Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

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CHAPTER 6 [24, 25]. MOFs have been used as catalysts for various types of oxidation reactions in the liquid phase, e.g. alcohol oxidation [26], epoxidation [27, 28], hydrocarbon oxidation [29, 30], hydroquinone oxidation [31], oxidation of organic sulfides [32] or the oxidation of aromatics [33]. Especially for these oxidation reactions, a certain degree of deactivation is frequently observed. Co‐ based MOFs were used previously for the oxidation of cyclohexene with TBHP resulting mainly in allylic oxidation products [34, 35]. In the present study the epoxidation of styrene and stilbene by molecular oxygen is investigated using DMF as solvent and the MOF catalyst STA‐12(Co). The MOF structure has been resolved by Rietveld refinement featuring an analogous structure to STA‐12(Ni) [36] and is therefore a high metal containing alternative to the frequently used zeolites. The influence of important reaction parameters is examined in detail in order to clarify the role of the Co‐MOF and the role of various activating and deactivating additives on the catalytic reaction were investigated. In situ electron paramagnetic resonance (EPR) and X‐ray absorption spectroscopy (XAS) studies provided additional valuable mechanistic information. 6.2 Experimental 6.2.1 Materials (E)‐stilbene (97 %), 4‐tert.‐butyl catechol (≥98 %), Cobalt (>99.8 %), dimethylacetamide (puriss.) and PPh3 (≈99 %) were obtained from Fluka. Benzaldehyde (99.5 %, redist.) was obtained from Acros Organics, biphenyl (99.5 %) and 2,6‐di‐tert.‐butyl‐4‐methylphenol (≥99 %) from Sigma‐Aldrich, and N,N‐dimethylformamide (99.8 %) from VWR. Oxygen was used from PanGas (grade 5.0). Styrene (Sigma‐Aldrich, 99.5 %, stabilized) was distilled prior to use. Synthesis of N‐formyl‐N‐ methylformamide (FMF): For the preparation of N‐formyl‐N‐methylformamide 12.5 ml (0.2 mol) of iodomethane (ABCR, 99 %) and 22.8 g (0.24 mol) of sodium diformylamide (Acros) were added to a flask containing 50 mL of acetonitrile (Sigma‐Aldrich, ≥ 99.5 %) [37]. The mixture was stirred for 4 hours under reflux. After cooling the solution was concentrated with a rotary evaporator until sodium iodide precipitated. The mixture was filtered and the process was repeated with the filtrate until no further precipitation occurred. Acetonitrile was removed by evacuation to afford N‐formyl‐N‐ methylformamide sufficiently pure for GC analysis. The synthesis of FMF was done by Bertram Kimmerle (ETH Zürich). 6.2.2 MOF synthesis STA‐12(Co) was synthesized hydrothermally by reaction of cobalt(II) acetate and N,N’‐ piperazinebis(methylenephosphonic acid) (H4L), prepared by the method reported by Mowat et al. 154
6.2 Experimental [38]. In a typical synthesis cobalt(II) acetate tetrahydrate (Sigma), H4L, potassium hydroxide solution (freshly prepared, 1 mol/L) and water were mixed, to give a reaction ratio of 2.0:1.0:2.12:900, in a 40 mL Teflon lined autoclave, using 20 mL of water. The reaction was stirred for 30 minutes and an initial pH of 8 recorded. The autoclave was then sealed and heated at 220 °C for 72 hours. The resulting purple powder was collected by vacuum filtration, washed with water and dried overnight at 40 °C. Phase purity was confirmed by powder X‐ray diffraction, using a Stoe STADI P powder diffractometer with an Fe Kα1 radiation source (λ = 1.930642 Å). The composition of STA‐12(Co) was determined jointly by elemental analysis, using a CEInstruments EA1110 CHNS analyzer; thermo‐ gravimetric analysis (TGA), using a Netzsch TG 209, and energy dispersive X‐ray spectroscopy (EDX) using a JEOL JSM‐5600 scattered electron microscope (SEM) fitted with an Oxford Instruments INCA Energy 200 EDX system. Porosimetry measurements were made gravimetrically using a Hiden Isochema IGA at 77 K. Synthesis and ex situ characterization of the freshly synthesized MOF material was done by Michael T. Wahrmby and Paul A. Wright from the University of St. Andrews (UK). 6.2.3 Catalytic test reactions Catalytic test reactions were performed in a 25 mL three‐necked flask equipped with reflux condenser, magnetic stirrer and gas inlet. Since the system was sensitive to minute amounts of Co, cleaning the flask with aqua regia prior to each experiment was necessary. In a typical reaction, the flask was charged with 30 mL DMF and immersed in an oil bath kept at 100 °C under vigorous stirring. Oxygen was fed to the reaction mixture via the gas inlet with 50 mL/min. After a short time (15‐30 min), 100 mg biphenyl as internal standard, 2.0 mg STA‐12(Co) and 2.00 mmol of the olefin ((E)‐, (Z)‐stilbene or styrene) were added. Samples for GC analysis were taken in regular intervals. GC analysis was performed with a HP 6000 series gas chromatograph equipped with an FID detector and a HP‐5 GC column (Agilent Technologies Inc.). Used catalyst for recycling experiments was obtained from an experiment where 20 mg instead of 2.0 mg were employed because of difficulties in recovering the small catalyst amount used in the standard experiment. Autoclave reactions were carried out in a 100 mL stainless steel autoclave with a PTFE inset. The reactor was charged with the same amounts of DMF, (E)‐stilbene, biphenyl and STA‐12(Co) as described above. A magnetic stirrer was added, the autoclave sealed, purged several times with oxygen and finally pressurized to the desired oxygen pressure. The autoclave was immersed in an oil bath heated at ca. 110 °C so that the internal temperature in the autoclave was 100 °C. After the reaction, the autoclave was cooled to room temperature and carefully vented to prevent loss of material. Product analysis was done by GC as described above. 155
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TECHNICAL UNIVERSITY OF DENMARK (DT
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Preface The present dissertation su
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the carboxylic acid, ceria inhibite
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Resume Denne afhandling giver indle
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hvorimod mængden af katalysator ku
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2.3.8 Oxidation of sulfides .......
