Kinetic study of the low temperature transformation of Co(HCOO) [(CH)NH]

The conventional model-fitting approach assumes a fixed mechanism throughout the reaction and extracts a single value of the apparent activation energy and pre-exponential factor. This approach was found to be too simplistic because the values of Arrhenius parameters obtained in such a way are an average that does not reflect changes in the reaction mechanism and kinetics with the extent of conversion. In this work, kinetic analysis of a low temperature solid-state phase transformation observed in a metal organic framework is performed on differential scanning calorimetry (DSC) data obtained from Co(HCOO)[(CH)NH]. The approach used here consists of fitting a mathematical expression without caring of its physical meaning. An important feature of this model is that allows for heat capacity baseline subtraction. Once the proposed model resulted to mathematically explain the curves obtained at three cooling rates for the extent of conversion, a physical meaning was investigated by testing how some physical assumptions match the mathematical model. In the end, non-Arrhenius kinetics was found, which is consistent with the experiments performed at three cooling rates and which makes use of a limited number of physical parameters: the ideal thermodynamic equilibrium transformation temperature, an energy barrier parameter, the peak temperature, and an asymmetry factor, which in this case is dependent on the cooling rate. © 2011 American Chemical Society.