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本文首次采用碱改性处理ZSM-5沸石,降低其酸性,以抑制低碳烯烃在ZSM-5沸石酸中心上的二次反应,结果大大提高了C_2~=—C_4~=选择性。尤其是经NaN_3强碱固相改性ZSM-5担载的Fe-MnO催化剂可得52％的低碳烯烃选择性。考察了金属活性组分调变对催化剂性能的影响,表明不同碱改性的催化剂中MnO助烯烃选择性作用也有差异。通过NH_3-TPD、吡啶-IR,CO_2-TPD和~(29)Si-NMR对催化剂表征表明,碱改性消除了ZSM-5强酸中心,大幅度降低了弱酸中心;提高了催化剂体系碱性及SiO_4四面体周围电子云密度。并对催化剂的活性及烯烃选择性随ZSM-5的碱改性不断提高的规律性作了解释。
In this paper, the first modification of ZSM-5 zeolite using alkali to reduce its acidity, in order to inhibit the second reaction of light olefins in ZSM-5 zeolite acid center, the result is greatly enhanced C_2 ~ = -C_4 ~ = selectivity. In particular, the Fe-MnO catalyst supported on the solid phase ZSM-5 by NaN3 strong alkali gave 52% lower olefins selectivity. The effect of the modulation of the metal active component on the catalyst performance was investigated, indicating that there is a difference in the selectivity of MnO to olefins in different alkali-modified catalysts. Characterization of the catalysts by NH_3-TPD, pyridine-IR, CO_2-TPD and ~ (29) Si-NMR indicated that the alkali modification eliminated the strong acid sites of ZSM-5 and greatly reduced the weak acid sites. The electron cloud density around the SiO 4 tetrahedron. The activity of the catalyst and the regularity of the selectivity of olefins with increasing base modification of ZSM-5 were also explained.