Effect of Donors on the Activation Mechanism in Ziegler–Natta Catalysis: A Computational Study

Abstract

Full quantum chemical calculations, using density functional theory (DFT), have been conducted to explain the effect of donors on the “activation mechanism” in the Ziegler–Natta (Z–N) catalyst system. In the activation mechanism, the inactive TiIVCl4 catalyst converts into the active TiIIICl2Et catalyst with the help of the AlEt3 present in the system. The donors that have been considered in this study are: ethyl benzoate (eb), two representative diether cases, a phthalate donor, and a silyl ester donor. The results indicate that eb and the diether donor cases donor have a negative effect on the barriers for the activation mechanism. However, the eb donor can be displaced from the MgCl2 surface by AlEt3, which matches experimental observations. For the phthalate, silyl ester and TiCl3–OC4H8Cl cases, the results indicate that a significant induction period would be present in Z–N systems employing such donors or having such a catalytic center, before catalysis could commence.

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl2‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

“…As an important industrial catalyst, the fourth-generation supported Ziegler-Natta (ZÀ N) catalyst played key roles in the industrial production of iPP. Although great progresses have been made in fundamental studies on the catalyst structure [1][2][3][4][5][6][7][8][9][10] and polymerization mechanism [11][12][13][14][15][16] of catalytic olefin polymerization with ZÀ N catalysts, many important basic questions still remain subjects of debates due to the complex formulation and microstructure of the catalyst, especially the structure of the active centers.…”

Adsorption of Titanium Tetrachloride on Magnesium Dichloride Clusters

“…7−10 Lateral cut of the MgCl 2 sheets exposes catalytically relevant (104) and (110) surfaces with five- and four-coordinate Mg atoms, respectively (Figure 1B), 11 which adsorb and coadsorb TiCl 4 , aluminum alkyls, and Lewis bases. 12−20 The (110) surface is less stable than the (104) surface because of the lower coordination numbers of surface Mg atoms, 18,19,21 but adsorption of other catalyst components may reverse the stability order in favor of (110). 22,23 Reactions taking place on the surface eventually lead to the formation of active sites for olefin polymerization.…”

Insights into the Nature of Self‐Extinguishing External Donors for Ziegler‐Natta Catalysis: A Combined Experimental and DFT Study

“…Donors are vital components of the ZN polymerization process that can enhance the stereo‐ and regioselectivity of the product by coordinating in the vicinity of the active titanium center [9,42,43,46] . It can influence the kinetics of the activation, insertion and termination steps in the polymerization reaction, and can also help the titanium to coordinate to the (104) MgCl 2 surface, which is otherwise unutilized [30,31,33] . It is interesting to note that tuning the structure of existing donors and developing new donors has always been challenging and a prominent area of research in ZN catalysis, because of their potential to produce polyolefins with desirable properties.…”

“…Ziegler‐Natta (ZN) catalysis is one of the most important catalytic processes, which produces around 150 million tons of polyolefins/year, and has a billion dollar market [1] . Since its discovery in the 1950s by Karl Ziegler and Giulio Natta, for which they received the Nobel prize in 1963, [2,3] continuous efforts to improve the performance of the ZN systems, concerning their activity and the selectivity, have been undertaken, along with understanding at the molecular level, by employing various experimental [4–11] and computational tools [12–34] . The main components of the ZN system are (i) MgCl 2 as a catalyst support, (ii) TiCl 4 as precatalyst, (iii) triethylaluminum ( teal ) as an alkylating agent, and (iv) Lewis base donors (e. g. oxygen‐containing molecules and nitrogen‐containing polymers [35] ).…”