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P-ZSM-5分子筛通常用来催化甲醇转化制轻烯烃,乙醇脱水制乙烯,芳烃的烷基化或者歧化等反应。目前,P-ZSM-5分子筛中磷和分子筛之间的相互作用仍不清楚。本文通过密度泛函理论(Density Functional Theory,DFT)计算了ZSM-5分子筛改性前后的结构及酸性变化。结果发现P骨架外改性后,磷酸分子的氢原子和分子筛骨架氧原子形成氢键作用,并且O_4,H_a和0_(zeo)总是保持在一条直线上,这是稳定的骨架外改性结构;骨架改性后,分子筛优化前后的结构发生较大变化,这是因为固定了8T模型中的终止氢原子,分子筛的骨架结构阻止了H_2PO_3基团的插入。本文还计算了磷酸分子和分子筛的酸性位之间的关系,研究发现,分子筛中引入P后,其酸性降低,且骨架改性后酸性减弱的程度更大。这一结果可以进一步指导实验,制备出不同酸性的分子筛。
P-ZSM-5 molecular sieve is usually used to catalyze the conversion of methanol to light olefins, dehydration of ethanol to ethylene, aromatic alkylation or disproportionation reaction. At present, the interaction between phosphorus and molecular sieve in P-ZSM-5 zeolite remains unclear. In this paper, the structure and acidity of ZSM-5 molecular sieve before and after modification were calculated by Density Functional Theory (DFT). As a result, it was found that the hydrogen atoms of the phosphoric acid molecule and the oxygen atoms of the molecular sieve skeleton form a hydrogen bond after the P skeleton is modified, and the O 4, H a and O zeo are always kept in a straight line, which is a stable extraframe-modified structure After the modification of the framework, the structure of the zeolite before and after the optimization greatly changed, because the termination of the hydrogen atom in the 8T model was fixed, and the framework structure of the molecular sieve prevented the insertion of the H_2PO_3 group. In this paper, the relationship between the acid sites of phosphoric acid molecules and zeolites was also calculated. It was found that the acidity of P zeolite was decreased when P was introduced into the molecular sieve. This result can further guide the experiment to prepare different acidic molecular sieves.