An Ultrahigh CO₂-Loaded Silicalite-1 Zeolite: Structural Stability and Physical Properties at High Pressures and Temperatures

We report the formation of an ultrahigh CO₂-loaded pure-SiO₂ silicalite-1 structure at high pressure (0.7 GPa) from the interaction of empty zeolite and fluid CO₂ medium. The CO₂-filled structure was characterized in situ by means of synchrotron powder X-ray diffraction. Rietveld refinements and Fourier recycling allowed the location of 16 guest carbon dioxide molecules per unit cell within the straight and sinusoidal channels of the porous framework to be analyzed. The complete filling of pores by CO₂ molecules favors structural stability under compression, avoiding pressure-induced amorphization below 20 GPa, and significantly reduces the compressibility of the system compared to that of the parental empty one. The structure of CO₂-loaded silicalite-1 was also monitored at high pressures and temperatures, and its thermal expansivity was estimated.