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5.3.5 Macroscopic mass transport in
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Chapter 1 Introduction With its gre
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1. Introduction Scheme 1‐1: High
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1. Introduction Figure 1‐2: Phase
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1. Introduction [28] S. Bawaked, N.
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2.1 Introduction 2.1 Introduction E
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2.2.1 Synthesis of gold catalysts 2
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2.2 Catalyst synthesis for oxidatio
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2.2 Catalyst synthesis for oxidatio
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2.3 Selective liquid‐phase oxidat
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Table 2-1: Overview over alcohol ox
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Ph O O Ph (4) (5) 2.3 Selective liq
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Table 2-4: Side-chain oxidation of
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2.3.4 Oxidation of cyclohexane 2.3
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Table 2-5: Oxidatin of cyclohexane.
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Table 2-6: Ring hydroxylation of ar
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Table 2-7: Aerobic oxidation of ami
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Table 2-8: Oxidation of hydroquinon
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Table 2-9: Oxidation of silanes wit
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Table 2-10: Oxidation reactions cat
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2.4 Strengths and opportunities of
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2.6 References 2.6 References [1] M
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2.6 References [56] H. Tumma, N. Na
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2.6 References [113] C. Keresszegi,
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2.6 References [169] Q. Zhu, Y. Lia
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2.6 References [223] M. Fetizon, M.
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Chapter 3 Selective Liquid-Phase Ox
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3.2 Experimental 3.2.1 Catalyst pre
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3.3 Results Scattering amplitudes a
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Absorption (a.u.) 1.2 1.0 0.8 0.6 0
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Conversion (%) 100 90 80 70 60 50 4
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3.3 Results Figure 3‐5: In situ X
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3.3 Results Table 3‐2: Conversion
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3.3 Results In order to gain insigh
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3.3 Results the cost of selectivity
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3.4 Discussion synergetic interacti
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3.5 Conclusions to corroborate the
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3.6 References [29] T. Mitsudome, Y
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Chapter 4 Selective Side-Chain Oxid
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Page 121 and 122: 4.3 Results Scheme 4‐1: Oxidation
Page 123 and 124: 4.3 Results Figure 4‐2: Formation
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Page 127 and 128: Absorption (a.u.) Absorption (a.u.)
Page 129 and 130: 4.3 Results atomic mixing of Ag and
Page 131 and 132: 4.3 Results Figure 4‐7: Influence
Page 133 and 134: 4.4 Discussion and mechanistic cons
Page 135 and 136: 4.5 Conclusions heterogeneous radic
Page 137 and 138: 4.6 References [29] S.I. Zabinsky,
Page 139 and 140: Chapter 5 Experimental Determinatio
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Page 143 and 144: 5.2 Experimental Eurotherm 2216e te
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Page 147 and 148: (Eq. 5‐5) AB i j ε AB i j β 5.2
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Page 153 and 154: Pressure (bar) 150 145 140 135 5.3
Page 155 and 156: 5.3 Results Figure 5‐7: Oxidation
Page 157 and 158: Weight (g) 5.3 Results Figure 5‐8
Page 159 and 160: 5.4 Discussion catalytic reactions
Page 161 and 162: 5.4 Discussion corresponding CO2‐
Page 163 and 164: 5.5 Conclusions 5.5 Conclusions The
Page 165 and 166: 5.6 References [29] I. Tsivintzelis
Page 167: 6.1 Introduction 6.1 Introduction A
Page 171 and 172: 6.3 Results out in 1 mm quartz tube
Page 173 and 174: 6.3 Results Figure 6‐2: Structure
Page 175 and 176: 6.3 Results Figure 6‐4: Epoxidati
Page 177 and 178: 6.3 Results Figure 6‐6: Compariso
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Page 181 and 182: 6.3 Results investigated the epoxid
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Page 185 and 186: 6.3 Results Figure 6‐11: EXAFS an
Page 187 and 188: 6.4 Discussion would need to be for
Page 189 and 190: 6.5 Conclusions Formation of the ep
Page 191 and 192: 6.6 References [28] J. Perles, N. S
Page 193 and 194: Chapter 7 Concluding Remarks 7.1 Co
Page 195 and 196: 7.2 Final remarks and outlook speci
Page 197 and 198: Acknowledgements Acknowledgements T
Page 199: Curriculum Vitae Matthias Josef Bei
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