TEXTURE, ELECTRON-ACCEPTOR, ACID-BASE, AND CATALYTIC PROPERTIES OF MODIFIED ZEOLITES OF ZSM-5 TYPE .3. STUDY OF THE PROCESS OF COKE FORMATION

Zeolites of the HZSM-5 type (SiO2/Al2O3 = 32, 40, 48, 55, 66, and 840) , both the parent form and those modified by tetraethoxysilane, were c oked by p-xylene or n-hexane treatment during ethylbenzene disproporti onation and studied by DTA-DTG and ESR spectroscopy. The sites on the outer surface of zeolites under investigation do not contribute to cok ing, at least, formation stage of low-condensed coke located inside ze olitic channels. The formed coke is not uniform: the polycondensed par t of coke is deposited on the outer surface and the oxygen from the ga s phase promotes its formation. We assume that only a small part of bo th acidic sites and sites of one-electron transfer takes part in the c oking of all the samples differing in the SiO2/Al2O3 ratio.