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Oxidation catalysis of a manganese(III)porphyrin intercalated in layered double hydroxide clays
Materials Letters 57 (2003) 2258 – 2261 www.elsevier.com/locate/matlet
Oxidation catalysis of a manganese(III)porphyrin intercalated in layered double hydroxide clays Zhiwei Tong a, Tetsuya Shichi a, Katsuhiko Takagi a,b,* a
Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Furocho, Chikusaku, Nagoya 464-8603, Japan b CREST, Japan Science and Technology (JST), Japan Received 26 June 2002; accepted 26 June 2002
Abstract Tetra( p-sulfonatophenyl)porphinatomanganese(III) anions, [Mn(III)TSPPCl]4 were intercalated into the interlayer spaces of Mg – Al-layered double hydroxide (LDH) and studied as a catalyst for the oxidation of 2,4,6-trichlorophenol (TCP). The Mn(III)TSPP anions could be efficiently intercalated into the LDH interlayers as a perpendicular Mn(III)TSPP/LDH complex by adsorbing the guest molecules, which is a characteristic for easy handling and a high catalytic activity. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Layered double hydroxide; Tetra( p-sulfonatophenyl)porphinatomanganese(III) anion; Intercalation; Catalysts; Nanocomposites
1. Introduction Metallo-porphyrins and -phthalocyanines and other macrocyclic complexes are capable of carrying out redox catalysis under ambient conditions [1 –5]. This property is of great interest for applications in the remediation of contaminated groundwater and industrial effluents. However, such metal complexes typically have only limited longevity due to the oxidative self-decomposition of the catalyst under the reaction conditions. Immobilization of the catalyst by attachment to an organic or inorganic polymer [1,6] has * Corresponding author. Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Furocho, Chikusaku, Nagoya 464-8603, Japan. Tel.: +81-52-7894501; fax: +81-52-789-3338. E-mail address: [email protected] (K. Takagi).
been reported to be one approach in reducing the degradation. This is assumed to be due to the suppression of the formation of A-oxo-dimer in the macrocyclic organometallic catalyst. In addition to the stability of the catalyst, it is advantageous because it is easily recovered from the reaction mixture. Layered double hydroxides (LDHs) possess an anion-exchange ability which is especially promising as a support for the organic materials under investigation. The formula for the LDH structure can be expressed as follows: [M2 +aM3 +b(OH)2a + 2b]X bH2O, Fig. 1; where M2 + and M3 + are the divalent and trivalent metal cations, respectively, and X is an exchangeable gallery anion. Catalytically active polyoxometallates can be intercalated as the X anions into the LDH structures by a variety of synthetic routes [7 – 9] The intercalated anionic macrocycle complex, cobalt(II) phthalocyaninetetrasulfonate, was orthogo-
0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-577X(02)01206-5
Z. Tong et al. / Materials Letters 57 (2003) 2258–2261
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Fig. 1. Schematic representation of the LDH structure.
nal to the LDH sheet, and was found to be active for the autoxidation of thiolate to disulfide [2,10]. The longevity of LDH-intercalated metallophthalocyanine and related macrocyclic complexes is of great significance, especially in cases where such materials are designed for the remediation of polluted aqueous environment. In the present work, we report on the catalytic oxidation of 2,4,6-trichlorophenol (TCP) by KHSO5 using a [MnTSPP]3 /LDH complex obtained by the intercalation of metalloporphyrins into the Mg – Al LDH clays through anion exchange.
Fig. 2. Powder X-ray diffraction patterns of (a) MnTSPP/LDH and (b) LDH before intercalation: shows remaining peaks of LDH.
.
Cl0.3xH2O by means of ICP elemental analysis. The X-ray powder diffraction patterns of LDH and MnTSPP/LDH are shown in Fig. 2. The basal spacing of MnTSPP/LDH was estimated to be 2.37 nm. Con-
2. Experimental The LDH employed in this study, Alcamack, manufactured by Kyowa Chemical, contains chloride ions as the exchangeable anions in its interlayers, i.e., [Al2Mg4.5(OH)13]Cl4H2O with an anion exchange capacity (AEC) of 350 meq/100 g. The MnTSPP was prepared according to previous literature [11]. The MnTSPP/LDH hybrid was prepared by an anion exchange method as follows: 0.1 g of LDH dispersed into 20 ml of distilled water was added to aqueous Na4[MnTSPPCl], the amount of which was eight times AEC of the LDH. The suspended mixture was sonicated for several minutes, stirred at 70 jC for a week and finally passed through a membrane filter.
3. Results and discussion The composition of the LDH composite, MnTSPP, was observed to be [Mg3.7Al2.3(OH)12](MnTSPPCl)0.5-
Fig. 3. Orientation of [MnTSPP]3
anions in LDH interlayers.
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Z. Tong et al. / Materials Letters 57 (2003) 2258–2261
Scheme 1. MnTSPP/LDH-catalyzed oxidation of 2,4,6-trichlorophenol (TCP) to 2,6-dichlorobenzoquinone (DCQ).
