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A Novel Catalytic System for the Oxidative Carboxylation of Stryene Based on a POM Embedded Cationic CTF Incorporated in Electro

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A Novel Catalytic System for the Oxidative Carboxylation of Stryene Based on a POM Embedded Cationic CTF Incorporated in Electro Sander Bossier Development of a novel Promotor: Prof. Dr. Karen Leus catalytic system for the Co-promotors: Prof. Dr. Peter Dubruel Prof. Dr Karen De Clerck Supervisors: Parviz Gohari Derakhshandeh oxidative carboxylation Dr. Tom Gheysens Dr. Eva Loccufier of styrene based on a Academic Year 2018-2019 POM embedded cationic CTF incorporated in A dissertation submitted to Ghent University in partial fulfilment of the requirements for the degree of Master of Science in Chemistry electrospun nanofibres Acknowledgments The realization of a thesis is never a solitary endeavour, without the people that I have met throughout this year, it could have never been done. I want to thank these people for their time, their support, their knowledge, and their help. Firstly, I would like to thank my promoter prof. dr. Karen Leus, and my co-promoters, prof. dr. Peter Dubruel and prof. dr. ir. Karen De Clerck, for allowing me to perform this research in their laboratories and use their equipment. Secondly, I would like to thank prof. dr. Pascal Van Der Voort for the use of his laboratory and equipment. Thirdly, my guides Parviz, Tom, and Eva, without you to show me the ropes, I do not know where I would be. And lastly of course, the COMOC, PBM, and CTSE groups, thank you for the good times. On top of this I would also like to thank Funda Ali¸cand Tom Planckaert for teaching me how to work with some of the equipment. Thank you dr. Anna Kaczmarek for supplying the heptammonium tridecavanadomanganate. I have to thank Katrien Haustraete too for the STEM-EDX images and Roseline Blanckaert for the ICP-AES analysis. And finally a shout-out to the Hellcats (thank you, Andreas and Geert for the great atmosphere), my fellow thesis students, my friends (time to go on another weekend with destination X) and everybody at KSA-Tielt for being a listening ear and the best friends I could have ever wished for. iii A Novel Catalytic System for the Oxidative Carboxylation of Styrene based on a POM Embedded Cationic CTF Incorporated in Electrospun Nanofibres S. Bossier, P. Gohari Derakhshandeha, T. Gheysensb, E. Loccufierc, A. Kazcmareka, P. Van Der Voorta, K. De Clerckc, P. Dubruelb, and K. Leusa a COMOC, Department of Chemistry, Ghent University, Ghent b PBM, Department of Organic and Macromolecular Chemistry, Ghent University, Ghent c CTSE, Department of Materials, Textiles and Chemical Engineering, Ghent University, Ghent The utilization of CO2 in the production of value-added chemicals is one way to reduce its emission. In this research, a dual-functional catalyst is envisaged to achieve the orthogonal tandem catalysis of the oxidative carboxylation of styrene to styrene carbonate (SC).1 This is achieved by incorporating a vanadium-based polyoxometalate (VPOM) in a cationic covalent triazine framework (cCTF) based on imidazolium moieties. More specifically, the embedded VPOM catalyses the epoxidation of styrene to styrene oxide with tert-butylhydroperoxide (TBHP) as the oxidant. Simultaneously, CO2 molecules are efficiently captured and activated by CO2-philic N-rich triazine groups of the CTF. Next, the bromide ion of the tetrabutylammonium bromide (TBAB) co- catalyst activates the epoxide via ring-opening. Subsequently the 2 activated CO2 is inserted to produce the desired styrene carbonate. The goal is to make this multistep reaction go to the desired product in one reactor without the need for separation, purification, and transfer of intermediates produced. The second part of the research is focused on embedding the VPOM@cCTF particles in a polyamide-4.6 (PA-4.6) nanofibre to increase ease of use and catalyst recovery. This is achieved by electrospinning a VPOM@cCTF and PA-4.6 solution from formic and acetic acid.3 Keywords Oxidative carboxylation; styrene; covalent organic framework; polyoxometalate; electrospinning; tandem catalysis; CO2 conversion; cyclic carbonate Introduction 4 Nowadays, the total annual anthropogenic CO2 emission is about 36 Gt. Combine this with the fact that there is already an excess of more than 900 Gt of CO2 in the atmosphere, 5 nearing 1 Tt, means that there is a huge reservoir of untapped CO2 ripe for exploitation . Utilizing this CO2 as a C1 building block for the synthesis of chemicals with high molecular complexity, and thus high value, would create an economical incentive to further invest in now costly direct-air-capture technologies6. To that end a substantial amount of research is dedicated to efficiently produce such chemicals using CO2 as a starting product or as an intermediary. An interesting class of such complex chemicals, of which a large increase in production/demand is expected7, is the (cyclic) organic carbonates. These compounds could be used as solvents for aromatic compounds, polymers, and