Identifizierung der Natur aktiver Chromkatalysatoren in der Tetramerisierung von Ethen mittels in situ Spektroskopie

Die 1-Octen-Selektivität ist stark abhängig von der Natur des Präkusors, des Aktivators und des Liganden. Für die Katalysatorentwicklung sind genaue Informationen über die Bildung der tatsächlich aktiven Komplexe und deren Einfluss auf die katalytische Leistung erforderlich. Ziel ist es, die Wirkung von verschiedenen AlR3-Aktivatoren, Liganden und unterschiedlichen Präkursoren auf die Natur der katalytisch aktiven Cr-Spezies zu analysieren mit Hilfe einer maßgeschneiderten Kombination spektroskopischer In-situ-Methoden.The 1-octene selectivity is strongly dependent on the nature of the precursor, the activator and the ligand. The catalyst development requires precise information about the formation of the actually active complexes and their influence on the catalytic performance. The aim is to analyze the effect of various AlR3 activators, ligands and different precursors on the nature of the catalytically active Cr species with the help of a tailored combination of spectroscopic in situ methods

Co-Oligomers of Renewable and "Inert" 2-MeTHF and Propylene Oxide for Use in Bio-Based Adhesives

Commercial polyether polyols are usually obtained by the ring-opening polymerization of epoxides or tetrahydrofuran. 2-Methyl-tetrahydrofuran (2-MeTHF) could be an alternative bio-based building block for the synthesis of these polyols. Although 2-MeTHF cannot be polymerized, we did achieve the copolymerization of 2-MeTHF with propylene oxide (PO) using Lewis and Brønsted acids as catalysts and water or diols as initiators. The resulting polyether polyols have a molecular weight range, which allows their use as components for adhesives. The molar content of 2-MeTHF in the oligomers can be up to 48%. A 1:1 copolymer of 2-MeTHF and PO is produced when stoichiometric amounts of BF3·OEt2 are used. Here, the monomeric units in the chains alternate, but also cyclic or other nondiol products are formed that are detrimental to its further use in adhesives. Linear dihydroxyl-terminated polyether chains were formed when the heteropolyacid H3PW12O40·24H2O was used as a catalyst and a diol as an initiator. The formation of cyclic products can be drastically reduced when the accumulation of propylene oxide during the reaction is avoided. 1H NMR experiments indicate that the step of 2-MeTHF incorporation is the alkylation of 2-MeTHF by protonated PO. It was shown that the 2-MeTHF/PO copolymer had increased tensile strength compared to polypropylene glycol in a two-component adhesive formulation

Impact of Al Activators on Structure and Catalytic Performance of Cr Catalysts in Homogeneous Ethylene Oligomerization – A Multitechnique in situ/operando Study

The effect of different AlR3 activators (R=methyl, ethyl, isobutyl, n‐octyl) has been studied in comparison to modified methylaluminoxane (MMAO) by operando EPR as well as by in situ UV‐vis, ATR‐IR and XANES/EXAFS spectroscopy during oligomerization of ethylene at 20 bar and 40 °C with a homogeneous Cr complex catalyst formed in situ upon mixing a Cr(acac)3 precursor, a Ph2PN(iPr)PPh2 ligand (PNP) and the activator. Coordination of PNP to Cr(acac)3 is initiated only in the presence of an activator. Highest 1‐octene productivity (detected during operando EPR measurements) was obtained with MMAO which promotes bidentate coordination of the ligand to form an active (PNP)CrII(CH3)2 chelate complex. Rising bulkiness of R in AlR3 leads to only monodentate coordination of PNP to the Cr center by one P atom and increasing reduction to CrI to a maximum extend of around 30 % for AlOct3. This lowers the catalytic performance, which is mainly governed by the mode of PNP coordination rather than by the CrI content