THE CHEMISTRY OF COKE DEPOSITS FORMED ON A PT-SN CATALYST DURING DEHYDROGENATION OF N-ALKANES TO MONO-OLEFINS

This work presents a detailed study of coke deposition on a Pt-Sn cata lyst under industrial conditions, The spent catalyst was submitted to Soxhlet extraction and the ''soluble coke'' was characterized by means of IR, UV and CC-MS. The catalyst before and after coke extraction wa s characterized by means of IR, carbon content and temperature-program med oxidation (TPO). Coke formation on the catalyst involves several p rocesses: (i) successive dehydrogenation/cyclization of alkyl chains ( polyene route); (ii) n-alkane oligomerization; (iii) Diels-Aldertype r eactions. The structure of insoluble coke is quite different from that of soluble coke: the elimination of the latter one causes disappearan ce of the low-temperature oxidation zone (TPO). Soluble coke contains dominant proportion of aliphatic groups whereas polyaromatic structure s predominate in insoluble coke.