Argon Adsorption on MCM-48 Mesoporous Crystal Studied by In Situ Synchrotron Powder X-ray Diffraction

The structure of the silica mesoporous crystal MCM-48 and the argon adsorption process were studied by in situ synchrotron powder X-ray diffraction (XRD). The diffraction intensity data were analyzed using the maximum entropy method (MEM). The Ar adsorption process within the mesopores was directly monitored through changes in the electron density distribution in the sample. The diffraction patterns clearly reflected different stages of adsorption as the gas pressure increased: gradual formation of an adsorbed film on the pore walls at low pressures, followed by stepwise pore filling due to capillary condensation. The real-space imaging of diffraction data presented in this paper is a robust and promising approach for improving our understanding of gas–solid interactions during adsorption and for characterizing the pore structures of mesoporous crystals.