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CuO-containing MCM-48 as catalysts for phenol hydroxylation
Catalysis Communications 6 (2005) 762–765 www.elsevier.com/locate/catcom
CuO-containing MCM-48 as catalysts for phenol hydroxylation Lan-Lan Lou, Shuangxi Liu
*
Institute of New Catalytic Materials Science, College of Chemistry, Nankai University, Tianjin 300071, PR China Received 9 March 2005; accepted 4 July 2005 Available online 19 September 2005
Abstract The CuO–MCM-48 catalysts prepared by wet impregnation technique were originally used as the catalysts, with high phenol conversion and diphenol selectivity, for phenol hydroxylation with hydrogen peroxide. Furthermore, the optimized reaction conditions over these catalysts for phenol hydroxylation were acquired. 2005 Elsevier B.V. All rights reserved. Keywords: CuO–MCM-48 catalyst; Phenol hydroxylation; Phenol conversion; Diphenol selectivity
1. Introduction
2. Experimental
Catechol and hydroquinone, two main diphenol products of phenol hydroxylation, have wide applications in many fields [1]. Additionally, phenol hydroxylation by hydrogen peroxide is a typical environmentally friendly catalytic reaction. So many researchers have devoted to the studies of this reaction, and various catalysts have been applied to this reaction, especially transition metal or transition metal complex containing micro/mesoporous materials such as CuNaY [2], MeAPOs [3], FeCl2/MCM-41 [4], Ti/HMA [5], TS-1 [6], etc. While as we learned, no work has been done on the CuO–MCM-48 used as catalyst in this reaction. MCM-48 with well-defined pore size and a three-dimensional channel may have some advantages over microporous zeolites and onedimensional MCM-41. We prepared CuO–MCM-48 and studied its catalytic performance.
The parent silica MCM-48 materials were synthesized according to a procedure outlined earlier [7] in autoclaves at 383 K for 72 h. A gel (molar) composition of 1TEOS:0.46CTAB:0.41NaOH:52.95H2O was used. The template was removed by calcining at 823 K in air for 5 h. The CuO–MCM-48 was prepared by the wet impregnation technique with the ethanol solution of copper nitrate. After impregnation the sample was dried at room temperature, and then calcined at 723 K for 5 h. The CuO–MCM-48 catalysts with different CuO content were prepared by using different Cu(NO3)2 Æ 3H2O concentrations in ethanol solution and detected by ICP-AES (IRIS Advantage, TJASolutions USA). The siliceous MCM-41 was synthesized by a slightly adapted literature procedure [8] from a mixture of reactants with the following composition: 1TEOS:0.12CTAB:8NH4OH:114H2O. CuO–MCM-41 was prepared by the wet impregnation technique, the same method as CuO–MCM-48. The catalytic experiments were performed in a homemade reactor equipped with a reflux condenser, a temperature controllable water-bath and a magnetic stirrer. 1.67 g of phenol, 0.08 g of catalyst and 15 ml of water were introduced into the reactor in turn, and after the
*
Corresponding author. Tel.: +86 22 23509005; fax: +86 22 23509005. E-mail address: [email protected] (S. Liu). 1566-7367/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2005.07.004
L.-L. Lou, S. Liu / Catalysis Communications 6 (2005) 762–765
desired temperature was reached, a calculated amount of aqueous H2O2 solution (30 wt%) was added into the reaction mixture. Both reaction mixture and product were analyzed by gas chromatograph (JINPU, GC 508A, PEG-20M 31 m · 0.32 mm capillary column). Considering the byproducts [9] the method of external standard was used. The byproducts, namely benzoquinone and other deep oxidation products (e.g., tar) were not quantitated. Moreover, the CuO–MCM-48 catalyst was characterized by powder X-ray diffraction (XRD, D/max-RAX) and temperature programmed reduction (TPR). The TPR measurements were carried out in a self-assembled instrument with a flow of 5–6 vol% H2 in Ar with a heating rate of 10 K min 1. Prior to this, the activation for sample was performed in an Ar flow up to 500 C at a rate of 10 K min 1.
