Characterization of Modified Nanoscale ZSM-5 Zeolite and Its Application in the Olefins Reduction in FCC Gasoline

Abstract

Nanoscale HZSM-5 zeolite was hydrothermally treated with steam containing 0.8 wt% NH₃ at 773 K and then loaded with La₂O₃ and NiO. Both the parent nanoscale HZSM-5 and the modified nanoscale HZSM-5 zeolites catalysts were characterized by TEM, XRD, IR, NH₃-TPD and XRF, and then the performance of olefins reduction in fluidized catalytic cracking (FCC) gasoline over the modified nanoscale HZSM-5 zeolite catalyst was investigated. The IR and NH₃-TPD results showed that the amount of acids of the parent nanoscale HZSM-5 zeolite decreased after the combined modification, so did the strong acid sites deactivating catalysts. The stability of the catalyst was still satisfactory, though the initial activity decreased a little after the combined modification. The modification reduced the ability of aromatization of nanoscale HZSM-5 zeolite catalyst and increased its isomerization ability. After 300 h onstream, the average olefins content in the gasoline was reduced from 56.3 vol% to about 20 vol%, the aromatics (C₇–C₉ aromatics mainly) and paraffins contents in the product were increased from 11.6 vol% and 32.1 vol% to about 20 vol% and 60 vol% respectively. The ratio of i-paraffins/n-paraffins also increased from 3.2 to 6.6. The yield of gasoline was obtained at 97 wt%, while the Research Octane Number (RON) remained about 90.