Abstract: The effect of liquid modification on the HZSM-5 zeolite for the xylene isomerization using alkaline reagents and fluorine-containing reagents (ammonium fluoride) was conducted; the modified samples were characterized by NH3-TPD, BET, XRD and XRF techniques. The isomerization performance was evaluated by de-ethyl type xylene isomerization reaction. The changes of morphology after modification by both reagents were observed. The alkali modification increases the surface roughness, lowers the Si/Al ratio due to removing the Si atoms selectively, resulting in more amount of acid; while for fluoride modified samples, some nano-scale microcrystalline clusters appear on the modified surface, ammonium fluoride modification has no selectivity for silicon removal, but the amount of acid is significantly reduced. The isomerization activity and xylene yield are improved by the alkali modification, indicating the better catalytic performance than the fluoride modification.

Key words: ZSM-5 molecular sieve, alkali modification, ammonium fluoride modification, xylene isomerization