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Catalytic phenol hydroxylation over Cu-incorporated mesoporous materials
Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.
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Catalytic phenol hydroxylation over Cuincorporated mesoporous materials Huili Tang, Yu Ren, Bin Yue, Shirun Yan and Heyong He* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, P.R. China
1. Introduction The production of diphenols from the hydroxylation of phenol under homogeneous and heterogeneous conditions has attracted much attention since 1970s [1]. Among many catalysts studied TS-1 is a promising environmentalfriendly one with aqueous H2O2 as the oxidant [2]. However, the small pore size of microporous molecular sieves restricts the substrates to access the active sites. The advent of mesoporous silica paved a new way for designing the catalysts with larger pore size where many active species can be immobilized or supported on the surface or incorporated into the matrix of mesoporous silicas [3]. In the previous work, we prepared Ti-containing mesoporous silicas through "one-pot" method using short chain carboxylic acids as the templates, exhibiting high catalytic activity in the cyclohexene epoxidation reaction [4]. Here we report the synthesis of Cu-incorporated mesoporous materials CMM-x (x stands for the Cu/Si molar ratio in starting materials) using glutaric acid as the template and their catalytic activity in phenol hydroxylation. 2. Experimental Section CMM-x (x = 0, 1/20, 1/50, 1/200) were synthesized by the sol-gel method. Copper(II) acetate, glutaric acid, HC1 (2 mol/1) and H2O were stirred together followed with TEOS to form a clear solution with a molar ratio of 1.00 Si : x metal: 0.50 glutaric acid : 2 HC1 : 45 H2O. After hydrolysis of TEOS for 1 h, the mixture was dried at 423 K for 2 h and the gel obtained was calcined in air at 773 K for 5 h. Phenol hydroxylation was carried out at 343 K in a three-necked flask (50 ml) equipped with a magnetic stirrer and a reflux condenser. 1.0 g phenol, 15.0 g distilled water and 50 mg catalyst were added successively into
676
the flask and heated to 343 K. 30 wt.% H2O2 was then added dropwisely and the reaction was carried out for 4 h. The analysis of products was carried out on an Agilent 1100 HPLC equipped with a 150 mm reversed phase C18 column at ambient temperature. The conversion of phenol, the selectivity of diphenol and the product distribution are all based on molar percentages. 3. Results and Discussion The XRD patterns of all CMM-x samples in the small angle region are similar to that of HMS mesoporous molecular sieve (Fig. 1) [5]. In the large angle region a hump at 15-30° from the amorphous silica is observed. Besides the hump, CMM-1/200 has no other diffreaction peak, whereas the samples with higher Cu content exhibit two weak peaks at 20 = 35.3 and 38.5° assigning to ( i l l ) and (111) diffractions of copper oxide, tenorite. The XRD results, along with the similar UV-visible diffuse reflectance spectra (not shown), indicate that the copper in the CMMs with low content mainly forms the highly dispersed Cu(II) oxide aggregates within mesoporous siliceous matrices [6].
CMM-0
a. u.)
CMM-0
CMM-1/200
CMM-1/200 c/>
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CMM-1/50
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111
111
CMM-1/20
CMM-1/20 4
5
6
7
8
9
10
10 15 20 25 30 35 40 45 50 55 60
2 Theta (°)
2Theta(°)
Fig. 1 X-ray diffraction patterns of Cu-incorporated mesoporous materials with different Cu/Si ratios in small angle region (a) and large angle region (b). Table 1 Physicochemical properties of the CMMs Sample CMM-1/20 CMM-1/50 CMM-1/200 CMM-0 "Analyzed by EDX
Molar ratio of Cu/Sia 1/19.6 1/49.8 1/196.4 0
Average pore size (nm) 5.67 3.84 3.36 3.30
Pore volume (cm3/g) 0.87 0.69 0.66 0.70
BET surface area (m2/g) 624 726 780 786
677
The typical N2 adsorption isotherm of the catalysts is of type IV classification with a H2 hysteresis loop (Fig. 2). CMM-x have BET surface areas of 620-780 m2g~' and pore volume of 0.66-0.87 cm3g~'. BET surface area of CMMs increases but pore size and pore volume roughly decrease with decreasing the molar ratio of Cu/Si (see Table 1). 400
0.0
Fig. 2 Typical N2 adsorption/desorption isotherm andpore size distribution for CMM-1/50.
