Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

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CHAPTER 2 however, overoxidation of phenol was observed with Cu‐AlPO4‐5 having larger pores than Cu‐AlPO4‐ 11 with which the phenol selectivity was close to 100%. Comparsion of ref.s [31] and [41] both using Cu‐AlPO4 as catalysts shows how much reaction conditions and catalyst preparation can influence the selectivity. Also here, the isomorphous incorporation of Cu into the framework of the aluminophosphate was assumed to be substantial for obtaining catalytic activity. Further Cu‐ phosphate catalysts, i.e. Cu2(OH)PO4 and Cu4O(PO4)2 also exhibited considerable catalytic activity, though being a bulk material (BET surface areas ~ 1‐2 m 2 /g), in the hydroxylation of benzene, phenol and 1‐naphthol (entry 5 and 6) [59, 181]. Both water and acetonitrile were suitable solvents in combination with H2O2 as oxidant. The importance of isolated Cu species was further underlined by studying Cu‐modified Al‐pillared interlayer clays [45]. Though the selectivity was somewhat lower than obtainable with Cu‐AlPO4 materials, high TOFs of up to 100 h ‐1 (60 °C) were obtained (Table 2‐6, entry 7). Leaching was assumed to be responsible for catalyst deactivation. Such Cu‐doped pillared clays (montmorillonites, Figure 2‐2) were also investigated as catalysts for toluene as well as o‐, m‐ and p‐xylene oxidation with hydrogen peroxide in acetonitrile [33]. Both ring and side‐chain oxidation was observed to a similar extent rendering the oxidation of alkylaromatics with Cu and H2O2 not very selective. The same was observed with Zn,Cu,Al‐layered double hydroxides (hydrotalcites like compounds) [147]. By means of EPR, in both studies isolated Cu(II) species and bulk CuO were identified. CuO was connected to H2O2 decomposition, thus, giving another example where isolated Cu(II) centers are mandatory for an effective catalyst. Benzene can also be oxidized with H2O2 using high amounts of ascorbic acid as a co‐reductant [47]. This allows the reaction to be carried out close to room temperature (TOF of ~5 h ‐1 at 30 °C) with Fe/Cu/V mixed oxides supported on TiO2 (Table 2‐6, entry 8). 2.3.5.2 Hydroxylation in other solvents Cu‐MCM‐41 is a catalyst which is active both in acetonitrile and in acetic acid [182]. Hence, the role of acetonitrile as either an inert or reactive solvent may be different depending on the type of Cu catalyst. Cu‐MCM‐41 in acetic acid was active already at 30 °C in acetic acid/H2O2 with comparably good TOFs around 45 h ‐1 at phenol selectivities above 90 % (entry 9) [182]. Again it was shown that the appearance of crystalline CuO particles had no beneficial effect on the activity. Cu‐MCM‐41 was also used for the selective oxidation of 4‐methylanisole with H2O2 to the corresponding benzoquinone (TOF ~30 h ‐1 ) [190]. No leaching was found in acetic acid. With acetonitrile as a solvent, almost no conversion was found. A comparative leaching experiment was unfortunately not reported. In another study [191], Cu‐MCM‐41 oxidized anthracene to antraquinone by TBHP or H2O2 in benzene solvent. Almost no catalyst deactivation was observed indicating that leaching was low. 46
2.3 Selective liquid‐phase oxidation reactions Contrary to homodispersed Cu in MCM‐41, CuxO particles supported on activated carbon exhibited only low efficacy in benzene hydroxylation [183] lower than that of iron and vanadium oxide particles (entry 10) supporting the assumption that CuxO particles are catalytically active, however, not the most efficient catalysts for aromatics hydroxylation. CuO incorporated in a polymer membrane was furthermore used in a more application‐oriented study [192]. Dubey et al. investigated in several reports the catalytic activity of Cu‐containing ternary hydrotalcites in the hydroxylation of phenol [58, 184, 185] affording both catechol and hydroquinone. The reaction studied with CuCoAl (Table 2‐ 6, entry 11) and CuNiAl hydrotalcites (entry 12) gave the best results and required H2O2. TBHP was no suitable oxidant. These hydrotalcites were also capable of oxidizing benzene to phenol with nearly 100 % selectivity when pyridine was used as a solvent though catalyzing the reaction rather slowly (entry 13) [186]. The combination of Cu with Ru in MCM‐41 was catalytically active in neat benzene with H2O2 at 50 °C [143]. Phenol was the only product observed and TOFs were outstandingly high (above 600 h ‐1 , based on the combined amount of Ru and Cu). The group of Tsuruya investigated the use of molecular oxygen as oxidizing agent which required the use of ascorbic acid as a sacrificial reductant in aqueous acidic solvents (entries 14‐17) [28, 29, 43, 50, 187]. Various Cu catalysts were tested as catalysts, including Cu supported on Al2O3, SiO2 (also MCM‐41) and TiO2 as well as ion exchanged zeolites. Conversions were rather low at 30 °C (TOF < 1 h ‐1 ). Higher reaction temperatures had a negative effect on the overall conversion which was ascribed partly to ascorbic acid decomposition. The formation of H2O2 was evidenced during the reaction. Thus, it is reasonable to assume H2O2 to act as the primary hydroxylating agent. It was found that both framework incorporated Cu(II) species were catalytically active as well as leached Cu(II). Leached species gradually deactivated to Cu2O making truly heterogeneous catalysts the most effective catalysts. This also explains why heterogeneous Cu‐zeolite catalysts are better suited for this type of reaction [28] than different homogeneous Cu catalysts. CuO/Al2O3 was additionally more stable against leaching when prepared via co‐precipitation rather than impregnation [187]. In a more recent publication V‐Cu catalysts on various supports were successfully applied with ascorbic acid/O2 in an acetic medium (entry 18a) [188]. The potential of this dyad was shown by more drastic reaction conditions, i.e. 80 °C as a reaction temperature and oxygen partial pressures of 7 bar. Probably due to decomposition, H2O2 was no suitable oxidant. Dissolved Cu was not observed in the reaction mixture (though insoluble Cu2O may form from leached species, vide supra), while V leaching was an issue. This approach resulted in more active catalysts with a TOF of 2 h ‐1 (based on the amount of both V and Cu). To the best of the author’s knowledge, this study is also the only example where Ag was found to be active (though also in combination with V, entry 18b). Indeed, the literature provides only few examples of heterogeneous silver or gold catalysts active for this reaction although both metals proved numerous times to be capable of activating hydrogen peroxide. A recent study 47
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 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: 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
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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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