Kinetics of Cu–Zn–Al Hydrotalcite Reconstruction Using a Modified Avrami–Erofeev Model: Preliminary Insights

Hydrotalcites exhibit the well-known phenomenon of spontaneously recovering their original structure upon calcination, in water (liquid or gas) or in the presence of exchangeable anions. In this work, we studied the reconstruction kinetics of a calcined Cu–Zn–Al hydrotalcite under moisture at room temperature. This material is of industrial importance in catalysis. Its reconstruction aids in simulating the handling, transportation, and storage under wet conditions of the manufactured calcined hydrotalcite─whether it changes and how fast. The calcined hydrotalcite was exposed to controlled moisture conditions, and the XRD patterns were measured over time. The degree of reconstruction was calculated using silicon as an internal standard in the XRD measurements. Raw data showed an unusual behavior with an apparent induction time. Initially, the induction time was ignored in the kinetic model (Avrami–Erofeev) to assess whether these particular data were relevant within the whole data set. Conventional Sharp–Hancock linearization of the Avrami–Erofeev model gave good R2 and mean squared error (MSE) values. However, the residual analysis and standard error failed, indicating that the induction time might be meaningful. A modified Avrami–Erofeev model accounting for the induction time was then considered. To implement this, multiparameter nonlinear fitting with least-squares minimization using Python code (unconstrained Levenberg–Marquardt algorithm) was employed. The modified model showed excellent fitting parameters (R2, MSE, standard errors and residuals), and it predicted the induction time consistent with the experimental data. Some mechanistic aspects were discussed.