Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

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CHAPTER 2 intermediate oxidation product, i.e. the aldehyde or ketone. Au nanoparticles supported on nanosized CeO2 gave impressive results [96] with TOFs higher than 400 h ‐1 for 3‐octanol oxidation and >99 % selectivity. Often significantly lower reaction rates are reported. As an example, Enache et al. investigated a number of standard supports including SiO2, TiO2, CeO2 and activated carbon where TOFs were between 10 – 80 h ‐1 for benzyl alcohol oxidation at 100 °C [97] which settles gold catalysts in the proximity of silver catalysts (cf. Table 2‐1, entry 9 and 19). Many gold catalysts require a strong base in order to facilitate alcohol oxidation which is why basic supports often are beneficial for the Au catalyzed alcohol oxidation [7]. 2.3.1.1 Anaerobic alcohol oxidation The selective oxidation of alcohols is also readily catalyzed by silver and copper. Many reports describe alcohol oxidation under anaerobic conditions, i.e. either by using a hydrogen acceptor or no oxidant giving H2 as a side product. This approach is especially attractive where the intermediate aldehyde is highly susceptible to overoxidation by molecular oxygen. Anaerobic dehydrogenation with silver and copper catalysts is long known in gas phase catalysis [11]. The oxidant‐free lactonization of 1,5‐pentandiol to δ‐valerolactone was already described in 1947 by Schniepp and Geller [99] using copper chromite (Scheme 2‐3). High temperatures above 200 °C were necessary to facilitate the reaction which is in general observed due to the highly endothermic nature of the oxidant‐free alcohol dehydrogenation. High temperatures can limit the selectivity, e.g. polymeric HO OH cat. Cu 2Cr 2O 5 Scheme 2‐3: Anaerobic dehydrogenation of 1,5‐pentandiol [99]. side products were obtained during 1,5‐pentandiol conversion. Continuing these studies, Zaccharia et al. investigated the dehydrogenation of 3‐octanol and other alcohols at low temperatures of 90 °C [100, 101] with Cu/Al2O3 (Table 2‐1 , entry 1). In a closed reactor, only low conversions over long reaction times were achieved because of thermodynamic limitations caused by remaining H2. Removal of hydrogen by either reactor venting or, more effectively, addition of styrene as hydrogen acceptor resulted in quantitative conversion and a TOF of 4 h ‐1 (entry 2). Cyclooctanol dehydrogenation proceeded especially readily with a TOF of 12.5 h ‐1 at full conversion. Substrates bearing double bonds can also be used as hydrogen acceptors, the catalyst thus affording an isomerization product as was demonstrated with carveol (entry 3, Scheme 2‐4). With styrene as 20 - 2 H 2 O O
2.3 Selective liquid‐phase oxidation reactions O OH O Cu/Al2O3 Cu/Al2O3 N 2 Scheme 2‐4: Anaerobic oxidation/ isomerization of carveol over Cu/Al2O3 [101]. “external” hydrogen acceptor, the selectivity could be tuned to the dehydrogenated product. Primary benzylic alcohols reacted slowly (benzyl alcohol 51.5% conversion (20 h); cyclohexanol 99% conversion (3h)) [100] in contrast to aerobic alcohol oxidation over Au catalysts where similar or higher reaction rates were often observed for benzylic alcohols (Figure 2‐8) [98, 109, 110]. While in this report primary alcohols exhibited low reactivity, Cu supported on basic supports, i.e. MgO (entry 4) [51] and La2O3 (entry 5) [53] were suitable for primary aliphatic alcohols like 1‐octanol at high reaction temperatures (150 °C), also with styrene as hydrogen acceptor. Both Cu catalysts were stable against leaching. Cu was fully reduced in these studies. Figure 2‐8: Different reactivities of alcohols on gold [98] and copper [100] catalysts. The hydrogen transfer principle offers interesting reaction routes. Copper‐aluminum hydrotalcite was used as a catalyst for the amination of primary alcohols (Scheme 2‐5) which proceeds via the imine (Table 2‐1, entry 6) [102]. K2CO3 as a base was necessary under the harsh reaction conditions (160 °C). Ph Scheme 2‐5: Reaction scheme for the amination of primary alcohols [102]. Note that the proposed imine was not observed as an intermediate. 21 2 ,N 2 Cu/Al O 2 3 + styrene Au/Cu Mg Al O + O 5 1 2 x 2 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 OH + Ph NH2 TOF (h -1 ) CuAl-HT/ K 2CO 3 160 °C Ph O + ( ) 4 OH OH OH 0 20 40 60 80 100 120 140 160 Ph NH + H 2 2 Ph N TOF (h -1 ) + H 2 Ph Ph N H Ph
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: Table 2-1: Overview over alcohol ox
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,
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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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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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