Competitive adsorption mechanism of thiophene with benzene in FAU zeolite: The role of displacement

•The competitive adsorption mechanism of benzene/thiophene was proposed.•The competitive adsorption relationships for the whole loadings were revealed.•Intrinsic reasons for the transformation in adsorption mechanism were found.•Three practical factors on thiophene adsorption were analyzed.

To explore the whole process of competitive relationship changing with increasing adsorption amount, the competitive adsorption mechanism of benzene/thiophene in siliceous faujasite (FAU) zeolite from infinite dilution to saturation adsorption was analyzed through grand canonical ensemble Monte Carlo simulations for the first time. Results showed that the competitive adsorption mechanism transferred from “ideal-displacement adsorption” to “insertion-displacement adsorption” with an inflection point of 40 molecule/UC, as the total loading amount of benzene and thiophene grew. At “ideal-displacement adsorption” stage, both benzene and thiophene molecules adsorbed ideally on S and W sites. Meanwhile, as the total loading closed to 40 molecule/UC, increasing amount of thiophene on favorable S adsorption sites was displaced by benzene and migrated to W sites. Comparatively, at “insertion-displacement adsorption” stage, benzene molecules continued displacing some thiophene adsorbed on S sites when the total loading increased. The displaced thiophene inserted near the center of the supercage. The transformation in this competitive adsorption mechanism was due to the interaction energy. Besides, higher thiophene concentration, adsorption temperatures and ratios of Si/Al to some extent contributed to the increase in the selectivity for thiophene.

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