The TEM images of all CMM-x catalysts show worm-like mesoporous structures (see Fig. 3), which is similar to HMS [4]. In order to confirm whether the pore structure of CMMs is three dimensional, an inverse carbonaceous mesoporous material was prepared using CMM-1/50 as the hard template [7]. The TEM image of carbonaceous structure reflects similar interconnected mesopore network, which is inferred that CMM-x catalysts have a threedimensional interconnected mesopore system. The catalytic performance of the CMM-x catalyst in phenol hydroxylation, as well as TS-1 and CuO are listed in Table 2. The non-porous bulk oxide CuO shows relatively low conversion of 9.8%. Although the catalytic activity of CMM-x does not change significantly with varying the copper content, the best phenol conversion of 25.1% is observed over CMM-1/50, which is comparable to that of TS-1 [8]. The catalyst also shows remarkable stability. In the third run reaction, CMM-1/50 still exhibits phenol conversion of 24.0%. Fig. 3 Typical TEM images of CMM-1/50
678 Table 2 The catalytic activities in the phenol hydroxylation reaction using H2O2 as oxidant Catalyst CMM-0 CMM-1/20 CMM-1/50 CMM-1/200 TS-1C CuO (tenorite)
Phenol Conversion
H2O2 efficiency3
0 22.5 25.1 18.4 20.8 9.8
67.6 75.4 55.3 62.5 29.4
Product distribution11 (%) HQ CAT BQ 53.9 2.3 43.8 59.5 39.3 1.2 54.0 0.6 45.4 44.4 55.5 0.1 40.9 11.8 7.3
a
H 2 O 2 efficiency = 100 * (H2O2 consumed in the formation of diphenol and benzoquinone, mole) •*• (total H2O2 added, mole) b HQ = hydroquinone, BQ = para-benzoquinone, CAT = catechol. The product of tar is not included. c Ti/(Ti+Si) = 0.022.
4. Conclusion Novel Cu-incorporated mesoporous materials CMMs were synthesized by a sol-gel method using glutaric acid as template. It was demonstrated that the CMMs had a 3D worm-like mesoporous structure with a large surface area of 600 to 800 m 2 g'', exhibiting high catalytic activity in the phenol hydroxylation with H2O2 comparable to TS-1. 5. Acknowledgement This work is supported by the National Basic Research Program of China (2003CB615807), the NSF of China (20421303, 20371013) and the Shanghai Science and Technology Committee (05DZ22313). 6. References [1] J. O. Edwards and R. Curci, in: Catalytic Oxidations with Hydrogen Peroxide As Oxidant, eds. G. Strukul (Kluwer Academic Publishers, Dordrecht, 1992) pp. 97. [2] M. Taramasso, G. Perego and B. Notari, US Patent 4410501 (1983). [3] L. Norena-Franco, I. Hernandez-Perez, P. Aguilar and A. Maubert-Franco, Catal. Today 75 (2002) 189. [4] Y. Ren, L.P. Qian, B. Yue and H. Y. He, Chinese J. Catal. 24 (2003) 947. [5] P. T. Tanev and T. J. Pinnavaia, Science 267 (1995) 865. [6] Tkachenko, K.V. Klementiev, E. Loffler, I. Ritzkopf, F. Schuth, M. Bandyopadhyay, S. Grabowski, H. Gies, V. Hagen, M. Muhler, L. H. Lu, R.A. Fischer and W. Griinert, Phys. Chem. Chem. Phys. 5 (2003) 4325. [7] R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem. B 103 (1999) 7743. [8] P. S. E. Dai, R. H. Petty, C. W. Ingram and R. Szostak, Appl. Catal. A: Gen. 143 (1996) 101.
