氨气改性对USY分子筛的结构及催化性能的影响

实验以NH_3对USY分子筛进行改性,以X射线衍射、N_2吸附-脱附、固体核磁共振和氨程序升温脱附等方法对改性前后的USY分子筛进行表征。考察了NH_3改性对USY分子筛的孔结构、酸性以及催化二异丙苯烷基转移反应性能的影响。结果表明,NH_3改性可在保持USY分子筛骨架结构的同时,有效地改善四配位骨架铝的畸变环境。改性后的USY分子筛的BET比表面积增大,介孔孔容增加。改性产生的二次介孔改善了反应物的扩散性能。催化剂性能评价表明,当反应温度为180℃,反应压力为3 MPa,质量空速为12h,n(苯):n(二异丙苯)=6:1时,经NH_3改性6 h的USY分子筛的催化性能最佳,其催化二异丙苯烷基转移反应的转化率由67.37%升至81.51%,三异丙苯含量由0.026 4%降至0.016 5%。

EFFECT OF AMMONIA MODIFICATION ON STRUCTURE AND CATALYTIC PERFORMANCE OF USY

USY zeolite was modified by NH_3.The USY samples before and after NH_3 modification were characterized by X-ray diffraction,N_2 adsorption-desorption,solid state NMR,and NH_3 temperature -programmed desorption.The effects of NH_3 modification on the structure,acidity,and catalytic performance of USY zeolite in the transalkylation of diisopropylbenzene were investigated.The results showed that NH_3 modification could maintain the USY zeolite framework structure,and at the same time,effectively improve the distortion environment of four-coordinated framework aluminum, which resulted in promoting the crystallinity of the USY zeolite.With the extension of NH_3 modification time,mesopore volume and specific surface areas of USY zeolite increased.Furthermore,the additional mesopores generated by NH_3 modification process improved the diffusion of the reactants and products.The USY zeolite modified by NH_3 for 6 h had the maximum acidity and the best catalytic performance,which increased the conversion of diisopropylbenzene by nearly 10%,and significantly improved the selectivity of the reaction,decreasing the content of triisopropylbenzene from 0.026 4% to 0.016 5%.