Influence of Pore Structure and Metal‐Node Geometry on the Polymerization of Ethylene over Cr‐Based Metal–Organic Frameworks

Abstract

Metal-organic frameworks (MOFs) have received increasing interesta ss olid single-site catalysts, owing to their tunable pore architecture and metal node geometry. The ability to exploit these modulators makest hem prominent candidates for producing polyethylene (PE) materials with narrow dispersity index ()v alues. Here as tudy is presented in which the ethylene polymerization properties, with Et 2 AlCl as activator,o ft hree renowned Cr-based MOFs, MIL-101(Cr)-NDC(NDC = 2,6-dicarboxynapthalene), MIL-53(Cr) and HKUST-1(Cr), are systematicallyi nvestigated. Ethylene polymerization reactions revealedv arying catalytic activities,w ith MIL-101(Cr)-NDC and MIL-53(Cr)b eing significantly more activet han HKUST-1(Cr). Analysis of the PE products revealed large values, demonstrating that polymerization occurs over am ultitudeo fa ctive Cr centers rathert han as ingulart ype of Cr site. Spectroscopic experiments, in the form of powder X-ray diffraction (pXRD), UV/ Vis-NIR diffuser eflectance spectroscopy (DRS) and CO probe molecule Fourier transform infrared (FTIR) spectroscopy corroborated these findings, indicating that indeed for each MOF unique active sites are generated, however without alteration of the original oxidation state. Furthermore, the pXRD experiments indicated that one major prerequisite for catalytica ctivity was the degree of MOF activation by the Et 2 AlCl co-catalyst, with the more active materials portraying al arger degree of activation.

MOFs as Versatile Catalysts: Synthesis Strategies and Applications in Value-Added Compound Production

“…In addition, PE products were synthesized with multiple types with active sites of Cr centers rather than a singular type of Cr site (Figure 8). 120 The gas-phase ethylene polymerization process has inherent solubility and viscosity that are not limited, unlike in liquidphase processes. This allows for the production of a wide range of polyethylenes without polymer agglomeration.…”

“…In addition, PE products were synthesized with multiple types with active sites of Cr centers rather than a singular type of Cr site ( Figure 8 ). 120 …”

“…(F) Geometry of the metal nodes in MIL-101(Cr). Reprinted with permission from ref ( 120 ). Copyright 2021 John Wiley and Sons.…”

Ethylene Polymerization over Metal–Organic Framework-Supported Zirconocene Complexes

“…This results in virtually limitless potential regarding composition, functionality, and porosity. , So far, MOFs have been utilized as materials for carbon capturing and storage (CCS), as well as in other applications, such as chemical sensing, gas adsorption, and separation. − In the past decade, there has also been research on the use of MOFs for olefin polymerization catalysis. Numerous studies have already encompassed the effects of properties, such as porosity, active site, crystallite size, and organic linker on ethylene polymerization activity, and also produced polyethylene materials. − However, comprehensive studies are still relatively rare for MOFs as support materials for metallocene complexes for catalytic olefin polymerization.…”

Ethylene polymerization with a crystallographically well-defined metal–organic framework supported catalyst

“…[25][26][27][28][29][30] Among these applications, catalysis has largely capitalized upon the tailorable nature of MOFs to enhance activity and selectivity across various transformations. [31][32][33][34][35][36][37][38] Notably, MOFs are crystalline and thus can be characterized via single crystal X-ray diffraction (SC-XRD), even after post-synthetic modification. [39][40][41][42][43][44][45] This allows MOFs to be used as crystalline analogues capable of yielding information that is complementary to what can be learned structurally by anchoring catalysts on traditional materials such as amorphous oxides including silica, alumina, and zirconia.…”