3. Results and discussion Table 1 shows that pure MCM-48 has no catalytic activity for phenol hydroxylation. All CuO–MCM-48 catalysts have good catalytic activity and selectivity for this reaction, and this implies that this reaction is associated with CuO. The highest phenol conversion obtained is 29.5%, which corresponds to the stoichiometric amount that can be hydroxylated with the available H2O2. With the enhancement of CuO content in MCM-48, the conversion of phenol increases, while catechol selectivity decreases, at the same time hydroquinone selectivity increases. It may be explained by the reduction of the pore size of MCM-48 with the enhancement of CuO content. Pure CuO catalyst leads to low phenol conversion and diphenol selectivity. So it can be concluded that both phenol conversion and diphenol selectivity increase remarkably after loading CuO onto MCM-48. CuO–MCM-41 has lower cataTable 1 Activity of different catalysts in phenol hydroxylationa
lytic activity than CuO–MCM-48, This may be attributed to the 3D topological structure of MCM-48 which makes material transmitting more favorable. In light of the comparison with literature [10], it is also displayed that MCM-48 can better play as a support of active species than MCM-41. With the increasing of reaction temperature, the enhancement of phenol conversion is observed in Table 2. At 60 C, the diphenol selectivity reaches its highest value of 85.4%. Table 3 displays the influence of reaction time on the catalytic activity of CuO–MCM-48 (4.89) catalyst. At the beginning of the reaction, surprisingly, phenol conversion is at a high level of 27.2% accompanying with low selectivity for both catechol and hydroquinone. This may be relating to the high sorption capacity of MCM-48, which results the lower concentration of phenol in the initial solution. With the increase of reaction time, phenol conversion decreases and reaches its lowest level of 19.8% at 2 h, and then increases gradually. After 3 h the reaction achieves steady-state, and the diphenol selectivity acquires a high value of 88.7%. Considering both phenol conversion and diphenol selectivity, the reaction temperature 60 C and the reaction time 4 h are suitable over this catalyst for phenol hydroxylation. The molar ratio of phenol to H2O2 has great effect on the catalytic activity for phenol hydroxylation (Table 4). When the molar ratio of phenol to H2O2 was changed from 1 to 3, phenol conversion decreased
Table 2 The effect of reaction temperature on phenol hydroxylationa Temperature (C)
40 50 60 70 80
Phenol conv. (%)
Selectivity (%) CAT
HQ
Other
17.1 18.8 21.8 22.7 25.9
43.0 52.4 52.0 47.7 42.9
30.9 29.0 33.4 29.9 28.7
26.1 18.6 14.6 22.4 28.4
a The reaction conditions are the same in Table 1, using CuO–MCM48(4.89) as catalyst.
Catalyst
Phenol conv. (%)
Selectivity (%) CAT
HQ
Other
MCM-48 CuO–MCM-48 CuO–MCM-48 CuO–MCM-48 CuO–MCM-48 CuO–MCM-41 CuOd
0.0 24.1 25.9 27.9 29.5 18.0 14.1
– 44.4 42.9 40.0 39.8 41.0 40.3
– 28.2 28.7 31.7 32.7 18.9 16.3
– 27.4 28.4 28.3 27.5 40.1 43.4
(3.10)b (4.89) (6.66) (8.28) (4.89)c
763
a Reaction conditions: reaction temperature 80 C, reaction time 3 h, phenol/H2O2 (molar ratio) = 3, solvent: water, CAT: catechol, HQ: hydroquinone. b The values in the parentheses are the weight percentage of CuO detected by ICP-AES. c Prepared by the same method as CuO–MCM-48. d The same weight of CuO as that for the CuO–MCM-48 (4.89) catalyst.
Table 3 The effect of reaction time on phenol hydroxylationa Time (h)
Phenol conv. (%)
Selectivity (%) CAT
HQ
Other
0.5 1 2 3 4 5
27.2 22.6 19.8 21.8 22.8 23.1
37.4 39.4 53.3 52.0 51.7 45.3
22.8 29.8 32.8 33.4 37.0 29.4
39.8 30.8 13.9 14.6 11.3 25.3
a
The reaction conditions are the same in Table 1 except for reaction temperature 60 C, using CuO–MCM-48 (4.89) as catalyst. The sampling was performed orderly in the same experiment.
