ENCAPSULATION STUDIES OF HYDROGEN ON CADMIUM EXCHANGED ZEOLITE-RHO ATATMOSPHERIC-PRESSURE

Temperature programmed diffusion (TPDi) has been used to study the enc apsulation 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 5 0 degrees C and 1 atm. This amount is over 30 times the amount of hydr ogen encapsulated with NaX or NaA at 37 degrees C for the same time an d pressure. Upon increasing the encapsulation temperature to 100 degre es C, the amount encapsulated increased to 161 mu mol/g (2 h of encaps ulation). At 200 degrees C, the encapsulate is about 620 mu mol/g, for the same pressure and time. With increasing temperature, more than on e 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 d egrees C. Large encapsulated amounts of hydrogen arise from blocking e ffects caused by the presence of cations (cadmium and/or cesium). Expe riments for encapsulation of hydrogen on H-rho (hydrogen exchanged zeo lite rho) show negligible uptake of hydrogen, proving that the presenc e of either the cadmium ion (5.05 Cd2+ per unit cell) or the cesium io n (1.87 Cs+ per unit cell) or both is directly responsible for the enc apsulation of hydrogen. For encapsulation at 200 degrees C, possible m igration of the encapsulate among the sites seems to occur with encaps ulation time. This could explain the relative changes in the intensiti es of the 3 peaks in the TPDi spectra for the encapsulation at 200 deg rees C.