A kinetic study of the thermal degradation of ammonium species inside a 3D zincophosphate

Abstract

Ammonium ions remain inside the 3D zincophosphate framework after the hydrothermal crystallization. These species in co-operation with sodium cations exert a specific templating role in the formation of the open-framework lattice. The decomposition of the ammonium species under non-isothermal conditions has been studied by the non-parametric kinetics (NPK) method. The process is characterized by a complex kinetic mechanism and a relatively high activation energy for the main reaction step, E a = 336 kJ/mol. These reflect the fact that the decomposition of the ammonium ions inside the zincophosphate framework involves not only the diffusion of the liberated species through the narrow channels of the microporous framework but also a prior overcoming of strong electrostatic interactions and the breaking of hydrogen bonds.