CeO2 under mild conditions

Catalysis Communications 10 (2009) 1095–1098

Contents lists available at ScienceDirect

Catalysis Communications journal homepage: www.elsevier.com/locate/catcom

Selective oxidation of alcohols with molecular oxygen catalyzed by Ru/MnOx/CeO2 under mild conditions Tetsuo Sato *, Tasuku Komanoya Department of Applied Chemistry, Akita National College of Technology, 1-1 Iijimabunkyotyo, Akita 011-8511, Japan

a r t i c l e

i n f o

Article history: Received 2 December 2008 Received in revised form 26 December 2008 Accepted 5 January 2009 Available online 10 January 2009 Keywords: Alcohol oxidation Ru heterogeneous catalyst Molecular oxygen Mild conditions

a b s t r a c t A manganese oxides supported on cerium(IV) oxide MnOx/CeO2 precatalyst by wetness impregnation with manganese(II) acetate and cerium(IV) oxide. A Ru/MnOx/CeO2 catalyst was prepared by wetness impregnation of MnOx/CeO2 precatalyst with aqueous solution of ruthenium(III) chloride. The Ru/ MnOx/CeO2 catalyst has high catalytic activities for the oxidation of alcohols to the corresponding carbonyl compounds. Especially, the advantage of the present catalyst is the smooth oxidation of alcohols at 300 K under molecular oxygen atmosphere. Ó 2009 Elsevier B.V. All rights reserved.

1. Introduction The selective oxidation of alcohols to aldehydes or ketones is an important transformation in organic synthesis [1–3]. Aldehydes and ketones are an important class of compounds used as chemical intermediates in carbon–carbon bond forming reactions such as Aldol, Michael reactions and reaction with organometallic reagents. The traditional selective oxidations of alcohols are carried out with stoichiometric heavy metal oxidants such as dichromate and permanganate [1–3]. Recently, many homogeneous [4–6] and heterogeneous [7–26] catalyzed selective oxidation of alcohols using molecular oxygen as oxidant that are more economically efficient and environmentally benign have been reported instead of the traditional methods. Especially, heterogeneous catalytic systems have several advantages such as ease of recovering and reuse. To achieve simple and efficient aerobic alcohol oxidation catalyst systems which does not need an additive, various heterogeneous ruthenium-, palladium-, platinum-, gold-, and copper-catalysts, for example, Ru/CeO2 [10], Ru-hydrotalcite [11,12], RuMn2-hydrotalcite [13], Ru-hydroxyapatite [14], Ru-hydroxyapatite-c-Fe2O3 [15], Ru/Al2O3 [16,17], Ru/ Fe3O4 [18], Ru/CeO2/CoO(OH) [19], Ru–Co oxide [20], Ru/TiO2 [21], Ru/ZrO2 [21], Pd/C [22], Pd-hydrotalcite [23], Pd-hydroxyapatite [24], Pt-Bi/Al2O3 [7], Au/CeO2 [25], Au–Pd alloy nanoparticles/TiO2 [26], Au–Cu/SiO2 [27], have been developed. Although the activities of the heterogeneous catalysts for oxidation of alcohols have improved in recent years, efforts of aim at the * Corresponding author. Tel.: +81 18 847 6065; fax: +81 18 847 6066. E-mail address: [email protected] (T. Sato). 1566-7367/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2009.01.004

further improvement of the catalytic activities are continued. Yamaguchi and Mizuno [16,17] reported that supported ruthenium hydroxide catalyst had high catalytic activities for the oxidation of alcohols with molecular oxygen. Furthermore, Kaneda et al. [13] proposed that heterotrimetallic Ru(IV)Mn(IV)Mn(IV) species and Ru(IV)OCe(IV) species [19] facilitated the high efficient aerobic oxidation of alcohols, respectively. Most of heterogeneous catalytic alcohol oxidations were performed at a temperature higher than 330 K. From a viewpoint of reduction of environmental loads, the developments of the alcohol oxidation catalysts which have high catalytic activities at low temperature are important. In this paper, we report the synthesis of ruthenium hydroxide supported on manganese oxides and cerium oxide Ru/MnOx/CeO2 and the effective heterogeneous oxidation of alcohols with molecular oxygen catalyzed by Ru/MnOx/CeO2 catalyst at 300 K.