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L.-L. Lou, S. Liu / Catalysis Communications 6 (2005) 762–765
Table 4 The effect of the molar ratio of phenol to H2O2 on phenol hydroxylationa Phenol/H2O2 (mol/mol)
Phenol conv. (%)
Selectivity (%) CAT
HQ
Other
1 2 3 TS-1b
51.1 38.1 22.8 36.0
37.9 38.1 51.7 51.0
24.5 26.0 37.0 5.0
37.6 35.9 11.3 44.0
a Reaction conditions: reaction temperature 60 C, reaction time 4 h, CuO–MCM-48 (4.89) as catalyst. b From [6], reaction conditions: reaction temperature 57 C, reaction time 6 h, phenol/H2O2 (molar ratio) = 1, phenol/catalyst (weight ratio) = 10, m(Ti)/m(Ti + Si) = 0.091/1, solvent: acetone.
Fig. 1. TPR profiles of CuO–MCM-48 and CuO.
while the selectivity for diphenol increased significantly. The result is comparable to the catalytic activity of TS1 catalyst at similar reaction conditions. Compared to other Cu-containing catalysts known from the literatures [2,11–15], the CuO–MCM-48 materials in this work gave higher conversions and comparable product selectivities, which was mainly attributed to the enlarged pore size and 3D topological structure of the carrier media MCM-48. Besides metal complex content, reaction temperature, reaction time and the molar ratio of phenol to H2O2, other factors such as the weight of catalyst, pH value of reaction mixture [16], reaction medium [17], may have great influence on catalytic activity of these catalysts in phenol hydroxylation with hydrogen peroxide. In this present work, in comparison with water, similar results were acquired with 0.01 M HCl as solvent, and very low phenol conversion and no diphenol selectivity were obtained by using acetone as reaction medium. The CuO–MCM-48 catalysts can be reused simply by washing with water and then drying at 110 C. Comparing the XRD patterns of reused CuO–MCM-48 catalyst and parent MCM-48, it is observed that after impregnation and catalyzing the hydroxylation of phenol, the intensity of the characteristic diffraction peaks of the cubic structure of MCM-48 only decreases slightly. When the catalyst was used in nine runs to catalyze the reaction of phenol hydroxylation, the phenol conversion was about 90% that in the first run. So the catalyst is stable for phenol hydroxylation and has potential industrial application. Fig. 1 shows the TPR profiles of CuO–MCM-48 and pure CuO. CuO–MCM-48 exhibits a sharp and symmetrical signal with the maximum of hydrogen consumption at 259 C, this implies the fine dispersion of CuO in MCM-48. Comparing with CuO–MCM-48, the reduction of pure CuO occurs at a remarkably higher temperature (320 C). The low reduction temperature of CuO in MCM-48 may be due to the interreaction between CuO and the framework of MCM-48 and/or the smaller
size [18] of CuO particles in MCM-48 than that of pure CuO. The result of TPR shows CuO loading in MCM48 is more active than pure CuO, which might be one of the reasons for CuO–MCM-48 to be prone to catalyze the reaction of phenol hydroxylation.
4. Conclusions The CuO–MCM-48 materials prepared here were originally used as the catalysts for phenol hydroxylation, high phenol conversion and diphenol selectivity obtained. The catalysts were stable and effective upon this reaction and have potential applications.
Acknowledgments We gratefully acknowledge the support of this research by the National Science Foundation of China (Nos. 29973016 and 20233030), the National Center for Innovation Research on Circular Economy of Nankai University, and the Ministry of Education, China.
