摘要
本文合成了五种不同硅铝比的ZSM-5,并分别用Mg^(2+),Ni^(2+)和K^+离子进行了交换改性。用NH_3和CO_2的TPD技术测定了它们的酸碱性质,并与甲苯甲醇的反应活性进行了关联。实验结果表明,ZSM-5分子筛的酸性和碱性不仅与骨架铝的含量有关,且与其阳离子的性质有关。甲苯与甲醇之间的苯环烷基化反应以及伴生的甲苯歧化反应均发生在ZSM-5的强酸中心上,弱酸中心不呈活性。由于改性后ZSM-5的碱性位少,即使是KZSM-5的碱性位也只有10^(18)/g,故不足以引发甲苯的侧链烷基化反应。
The surface acidity and basicity of various modified ZSM-5 zeolites with different SiO2/Al2O3 ratios have been determined quantitatively by TPD technique with NH3 and CO2 respectively, and their catalytic activity for toluene al-kylation with methanol has been correlated. It is found that the acid-base proper-tics of zeolites are not only affected by the SiO2/Al2O3 ratio but also by the property cf the exchanged cations. The results of catalytic reaction show that both the ring alkylation and simultaneous disproportionalion of toluene take place on the strong acidic sites of ZSM-5 zeolites, and no side-chain alkylation of toluene is observed even on the KZSM-5 zeolites, because of the less basic Sites of the modified ZSM-5 zeolites.
基金
国家自然科学基金
