Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

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CHAPTER 2 Benzyl alcohols both with electron‐donating and electron‐withdrawing substituents (entry 7) were aminated with similar reaction rates. Secondary alcohols were unreactive under the described reaction conditions which is in contrast to the previously described studies on alcohol dehydrogenation where secondary alcohols were always more reactive. Hydrogen‐acceptor free dehydrogenation was investigated in more detail in a recent paper using metallic Cu nanoparticles also supported on hydrotalcite [52]. As in the previous studies, primary benzylic alcohols were less reactive than secondary aliphatic alcohols. High temperatures were required (≥130 °C). At 180 °C, neat cyclooctanol could be transferred to cyclooctanone in 87 % yield with a TOF of 388 h ‐1 (entry 8). A related publication from the same group used Cu catalysts for the anaerobic lactonization of diols [111]. Hydrotalcite prepared by hydrothermal synthesis gave the best results but also other supports such as SiO2, TiO2 and Al2O3 exhibited good catalytic activity in mesitylene solvent at 150 °C. Yield (%) 100 80 60 40 20 0 Ag/HT Ru/HT Pd/HT Figure 2‐9: Oxidant‐free dehydrogenation of cinnamic alcohol over Ag/Ht, Ru/HT and Pd/HT [86]; CA: cinnamic aldehyde, PPal: 3‐phenylpropanal, PPol: 3‐phenylpropan‐1‐ol. In analogy to Cu/HT catalysts, Ag nanoparticles supported on hydrotalcites are also capable of facilitating the dehydrogenation of a broad variety of samples [86] with very high selectivity. Due to the low silver loading (0.005 wt.‐%), high TOFs were obtained, e.g. for benzyl alcohol oxidation (Table 2‐1, entry 9). Despite the low loading TEM images with silver nanoparticles could be recorded and revealed an average Ag particle size of 3.3 nm. Based on the catalyst mass, however, the catalyst activity appears only moderate. Usually 0.10 g of catalyst were required to convert 1 mmol of substrate over 24 h. Cinnamyl alcohol containing a double bond which could be susceptible to 22 CA PPal PPol
2.3 Selective liquid‐phase oxidation reactions transfer hydrogenation was converted to cinnamaldehyde with 100 % selectivity potentially due to the weak interaction between H2 and the Ag surface [112]. Ru/HT and Pd/HT on the contrary afforded large amounts of isomerization or hydrogenated products (Figure 2‐9). OH Scheme 2‐6: Dehydrogenation mechanism over Ag/Al2O3 featuring basic and acidic sites, adapted from ref. [67]. Ag/Al2O3 was thoroughly investigated at lower temperatures (100 °C) where also the evolution of H2 was proved (Table 2‐1, entry 10) [67]. High selectivies were obtained for various alcohols. Based on IR investigations, a reaction mechanism was proposed which involved both acidic and basic sites on the catalyst support (Scheme 2‐6). The catalyst deactivated during the reaction. Reactivation was achieved by treatment with O2 at 600 °C and subsequent hydrogen treatment, which might indicate the involvement of subsurface silver‐oxygen species in the reaction. These are specifically formed under the air treatment conditions and stable towards low‐temperature hydrogen treatment [12, 13]. EXAFS analysis suggested unusually small Ag particle sizes < 1nm. Note that Ag‐O species might interfere with the EXAFS analysis (vide infra) [71] affording underestimated Ag particle sizes. Ag/Al2O3 could also be used for oxidant‐free amide synthesis from alcohols and amines [68]. Ag n O H δ- δ+ OH OH Ag n Al O Al δ- δ+ OH OH Al Al H 2 Ag n Note that the oxidant‐free oxidation of alcohols is also catalyzed by palladium [113, 114] though there are some important differences. Side reactions observed over palladium are the C‐O bond cleavage of the alcohol by surface‐adsorbed hydrogen (affording e.g. toluene in benzyl alcohol oxidation). Additionally, CO as a side product from alcohol oxidation poisons the palladium catalysts 23 H Ag n H O H O OH δ+ Al Al O δ+ H H δ- O H Al O Al OH δ+ δ- H Ag n δ+ H O H O OH δ+ Al Al O O
Page 1 and 2: TECHNICAL UNIVERSITY OF DENMARK (DT
Page 3 and 4: Preface The present dissertation su
Page 5 and 6: the carboxylic acid, ceria inhibite
Page 7 and 8: Resume Denne afhandling giver indle
Page 9 and 10: hvorimod mængden af katalysator ku
Page 11 and 12: 2.3.8 Oxidation of sulfides .......
