State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, P. R. China.
Phys Chem Chem Phys. 2018 May 3;20(17):11702-11712. doi: 10.1039/c8cp00946e.
In this work, a density functional theory (DFT) study was carried out to address the fundamental description of the effective phosphorous species that could improve the framework stability and reduce the coke deposition formation on the P-ZSM-5 zeolite. On the basis of the dealumination barriers of ZSM-5 with all the possible phosphorous species bound on the zeolite framework, PO4H4 was ascertained to be the effective phosphorous species that could improve the ZSM-5 zeolite hydrothermal stability and reduce its acid strength. Apart from this, the olefin polymerization reaction is the main cause of coking deactivation for ZSM-5. Thus, the effect of the modification P-ZSM-5 on the reactivity of light olefins dimerization was also studied. Compared to the unmodified ZSM-5, the activation energy of the rate-limiting step of ethylene dimerization was increased from 20.3 kcal mol-1 to 34.6 kcal mol-1, thereby apparently inhibiting ethylene dimerization and improving the resistance to coke deposition for P-ZSM-5. Our calculation results should provide a beneficial theoretical guide for designing and improving a catalyst for the methanol-to-olefins process and bioethanol dehydration.
在这项工作中，进行了密度泛函理论（DFT）研究，以解决能够提高骨架稳定性和减少 P-ZSM-5 沸石上积碳形成的有效磷物种的基本描述。基于所有可能的磷物种结合在沸石骨架上的 ZSM-5 的脱铝势垒，确定 PO4H4 是能够提高 ZSM-5 沸石水热稳定性并降低其酸强度的有效磷物种。除此之外，烯烃聚合反应是 ZSM-5 失活的主要原因。因此，还研究了改性 P-ZSM-5 对轻烯烃二聚反应活性的影响。与未改性的 ZSM-5 相比，乙烯二聚反应的速率限制步骤的活化能从 20.3 kcal mol-1 增加到 34.6 kcal mol-1，从而明显抑制了乙烯二聚反应，提高了 P-ZSM-5 的抗积碳能力。我们的计算结果应为甲醇制烯烃工艺和生物乙醇脱水设计和改进催化剂提供有益的理论指导。
