Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

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CHAPTER 2 Cu/Al2O3 and Fe/Al2O3 where almost inactive. All the catalysts in this study where synthesized by impregnation which usually leads to formation of metal oxide particles. In the case of Cu, this can lead to excessive leaching which was unfortunately not investigated. The synergistic effect of Fe on Cu might result from a stabilization of CuO particles. CuxMn3‐xO4 spinels were also investigated under the same conditions [25]. A 1:1 ratio of Cu to Mn gave the best catalyst and the spinel was clearly favored over amorphous mixed CuMn oxides obtained by calcination of the coprecipitate at lower temperatures. With this catalyst, the selectivity to benzaldehyde dropped rapidly. After 3 hours reaction time 75 % selectivity to benzoic acid was obtained at 21.3 % conversion (entry 7). Already in the 1970s it was shown that Cu2O initiates the autoxidation of cumene (entry 8) [151], though being highly inferior to Co3O4. The oxidation of cumene occurs readily due to the low bond dissociation energy of the tertiary C‐H of 351.6 kJ/mol (toluene 375.0 kJ/mol) [152]. Metallic Cu was found to be inactive as a catalyst contrary to bulk metallic silver being a good initiator for the radical autoxidation of cumene [153]. Interestingly, the decomposition of cumene hydroperoxide depended on the gas atmosphere and occurred only in N2 but not in O2. Ag/SiO2 was also found to be a useful catalyst [154]. Alloying of Ag with Au supported on SiO2 via impregnation improved the catalyst performance, Au/SiO2 being entirely inactive [155]. Ag2O supported on α‐ and γ‐Al2O3 and zeolite 15X oxidized ethylbenzene to 1‐phenylethanol, acetophenone and ethylbenzene hydroperoxide (entry 9) [72]. The role of silver was also to initiate a radical autoxidation but while AiBN – also acting as an initiator – afforded mainly the peroxide, this species was decomposed on the silver catalysts. At 70 °C, the reaction proceeded only slowly (initial TOF between 3‐8.5 h ‐1 for the three different silver catalysts). At higher reaction temperatures (135 °C), ethylbenzene is oxidized more rapidly in the presence of oxygen by an impregnated Ag/SiO2 catalyst [91]. Also p‐xylene and cumene could be successfully oxidized though for p‐xylene only one methyl group was activated by this catalyst. CeO2 and a carboxylic acid as additives increased the p‐xylene oxidation rate. On the other hand, cumene oxidation was markedly hindered by the presence of CeO2 nanoparticles. In the absence of a carboxylic acid, CeO2 completely suppressed the alkyl aromatic oxidation being a radical scavenger. Toluene required higher reaction temperatures (entry 10). Significant silver leaching was observed with the impregnated catalyst which could be circumvented by using flame‐spray pyrolysis as a synthesis technique for Ag/SiO2‐CeO2 catalysts. This way, TOFs of 650 h ‐1 were obtained (Table 2‐ 4, entry 11‐13). To the best of the author's knowledge, no studies focus on using heterogenous gold catalysts for this reaction. However, Corma's group demonstrated the usability of gold for this reaction by using the peroxides formed during cumene oxidation by Au/CeO2 for epoxidation of aliphatic olefins [124]. 38
2.3.4 <strong>Oxidation</strong> of cyclohexane 2.3 Selective liquid‐phase oxidation reactions The oxidation of cyclohexane is of enormous industrial importance for the production of K/A‐oil, a mixture of cyclohexanone (K) and cyclohexanol (A) (preferably with a high ketone fraction) serving as an intermediate in the production of Nylon 6,6 and Nylon 6 [11]. Industrially, K/A‐oil is either obtained via non‐catalytic autoxidation or by using homogeneous Co catalysts in ppm‐amounts. A large variety of products is formed. High K/A selectivities are only obtained at low conversions. Harsh conditions are necessary with 10‐15 bar of air at temperatures around 150 °C being last but not least a considerable safety concern [11]. Ever since industrial processes where established in the 1940s, considerable research towards more efficient and especially heterogeneous catalysts has been conducted, yet finding better catalysts active under more benign conditions remains a challenge [157]. Even more, the reaction is also complex from an experimental point of view: oxidation of cyclohexane to different gaseous, volatile and products of low solubility partly being thermo‐ sensitive makes the accurate determination of conversions and selectivities challenging [158]. The formation of around 40 products was reported the most important products besides K/A oil being cyclohexane peroxides, as well as C5 and C6 acids (Scheme 2‐14) [156]. At least the use of a suitable internal standard is mandatory to obtain K/A yields not being overestimated [156, 159]. The last point has led to considerable discrepancy in the open literature on the catalytic activity of gold catalysts. HO O HO O O OH O OH OH C 6-polyoxygenates HO Scheme 2‐14: Main products of cyclohexane oxidation [156]. 39 O CO 2 CO OOH K/A oil 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 45 and 46: Ph O O Ph (4) (5) 2.3 Selective liq
Page 51: Table 2-4: Side-chain oxidation of
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
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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
Page 199:
Curriculum Vitae Matthias Josef Bei
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