Page 13 and 14: 5.3.5 Macroscopic mass transport in
Page 15 and 16: Chapter 1 Introduction With its gre
Page 17 and 18: 1. Introduction Scheme 1‐1: High
Page 19 and 20: 1. Introduction Figure 1‐2: Phase
Page 21 and 22: 1. Introduction [28] S. Bawaked, N.
Page 23 and 24: 2.1 Introduction 2.1 Introduction E
Page 25 and 26: 2.2.1 Synthesis of gold catalysts 2
Page 27 and 28: 2.2 Catalyst synthesis for oxidatio
Page 29 and 30: 2.2 Catalyst synthesis for oxidatio
Page 31 and 32: 2.3 Selective liquid‐phase oxidat
Page 33 and 34: Table 2-1: Overview over alcohol ox
Page 35: 2.3 Selective liquid‐phase oxidat
Page 45 and 46: Ph O O Ph (4) (5) 2.3 Selective liq
Page 51 and 52: Table 2-4: Side-chain oxidation of
Page 53 and 54: 2.3.4 Oxidation of cyclohexane 2.3
Page 55 and 56: Table 2-5: Oxidatin of cyclohexane.
Page 59 and 60: Table 2-6: Ring hydroxylation of ar
Page 63 and 64: Table 2-7: Aerobic oxidation of ami
Page 65 and 66: Table 2-8: Oxidation of hydroquinon
Page 69 and 70: Table 2-9: Oxidation of silanes wit
Page 71 and 72: Table 2-10: Oxidation reactions cat
Page 73 and 74: 2.4 Strengths and opportunities of
Page 81 and 82: 2.6 References 2.6 References [1] M
Page 83 and 84: 2.6 References [56] H. Tumma, N. Na
Page 85 and 86: 2.6 References [113] C. Keresszegi,
Page 87 and 88:
2.6 References [169] Q. Zhu, Y. Lia
Page 89 and 90:
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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4.2 Experimental single‐step flam
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4.2 Experimental alcohol (Aldrich,
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4.3 Results Scheme 4‐1: Oxidation
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4.3 Results Figure 4‐2: Formation
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4.3 Results oxidation by either 2,6
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Absorption (a.u.) Absorption (a.u.)
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4.3 Results atomic mixing of Ag and
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4.3 Results Figure 4‐7: Influence
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4.4 Discussion and mechanistic cons
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4.5 Conclusions heterogeneous radic
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4.6 References [29] S.I. Zabinsky,
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Chapter 5 Experimental Determinatio
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5.2 Experimental The most important
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5.2 Experimental Eurotherm 2216e te
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Figure 5-1: Schematic view of the e
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(Eq. 5‐5) AB i j ε AB i j β 5.2
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(a) (b) (c) (d) (e) (f) (g) (h) (i)
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5.3 Results two association sites o
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Pressure (bar) 150 145 140 135 5.3
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5.3 Results Figure 5‐7: Oxidation
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Weight (g) 5.3 Results Figure 5‐8
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5.4 Discussion catalytic reactions
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5.4 Discussion corresponding CO2‐
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5.5 Conclusions 5.5 Conclusions The
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5.6 References [29] I. Tsivintzelis
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6.1 Introduction 6.1 Introduction A
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6.2 Experimental [38]. In a typical
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6.3 Results out in 1 mm quartz tube
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6.3 Results Figure 6‐2: Structure
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6.3 Results Figure 6‐4: Epoxidati
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6.3 Results Figure 6‐6: Compariso
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6.3 Results Figure 6‐8: Influence
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6.3 Results investigated the epoxid
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6.3 Results Figure 6‐10: Co‐epo
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6.3 Results Figure 6‐11: EXAFS an
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6.4 Discussion would need to be for
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6.5 Conclusions Formation of the ep
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6.6 References [28] J. Perles, N. S
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Chapter 7 Concluding Remarks 7.1 Co
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7.2 Final remarks and outlook speci
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Acknowledgements Acknowledgements T
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Curriculum Vitae Matthias Josef Bei
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