Encapsulation studies of hydrogen on cadmium exchanged zeolite rho at atmospheric pressure

Temperature programmed diffusion (TPDi) has been used to study the encapsulation of hydrogen in cadmium exchanged Cs-rho zeolite. The amount encapsulated after 2 h has been observed to be about 71 mu mol/g at 50 degrees C and 1 atm. This amount is over 30 times the amount of hydrogen encapsulated with NaX or NaA at 37 degrees C for the same time and pressure. Upon increasing the encapsulation temperature to 100 degrees C, the amount encapsulated increased to 161 mu mol/g (2 h of encapsulation). At 200 degrees C, the encapsulate is about 620 mu mol/g, for the same pressure and time. With increasing temperature, more than one peak is seen in the TPDi spectra, revealing the availability of more than one site(1) for the encapsulation. 3 peaks are observed in TPDi spectra for the encapsulation at 200 degrees C - at 107, 295 and 345 degrees C. Large encapsulated amounts of hydrogen arise from blocking effects caused by the presence of cations (cadmium and/or cesium). Experiments for encapsulation of hydrogen on H-rho (hydrogen exchanged zeolite rho) show negligible uptake of hydrogen, proving that the presence of either the cadmium ion (5.05 Cd2+ per unit cell) or the cesium ion (1.87 Cs+ per unit cell) or both is directly responsible for the encapsulation of hydrogen. For encapsulation at 200 degrees C, possible migration of the encapsulate among the sites seems to occur with encapsulation time. This could explain the relative changes in the intensities of the 3 peaks in the TPDi spectra for the encapsulation at 200 degrees C.