675 675
Catalytic phenol hydroxylation over Cuincorporated mesoporous materials Huili Tang, Yu Ren, Bin Yue, Shirun Yan and Heyong He* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, P.R. China
1. Introduction The production of diphenols from the hydroxylation of phenol under homogeneous and heterogeneous conditions has attracted much attention since 1970s [1]. Among many catalysts studied TS-1 is a promising environmentalfriendly one with aqueous H2O2 as the oxidant [2]. However, the small pore size of microporous molecular sieves restricts the substrates to access the active sites. The advent of mesoporous silica paved a new way for designing the catalysts with larger pore size where many active species can be immobilized or supported on the surface or incorporated into the matrix of mesoporous silicas [3]. In the previous work, we prepared Ti-containing mesoporous silicas through "one-pot" method using short chain carboxylic acids as the templates, exhibiting high catalytic activity in the cyclohexene epoxidation reaction [4]. Here we report the synthesis of Cu-incorporated mesoporous materials CMM-x (x stands for the Cu/Si molar ratio in starting materials) using glutaric acid as the template and their catalytic activity in phenol hydroxylation. 2. Experimental Section CMM-x (x = 0, 1/20, 1/50, 1/200) were synthesized by the sol-gel method. Copper(II) acetate, glutaric acid, HC1 (2 mol/1) and H2O were stirred together followed with TEOS to form a clear solution with a molar ratio of 1.00 Si : x metal: 0.50 glutaric acid : 2 HC1 : 45 H2O. After hydrolysis of TEOS for 1 h, the mixture was dried at 423 K for 2 h and the gel obtained was calcined in air at 773 K for 5 h. Phenol hydroxylation was carried out at 343 K in a three-necked flask (50 ml) equipped with a magnetic stirrer and a reflux condenser. 1.0 g phenol, 15.0 g distilled water and 50 mg catalyst were added successively into
676
the flask and heated to 343 K. 30 wt.% H2O2 was then added dropwisely and the reaction was carried out for 4 h. The analysis of products was carried out on an Agilent 1100 HPLC equipped with a 150 mm reversed phase C18 column at ambient temperature. The conversion of phenol, the selectivity of diphenol and the product distribution are all based on molar percentages. 3. Results and Discussion The XRD patterns of all CMM-x samples in the small angle region are similar to that of HMS mesoporous molecular sieve (Fig. 1) [5]. In the large angle region a hump at 15-30° from the amorphous silica is observed. Besides the hump, CMM-1/200 has no other diffreaction peak, whereas the samples with higher Cu content exhibit two weak peaks at 20 = 35.3 and 38.5° assigning to ( i l l ) and (111) diffractions of copper oxide, tenorite. The XRD results, along with the similar UV-visible diffuse reflectance spectra (not shown), indicate that the copper in the CMMs with low content mainly forms the highly dispersed Cu(II) oxide aggregates within mesoporous siliceous matrices [6].
CMM-0
a. u.)
CMM-0
CMM-1/200
CMM-1/200 c/>
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CMM-1/50
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111
111
CMM-1/20
CMM-1/20 4
5
6
7
8
9
10
10 15 20 25 30 35 40 45 50 55 60
2 Theta (°)
2Theta(°)
Fig. 1 X-ray diffraction patterns of Cu-incorporated mesoporous materials with different Cu/Si ratios in small angle region (a) and large angle region (b). Table 1 Physicochemical properties of the CMMs Sample CMM-1/20 CMM-1/50 CMM-1/200 CMM-0 "Analyzed by EDX
Molar ratio of Cu/Sia 1/19.6 1/49.8 1/196.4 0
Average pore size (nm) 5.67 3.84 3.36 3.30
Pore volume (cm3/g) 0.87 0.69 0.66 0.70
BET surface area (m2/g) 624 726 780 786
677
The typical N2 adsorption isotherm of the catalysts is of type IV classification with a H2 hysteresis loop (Fig. 2). CMM-x have BET surface areas of 620-780 m2g~' and pore volume of 0.66-0.87 cm3g~'. BET surface area of CMMs increases but pore size and pore volume roughly decrease with decreasing the molar ratio of Cu/Si (see Table 1). 400
0.0
Fig. 2 Typical N2 adsorption/desorption isotherm andpore size distribution for CMM-1/50.
