Study on the Mechanism and Kinetics of the Thermal Decomposition of Ni/Al Layered Double Hydroxide Nitrate

Abstract

In the paper, the mechanism and kinetics of thermal decomposition of Ni/Al layered double hydroxide nitrate with a Ni/Al molar ratio of 3.0 (NiAl-LDH) were studied by thermogravimetry/differential thermal analysis coupled with mass spectrometry (TG/DTA−MS). The results indicated that the thermal decomposition of NiAl-LDH proceeds in three individual processes, i.e., removal of the physisorbed and interlayer water, dehydroxylation of the layers, and decomposition of the interlayer nitrate ions (denitration). The mechanism and kinetics of dehydroxylation and denitration, which take place simultaneously almost in the same region of temperatures, were separately achieved by only using MS data sets recorded at different heating rates. The dehytroxylation follows a two-dimensional diffusion-controlled mechanism with instantaneous nucleation represented by the first-order Avrami−Erofe’ev equation with an average activation energy of ca. 129.0 kJ·mol−1, while the denitration obeys a three-dimensional diffusion-controlled mechanism represented by the Zhuralev−Lesokin−Tempelman equation with an average activation energy of ca. 137.2 kJ·mol−1.