An ex situ methodology for characterization of coke by TGA and 13C CP-MAS NMR spectroscopy

A new methodology is reported for the comprehensive characterization of carbonaceous deposits (cokes) formed during hydrocarbon conversions over zeolite catalyst. Different boiling fractions of the carbonaceous deposits are successively removed by vacuum evacuation at selected temperatures. The nature and relative distribution of the carbonaceous residues are analysed by C-13 CP-MAS NMR spectroscopy and thermogravimetric analysis. The methodology is tested on two catalytic reactions on zeolite H-USY catalyst: Ethylbenzene disproportionation and n-heptane cracking. For the former, the carbonaceous deposits mainly consist of retained reactant ethylbenzene, product diethylbenzene (DEB) isomers and alkyl polyaromatic compounds. For the latter, in addition to the retained reactant iz-heptane, the major constituents of the carbonaceous deposits are methyl polyaromatic compounds. (C) 1997 Elsevier Science B.V.