R. Bhat et al., NICKEL ION-EXCHANGED ZEOLITE-4A - REDUCTION BEHAVIOR OF NICKEL AND STRUCTURE STABILITY, Journal of the Chemical Society. Faraday transactions, 91(21), 1995, pp. 3983-3986
Citations number
24
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
The structural stability of ion-exchanged Ni-4A samples prepared at 25
and 90 degrees C was examined by thermogravimetric, X-ray diffraction
(XRD), degree of reduction and temperature-programmed reduction (TPR)
studies. The crystallinity of the zeolite-4A framework decreased with
an increase in the nickel loading and the temperature of ion-exchange
. The collapse of the structure is more significant in the reduced Ni-
4A samples. The TPR profile of the fresh Ni-4A samples showed a broad
reduction peak with a T-max at high temperatures, i.e. 480-500 degrees
C and 440-450 degrees C for Ni-4A (25 degrees C) and Ni-4A (90 degree
s C) samples, respectively. The T-max shifts to lower temperatures, i.
e. 380-400 degrees C, during the second reduction (of the oxide obtain
ed from the oxidation of the first reduced Ni-4A samples). After the s
econd reduction, the Ni-4A samples did not show sharp XRD peaks charac
teristic of nickel metal, which confirms the absence of migration of n
ickel to the external surface of the zeolite. At higher nickel loading
s, the reduction step favours partial structure collapse of zeolite 4A
, rather than promotion of the surface migration of nickel.