Shape selective reactions with zeolite catalysts III. Selectivity in xylene isomerization, toluene-methanol alkylation, and toluene disproportionation over ZSM-5 zeolite catalysts

Abstract Data are presented for para-selective and nonselective formation of xylenes from alkylation of toluene with methanol and toluene disproportionation over ZSM-5 class zeolite catalysts. Possible mechanisms leading to para-selectivity are discussed. Isomerization of the pure xylene isomers has been used as a mechanistic probe. Distinctly different reaction paths (i.e., isomer composition curves) for xylene isomerization have been observed for para-selective in comparison to nonselective catalysts. Reaction paths followed by the para-selective catalysts are probably a consequence of diffusional effects possibly superimposed on the sterically altered intrinsic kinetics, both of which favor formation of the more rapidly diffusing para isomer.