The in situ time-resolved analysis of Co-exchanged synthetic ferrierite was performed in the range 53-810 degreesC by Rietveld refinements of powder diffraction data. The small contraction of the unit cell volume (-2.35%) confirmed that the ferrierite framework behaves as a noncollapsible framework. Moreover, continuous monitoring of the structural modifications induced by heating showed that cobalt ions migrate to new positions following the dehydration process step by step. Above 500 degreesC, five cation sites were localized; four of these are readily accessible to absorbed molecules and act as Lewis acid sites.