Catalytic cracking of n-hexane for producing propylene on MCM-22 zeolites

The catalytic cracking of n-hexane for producing propylene on MCM-22 catalysts was carried out as a model reaction of naphtha cracking. H-MCM-22 catalysts with different Si/Al ratios were prepared by direct or post-synthesis methods. The propylene selectivity was improved with an increase in the Si/Al ratio. Dealumination of H-MCM-22 with ammonium hexaflurosilicate (AHFS) (Del-Al-MCM-22) resulted in the increase in the catalytic life and propylene selectivity at a very high n-hexane conversion. This may be attributed to the decrease in the amount of Lewis acid sites which accelerate the hydride transfer and resultant coke formation. Del-Al-MCM-22 (Si/Al = 62) catalyst showed a high propylene selectivity (40 C-%) which was higher than H-ZSM-5 and H-Beta catalysts with similar Si/Al ratios at a high n-hexane conversion of 95%. Moreover, it showed a catalytic life comparable with H-ZSM-5 and longer than H-Beta catalyst.