Compensation effects and compensation defects in kinetic and mechanistic interpretations of heterogeneous chemical reactions

Abstract

A case is presented for kinetic compensation effects (KCEs) reported for sets of heterogeneous rate processes to be classified. Because many of these KCEs do not conform to the ideal of isokinetic behavior, a quantitative method for describing the degree of compensation (κ) is introduced. In the case of solid-promoted catalytic reactions, it is suggested that (unlike simple homogeneous reactions) the effective concentrations and dispositions of surface intermediates can vary with temperature. Thus, the rate constants vary differently with temperature for the individual reactions of a set and, thereby, influence apparent magnitudes of the measured Arrhenius parameters. As a consequence, compensation is observed for sets of chemically related reactions occurring within a common temperature interval. KCEs are thus linked to mechanistic information and, depending on the magnitude of κ, for identifying shared features of catalytic rate controls. In this respect, the classification of KCEs is useful and can be based on similarities or differences between the reactants, catalysts, or experimental conditions in a given set of measurements. These ideas are demonstrated for selected sets of catalytic reactions. KCEs reported from a range of thermal decompositions of solids are also discussed. It is argued that, for mathematical as well as term definition reasons, compensation in this type

Evaluation by thermogravimetry of the interaction of the poly(ethylene terephthalate) with oil-based paint

“…Therefore, in this study, it was verified that the amount of mass of PET in the increased up to a limit of 1% limit. The decomposition reaction mechanism for all the samples was the same, as is observed from the sloped straight line for the relationship between ln A and E a [27][28][29][30][31][32][33]. …”

Kinetic compensation effects observed during oxidation of carbon monoxide on γ‐alumina supported palladium, platinum, and rhodium metal catalysts: Toward a mechanistic explanation

“…This suggests that there may exist a single theoretical explanation capable of accounting for all instances of compensation behavior, irrespective of circumstances. However, given the wide range of reaction types and experimental conditions for which KCEs have been reported, an alternative view, that compensation may appear for several distinct and different reasons, has already been suggested [13,14]. This approach is further explored in the present work, from which it is concluded that the introduction of the (new) concept of a "degree of compensation" is a useful aid in the recognition and classification of KCEs.…”

Kinetic characterization of multistep thermal oxidation of carbon/carbon composite in flowing air

“…This trend well describes the temperature region of the respective reaction steps, which is higher for the second reaction steps. The A i values of each reaction step vary with the change in the E a,i values, suggesting the possible behavior of the kinetic compensation effect, which is an empirical linear relationship observed between E a and ln A [66,67]. Although it is a somewhat qualitative comparison because of the different kinetic model functions used for the evaluation of the Arrhenius parameters, the Arrhenius plots drawn using the optimized Arrhenius parameters of the first and second reaction steps of each sample and also those of the different samples in each reaction step were compared (see Figures S11 and S12 in Supplementary Material).…”