CO₂ Desorbs Water from K-MER Zeolite under Equilibrium Control

Area of Science:

• Materials Science
• Chemical Engineering
• Physical Chemistry

Background:

• Established methods assume humid CO2 does not affect preadsorbed water in zeolites.
• Water adsorption is typically dominant over CO2 in zeolites under humid conditions.

Purpose of the Study:

• To investigate the competitive adsorption of CO2 and water in zeolites under humid conditions.
• To identify specific zeolite sites where CO2 can displace preadsorbed water.

Main Methods:

• Gravimetric techniques and diffuse reflectance infrared spectroscopy.
• Experiments conducted on small-pore zeolite K-MER and Cs-RHO at 30 °C and 5% relative humidity.

Main Results:

• CO2 adsorption caused 20% of preadsorbed water to desorb from K-MER zeolite.
• Diffuse reflectance IR spectroscopy revealed selective displacement of dimeric water species by CO2 in K-MER.
• No CO2-water competition was observed in Cs-RHO, despite weaker water binding.

Conclusions:

• CO2 displaces water in K-MER due to a highly preferred CO2 adsorption site, not weak water binding.
• This demonstrates CO2 can outcompete water in zeolites under specific humid conditions.
• Highlights the need for independent characterization of adsorbed water and CO2 in zeolite systems.