Probing zeolites by vibrational spectroscopies

Area of Science:

• Materials Science
• Spectroscopy
• Catalysis

Background:

• Zeolites and zeotypes are crucial microporous materials in catalysis.
• Understanding their surface properties, such as acidity and basicity, is key to optimizing their performance.
• Vibrational spectroscopies offer powerful tools for probing these properties at an atomic level.

Purpose of the Study:

• To provide a comprehensive overview of vibrational spectroscopies (IR, Raman, INS) applied to zeolites and zeotype materials.
• To critically discuss the role of probe molecules in characterizing surface sites.
• To highlight quantitative and advanced experimental techniques for analyzing these materials.

Main Methods:

• Infrared (IR) spectroscopy
• Raman spectroscopy
• Inelastic Neutron Scattering (INS)
• Use of probe molecules with varying proton affinity and steric hindrance
• Variable-temperature studies
• Space- and time-resolved experiments

Main Results:

• Detailed analysis of surface Brønsted and Lewis acidity and basicity in zeolites.
• Demonstration of IR spectroscopy as a quantitative technique through precise absorption coefficient determination.
• Extraction of thermodynamic parameters for adsorption processes from variable-temperature IR studies.
• Review of advanced experimental techniques for in-situ and dynamic analysis.

Conclusions:

• Vibrational spectroscopies are indispensable for characterizing the complex surface chemistry of zeolites.
• Quantitative methods and advanced experimental setups enable a deeper understanding of zeolite active sites.
• Theoretical calculations are crucial for interpreting vibrational spectra and elucidating mechanisms at an atomic level.