2. Experimental 2.1. Materials and instruments CeO2 was purchased from Aldrich Chemical Co. (nanopowder grade). Mn(OCOCH3)2
4H2O was purchased from Wako Pure Chemical Industries, Ltd. RuCl3
nH2O was purchased from Kanto Chemical Co., Inc. They were used as received without further purification. All alcohols and solvents were purchased from Aldrich Chemical Co. or Wako Pure Chemical Industries, Ltd. and purified by standard procedures used before. Powder X-ray diffraction patterns were recorded using BRUKER AXS MXP3A with CuKa

T. Sato, T. Komanoya / Catalysis Communications 10 (2009) 1095–1098

radiation of wavelength 0.154056 nm. The current and voltage during the measurement were 30 mA and 40 kV, respectively. Raman spectra were measured at room temperature using JASCO NRS1000 Laser Raman Spectrophotometer with a liquid nitrogen cooled CCD detector. Infrared spectra were recorded on JASCO FTIR-610 spectrometer at ambient conditions using KBr disk. Inductively coupled plasma measurements were performed by SII NanoTechnology SPS-1700HVR instrument. Analytical GC was performed by Shimadzu GC-14B with flame ionization detector equipped with Rtx WAX column. 2.2. Catalyst preparation and characterization A manganese oxides supported on cerium(IV) oxide MnOx/CeO2 precatalyst was prepared by wetness impregnation method. Cerium(IV) oxide CeO2 (2.00 g) was vigorously stirred with a solution of Mn(OCOCH3)2
4H2O (2.32 mmol) in distilled water (5 ml) for 15 min. The slurry was dried at 353 K for 20 h. After the dried mixture was kneaded for 30 min in a mortar with a pestle, the powder was calcined in air at 873 K or 1273 K for 3 h, yielding MnOx/CeO2 as a dark brown powder (2.01 g) or MnOx/CeO2-2 as a light brown powder (1.89 g), respectively. Mn2O3 and Mn3O4 were prepared by polymerizable complex methods calcined in air at 873 K and 1273 K, respectively [28], and these structures were determined by XRD. The Ru/MnOx/CeO2 catalyst was prepared by a modification of the preparation of Ru/Al2O3 according to the literature [16,17]. The MnOx/CeO2 (1.00 g) was vigorously stirred with a solution of RuCl3
nH2O (0.25 mmol) in distilled water (50 ml) at 358 K for 20 h. The slurry was centrifuged, washed with a large amount of distilled water, and dried in vacuo. The obtained powder was added into distilled water (20 ml) and the pH value of the solution was adjusted to 13.2 by addition of an aqueous solution of NaOH (1.00 M). The slurry was stirred at room temperature for 20 h. The resulting slurry was centrifuged, washed with a large amount of distilled water, and dried at 333 K for 24 h to afforded Ru/MnOx/ CeO2 (0.722 g) as a dark green powder. The loading amount of Ru on Ru/MnOx/CeO2 was 2.5 wt%. 2.3. Typical procedure for the oxidation of alcohols

+

(e)

(d)

The XRD patterns of the precatalysts MnOx/CeO2 calcined at 873 K and MnOx/CeO2-2 calcined at 1273 K, Mn3O4, Mn2O3, and CeO2 are shown in Fig. 1. Both XRD patterns of the MnOx/CeO2 and MnOx/CeO2-2 include the peaks ascribable to CeO2, Mn3O4, Mn2O3. A clear difference is not seen between the XRD patterns of the MnOx/CeO2 and MnOx/CeO2-2. Although calcinations temperature required 1273 K for preparation of Mn3O4 by the polymerizable complex method and Mn2O3 generated as an only product at 873 K, in preparation of the MnOx/CeO2, Mn3O4 generated at least 873 K. In the previous report, only Mn2O3 was contained in MnOx-CeO2 prepared by coprecipitation method calcined at 1073 K [29]. The lattice parameters of the CeO2 cubic fluorite phase in the MnOx/CeO2 and MnOx/CeO2-2 are both 0.543 nm, which is agreement with 0.543 nm for pure CeO2. These

