Saelee Tinnakorn, Sitthijun Pichayapong, Ngamlaor Chinanang, Kerdprasit Nuttapat, Rittiruam Meena, Khajondetchairit Patcharaporn, Da Silva Juarez L F, Buasuk Nichakorn, Praserthdam Piyasan, Praserthdam Supareak
High-Performance Computing Unit (CECC-HCU), Center of Excellence on Catalysis and Catalytic Reaction Engineering (CECC), Faculty of Engineering, Chulalongkorn University, Bangkok, 10330, Thailand.
Center of Excellence on Catalysis and Catalytic Reaction Engineering (CECC), Faculty of Engineering, Chulalongkorn University, Bangkok, 10330, Thailand.
Sci Rep. 2024 Aug 1;14(1):17835. doi: 10.1038/s41598-024-68289-8.
One class of the Ziegler-Natta catalysts (ZNC) - the TiCl/MgCl having triethyl aluminum (AlEt), has been widely utilized during ethylene polymerization. Although the Ti species plays the role of a major active site, an increase of Ti species does not always improve the activity of ZNC. Herein, investigations of experiments and density functional theory (DFT) elucidate this inverse effect of the increased amount of TiCl deposition in ZNC because of the pretreatment process. However, the activity of ZNC on pretreated MgCl dropped to 60% of the unpretreated one. The DFT demonstrates that the pretreatment strengthened the interaction between TiCl and ZNC, especially on the (104) surface, forming the TiCl-TiCl cluster. The existence of this TiCl-TiCl cluster found on the ZNC (104) surface weakens the adsorption of the first AlEt molecule and obstructs further alkylation process, making another Ti site of the alkylated TiCl-TiCl cluster inactive. However, the difficult formation of the TiCl4-TiCl4 cluster found on the ZNC (110) is an important key point that enables the activation of all adsorbed TiCl on this surface by facilitating the alkylation process. Moreover, the existence of the MgCl (110) surface prevents the formation of the TiCl-TiCl cluster significantly. Hence, it is suggested that the existence of the (110) plane on ZNC plays a key role in controlling the performance of the ZNC, especially the stability via the prevention of deactivation caused by the clustering of TiCl.
一类齐格勒-纳塔催化剂（ZNC）——含有三乙基铝（AlEt）的TiCl/MgCl，已在乙烯聚合过程中得到广泛应用。尽管Ti物种起着主要活性位点的作用，但Ti物种的增加并不总是能提高ZNC的活性。在此，通过实验研究和密度泛函理论（DFT）阐明了由于预处理过程导致ZNC中TiCl沉积量增加所产生的这种相反效应。然而，ZNC在预处理的MgCl上的活性降至未预处理的MgCl的60%。DFT表明，预处理增强了TiCl与ZNC之间的相互作用，特别是在（104）表面，形成了TiCl-TiCl簇。在ZNC（104）表面发现的这种TiCl-TiCl簇的存在削弱了第一个AlEt分子的吸附，并阻碍了进一步的烷基化过程，使烷基化的TiCl-TiCl簇的另一个Ti位点失活。然而，在ZNC（110）上难以形成TiCl4-TiCl4簇是一个重要关键点，它通过促进烷基化过程使该表面上所有吸附的TiCl活化。此外，MgCl（110）表面的存在显著阻止了TiCl-TiCl簇的形成。因此，有人认为ZNC上（110）面的存在在控制ZNC的性能方面起着关键作用，特别是通过防止由TiCl聚集引起的失活来保持稳定性。
