Structural stability and adsorption behaviour of CO2-loaded pure silica CHA and ITW zeolites upon compression

Abstract

The present study investigates the structural stability and adsorption behavior of ultrahigh CO₂-loaded pure-silica zeolites chabazite (CHA) and ITQ-12 (ITW) under high pressure conditions. To analyze these properties, we have utilized in situ synchrotron-based X-ray powder diffraction techniques. Lattice indexation provides information of the filling process and, through Rietveld refinements and Fourier recycling methods, we have been able to (i) determine the location and amount of guest carbon dioxide molecules within the cavities of pure-SiO₂ CHA zeolite and (ii) tentatively determine that within the channels of the porous pure-SiO₂ ITW framework. The filling of the zeolite pores with CO₂ molecules was found to have a positive impact on the structural stability of both CHA and ITW under compression, which do not undergo pressure-induced amorphization up to 12.2 GPa and 15.9 GPa, respectively. Interestingly, low compressibility takes place in CHA zeolite below 4 GPa during CO₂ loading and a second-order phase transition occurs in CO₂-filled ITW zeolite at 2.1 GPa. These results highlight the influence of CO₂ adsorption on the compressibility behavior of these zeolites. Overall, our study provides detailed insights into the structural behavior of CO₂-loaded CHA and ITW under high pressure and allows comparison with other pure silica zeolites described in the literature.