摘要
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。
The results showed that the number of acid sites in alkali-modified ZSM-5 zeolite could be decreased, and thus the secondary reactions of light olefins were prohibited. When ZSM-5 was modified with NaN3 (a solid strong alkali), a selectivity of 52% for C-2-C-4 was obtained. It was found that the Fe/Mn (wt) ratio for the highest light olefins selectivity was different when different alkalis or different modification methods were used, i.e. the promoting action of MnO for light olefins selectivity is not the same in different chemical environments. The acid-base property of the supported catalysts was characterized by NH3-TPD, pyridine-IR, CO2-TPD and 29Si-NMR techniques, it is clear that the strong acid sites were eliminated and the weak acid sites were reduced largely by modifying ZSM-5 with alkalies. Meanwhile, the basicity of the catalyst systems and the electron cloud density were both enhanced. The catalytic activity and C-2-C-4 selectivity both increased by the alkali modification of ZSM-5 were discussed and explained,
基金
国家自然科学基金