* CeO2

+

+

+

+

+

# #

#

#

#

#

#

#

#

#

* (c) #

* +

#

+

#

* 20

* *

* 30

40

*

**

*

*

*

*

*

**

*

*

#

(a) 10

*

+

* *+

(b)

* 50

60

70

80

90

2 (degree) Fig. 1. XRD patterns of (a) CeO2, (b) MnOx/CeO2, (c) MnOx/CeO2-2, (d) Mn3O4, (e) Mn2O3.

results differ from a report that the lattice parameter of the fluorite phase in MnOx-CeO2 prepared by coprecipitation method decreases as compared with one of CeO2 [30] and suggest that MnOx is dispersing on the surface of CeO2, does not form homogeneous solid solution with CeO2. The XRD pattern of the Ru/MnOx/CeO2 catalyst was the same as that of the MnOx/CeO2. The FT-IR spectra of the MnOx/CeO2, MnOx/CeO2-2, Mn3O4, Mn2O3 and CeO2 are shown in Fig. 2. In the FT-IR spectrum of the MnOx/CeO2, broad bands were observed at 609, 521 (shoulder), and 501 cm 1. A similar spectrum was also observed in Ce0.7Mn0.3O2 prepared by coprecipitation method [30]. The band at 609 cm 1 is assigned to the asymmetric Mn-O-Mn stretching

(e)

(d) (c)

Transmissivity (%T)

3.1. Catalyst characterization

+

*

A suspension of Ru/MnOx/CeO2 (0.202 g, 5.0 mol% Ru) in a,a,atrifluorotoluene (1.5 ml) was stirred for 10 min under O2 atmosphere. The suspension was heated at 300 K and benzyl alcohol (0.108 g) was then added. The mixture was stirred at 300 K for 90 min under O2 atmosphere. Benzaldehyde was produced in >99% GC yield.

3. Results and discussion

+ Mn2O3 # Mn3O4

#

Intensity (cps)

1096

(b) (a)

800

700

600

500

400

Wavenumber (cm-1) Fig. 2. FT-IR spectra of (a) MnOx/CeO2, (b) MnOx/CeO2-2, (c) Mn3O4, (d) Mn2O3 and (e) CeO2.

1097

T. Sato, T. Komanoya / Catalysis Communications 10 (2009) 1095–1098

vibration, and the band at 501 cm 1 corresponds to the symmetric one [31]. In Mn3O4 and Mn2O3, bands were observed at 607, 571, 522, and 502 (shoulder) cm 1 and at 667, 605 (shoulder), 576, 526, and 502 (shoulder) cm 1, respectively, in good agreement with the literature [30–32]. Clearly, it is thought that both FT-IR spectra of the MnOx/CeO2 and MnOx/CeO2-2 are constituted of elements of Mn3O4, CeO2, and slight Mn2O3. In the Ru/MnOx/CeO2 catalyst, a very broad band assigned to the OAH stretching vibration in ruthenium hydroxide was observed in the range 3100–3700 cm 1 except for the bands ascribable to MnOx/CeO2. The Raman spectra of the MnOx/CeO2 and MnOx/CeO2-2, and CeO2 are shown in Fig. 3. In the Raman spectrum of CeO2, one band was observed at 463 cm 1 assigned to the F2g symmetric O-Ce-O stretching vibration of the CeO2 cubic fluorite structure [33]. In both MnOx/CeO2 and MnOx/CeO2-2, bands were observed at 434 cm 1 ascribable to CeO2 and at 640 cm 1 ascribable to MnOx. The bands assigned to the F2g symmetric O-Ce-O stretching vibration in the MnOx/CeO2 and MnOx/CeO2-2 were shifted to the lower Raman shift compared with the band in CeO2. These results suggest that a solid solution phase of MnOx/CeO2 is formed on the surface of CeO2 [34,35]. 3.2. Oxidation of alcohols

Intensity (a.u.)

