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 δR LFER equation is proposed with an adequate consideration of the reaction temperature, log K i ( R 1 ,T) = log K i (0, ∞) − {γ′ i Δ H 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 ΔHC+(R1), 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 ΔHC+(R1) and its coefficient coincides with γ′i of the δR 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 Ki(R1,T) = λ(R1,T) log ki(i-Pr,T) + κ(R1,T) This relationship, δC effects, is derived from the δR LFER. The compensation effect is observed among the catalysts, and discussed in connection with the δC LFER.