MAO- and Borate-Free Activating Supports for Group 4 Metallocene and Post-Metallocene Catalysts of α-Olefin Polymerization and Oligomerization

Modern industry of advanced polyolefins extensively uses Group 4 metallocene and post-metallocene catalysts. High-throughput polyolefin technologies demand the use of heterogeneous catalysts with a given particle size and morphology, high thermal stability, and controlled productivity. Conventional Group 4 metal single-site heterogeneous catalysts require the use of high-cost methylalumoxane (MAO) or perfluoroaryl borate activators. However, a number of inorganic phases, containing highly acidic Lewis and Brønsted sites, are able to activate Group 4 metal pre-catalysts using low-cost and affordable alkylaluminums. In the present review, we gathered comprehensive information on MAO- and borate-free activating supports of different types and discussed the surface nature and chemistry of these phases, examples of their use in the polymerization of ethylene and α-olefins, and prospects of the further development for applications in the polyolefin industry.

Coloured hybrid materials: exploiting an emergent surface property of fluorinated Al2O3 containing anthocyanins and betacyanins

Two fluorinated γ-Al₂O₃ series were synthesized by a sol-gel method with two solvents (2-propanol and 2-butanol), two aluminium sources (ATB and ATP) and one fluorine source (Na₃AlF₆). The resulting inorganic matrixes were evaluated to characterize aluminium and fluorine species ([AlO₄^5-], [AlO₅^7-], [AlO₆^9-], [AlF₄^-], [AlF₅^2-] and [AlF₆^3-]) by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ²⁷Al magic angle spinning nuclear magnetic resonance (²⁷Al MAS-NMR) and infrared spectroscopy (IR-ATR). BET and BJH analyses using the nitrogen isotherms of these materials allowed identifying a clear trend in some textural parameters such as specific surface area and fluorine content. These results were confirmed by scanning electron microscopy (SEM). Chemical affinity and acid surface properties were evidenced with colour shifts in two groups of hybrid pigments, prepared with natural anthocyanins (Brassica oleracea) and betacyanins (Bougainvillea glabra).

The ethylene glycol-mediated sol-gel synthesis of nano AlF3: structural and acidic properties after different post treatments

In this work, the structure and surface acidity of nano AlF₃ prepared by the ethylene glycol-mediated sol-gel process, followed by different post treatments including post-fluorination and calcination, were systematically investigated. FT-IR, elemental analysis, XPS and TG-DTA-MS results indicate the ethylene glycol strongly interacts with the as-prepared AlF₃ precursor, thus stabilizing the formed nano particles. MAS NMR spectroscopy combined with in situ FT-IR and HRTEM techniques reveal that AlF₆, AlO_6-xF_x and AlO₆ species are present in the resulting X-ray amorphous nano AlF₃. The fraction of AlF₆ species formed after post-fluorination significantly increases, whereas more AlO_6-xF_x species are formed just after calcination. After a comparable post-fluorination treatment, the CHClF₂ dismutation activity at room temperature indicates that nano AlF₃ prepared according the ethylene glycol-mediated route does not possess the same super-strong acidity as HS-AlF₃ prepared by the fluorolytic sol-gel method, although NH₃-TPD and N₂-sorption results indicate larger BET surface areas and high concentration of acid sites for the former as compared to the latter. This might be rationalized based on the absence of terminal fluorine species and the presence of a significant number of AlO_6-xF_x and AlO₆ species in the resulting nano AlF₃ as revealed by ²⁷Al, ¹⁹F MAS NMR and HRTEM. An interesting consequence is that these oxygen-containing species stabilize the microstructure of AlF₃ formed, resulting in improved thermal stability of these phases as compared to "classically" prepared HS-AlF₃.

Metal-Organic Framework-Derived Strategy for Improving Catalytic Performance of a Chromia-Based Catalyst in the Chlorine/Fluorine Exchange Reactions for Unsaturated Fluorocarbons

Hydrofluoroolefins (HFOs) and cyclic hydrofluorocarbons (c-HFCs) have been the most favored alternatives of the ozone depletion substances; however, because of the poor performance of the present chlorine/fluorine (Cl/F) exchange catalysts, the development and production of HFOs and c-HFCs are hindered. Here, we first report a novel and facile route to fabricate high-performance Cl/F exchange catalysts via a metal-organic framework (MOF) carbonization method. The MOF-derived catalyst not only has high selectivity but also can significantly lower the reaction temperature. Moreover, benefiting from the stable structure and coke-inhibiting ability, the MOF-derived catalyst has a long service life compared with the traditional precipitation method. Furthermore, the nanoscopic MOF-derived catalyst can greatly reduce the Cr dosage, which would help to minimize the risk of Cr contamination.

Facile construction of ultrastable alumina anchored palladium catalysts via a designed one pot strategy for enhanced methane oxidation

A highly stable Pd–Al₂O₃ catalyst with anchored palladium species was facilely prepared through a one pot strategy for efficient methane oxidation.

Strong Lewis acidic catalysts for C–F bond activation by fluorination of activated γ-Al2O3

A strong solid Lewis acid catalyst has been successfully obtained by modifying a known procedure of fluorinating γ-aluminium oxide, which was pre-calcined under vacuum.