Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

More documents

Recommendations

Info

2.3.2 <strong>Oxidation</strong> of alkenes CHAPTER 2 The oxidation of alkenes in the gas phase is well‐established over silver catalysts for the oxidation of ethylene to ethylene oxide where molecular oxygen can be used. In liquid phase olefin oxidations, oxygen often has to be supplied in an activated form, e.g. as m‐chloroperoxybenzoic acid. Catalysts have been developed to use less expensive peroxides, typically hydrogen peroxide and TBHP [11]. Also procedures using an additional sacrificial reductant, e.g. an aldehyde or H2, in combination with and in order to activate molecular oxygen are described, but examples for catalysts achieving epoxidation with molecular oxygen only are rare. Typical substrates used in epoxidation studies are cyclohexene and styrene. Epoxidation reactions can be catalyzed by Cu, Ag and Au. Au epoxidation catalysis is already widely covered by recent reviews on Au catalysis [4‐6] and thus will only shortly be disscussed here. Typical substrates are styrene and cyclohexene (Table 2‐2 and Table 2‐3). (1) (2) catalyst O2 catalyst O2 OO Scheme 2‐7: Schematic reaction pathway for secondary epoxidation via primary oxidation products for cyclohexene (1) and styrene (2). 2.3.2.1 <strong>Oxidation</strong> of aliphatic olefines O catalyst O2 High epoxide selectivities are difficult to obtain for cyclohexene and other aliphatic substrates since allylic C‐H bonds easily break in the presence of radicals typically occurring in this type of oxidation reaction. Especially with molecular oxygen, peroxo radicals or peroxides can form as intermediates which can serve as the primary epoxidizing agent (Scheme 2‐7) being principally also conceivable for styrene. This reaction pathway can only be excluded when the epoxide selectivity is high. The group of Hutchings successfully applied Au/graphite, Au/SiO2 and Au/TiO2 catalysts for the aerobic oxidation of cyclohexene and cyclooctene [97]. The reaction was greatly depending on the choice of solvent and required catalytic amounts of TBHP suggesting that the underlying mechanism was based on radicals. Epoxides were only formed to a significant amount with 1,2,3,5‐tetramethylbenzene and 26 O O O OO O O O
2.3 Selective liquid‐phase oxidation reactions hexafluorobenzene as solvents, the former giving a selectivity of 50 % to the epoxide (Table 2‐2, entry 1). The high selectivity excludes the epoxidation to occur via the mentioned cyclohexenylperoxo/ ‐peroxide as the main reaction pathway. Apparently, oxygen supply by leaving the reaction vessel open to air was sufficient. Cyclooctene could be epoxidized with selectivities around 80 % even under solvent‐free conditions, TOFs of up to 35 h ‐1 were achieved [120] at temperatures around 80 °C (Table 2‐2, entry 2). Gold nanoparticles supported on La‐doped manganese oxide octahedral molecular sieves applied for solventless oxidation of cyclohexene yielded mostly allylic oxidation products (entry 3, small amounts of epoxide were also formed) showing that gold has no intrinsic aerobic epoxidation activity [122]. Gold and copper modified silicon nanowires (Au/ and Cu/SiNWs), respectively, were tested in the aerobic epoxidation in the absence of solvent [123] for both cyclohexene and cyclooctene with TBHP as radical initiator in an open reactor system. Outstanding selectivities to the epoxide with Au/SiNWs for cyclooctene oxidation (>90 %), TOFs being in the range of 50 h ‐1 and higher (entry 4a) were reported. In strong contrast, for cyclohexene with Au/SiNWs exclusively allylic oxidation products were observed (entry 4b). Cu/SiNWs also afforded only allylic oxidation products (entry 5a,b). No internal standard was used, so substrate evaporation occurring over the long reaction time (24 h) at elevated temperatures (80 °C) might have interfered. As an alternative to the direct reaction with oxygen, the combination of Au/CeO2 as a peroxide generating catalyst and Ti‐MCM‐41 as an epoxidizing catalyst was proposed [124]. The formation of gold‐peroxy species from reaction with azo‐bis(isobutyronitrile) (AiBN) on the surface of Au nanoparticles was evidenced by IR investigations and assumed to be responsible for the formation of cumene hydroperoxide from cumene. With cumene as sacrificial reductant, selectivities in 1‐octene oxidation approached 90 %. TOFs close to 50 h ‐1 were obtained at low conversion at 100 °C (entry 6, Scheme 2‐8). Au/CeO 2 + AiBN O 2 OOH silylated Ti-MCM-41 Scheme 2‐8: Epoxidation of 1‐octene by oxygen activated by cumene with Au/CeO2 and Ti‐MCM‐41 in a one‐ pot synthesis [124]. 27 ( ) 5 ( ) 5 O + OH
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 39: 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.
Page 91 and 92:
Chapter 3 Selective Liquid-Phase Ox
Page 93 and 94:
3.2 Experimental 3.2.1 Catalyst pre
Page 95 and 96:
3.3 Results Scattering amplitudes a
Page 97 and 98:
Absorption (a.u.) 1.2 1.0 0.8 0.6 0
Page 99 and 100:
Conversion (%) 100 90 80 70 60 50 4
Page 101 and 102:
3.3 Results Figure 3‐5: In situ X
Page 103 and 104:
3.3 Results Table 3‐2: Conversion
Page 105 and 106:
3.3 Results In order to gain insigh
Page 107 and 108:
3.3 Results the cost of selectivity
Page 109 and 110:
3.4 Discussion synergetic interacti
Page 111 and 112:
3.5 Conclusions to corroborate the
Page 113 and 114:
3.6 References [29] T. Mitsudome, Y
Page 115 and 116:
Chapter 4 Selective Side-Chain Oxid
Page 117 and 118:
4.2 Experimental single‐step flam
Page 119 and 120:
4.2 Experimental alcohol (Aldrich,
Page 121 and 122:
4.3 Results Scheme 4‐1: Oxidation
Page 123 and 124:
4.3 Results Figure 4‐2: Formation
Page 125 and 126:
4.3 Results oxidation by either 2,6
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
Page 141 and 142:
5.2 Experimental The most important
Page 143 and 144:
5.2 Experimental Eurotherm 2216e te
Page 145 and 146:
Figure 5-1: Schematic view of the e
Page 147 and 148:
(Eq. 5‐5) AB i j ε AB i j β 5.2
Page 149 and 150:
(a) (b) (c) (d) (e) (f) (g) (h) (i)
Page 151 and 152:
5.3 Results two association sites o
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 and 168:
6.1 Introduction 6.1 Introduction A
Page 169 and 170:
6.2 Experimental [38]. In a typical
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
Page 179 and 180:
6.3 Results Figure 6‐8: Influence
Page 181 and 182:
6.3 Results investigated the epoxid
Page 183 and 184:
6.3 Results Figure 6‐10: Co‐epo
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
show all

Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?