References [1] W. Zhao, Y.F. Luo, P. Deng, Q.Z. Li, Catal. Lett. 73 (2001) 199. [2] J. Wang, J.N. Park, H.C. Jeong, K.S. Choi, X.Y. Wei, S.I. Hong, C.W. Lee, Energy Fuels 18 (2004) 470. [3] P.S.E. Dai, R.H. Petty, C.W. Ingram, R. Szostak, Appl. Catal. A 143 (1996) 101. [4] C.W. Lee, D.H. Ahn, B. Wang, J.S. Hwang, S.E. Park, Micropor. Mesopor. Mater. 44–45 (2001) 587. [5] S.K. Mohapatra, F. Hussain, P. Selvam, Catal. Commn. 4 (2003) 57. [6] A. Thangaraj, R. Kumar, P. Ratnasamy, J. Catal. 131 (1991) 294. [7] R. Ko¨hn, M. Fro¨ba, Catal. Today 68 (2001) 227. [8] Y. Yang, Z. Hu, Y.N. Lu¨, Y. Chen, Mater. Chem. Phys. 82 (2003) 440.
L.-L. Lou, S. Liu / Catalysis Communications 6 (2005) 762–765 [9] A. Santos, P. Yustos, A. Quintanilla, S. Rodriguez, F. GarciaOchoa, Appl. Catal. B 39 (2002) 97. [10] L. Noren˜a-Franco, I. Hernandez-Perez, J. Aguilar-Pliego, A. Maubert-Franco, Catal. Today 75 (2002) 189. [11] A. Dubey, V. Rives, S. Kannan, J. Mol. Catal. A 181 (2002) 151. [12] V. Rives, A. Dubey, S. Kannan, Phys. Chem. Chem. Phys. 3 (2001) 4826. [13] J. Sun, X. Meng, Y. Shi, R. Wang, S. Feng, D. Jiang, R. Xu, F.-S. Xiao, J. Catal. 193 (2000) 199.
765
[14] F.-S. Xiao, J. Sun, X. Meng, R. Yu, H. Yuan, J. Xu, T. Song, D. Jiang, R. Xu, J. Catal. 199 (2001) 273. [15] Robert Raja, Paul Ratnasamy, Appl. Catal. A 143 (1996) 145. [16] A. Germain, M. Allian, F. Figueras, Catal. Today 32 (1996) 145. [17] C. Liu, Y.K. Shan, X.G. Yang, X.K. Ye, Y. Wu, J. Catal. 168 (1997) 35. [18] M. Hartmann, S. Racouchot, C. Bischof, Chem. Commun. 997 (1997) 2367.
CuO-containing MCM-48 as catalysts for phenol hydroxylation Lan-Lan Lou, Shuangxi Liu
*
Institute of New Catalytic Materials Science, College of Chemistry, Nankai University, Tianjin 300071, PR China Received 9 March 2005; accepted 4 July 2005 Available online 19 September 2005
Abstract The CuO–MCM-48 catalysts prepared by wet impregnation technique were originally used as the catalysts, with high phenol conversion and diphenol selectivity, for phenol hydroxylation with hydrogen peroxide. Furthermore, the optimized reaction conditions over these catalysts for phenol hydroxylation were acquired. 2005 Elsevier B.V. All rights reserved. Keywords: CuO–MCM-48 catalyst; Phenol hydroxylation; Phenol conversion; Diphenol selectivity
1. Introduction
2. Experimental
Catechol and hydroquinone, two main diphenol products of phenol hydroxylation, have wide applications in many fields [1]. Additionally, phenol hydroxylation by hydrogen peroxide is a typical environmentally friendly catalytic reaction. So many researchers have devoted to the studies of this reaction, and various catalysts have been applied to this reaction, especially transition metal or transition metal complex containing micro/mesoporous materials such as CuNaY [2], MeAPOs [3], FeCl2/MCM-41 [4], Ti/HMA [5], TS-1 [6], etc. While as we learned, no work has been done on the CuO–MCM-48 used as catalyst in this reaction. MCM-48 with well-defined pore size and a three-dimensional channel may have some advantages over microporous zeolites and onedimensional MCM-41. We prepared CuO–MCM-48 and studied its catalytic performance.
