INVESTIGATION OF THE ZEOLITE CATALYZED ALKYLATION OF TOLUENE USING C-13 NUCLEAR MAGNETIC-RESONANCE

The role of alkali metal cation exchange in the catalytic synthesis of styrene monomer from methanol and toluene over X-type zeolites has been investigated by 13C NMR. Catalytic materials were examined with respect to both their physical and chemical interactions with various substrates. The replacement of sodium cations by cesium alters the distribution of methanol thermolysis products and enhances the yield of styrene and ethylbenzene via a restricted transition-state selectivity. As identified from the 13C NMR spectra, the predominant reaction of the NaX is the dehydration of methanol to dimethyl ether followed by aromatic substitution on the toluene to yield undesirable ring alkylation byproducts. Cracking competes favorably with dehydration on the CsX, thereby reducing the yield of dimethyl ether. The restricted mobility of aromatic adsorbates on the CsX, as indicated by the NMR line shape, suggests that ring alkylation is hindered by the presence of cesium cations in the adsorption cavity which sterically restrict the formation of transition states which lead to these products. © 1979, American Chemical Society. All rights reserved.