A kinetic study of the nonisothermal decomposition of palladium acetylacetonate investigated by thermogravimetric and x-ray diffraction analysis determination of distributed reactivity model

Abstract

The nonisothermal decomposition process of the powder sample of palladium acetylacetonate [Pd(acac)2] was investigated by thermogravimetric (TG) and X-ray diffraction (XRD) techniques. The experimental TG and differential thermogravimetric (DTG) curves were obtained at different heating rates (β = 2 °C min-1, 5 °C min-1, 10 °C min-1, 20 °C min-1, and 30 °C min-1) under a pure nitrogen (N2) atmosphere. The kinetic triplet (A, E a, and model function f (α)) was determined using different kinetic methods. It was found that the apparent activation energy was not really changed and was almost independent with respect to the level of conversion (α). This result suggests that the nonisothermal decomposition process of palladium acetylacetonate follows a single-step reaction. Practically constant Ea values approximating 140.1 ± 1.5 kJ mol-1 were found. It was concluded that the reaction model R3, for the integral composite method I, is the model with the best regression and with kinetic parameters that are both unique and very similar to those obtained by the Friedman isoconversional method. In addition, it was found that the results obtained from both the Master-plot and Málek methods confirm the results obtained from the multiple-rate isotemperature method, specifically, that the R3 (contracting volume) reaction mechanism can best describe the investigated decomposition process. By applying the Miura procedure, a distributed reactivity model (DRM) for the investigated decomposition process was established. From the α = α (Ea) dependence, the experimental distribution curve of Ea was estimated. Using the nonlinear (NL) least-squares analysis, it was found that the Gaussian distribution model (with distribution parameters: E 0 = 138.4 kJ mol-1 and β = 0.71 kJ mol-1) represents the best reactivity model for describing the investigated process. Also, it was concluded that the Ea values calculated by the Friedman isoconversional method and the estimated distribution curve (f(Ea)), are correct, even in the case in which the investigated decomposition process occurs through a single-step reaction mechanism. © The Minerals, Metals & Materials Society and ASM International 2009.