The catalytic activities for the oxidation of benzyl alcohol to benzaldehyde under O2 atmosphere were compared with various heterogeneous ruthenium catalysts, as shown in Table 1. The catalyst ruthenium hydroxide and manganese oxides supported on cerium oxide Ru/MnOx/CeO2 shows a high catalytic activity (entry 1). Although the Ru/MnOx/CeO2-2 did not almost have a difference with the Ru/MnOx/CeO2 as the results of XRD, FT-IR, and Raman measurements, it is noteworthy that the catalytic activity for present oxidation remarkably decreased when the Ru/MnOx/CeO2-2 catalyst used (entry 4). Similarly, Ru/Co3O4/CeO2, Ru/MoO3/CeO2, and Ru/CrO3/CeO2 had less activities than Ru/MnOx/CeO2 (entries 5–7). The CeO2 was particularly suitable for the support compared with c-Al2O3 or ZrO2 (entries 8 and 9). Without any one of the Ru species, MnOx, or CeO2 in catalyst, the yield of benzaldehyde lowered (entries 10–12). These results were suggested that a combination of the three components, the Ru species, MnOx, and CeO2, was needed to achieve the high yield of the aldehyde. The Ru/MnOx/ CeO2 catalyst was reusable without decrease in catalytic activity

(c)

Table 1 Effects of catalyst for oxidation of benzyl alcohol to benzaldehyde with molecular oxygena. Entry

Catalyst

Conversion (%)

Yield (%)

1 2 3 4 5 6 7 8 9 10 11 12b

Ru/MnOx/CeO2 Reuse 1 Reuse 2 Ru/MnOx/CeO2-2 Ru/Co3O4/CeO2 Ru/MoO3/CeO2 Ru/CrO3/CeO2 Ru/MnOjc/x-Al2O2 Ru/MnOx/ZrO2 Ru/CeO2 Ru/Mn2O3 MnOx/CeO2

>99 >99 >99 44 89 62 53 91 47 69 76 13

>99 >99 >99 35 89 62 49 89 40 66 68 2

a Benzyl alcohol (2 mmol), catalyst (4.5 mol% Ru), PhCF3 (3 ml), 313 K, O2 atmosphere, 1 h. Conversion and yield were determined by GC using naphthalene as an internal standard. b MnOx/CeO2 (0.36 g).

(entries 2 and 3). When the catalyst was removed by filtration after 30 min, further oxidation of alcohol that remained in the filtrate did not proceed under identical conditions. This result suggests that the present oxidation of benzyl alcohol is a heterogeneous reaction proceeded on the catalyst surface, and is not a homogeneous reaction. The potential of catalytic activity of the Ru/MnOx/CeO2 catalyst in oxidation of benzyl alcohol under O2 atmosphere was explored in several conditions. The results are summarized in Table 2. Ru/ MnOx/CeO2 is one of the heterogeneous Ru catalysts with the highest activity in the oxidation of benzyl alcohol to benzaldehyde. In the oxidation of benzyl alcohol using 2.5 mol% or 1.5 mol% of the Ru/MnOx/CeO2 catalyst, benzaldehyde was quantitatively produced within 1 h at 323 K or 333 K and the corresponding turnover frequency (TOF) based on Ru were 40 h 1 or 67 h 1, respectively (entries 1 and 2). Moreover, the present oxidation using 1.25 mol% catalyst proceeded smoothly at 300 K, giving benzaldehyde quantitatively in 20 h without any additive, the TOF was 4.0 h 1 (entry 3). It is worth noting that the TOFs of the Ru/MnOx/CeO2 catalyst were higher than those reported for other heterogeneous Ru catalysts, such as Ru/Al2O3 (40 h 1 at 356 K) [16,17], RuMn2-hydrotalcite (50 h 1 at 333 K) [13], Ru-hydroxyapatite-c-Fe2O3 (3.3 h 1 at room temperature) [15]. Because the Ru/MnOx/CeO2 catalyst had high catalytic activity even at low temperature compared with other heterogeneous Ru catalysts, the oxidation of several alcohols using 5.0 mol% of the Ru/MnOx/CeO2 catalyst under O2 atmosphere at 300 K was examined. The results are summarized in Table 3. Benzylic, allylic, and aliphatic alcohols were oxidized to the corresponding benzaldehydes, a,b-unsaturated aldehyde and ketones. In particular, primary benzylic alcohols showed high reactivity and were converted into benzaldehydes quantitatively within short reaction times (entries 1 and 2). 1-Phenylethanol, secondary benzylic alcohol, was selectively oxidized to acetophenone with excellent yield

