Evidence for the formation of stable CO2 hydrates in zeolite Na-Y: Structural characterization by synchrotron X-ray powder diffraction

Preferential adsorption of water is a major problem in the processes of CO2 adsorption on molecular sieves. Adsorption and desorption of CO2 on partially hydrated zeolite NaeY have been monitored by in situ synchrotron X-ray powder diffraction. The structural refinement of the CO2-saturated diffraction pattern highlighted the formation of tetrameric CO2 clusters connected by water bridges to the sodium cations of two adjacent faujasite supercages. The CO2 desorption was followed by collecting a series of diffraction patterns upon heating from room temperature up to 350 C. The hydrated CO2 clusters are completely desorbed between 250 C and 350 C. This high thermal stability suggests that the formation of hydrated complexes could represent a potentially important mechanism of retention of CO2 during the regeneration of CO2 adsorbents.