Dehydrated and Cs + -Exchanged MFI Zeolites: Location and Population of Cs + from In Situ Diffraction Data as a Function of Temperature and Degree of Exchange

H-MFI type zeolitic materials of different Si/Al ratios have been completely or partially cesium-exchanged (cesium content ranging from 0.7 to 7.7 Cs/unit-cell (uc)). Examined with synchrotron X-ray powder diffractometry, an anhydrous sample with the Cs6.6H0.3Al6.9Si89.1O192 chemical composition revealed at ambient temperature the presence of five discrete Cs locations:  Cs1 located in the channel intersection near a 10-ring window of the zigzag channel; Cs2 and Cs2‘, both located in the straight channel but 1.23 A apart; Cs3 and Cs3‘, both located in the zigzag channel and rather close to each other (2.51 A). The populations of the Cs species amounted to 2.61/0.81/1.85/0.86/0.47/uc for Cs1/2/2‘/3/3‘, respectively. The continuous but multimodal nature of the C2 split site is well-described by a joint-probability density function. The 10-ring of the straight channel in the framework is highly elliptical (e = 1.218). The populations for the same sites were also determined at higher temperatures:  131, 237, ...