ZnAPO-5分子筛的合成、表征及正己烷催化裂解反应活性

采用静态水热法合成了含有不同锌含量的锌铝磷酸盐分子筛（ZnAPO-5）,利用XRD、SEM、N2-吸附、MAS-NMR及ICP-AES等方法对合成的ZnAPO-5分子筛进行了表征。研究结果表明在选定的合成条件下,可以合成出AFI结构类型的ZnAPO-5分子筛,合成的ZnAPO-5分子筛结晶度较高,具有规整的六方棱柱晶体外形,杂原子同晶取代为锌取代骨架元素铝。ZnAPO-5分子筛上的正己烷催化裂解反应活性评价结果显示在反应温度为723 K~823 K时正己烷的催化裂解呈中等反应活性,正己烷的转化率随反应温度和接触时间的增加而增加,正己烷的浓度项反应级数为1,裂解反应表观速率常数随反应温度的升高而增大,且遵从Arrhenius公式;由裂解产物分布可知,在选定的实验条件下该反应以单分子反应为主。

Synthesis, characterization and n-hexane catalytic cracking activity of zinc-substituted aluminophosphate molecular sieves (ZnAPO-5)

Zinc-substituted aluminophosphate molecular sieves (ZnAPO-5, AFI topology) containing different zinc contents were synthesized by static hydrothermal method, using triethylamine as an organic template agent. The as-synthesized ZnAPO-5 molecular sieves were characterized by XRD, SEM, N2-adsorption, MAS-NMR and ICP-AES techniques. Experimental data indicate that Zn as a heteroatom was successfully incorporated into the framework of AlPO4-5. The resultant ZnAPO-5 molecular sieves with regular hexagonal prism morphology are of high crystallinity and purity. The n-hexane cracking over ZnAPO-5 was examined under different reaction conditions. It is found that ZnAPO-5 molecular sieves exhibit a moderate activity for the n-hexane cracking conversion in the temperature range of 723K~823K. The cracking results obtained show that the conversion level of n-hexane increased with increasing reaction temperature and contact time, and that the first order was determined in the n-hexane concentration. Relations between rates and reaction temperature can be expressed in terms of Arrhenius formula in the whole temperature range. Based on the kinetic data and product distributions, monomolecular protolytic mechanism was concluded to prevail under the reaction conditions applied.