The parent silica MCM-48 materials were synthesized according to a procedure outlined earlier [7] in autoclaves at 383 K for 72 h. A gel (molar) composition of 1TEOS:0.46CTAB:0.41NaOH:52.95H2O was used. The template was removed by calcining at 823 K in air for 5 h. The CuO–MCM-48 was prepared by the wet impregnation technique with the ethanol solution of copper nitrate. After impregnation the sample was dried at room temperature, and then calcined at 723 K for 5 h. The CuO–MCM-48 catalysts with different CuO content were prepared by using different Cu(NO3)2 Æ 3H2O concentrations in ethanol solution and detected by ICP-AES (IRIS Advantage, TJASolutions USA). The siliceous MCM-41 was synthesized by a slightly adapted literature procedure [8] from a mixture of reactants with the following composition: 1TEOS:0.12CTAB:8NH4OH:114H2O. CuO–MCM-41 was prepared by the wet impregnation technique, the same method as CuO–MCM-48. The catalytic experiments were performed in a homemade reactor equipped with a reflux condenser, a temperature controllable water-bath and a magnetic stirrer. 1.67 g of phenol, 0.08 g of catalyst and 15 ml of water were introduced into the reactor in turn, and after the
*
Corresponding author. Tel.: +86 22 23509005; fax: +86 22 23509005. E-mail address: [email protected] (S. Liu). 1566-7367/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2005.07.004
L.-L. Lou, S. Liu / Catalysis Communications 6 (2005) 762–765
desired temperature was reached, a calculated amount of aqueous H2O2 solution (30 wt%) was added into the reaction mixture. Both reaction mixture and product were analyzed by gas chromatograph (JINPU, GC 508A, PEG-20M 31 m · 0.32 mm capillary column). Considering the byproducts [9] the method of external standard was used. The byproducts, namely benzoquinone and other deep oxidation products (e.g., tar) were not quantitated. Moreover, the CuO–MCM-48 catalyst was characterized by powder X-ray diffraction (XRD, D/max-RAX) and temperature programmed reduction (TPR). The TPR measurements were carried out in a self-assembled instrument with a flow of 5–6 vol% H2 in Ar with a heating rate of 10 K min 1. Prior to this, the activation for sample was performed in an Ar flow up to 500 C at a rate of 10 K min 1.
3. Results and discussion Table 1 shows that pure MCM-48 has no catalytic activity for phenol hydroxylation. All CuO–MCM-48 catalysts have good catalytic activity and selectivity for this reaction, and this implies that this reaction is associated with CuO. The highest phenol conversion obtained is 29.5%, which corresponds to the stoichiometric amount that can be hydroxylated with the available H2O2. With the enhancement of CuO content in MCM-48, the conversion of phenol increases, while catechol selectivity decreases, at the same time hydroquinone selectivity increases. It may be explained by the reduction of the pore size of MCM-48 with the enhancement of CuO content. Pure CuO catalyst leads to low phenol conversion and diphenol selectivity. So it can be concluded that both phenol conversion and diphenol selectivity increase remarkably after loading CuO onto MCM-48. CuO–MCM-41 has lower cataTable 1 Activity of different catalysts in phenol hydroxylationa
lytic activity than CuO–MCM-48, This may be attributed to the 3D topological structure of MCM-48 which makes material transmitting more favorable. In light of the comparison with literature [10], it is also displayed that MCM-48 can better play as a support of active species than MCM-41. With the increasing of reaction temperature, the enhancement of phenol conversion is observed in Table 2. At 60 C, the diphenol selectivity reaches its highest value of 85.4%. Table 3 displays the influence of reaction time on the catalytic activity of CuO–MCM-48 (4.89) catalyst. At the beginning of the reaction, surprisingly, phenol conversion is at a high level of 27.2% accompanying with low selectivity for both catechol and hydroquinone. This may be relating to the high sorption capacity of MCM-48, which results the lower concentration of phenol in the initial solution. With the increase of reaction time, phenol conversion decreases and reaches its lowest level of 19.8% at 2 h, and then increases gradually. After 3 h the reaction achieves steady-state, and the diphenol selectivity acquires a high value of 88.7%. Considering both phenol conversion and diphenol selectivity, the reaction temperature 60 C and the reaction time 4 h are suitable over this catalyst for phenol hydroxylation. The molar ratio of phenol to H2O2 has great effect on the catalytic activity for phenol hydroxylation (Table 4). When the molar ratio of phenol to H2O2 was changed from 1 to 3, phenol conversion decreased
Table 2 The effect of reaction temperature on phenol hydroxylationa Temperature (C)
40 50 60 70 80
Phenol conv. (%)
Selectivity (%) CAT
HQ
Other
17.1 18.8 21.8 22.7 25.9
43.0 52.4 52.0 47.7 42.9
30.9 29.0 33.4 29.9 28.7
26.1 18.6 14.6 22.4 28.4
a The reaction conditions are the same in Table 1, using CuO–MCM48(4.89) as catalyst.
