Next, we turned our attention to zirconia. Consistent sigmoidal decomposition kinetics were observed under all reaction conditions investigated. Therefore, we fitted the data with the FW model, thus extracting k 1 and k 2 . With increasing temperature, the induction delay visibly shortens (Figure ) and both rate constants increase, following Arrhenius type behavior (see Table and Figures and). At 300 • C, we varied the amount of TOPO, taking either 2, 4, 6 or 11.4 equivalents, see Figure and Table . Although one expects the same stabilizing effect of TOPO on the transition state for the decomposition of zirconium isopropoxide as observed for titanium (Scheme 1), this should only affect k 1 since k 2 reflects the auto-catalysis by a reaction product. While there appears to be the expected trend for k 1 in the formation of zirconia (Table ), the large errors on the fitted values do not allow for a strong conclusion. This is likely because the effect of TOPO on k 1 is small, as is also the case for titania: the initial rate only increased by a factor of 2 when the amount of TOPO was increased from 2 to 11.4 eq. Nevertheless, in stark contrast to titania, TOPO clearly slows down the overall reaction rate and this is reflected in a decreasing k 2 with the TOPO amount, see Figure (note the logarithmic y-axis). We infer that TOPO binds to the product that is capable of auto-catalysis. We thus adapted the FW 2-step model by adding a third step where the catalyzing reaction product (B) reversibly binds to TOPO. A