Formation of surface barriers on silicalite-1 crystal fragments by residual water vapour as probed with isobutane by interference microscopy

In the framework of this study and for the very first time interference microscopy has been applied to examine molecular uptake and release on only one segment rather than on the whole unity of an MFI crystal. We performed subsequent cycles of uptake/release of isobutane in/from the fragments and recorded the evolution of the intracrystalline concentration profiles. The measurements exhibit perfect reproducibility and show that the overall process is dominated by intracrystalline diffusion. Most remarkably, under the presence of even traces of spurious water molecules inside the sorption vessel, with increasing cycle numbers uptake and release are progressively controlled by resistances on the crystal surface, indicating the formation of surface barriers.