Influence of olefin on the mechanism of thiophene adsorption on the active species of Al-MCM-41 mesoporous zeolites

The Al-MCM-41 zeolites with different Al contents were prepared by post-grafting method and characterized by means of XRD, N₂ adsorption-desorption, NH₃-TPD, and Py-FTIR. The adsorptive performance of thiophene on these samples was investigated in a fixed bed by using micro coulombmeter and GC-SCD technique. The thiophene adsorption capacity was correlated with the acid properties and texture properties of the molecular sieve, and the effect of olefin on the adsorption desulfurization mechanism of active species in Al-MCM-41 was investigated. The results show that the introduction of lower content aluminum species is conducive to the formation of B (Brønsted) acid center and L₁ (Lewis) acid center, while higher content aluminum species is conducive to the formation of L₂ (Lewis) acid center. L₂ acid center exhibits a far stronger thiophene adsorption ability than L₁ acid center that has a slightly stronger thiophene adsorption ability than B acid center. Competitive adsorption and catalytic conversion of olefin and thiophene take place on the B acid center, and the catalytic reaction is dominated. The existence of L₂ acid center greatly promotes the catalytic conversion reaction on the B acid center. The adsorption of macromolecular sulfide instead of thiophene increases the saturated adsorption capacity of Al-MCM-41 zeolites.