Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

More documents

Recommendations

Info

CHAPTER 6 conditions where, however, free organic radicals could not be detected. Potential free radicals could be EPR inactive due to coupling or their concentration is below the limit of detection. The inhibiting effect of radical scavengers might also be due to adsorption or coordination to free Co sites [48]. A signal at g = 2.0076 was found which can be ascribed to Co III ‐O2* ‐ (superoxo‐) species formed from reaction of Co II with oxygen [49]. These can already be found in the solid catalyst measured ex situ and thus are not formed specifically under reaction conditions. Hence, their formation is likely not connected to the induction phase. Note that Co III ‐peroxo‐species, which might also form from reaction of Co II with O2, are not EPR active [50]. 6.3.7 Co-epoxidation of styrene and (E)-stilbene Driven by the observation that styrene epoxidation does not only proceed faster but also features a shorter induction phase, the co‐epoxidation of styrene and (E)‐stilbene was investigated thus doubling the substrate/catalyst ratio (Figure 6‐10a). Although the catalyst amount was not increased, styrene induced a much faster conversion of (E)‐stilbene. At the same time, the conversion of styrene became only slightly but significantly slower at medium conversions. Co‐ epoxidation with styrene had the strongest effect on the conversion of (Z)‐stilbene which increased from 11 % to 58 % with styrene (Table 6‐3, entry 1,2). This effect was not observed for the homogeneous Co catalysts neither for (E)‐ nor (Z)‐stilbene epoxidation (Table 6‐3, entry 3, 4) and might be an effect related to the special features of the MOF. Styrene being smaller than (E)‐stilbene can diffuse more easily into the micropores of the MOF. However, a transfer‐epoxidation from styrene oxide to (E)‐stilbene does not account for the styrene promotion since styrene oxide as an additive did not have any promoting effect even in large quantities. Oxygen transfer from styrene oxide as the potential oxidizing agent to (E)‐stilbene was also not observed under reaction conditions with flowing N2 instead of O2. 168
6.3 Results Figure 6‐10: Co‐epoxidation of styrene and (E)‐stilbene and the effect of benzaldehyde. (a) Comparison of only styrene and (E)‐stilbene conversion (solid symbols) with co‐epoxidation of styrene and (E)‐stilbene (open symbols), (■,□) (E)‐stilbene; (•,○) styrene conversion; (b) effect of benzaldehyde addition (0.2 mmol) on (E)‐stilbene conversion. <strong>Reactions</strong> conditions: 2.0 mmol (E)‐stilbene and/or styrene, 100 mg biphenyl, 30 mL DMF, 50 mL min ‐1 O2, 2.0 mg STA‐12(Co), 100 °C. Table 6‐3: Epoxidation of (Z)‐stilbene with heterogeneous and homogeneous Co catalysts. Reaction conditions: 2.0 mmol (Z)‐stilbene, 6.8 µmol Co as catalyst, 100 mg biphenyl, 30 mL DMF, 10 h, 50 mL min ‐1 O2. Optional styrene addition: 2.0 mmol. Entry Catalyst Styrene Promotion Conversion (%) Selectivity (%) 1 STA‐12(Co) NO 11 92 2 STA‐12(Co) YES 58 86 3 Co(acac)3 NO 66 80 4 Co(acac)3 YES 65 92 5 Co3O4 NO 9.4 53 Two major differences between MOF‐catalyzed styrene and (E)‐stilbene conversion are the higher reaction rate and the higher benzaldehyde selectivity (styrene ca. 12 %; (E)‐stilbene ca. 5 %) for the former. Thus, styrene conversion affords a comparably high benzaldehyde concentration already in the beginning of the reaction. Indeed, benzaldehyde as the major by‐product can explain the observed promoting effect – as with styrene, the (E)‐stilbene reaction rate was enhanced by addition of small substoichiometric amounts of benzaldehyde (Figure 6‐10b). In analogy to the previous observations, benzaldehyde did not have a promoting effect on homogeneous Co catalysts. 6.3.8 Formation of oxidizing species (a) (b) Triphenylphosphine is frequently used to scavenge thermally unstable peroxides for GC analysis. Also in the present study, triphenylphosphine oxide was found when PPh3 was added to the samples taken for GC analysis indicating the presence of peroxides. Over time the amount of peroxides increased steadily. Similar to FMF‐formation, peroxides also formed in lower amounts in the absence 169
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 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Ph O O Ph (4) (5) 2.3 Selective liq
Page 47 and 48:
Page 49 and 50:
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 57 and 58:
Page 59 and 60:
Table 2-6: Ring hydroxylation of ar
Page 61 and 62:
Page 63 and 64:
Table 2-7: Aerobic oxidation of ami
Page 65 and 66:
Table 2-8: Oxidation of hydroquinon
Page 67 and 68:
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 75 and 76:
Page 77 and 78:
Page 79 and 80:
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: 6.3 Results investigated the epoxid
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

Create successful ePaper yourself

Delete template?

Save as template?