TEXTURE, ELECTRON-ACCEPTOR, ACID-BASE, AND CATALYTIC PROPERTIES OF MODIFIED ZSM-5-TYPE ZEOLITES .4. CATALYTIC ACTIVITY IN ETHYLBENZENE DISPROPORTIONATION

The reactions of ethylbenzene and toluene disproportionation are studi ed under flow conditions on ZSM-5-type zeolites with SiO2/Al2O3 ratios of 32, 48, 66, and 840 calcined at 500 and 800 degrees C (nonmodified and modified catalysts). The data obtained are considered together wi th the acidic properties of the zeolites. It is shown that the formati on of p- and m-isomers of diethylbenzene and benzene proceeds on Brons ted acid sites, whereas modification of the zeolites substantially imp roves the para-selectivity. The high-temperature calcination of the sa mples (800 degrees C) is accompanied by a decrease in the concentratio n of Bronsted acid sites and, accordingly, by a diminution of the spec ific activity (rate per 1 g of a zeolite) in the disproportionation re action. The specific rates per one active site are analyzed in terms o f the changes in the nature of active sites, depending on the modifica tion and calcination temperature. The reasons behind the high para-sel ectivity in the reaction of ethylbenzene conversion and the low para-s electivity in toluene transformations are discussed in detail.