Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

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CHAPTER 2 2.2 Catalyst synthesis for oxidation reactions Cu Cu O x (supported) oxidic (nano)particles Ag O 2 Cu O x surface oxidized (nano)particles Cu (Ag) Cu Ag Cu (Ag) mixed oxides Figure 2‐1: Schematic overview over catalyst types synthesized from coinage metals. Due to the high standard potential of gold, the most prevalent type of gold catalysts consists of metallic gold nanoparticles distributed on a high‐surface area support material. For silver and especially for copper, ionic species also play a role and thus the types of catalysts derived from those metals feature a higher versatility. A simplified schematic overview over the most abundant types of catalysts is given in Figure 2‐1. Supported metallic nanoparticles are common for all metals. By high‐ temperature treatment in oxygen, subsurface silver‐oxygen species (among others) are generated. Due to (mostly) ionic character of Cu under oxidizing conditions, a variety of Cu catalysts can be synthesized. Hence, fully and surface‐oxidized metal nanoparticles are used as catalysts though these are usually prone to leaching problems. Combination with other metals affords mixed oxides which can of course also be dispersed on a support. Cu catalysts with highly dispersed Cu centers are mostly synthesized via ion exchange. The metal‐organic frameworks (MOFs) constitute a relatively new type of catalyst class. Synthesis routes for the different catalysts will be summarized in this section. Note that the boundaries between the different types are fluid since e.g. the oxidation state of the metal can change during the catalytic reaction. MOFs Cu (Au) (Ag) CATALYST TYPES Cu 10 (Ag) Ag Cu Au Ag (supported) metallic (nano)particles Au Ag Ag Cu subsurface-oxygen modified metals homodispersed ions
2.2.1 Synthesis of gold catalysts 2.2 Catalyst synthesis for oxidation reactions Gold has attracted much interest and high efforts were put into developing efficient gold catalysts which undoubtedly contributed to the success of this noble metal. The most prevalent method to synthesize supported noble metal catalyst, i.e. (dry) impregnation usually affords undesirable large particles when used for Au catalysts. Therefore, other techniques were developed in order to synthesize Au nanoparticles on various supports such as deposition‐precipitation, adsorption of colloidal Au, vacuum deposition, grafting and reduction, etc. An extensive overview over these techniques was given in two reviews [4, 24]. Catalysts featuring metallic copper and silver particles can be prepared similarly; e.g. colloidal methods where pre‐reduced metal nanoparticles are adsorbed on a support. 2.2.2 Synthesis of copper catalysts The most prominent types of Cu catalysts feature Cu as (1) homodisperse ionic Cu species, (2) supported (potentially metallic) Cu nanoparticles and (3) (mixed) oxides or other bulk ionic materials (e.g. phosphates [25]). Note that often several Cu species are abundant in one catalyst, e.g. both CuxO particles and isolated Cu ions (Figure 2‐2). Therefore the categorization into different catalyst types and hence synthesis techniques shall only be understood as a rough classification. Copper catalysts with isolated Cu centers are most abundant and catalytically active in many oxidation reactions and often more stable against leaching than oxidic Cu nanoparticles. These species are frequently synthesized by ion exchange of zeolites [26‐30], similar porous materials [31, 32] and other minerals with ion exchanger properties like clays [33] or hydroxyapatite [34]. The ion exchange procedure is straightforward and therefore industrially applicable; the parent material is treated with a solution of the desired ion followed by filtration and drying. A higher concentration of the active metal can be obtained by repeating this treatment several times [27, 31] though high metal concentrations and/or calcination treatment can afford Cu domains which are often undesired due to the aforementioned leaching issue. In principal, supports modified by organic linkers can also be ion‐exchanged in order to graft Cu complexes [35, 36] but this class of catalysts will not be covered here. 11
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: 2.1 Introduction 2.1 Introduction E
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 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
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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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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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