The catalytic cracking of arènes on SiO2–AlPO4 catalysts. A study of the mechanism

Abstract

The catalytic protodealkylation mechanism of arenes (R—Ph), using a SiO2–AlPO4 catalyst has been studied using the microcatalytic pulse technique. Two hydrocarbon series were used: normal series (R = Me, Et, n-Pr, and n-Bu) and α-methylated series (R = Me, Et, i-Pr, and t-Bu). In all cases it was shown that the process may be described by means of Bassett–Habgood's kinetics. That is to say, the process is a first order reaction (r = kPHC) where the rate-controlling step is the surface reaction.Real activation energies of the superficial process have been determined, all results showing values of the same order within the experimental error, which indicates that the transition state is the same for all alkylbenzenes because all the kinetics are first order.Correlations between kinetic constants and electrical (σ*) and steric (Es) parameters have been sought. The best are obtained when values for the α-methylated series are plotted against σ* and those for the normal series against Es.A possible reaction pathway of the SE2 (Ad–E) type is proposed.