salt like compounds. Some other (potential) uses that are less to not industrially applied (but are being Ghent University, 2019 investigated) are e.g. as monomers to polymerize into a variety of homo- and copolymer polycarbonates with high molecular masses, extractants, plasticizers, electrolytes, intermediates in organic synthesis, spinning dopes for synthetic fibres, specific solvents for pharmaceutical and cosmetic preparations, or other niche usage applications.8 Tandem catalysis, in which multi-step chemical transformations are catalysed by multifunctional catalysts, has attracted increasing research attention. Selective multifunctional catalysts make a multi-step reaction go to the desired products in one reactor without the need for separation, purification, and transfer of intermediates produced in each step. Great efforts have been made to design heterogeneous catalysts for tandem reactions through the immobilization of metal complexes and nanoparticles on the surface of various porous supports such as polymers, zeolites, molecular sieves, and metal-organic frameworks (MOFs). Recently, covalent triazine frameworks (CTFs) emerged as a new type of porous materials. CTFs have similar characteristics in comparison to the well- known MOFs but exhibit enhanced chemical stability. Here, a novel approach is devised based on the incorporation of the vanadium-based POM (VPOM), heptammonium tridecavanadomanganate ([NH4]7[MnV13O38]), in a cCTF, based on a 1,3-bis(5-cyanopyridyl)-imidazolium bromide (bpim) cationic linker, as dual- functional materials to achieve a tandem catalyst for the efficient conversion of CO2 and 9 styrene into value-added styrene carbonate (SC) , see figure 1. More specifically, the CO2 molecules are efficiently activated by CO2-philic N-species of the cCTF. Concurrently to the activation of CO2, the POM catalyses the epoxidation of styrene. This is followed by the cycloaddition of the activated CO2 to the formed epoxide. CTFs exhibited great base 10 catalytic properties for the chemical conversion of CO2. High conversions and good recyclability would demonstrate the unique potential of this new multifunctional catalyst. Additionally, following the work of a previous student, an attempt will be made to embed the catalyst particles in a mesh of electrospun polyamide-4.6 (PA-4.6) nanofibres to increase the ease of catalyst recycling and prevent catalyst loss by filtration.11,12 Figure 1: Schematic representation of a) the envisaged structure of the POM@cCTF catalyst and b) the tandem reaction. 2 Ghent University, 2019 Experimental The following chemicals were used as received: acetic acid (Sigma-Aldrich, ≥99%), ACN (Fisher Scientific, HPLC grade), 2-bromo-5-cyanopyridine (TCI, >97.0%), CO2 (Air Liquide, ≥99.7%), chlorobenzene (Sigma-Aldrich, 99.8%), CHCl3 (Sigma-Aldrich, ≥99.5%), DCM (Sigma-Aldrich, 99%), 1,2-dichloroethane (ROMIL Chemicals, ≥99.8%), DMSO (Sigma-Aldrich, ≥99.5%), formic acid (Sigma-Aldrich, ≥95%), HCl (Carl Roth, 37wt.%), MeOH (Fisher Scientific, ≥99.5%), 1-Methyl-1H-imidazole (Sigma-Aldrich, 99%), polyamide-4.6 (Goodfellow, -), styrene (Sigma-Aldrich, ≥99%), tetrabutyl- ammonium bromide (Sigma-Aldrich, ≥98.0%), THF (Sigma-Aldrich, ≥99.0%), tert- butylhydroperoxide (Sigma-Aldrich, 5.0-6.0 M in decane), and ZnCl2 (TCI, ≥98.0%). Synthesis of the Cationic Dinitrile Linker; bpim The cCTF used in this research, from the work of Park et al.13, is synthesized from 1,3- bis(5-cyanopyridyl)-imidazolium bromide (bpim). This linker is prepared according to the recipe of Chen et al.14. 2-Bromo-5-cyanopyridine (2.176 g, 11.9 mmol, 2 eq.) and 1- methyl-1H-imidazole (472 µL, 5.9 mmol, 1 eq.) were charged into a Pyrex ampoule, which was degassed, flame sealed and heated up to 190°C at 1°C.min-1 in a muffle furnace and retained at that temperature for 18 h. After the reaction, the ampoule was cooled to room temperature (RT) and opened with a glass cutter. The collected crude black powder was dissolved in ca. 100 mL hot methanol (MeOH) to extract the pure compound. The linker dissolves poorly in MeOH and remains as a precipitate, which was filtered of and kept aside. The filtrate was allowed to cool to RT and put on the rotavapor until ca. 20mL MeOH remained, the formed crystals were filtered off. Important to note: if too much MeOH was evaporated, unreacted starting materials can precipitate. The obtained light brownish powders were added together, washed with chloroform, and dried for 24 h under vacuum at 120°C. Synthesis of the bpim-based cCTF The synthesis method of the cCTF was adapted from the work by Park et al.13. Dried bpim (0.5 g, 1.42 mmol) and zinc chloride (ZnCl2, 0.95 g, 6.97 mmol) were loaded in a Pyrex ampoule and degassed under vacuum for 5 h to remove residual water. The ZnCl2 was dried beforehand under vacuum at 120°C overnight. The ampoule was flame sealed and placed in a muffle furnace and heated at a rate of 1°C.min-1 to 400, 500 or 600°C and kept at that temperature for 48 h. After 48 h, the ampoule was left to cool down to RT and opened with a glass cutter.
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