How does CO capture process on microporous NaY zeolites? A FTIR and DFT combined study

Area of Science:

• Materials Science
• Surface Chemistry
• Physical Chemistry

Background:

• NaY faujasites are effective industrial adsorbents for gas separation and purification.
• Understanding CO adsorption mechanisms is crucial for optimizing adsorbent performance.
• Previous studies suggest CO capture involves Na+ cations in S(II) sites.

Purpose of the Study:

• To investigate the mechanism of CO adsorption on NaY faujasites using combined experimental and theoretical methods.
• To characterize the formation and spectral properties of polycarbonyl species.
• To explore the influence of framework composition on CO adsorption.

Main Methods:

• Infrared (IR) spectroscopy to experimentally observe CO adsorption.
• Density Functional Theory (DFT) calculations to model adsorption and predict spectral shifts.
• Investigation of varying Si/Al ratios in the faujasite framework.

Main Results:

• CO adsorption occurs via coordination to Na+ cations in S(II) sites, forming polycarbonyl species.
• Each additional CO molecule captured causes a distinct IR frequency down-shift (11-12 cm-1).
• DFT calculations accurately reproduce experimental IR shifts for mono-, di-, and tricarbonyl species.
• Framework composition (Si/Al ratio) influences the acidic strength of cationic sites, affecting polycarbonyl formation.

Conclusions:

• The study provides a detailed understanding of CO adsorption on NaY faujasites at 80 K.
• Experimental and theoretical data confirm the coordination mechanism and spectral signatures of CO adsorption.
• Findings contribute to the design and application of NaY faujasites in gas separation and purification processes.