Isoconversion method

For lifetime determination, the jump method is described by Flynn JH, Dickens B (1976) Thermochim Acta 15 1-16. The isoconversion method, by Ozawa T (1965) Bull Chem Soc, Japan 38 1881-1886. 

In order to find points of equal degrees of conversion (or equal Q-values) in Figure 2.18, van Geel [115] developed the method to evaluate kinetic data from the so-called isoconversion lines. A heat generating substance that follows Equation (2-11), when stored under isothermal conditions at different temperatures has generated an equal amount of heat (Q) when the product of t exp(-Ea/RT) has the same value. Thus, for two heat generation/time curves measured at Ti and T2, the same amount of heat (Q) has been generated, and thus the conversion is equal when ... 

The second method makes use of data on mass loss, collected in a series of different constant-heating-rate experiments as outlined in Fig. 4.198 for polystyrene. Isoconversion occurs at different temperatures for different heating rates. As one reaches the point of isoconversion, the integrated, mass-dependent functions f(p) must be identical. Thus, one has again achieved information about k(T) at different temperatures. Naturally this analysis is only valid if the kinetics has not changed over the range of temperature and conversion. 

Various Nb containing catalysts were also studied for the ODH of propane. Smits and coworkers [61] observed that niobium oxide shows a very high selectivity in this reaction although the conversion was very low. The activity of the Nb containing catalysts was improved without diminishing its selectivity by adding elements, such as V, Cr, or Mo, all of which are reducible transition metals. For a series of V-based catalysts and at isoconversion levels ( 30% conversion), the propene selectivity for 1 1 Nb-V and Sb-V catalysts was 20 and 40%, respectively. The 1 1 Sb-V and 1 1 5 Nb-V-Si prepared via the nonhydrolytic method offer the best results in terms of propane conversion and propene yield. With the 1 1 5 Nb-V-Si catalysts the propene productivity of 0.23 kg of propene per kilogram of catalyst per hour was achieved at 823 K [62]. 

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