C-14 studies in xylene isomerization on modified HZSM-5

Deposition of carbonaceous residues and tetraethoxysilane has been used to passivate the external surface of nano-sized HZSM-5. Using a real C 8 aromatic feedstock, both modification methods let to a reduction of xylene loss during xylene isomerization, i.e., a decrease in undesired disproportionati...

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Bibliographic Details
Published in:Applied catalysis. A, General General, 2005-08, Vol.289 (1), p.2-9
Main Authors: Bauer, Frank, Bilz, Evelin, Freyer, Annette
Format: Article
Language:English
Subjects:
Catalysis
Chemistry
Exact sciences and technology
General and physical chemistry
HZSM-5
Ion-exchange
Pre-coking
Silanization
Surface modification
Surface physical chemistry
Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
Xylene isomerization
Zeolites: preparations and properties
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Summary:Deposition of carbonaceous residues and tetraethoxysilane has been used to passivate the external surface of nano-sized HZSM-5. Using a real C 8 aromatic feedstock, both modification methods let to a reduction of xylene loss during xylene isomerization, i.e., a decrease in undesired disproportionation reactions yielding toluene and trimethylbenzenes. The higher performance obtained for the pre-coked sample can be explained by a more efficient deactivation of strong external acid sites. The effect of surface modification on reaction mechanism was studied by using C-14-labeled toluene and ethylbenzene. At low ethylbenzene conversion, transalkylation reactions forming ethylmethylbenzene have been observed, whereas at higher conversion the additional build-up of aromatics from the ethyl group (splitted off during dealkylation) can be revealed by Radio-HPLC data. Experiments with C-14-labeled toluene confirm a supplementary bimolecular pathway of xylene isomerization via transmethylation reactions, which are assumed to take place predominantly on the external surface of medium-pore zeolite ZSM-5.
ISSN:0926-860X
1873-3875
DOI:10.1016/j.apcata.2005.04.008