(b) Table 2 Oxidation of benzyl alcohol catalyzed by Ru/MnOx/CeO2 in various conditionsa. Entry

Catalyst (mol% Ru)

Temperature (K)

Time (h)

Conversion (%)

Yield (%)

TOF (h 1)

1 2 3

2.5 1.5 1.25

323 333 300

1 1 20

>99 >99 >99

>99 >99 >99

40 67 4.0

(a) 900

800

700

600

500

400

300

Raman shift (cm-1) Fig. 3. Raman spectra of (a) CeO2, (b) MnOx/CeO2, (c) MnOx/CeO2-2.

a Benzyl alcohol (2 mmol), Ru/MnOx/CeO2 (1.25–2.5 mol% Ru), PhCF3 (3 ml), O2 atmosphere. Conversion and yield were determined by GC using naphthalene as an internal standard.

1098

T. Sato, T. Komanoya / Catalysis Communications 10 (2009) 1095–1098

Table 3 Oxidation of various alcohols catalyzed by Ru/MnOx/CeO2 at 300 Ka. Entry

Alcohol

1

OH OH

2

3

OH

OH

4

References

Time (h)

Conversion (%)

Yield (%)

1.5

>99

>99

1.5

>99

97

7

99

99

8

>99

83

24

90

83

40

54

40

OH 5

5 6

6

OH

a

Alcohol (2 mmol), Ru/MnOx/CeO2 (5.0 mol% Ru), PhCF3 (3 ml), 300 K, O2 atmosphere. Conversion and yield were determined by GC using naphthalene as an internal standard.

although its oxidation required a long reaction time (entry 3). Cinnamyl alcohol completely reacted within 8 h, giving cinnamaldehyde in 83% yield. Furthermore, nonactivated aliphatic alcohols could be oxidized although the aliphatic alcohols required longer reaction time than the other activated benzylic and allylic alcohols. A secondary aliphatic 2-octanol was oxidized, giving the corresponding 2-octanone in 83% yield after 24 h. A primary aliphatic 1-octanol was less reactive than 2-octanol. 4. Conclusions In summary, the results of the characterization of the MnOx/ CeO2 precatalyst have suggested that manganese oxides MnOx containing Mn3O4 and Mn2O3 forms the solid solution on the surface of CeO2. The Ru/MnOx/CeO2 has high catalytic activities for the oxidation of alcohols to the corresponding carbonyl compounds. Especially, the advantage of the Ru/MnOx/CeO2 catalyst is the smooth oxidation of alcohols at 300 K under molecular oxygen atmosphere. It is thought that such high catalytic activities are attributable to the cooperative action among the Ru species, MnOx, and CeO2 in the catalyst.

