Abstract
Metal-ion-exchanged Y zeolites are a promising adsorptive desufurization (ADS) adsorbent. However, the ADS performance is inhibited significantly by diffusion limitations of sulfur compounds in micropores, especially when refractory sulfur compounds are present in fuels. The aim of this work was to develop a novel highly active, hierarchically structured bimetal Y zeolite and to evaluate the role of mesopores on the ADS performance from fuel oils that contained large amounts of competitors. A mesoporosity was introduced in the NaY by a top-down approach (sequential dealumination–desilication). A hierarchically structured zeolite meso-AgCeY was synthesized by introducing metals, Ag and Ce, by liquid-phase ion-exchange. The prepared meso-AgCeY was characterized and evaluated in terms of ADS performance using gasolines that contained different-sized sulfides and different amounts of toluene or cyclohexene. The adsorption strength was determined by the isosteric heat of adsorption calculations. The mesopores centered around 4–30 nm was obtained for meso-AgCeY, with the preservation of the original zeolite structure. Mesopore introduction suppressed the diffusion limitation of sulfur compounds effectively. In addition, transition metal Ag and rare earth metal Ce cations, which can bind organic sulfur compounds through π-complexation and sulfur-metal interaction, respectively, provided the meso-AgCeY with a high ADS performance. The meso-AgCeY showed a thiophene ADS capacity of 4.4 or 4.1 times more than that of microporous AgCeY for gasolines that contained large amounts of toluene or cyclohexene, respectively. This result may occur because of the suppression of the non-selective molecule adsorption, improvement in mass transfer, full use of active metal sites and strong adsorption energy related with the mesopore introduction. The meso-AgCeY, which combined multiple adsorption metal ions and modified Y zeolite with mesopores, is a promising ADS adsorbent.
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