Isobutane/1-butene Alkylation Performance of Ammonium Fluoride-Modified HUSY Zeolite

Abstract: A series of modified HUSY zeolites were prepared by immersing with different concentration of NH₄F solution at low temperature, and their catalytic performance for isobutane/1-butene alkylation reaction was investigated. The physicochemical properties of modified catalysts were characterized by XRD, N₂ adsorption–desorption isotherms, ICP, pyridine-IR and SEM. The results indicated that HUSY zeolite with higher Si/Al ratio is more sensitive to NH₄F leaching, resulting in more severe structural amorphization. NH₄F modification affects not only the pore structure but also the acid properties. The amount of Lewis acid sites on the modified zeolites was reduced and the ratio of Brønsted/Lewis acid sites was significantly enhanced in comparison with that of parent zeolite. Such properties of modified zeolites account for the superior performance for isobutane/1-butene alkylation. The initial C8 selectivity was increased to 74 wt% over the modified HUSY (Si/Al = 2.7) zeolite using 5 wt% NH₄F solution, which was about 15 wt% higher than that achieved on the HUSY parent. TG and in situ IR analyses of the deactivated catalyst indicated that some deposits were formed on the catalyst and the alkylation activity could be restored by regeneration at suitable conditions (520 °C under air atmosphere). Graphic Abstract: [Figure not available: see fulltext.].