Catalyst
Phenol conv. (%)
Selectivity (%) CAT
HQ
Other
MCM-48 CuO–MCM-48 CuO–MCM-48 CuO–MCM-48 CuO–MCM-48 CuO–MCM-41 CuOd
0.0 24.1 25.9 27.9 29.5 18.0 14.1
– 44.4 42.9 40.0 39.8 41.0 40.3
– 28.2 28.7 31.7 32.7 18.9 16.3
– 27.4 28.4 28.3 27.5 40.1 43.4
(3.10)b (4.89) (6.66) (8.28) (4.89)c
763
a Reaction conditions: reaction temperature 80 C, reaction time 3 h, phenol/H2O2 (molar ratio) = 3, solvent: water, CAT: catechol, HQ: hydroquinone. b The values in the parentheses are the weight percentage of CuO detected by ICP-AES. c Prepared by the same method as CuO–MCM-48. d The same weight of CuO as that for the CuO–MCM-48 (4.89) catalyst.
Table 3 The effect of reaction time on phenol hydroxylationa Time (h)
Phenol conv. (%)
Selectivity (%) CAT
HQ
Other
0.5 1 2 3 4 5
27.2 22.6 19.8 21.8 22.8 23.1
37.4 39.4 53.3 52.0 51.7 45.3
22.8 29.8 32.8 33.4 37.0 29.4
39.8 30.8 13.9 14.6 11.3 25.3
a
The reaction conditions are the same in Table 1 except for reaction temperature 60 C, using CuO–MCM-48 (4.89) as catalyst. The sampling was performed orderly in the same experiment.
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L.-L. Lou, S. Liu / Catalysis Communications 6 (2005) 762–765
Table 4 The effect of the molar ratio of phenol to H2O2 on phenol hydroxylationa Phenol/H2O2 (mol/mol)
Phenol conv. (%)
Selectivity (%) CAT
HQ
Other
1 2 3 TS-1b
51.1 38.1 22.8 36.0
37.9 38.1 51.7 51.0
24.5 26.0 37.0 5.0
37.6 35.9 11.3 44.0
a Reaction conditions: reaction temperature 60 C, reaction time 4 h, CuO–MCM-48 (4.89) as catalyst. b From [6], reaction conditions: reaction temperature 57 C, reaction time 6 h, phenol/H2O2 (molar ratio) = 1, phenol/catalyst (weight ratio) = 10, m(Ti)/m(Ti + Si) = 0.091/1, solvent: acetone.
Fig. 1. TPR profiles of CuO–MCM-48 and CuO.