[1] R.A. Sheldon, J.K. Kochi, Metal-Catalyzed Oxidations of Organic Compound, Academic Press, New York. [2] M. Hudlucky, Oxidations in Organic Chemistry, ACS Monograph Series, American Chemical Society, Washington, 1990. [3] S.V. Ley, A. Madin, in: B.M. Trost, I. Fleming, S.V. Ley (Eds.), Comprehensive Organic Synthesis, vol. 7, Pergamon, Oxford, 1991, p. 251. [4] R.A. Sheldon, in: L.L. Simandi (Ed.), Dioxygen Activation and Homogeneous Catalytic Oxidation, Elsevier, Amsterdam, 1991, p. 573. [5] I.E. Markó, P.R. Giles, M. Tsukazaki, S.M. Brown, C.J. Urch, Science 274 (1996) 2044. [6] G.-J. ten Brink, I.W.C.E. Arends, R.A. Sheldon, Science 287 (2000) 1636. [7] R.A. Anderson, K. Griffin, P. Johnson, P.L. Alsteres, Adv. Synth. Catal. 345 (2003) 517. [8] T. Mallat, A. Baiker, Chem. Rev. 104 (2004) 3037. [9] D. Astruc, F. Lu, R. Aranzaes, Angew. Chem. Int. Ed. 44 (2005) 7852. [10] F. Vocanson, Y.P. Guo, I.L. Namy, H.B. Kagan, Synth. Commun. 28 (1998) 2577. [11] K. Kaneda, T. Yamashita, T. Matsushita, K. Ebitani, J. Org. Chem. 63 (1998) 1750. [12] T. Matsushita, K. Ebitani, K. Kaneda, Chem. Commun. (1999) 265. [13] K. Ebitani, K. Motokura, T. Mizugaki, K. Kaneda, Angew. Chem. Int. Ed. 44 (2005) 3423. [14] K. Yamaguchi, K. Mori, T. Mizugaki, K. Ebitani, K. Kaneda, J. Am. Chem. Soc. 122 (2000) 7144. [15] K. Mori, S. Kanai, T. Hara, T. Mizugaki, K. Ebitani, K. Jitsukawa, K. Kaneda, Chem. Mater. 19 (2007) 1249. [16] K. Yamaguchi, N. Mizuno, Angew. Chem. Int. Ed. 41 (2002) 4538. [17] K. Yamaguchi, N. Mizuno, Chem. Eur. J. 9 (2003) 4353. [18] M. Kotani, T. Koike, K. Yamaguchi, N. Mizuno, Green Chem. 8 (2006) 735. [19] K. Ebitani, H.-B. Ji, T. Mizugaki, K. Kaneda, J. Mol. Catal. A: Chem. 212 (2004) 161. [20] M. Musawir, P.N. Davey, G. Kelly, I.V. Kozhevnikov, Chem. Commun. (2003) 1414. [21] A. Köckritz, M. Sebek, A. Dittmar, J. Radnik, A. Brückner, U. Bentrup, M.-M. Pohl, H. Hugl, W. Mägerlein, J. Mol. Catal. A: Chem. 246 (2006) 85. [22] T. Mallat, A. Baiker, Catal. Today 19 (1994) 247. [23] T. Nishimura, N. Kakiuchi, M. Inoue, S. Uemura, Chem. Commun. (2000) 1245. [24] K. Mori, K. Yamaguchi, T. Mizugaki, K. Ebitani, K. Kaneda, J. Am. Chem. Soc. 124 (2002) 11573. [25] A. Abad, P. Concepción, A. Corma, H. García, Angew. Chem. Int. Ed. 44 (2005) 4066. [26] D.I. Enache, J.K. Edwards, P. Landon, B. Solsona-Espriu, A.F. Carley, A.A. Herzing, M. Watanabe, C.J. Kiely, D.W. Knight, G.J. Hutchings, Science 311 (2006) 362. [27] C.D. Pina, E. Falletta, M. Rossi, J. Catal. 260 (2008) 384. [28] P.A. Lessing, Am. Ceram. Soc. Bull. 168 (1989) 1002. [29] M. Machida, M. Uto, D. Kurogi, T. Kijima, J. Mater. Chem. 11 (2001) 900. [30] P. Borker, A.V. Salker, Mater. Chem. Phys. 103 (2007) 366. [31] Z.W. Chen, J.K.L. Lai, C.H. Shek, J. Non-Cryst. Solids 352 (2006) 3285. [32] M.R. Morales, B.P. Barbero, L.E. Cadús, Fuel 87 (2008) 1177. [33] V.S. Escribano, E.F. Lópes, J.M. Gallardo-Amores, C. Del, H. Martínez, C. Pistarino, M. Panizza, C. Resini, G. Busca, Combst. Flame 153 (2008) 97. [34] J.E. Spanier, R.D. Robinson, F. Zhang, S.W. Chan, I.P. Herman, Phys. Rev. B 64 (2001) 245. [35] W. Shan, W. Shen, C. Li, Chem. Mater. 15 (2003) 4761.