A mechanistic investigation and kinetic analysis of the thermal decomposition of diammonium hexanitrato cerate catalysed by CdxCo1−xFe2O4 catalysts

The isothermal and non-isothermal decomposition of pure diammonium hexanitrato cerate(IV) and its mixtures with 10% (wt/wt) of Cd(x)Co(1-x)Fe2O4 catalysts (x = 0.0, 0.5 and 1.0) were investigated. The effect of catalyst additives on the kinetics of isothermal decomposition of the parent salt was also studied. Their isothermal curves of fraction decomposed (alpha) against time were sigmoid in nature and the decomposition reaction in the presence of these catalyst additives obeys the Avrami-Erofe'ev equation. Such catalytic pretreatment reduced the induction period to the onset of the reaction decomposition. From the complementary consideration of microscopic observations and kinetic evidence, we conclude that the thermal decomposition of the parent salt in the presence of these catalyst additives, in the temperature range 250-325-degrees-C, proceeds by the nucleation-and-growth mechanism. The promotional effect of the catalysts used was also described. It can be stated that the activity of these catalysts in promoting salt breakdown is a consequence of their appreciable solubility in the parent salt and that the chemistry of the reaction in such conditions is complicated. It involves several participants, including the unstable ammine complexes of both Cd and Co ions, located in the octahedral sites of the catalysts, formed as intermediates of the type [M(NH3)6]2+.