while the selectivity for diphenol increased significantly. The result is comparable to the catalytic activity of TS1 catalyst at similar reaction conditions. Compared to other Cu-containing catalysts known from the literatures [2,11–15], the CuO–MCM-48 materials in this work gave higher conversions and comparable product selectivities, which was mainly attributed to the enlarged pore size and 3D topological structure of the carrier media MCM-48. Besides metal complex content, reaction temperature, reaction time and the molar ratio of phenol to H2O2, other factors such as the weight of catalyst, pH value of reaction mixture [16], reaction medium [17], may have great influence on catalytic activity of these catalysts in phenol hydroxylation with hydrogen peroxide. In this present work, in comparison with water, similar results were acquired with 0.01 M HCl as solvent, and very low phenol conversion and no diphenol selectivity were obtained by using acetone as reaction medium. The CuO–MCM-48 catalysts can be reused simply by washing with water and then drying at 110 C. Comparing the XRD patterns of reused CuO–MCM-48 catalyst and parent MCM-48, it is observed that after impregnation and catalyzing the hydroxylation of phenol, the intensity of the characteristic diffraction peaks of the cubic structure of MCM-48 only decreases slightly. When the catalyst was used in nine runs to catalyze the reaction of phenol hydroxylation, the phenol conversion was about 90% that in the first run. So the catalyst is stable for phenol hydroxylation and has potential industrial application. Fig. 1 shows the TPR profiles of CuO–MCM-48 and pure CuO. CuO–MCM-48 exhibits a sharp and symmetrical signal with the maximum of hydrogen consumption at 259 C, this implies the fine dispersion of CuO in MCM-48. Comparing with CuO–MCM-48, the reduction of pure CuO occurs at a remarkably higher temperature (320 C). The low reduction temperature of CuO in MCM-48 may be due to the interreaction between CuO and the framework of MCM-48 and/or the smaller
size [18] of CuO particles in MCM-48 than that of pure CuO. The result of TPR shows CuO loading in MCM48 is more active than pure CuO, which might be one of the reasons for CuO–MCM-48 to be prone to catalyze the reaction of phenol hydroxylation.
4. Conclusions The CuO–MCM-48 materials prepared here were originally used as the catalysts for phenol hydroxylation, high phenol conversion and diphenol selectivity obtained. The catalysts were stable and effective upon this reaction and have potential applications.
Acknowledgments We gratefully acknowledge the support of this research by the National Science Foundation of China (Nos. 29973016 and 20233030), the National Center for Innovation Research on Circular Economy of Nankai University, and the Ministry of Education, China.
References [1] W. Zhao, Y.F. Luo, P. Deng, Q.Z. Li, Catal. Lett. 73 (2001) 199. [2] J. Wang, J.N. Park, H.C. Jeong, K.S. Choi, X.Y. Wei, S.I. Hong, C.W. Lee, Energy Fuels 18 (2004) 470. [3] P.S.E. Dai, R.H. Petty, C.W. Ingram, R. Szostak, Appl. Catal. A 143 (1996) 101. [4] C.W. Lee, D.H. Ahn, B. Wang, J.S. Hwang, S.E. Park, Micropor. Mesopor. Mater. 44–45 (2001) 587. [5] S.K. Mohapatra, F. Hussain, P. Selvam, Catal. Commn. 4 (2003) 57. [6] A. Thangaraj, R. Kumar, P. Ratnasamy, J. Catal. 131 (1991) 294. [7] R. Ko¨hn, M. Fro¨ba, Catal. Today 68 (2001) 227. [8] Y. Yang, Z. Hu, Y.N. Lu¨, Y. Chen, Mater. Chem. Phys. 82 (2003) 440.
L.-L. Lou, S. Liu / Catalysis Communications 6 (2005) 762–765 [9] A. Santos, P. Yustos, A. Quintanilla, S. Rodriguez, F. GarciaOchoa, Appl. Catal. B 39 (2002) 97. [10] L. Noren˜a-Franco, I. Hernandez-Perez, J. Aguilar-Pliego, A. Maubert-Franco, Catal. Today 75 (2002) 189. [11] A. Dubey, V. Rives, S. Kannan, J. Mol. Catal. A 181 (2002) 151. [12] V. Rives, A. Dubey, S. Kannan, Phys. Chem. Chem. Phys. 3 (2001) 4826. [13] J. Sun, X. Meng, Y. Shi, R. Wang, S. Feng, D. Jiang, R. Xu, F.-S. Xiao, J. Catal. 193 (2000) 199.
765
[14] F.-S. Xiao, J. Sun, X. Meng, R. Yu, H. Yuan, J. Xu, T. Song, D. Jiang, R. Xu, J. Catal. 199 (2001) 273. [15] Robert Raja, Paul Ratnasamy, Appl. Catal. A 143 (1996) 145. [16] A. Germain, M. Allian, F. Figueras, Catal. Today 32 (1996) 145. [17] C. Liu, Y.K. Shan, X.G. Yang, X.K. Ye, Y. Wu, J. Catal. 168 (1997) 35. [18] M. Hartmann, S. Racouchot, C. Bischof, Chem. Commun. 997 (1997) 2367.