烯烃对噻吩在介孔分子筛Al-MCM-41活性位物种上吸附脱硫机制的影响

采用后嫁接法制备了不同铝负载量的Al-MCM-41分子筛。运用XRD、N₂吸附-脱附、NH₃-TPD、Py-FTIR等方法对分子筛进行物性表征，利用固定床评价其对噻吩的吸附性能。通过将分子筛吸附噻吩能力与分子筛的酸性质及织构性质进行关联，考察烯烃存在对Al-MCM-41活性位物种吸附脱硫机制的影响。结果表明，铝物种的引入即产生了B酸中心，也同时产生了两种类型的L酸中心L₁和L₂。引入低含量铝物种利于形成B酸中心和L₁型酸中心，引入高含量铝物种利于形成L₂型酸中心。其中，L₂型酸中心对噻吩的吸附效果最佳。烯烃和噻吩在B酸中心发生竞争吸附和催化转化反应，且催化转化反应占主导地位。L₂酸中心的存在促进了B酸中心上的催化转化反应，其所生成的大分子硫化物取代噻吩吸附在分子筛酸活性中心上提高了Al-MCM-41分子筛的饱和吸附硫容量。

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.