Linear Free Energy Relationships in heterogeneous catalysis: III. Temperature effects in dealkylation of alkylbenzenes on the cracking catalysts

Abstract

Temperature effects in the Linear Free Energy Relationships (LFER) for dealkylation of monoalkylbenzenes at the temperatures of 300 ° to 450 °C are discussed. The following δ R LFER equation is proposed with an adequate consideration of the reaction temperature, logK i( R 1 ,T) = logK i(0, ∞) − {γ′ i ΔH C + ( R 1 ) + E A,i (0)} 2.303RT . The rate constants of dealkylation at any temperature can thus be estimated with the knowledge of ΔH C + (R 1), the enthalpy change of hydride abstraction from the corresponding paraffin, and a few empirical constants independent of the reaction temperature. The applicability of the LFER is extended and the constants introduced for the LFER equation are determined more accurately from a set of rate data both at every reaction temperature and of every reactant with the aid of the multiple-variable nonlinear method of least squares. Activation energy is linearly correlated with ΔH C + (R 1) and its coefficient coincides with γ′ i of the δ R LFER equation, whereas the activation entropy of every reactant employed is constant within error. The following linear relationship is obtained among the activity of all catalysts in this work: log K i (R 1, T) = λ(R 1, T) log k i (i-Pr, T) + κ(R 1, T) This relationship, δ C effects, is derived from the δ R LFER. The compensation effect is observed among the catalysts, and discussed in connection with the δ C LFER.