77 and 300 K in situ Mossbauer spectra recorded after redox treatments of Fe-FER and Fe-MFI ferrisilicates are compared. Similar behavior is found for the two catalysts; reversible redox processes can be detected. Oxidation and coordination states are identified after various treatments, and the value of the average Debye temperature is estimated (260 < Theta(D) < 300 K). Analysis and comparison of data support the assignment of redox centers to Fe-framework-O-Feextra-framework pairs.