Ratio of the equilibrium and kinetic acidities of solid catalysts

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The feasibility of using the equation log k = const - H0s was examined for solid acid catalysts. Data for the thermoprogrammed dealkylation of cumene showed that the temperature dependence of the strength of the acid sites of the catalyst H0s(T) should be considered in calculating the coefficient . In this case, 1. However, as shown for the isomerization of o-xylene, dimerization of butylenes, dehydration of 2-propanol (2), and the dealkylation of cumene (3), the values found for coefficient are in the range 0.15-0.6 (4) and do not approach 1 as in solution. For example, in the cracking of cumene, an increase in H 0 by six leads to an increase in the rate constant k not by six orders of magnitude but only by a factor of 10. A possible explanation of the low values of is based on the assumption that a proton is not added to the adsorbed molecule but rather polarized hydrogen-bonded complexes are formed (4). In the present work, we have shown that catalytic reactions with proton transfer on the surface in the dealkylation of cumene on acid catalysts may be characterized by "normal" values of 1. In this case, the temperature dependence of the strength of the acid sites of the catalyst is taken into account. Equation (1) clearly reflects the relationship of the equilibrium and kinetic acidities of the catalyst sites and, thus, presupposes a reaction mechanism with consecutive formation of an adsorbed proton-transfer complex with equilibrium constant K s , a transition state with rate constant k, and the reaction products: