Toluene ethylation on ZSM zeolites

The activity and selectivity to para -ethyltoluene in toluene alkylation with ethanol have been correlated to the structural and morphological features of the ZSM-5 and ZSM-11 zeolites employed as catalysts. In particular, as the particle size increases and correspondingly the surface area outside the zeolite channels decreases, lower activities and higher para -isomer selectivities (up to 90%) are obtained. This behavior has been interpreted by supposing a two-step mechanism: in the first step, para -isomer forms by toluene alkylation with high selectivity inside the zeolitic channels (shape selectivity), while in the second step the isomerization toward the thermodynamic equilibrium of the three isomers proceeds just on the external surface