磷酸三乙酯改性HZSM-5沸石的活性及理论研究

采用XRD表征了水蒸气和磷联合改性的HZSM-5沸石分子筛的结构．通过NH3-TPD和N2吸附脱附研究了样品的酸性和比表面．采用正庚烷的裂化反应研究了样品的裂化活性，研究结果表明，磷改性样品与母体样品相比，经过水蒸气处理后显示出较高的酸量和正庚烷裂化活性．上述结果首次用模型簇和计算量子化学方法进行了解释．采用Gaussian94软件包和PM3半经验量子化学方法对模型簇进行了全优化和频率分析．计算结果显示磷改性后样品的脱铝补硅反应热大于母体样品脱铝补硅反应热，从而显示出磷对骨架的稳定化作用．

The Activity and Theoretical Study of Triethyl Phosphate Modified HZSM-5 Zeolite

The steam treatment and phosphorus modification of HZSM-5 zeolites have been investigated. The structure of the samples has been characterized by XRD. Acidic properties of the samples have been characterized by means of temperature programmed desorption of ammonia and the BET surface area was determined by nitrogen adsorption-desorption. The n-heptane cracking was carried out as probe reaction to investigate the activity of the samples. The results show that phosphorus modified HZSM-5 had larger acidic amount and higher n-heptane cracking conversion than parent HZSM-5 when they were steam-treated at 1 073 K. The results are first elucidated by model cluster method and computational quantum chemistry method. Full optimization and frequency analysis of all cluster model are carried out using Gaussian94 soft-package with PM3 semi-empirical method performed on small cluster models. The computational results show that the dealumination of triethyl phosphate modified zeolite model cluster is more difficult than that of non-modified zeolite model cluster when they are treated with steam in terms of the reaction heat.