The TEM images of all CMM-x catalysts show worm-like mesoporous structures (see Fig. 3), which is similar to HMS [4]. In order to confirm whether the pore structure of CMMs is three dimensional, an inverse carbonaceous mesoporous material was prepared using CMM-1/50 as the hard template [7]. The TEM image of carbonaceous structure reflects similar interconnected mesopore network, which is inferred that CMM-x catalysts have a threedimensional interconnected mesopore system. The catalytic performance of the CMM-x catalyst in phenol hydroxylation, as well as TS-1 and CuO are listed in Table 2. The non-porous bulk oxide CuO shows relatively low conversion of 9.8%. Although the catalytic activity of CMM-x does not change significantly with varying the copper content, the best phenol conversion of 25.1% is observed over CMM-1/50, which is comparable to that of TS-1 [8]. The catalyst also shows remarkable stability. In the third run reaction, CMM-1/50 still exhibits phenol conversion of 24.0%. Fig. 3 Typical TEM images of CMM-1/50
678 Table 2 The catalytic activities in the phenol hydroxylation reaction using H2O2 as oxidant Catalyst CMM-0 CMM-1/20 CMM-1/50 CMM-1/200 TS-1C CuO (tenorite)
Phenol Conversion
H2O2 efficiency3
0 22.5 25.1 18.4 20.8 9.8
67.6 75.4 55.3 62.5 29.4
Product distribution11 (%) HQ CAT BQ 53.9 2.3 43.8 59.5 39.3 1.2 54.0 0.6 45.4 44.4 55.5 0.1 40.9 11.8 7.3
a
H 2 O 2 efficiency = 100 * (H2O2 consumed in the formation of diphenol and benzoquinone, mole) •*• (total H2O2 added, mole) b HQ = hydroquinone, BQ = para-benzoquinone, CAT = catechol. The product of tar is not included. c Ti/(Ti+Si) = 0.022.
4. Conclusion Novel Cu-incorporated mesoporous materials CMMs were synthesized by a sol-gel method using glutaric acid as template. It was demonstrated that the CMMs had a 3D worm-like mesoporous structure with a large surface area of 600 to 800 m 2 g'', exhibiting high catalytic activity in the phenol hydroxylation with H2O2 comparable to TS-1. 5. Acknowledgement This work is supported by the National Basic Research Program of China (2003CB615807), the NSF of China (20421303, 20371013) and the Shanghai Science and Technology Committee (05DZ22313). 6. References [1] J. O. Edwards and R. Curci, in: Catalytic Oxidations with Hydrogen Peroxide As Oxidant, eds. G. Strukul (Kluwer Academic Publishers, Dordrecht, 1992) pp. 97. [2] M. Taramasso, G. Perego and B. Notari, US Patent 4410501 (1983). [3] L. Norena-Franco, I. Hernandez-Perez, P. Aguilar and A. Maubert-Franco, Catal. Today 75 (2002) 189. [4] Y. Ren, L.P. Qian, B. Yue and H. Y. He, Chinese J. Catal. 24 (2003) 947. [5] P. T. Tanev and T. J. Pinnavaia, Science 267 (1995) 865. [6] Tkachenko, K.V. Klementiev, E. Loffler, I. Ritzkopf, F. Schuth, M. Bandyopadhyay, S. Grabowski, H. Gies, V. Hagen, M. Muhler, L. H. Lu, R.A. Fischer and W. Griinert, Phys. Chem. Chem. Phys. 5 (2003) 4325. [7] R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem. B 103 (1999) 7743. [8] P. S. E. Dai, R. H. Petty, C. W. Ingram and R. Szostak, Appl. Catal. A: Gen. 143 (1996) 101.