Fig. 4. IR spectra of (a) MnTSPP/Mg – Al intercalation compound, (b) MnTSPP in KBr.
sidering the original brucite layer thickness of 0.48 nm, the MnTSPP complex was seen to expand the interlayer space up to 1.89 nm, a value close to the van der Waals width (1.8 1.8 nm) of the sulfonated por-
Fig. 5. The UV – visible diffuse reflectance spectra of (a) MnTSPP/ Mg – Al intercalation compound, visible absorption of (b) MnTSPP in water.
phyrin ring. Therefore, MnTSPPCl is assumed to be intercalated almost perpendicularly to the LDH layers and can be referred to as an ‘‘edge on’’ alignment, as shown in Fig. 3. This ‘‘edge on’’ alignment has been proposed by Carrado et al. [12] for a Cu-phtharocyanine/LDH inclusion compound with a similar basal spacing (2.3 nm) and XRD patterns. The IR spectra of the MnTSPP alone and its LDHintercalated hybrid were observed to have almost unchanged each other, as shown in Fig. 4. The SO3H absorption bands of the hybrid in KBr disk at 1040 – 1037 cm 1 shifted slightly to lower frequency regions than those of the guest molecules. It was suggested that an interaction of the intercalated guest anions with the host hydroxide layers occurred [13]. The blue-colored MnTSPP-intercalated LDH powder showed a visible diffuse reflectance spectrum similar to the guest molecules in water (Fig. 5).
Fig. 6. Catalyst recycling in repetitive oxidation of 2,4,6trichlorophenol (TCP) by MnTSPP-KHSO5 homogeneous system ( , n) and MnTSPP/LDH-KHSO5 suspended system (o, 5). The moral ratios of the catalysts are 0.25% ( , o) and 1% (n, 5) based on TCP.
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Z. Tong et al. / Materials Letters 57 (2003) 2258–2261
The selective oxidation of 2,4,6-trichlorophenol (TCP) by KHSO5 into 2,6-dichloroquinone (DCQ) could be accomplished by the present LDH-intercalated MnTSPP(MnTSPP/LDH), with a significant improvement over the less-effective catalytic conversions by homogeneous and polymer-supported MnTSPP [14], as shown in Scheme 1. Fig. 6 provides the conversion of TCP for homogeneous and LDH-intercalated catalysts. The reactions were carried out in aqueous media of 1 10 3 mol/dm 3 TCP and 5 10 3 mol/dm 3 KHSO 5 adjusted to pH 7.3 by the addition of a buffer solution. The oxidation was seen to proceed efficiently in the presence of the LDH-intercalated MnTSPP catalyst, and which was more effective than with a homogeneous catalyst without LDH. Assuming that the reaction of TCP with KHSO5 proceeds bimolecularly, the reaction rates for both the homogeneous and LDHintercalated catalysts were estimated to be 0.66 and 1.38 M 1 s 1 (MnTSPP/TCP = 0.25 mol%), and 2.73 and 5.36 M 1 s 1 (MnTSPP/TCP = 1%), respectively, in contrast to the control experiments, showing that the conversion of TCP was negligible in the absence of the catalyst. The metalloporphyrin-catalyzed oxidation of TCP is assumed to proceed on the basis of a mechanism proposed by Meunier et al. [14]. That is, MnTSPP may be oxidized to a high-valent metal-oxo intermediate, MnVj O, which reacts with TCP to form aryloxy radicals and MnIV –OH. The resulting aryloxy radical is oxidized to DCQ with MnIV – OH, as the MnTSPP species is immobilized in the interlayers. In the LDH-intercalated catalyst, the first oxidation step from TCP to aryloxy radical is immediately followed by the second oxidation step to DCQ. Moreover, the remarkable enhancement of the catalytic activity by intercalation can be explained by the immobilization of the MnTSPP species. In summary, LDH-immobilized metalloporphyrin complexes were found to possess high catalytic efficiencies for the oxidation of 2,4,6-trichlorophenols.
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Furthermore, since these solid catalysts can be recovered easily by filtration, LDH-supported catalysts have great potential for the actual applications in the remediation of polluted groundwater or industrial effluents.
Acknowledgements This work was supported by a Grant-in-Aid Fund from the Ministry of Education, Culture, Sports, Science and Technology, and by the Industrial Technology Research Grant Program for ’01 of the New Energy and Industrial Technology Development Organization (NEDO). We would like express our thanks for their support.
References [1] D.C. Sherrington, Pure Appl. Chem. 60 (1988) 401. [2] M.E. Perez-Bernal, R. Ruano-Casero, T.J. Pinnavaia, Catal. Letters 11 (1991) 55. [3] A. Sorokin, J.L. Seris, B. Meunier, Science 268 (1995) 1163. [4] L. Barloy, J.P. Lallier, P. Battioni, D. Mansuy, Y. Piffard, M. Tournoux, J.B. Valim, W. Jones, New J. Chem. 16 (1992) 71. [5] H.C. Sacco, Y. Iamamoto, J.R. Lindsay Smith, J. Chem. Soc., Perkin Trans. 2 (2001) 181. [6] N. Herron, G.D. Stucky, C.A. Tolman, J. Chem. Soc., Chem. Commun. (1986) 1521. [7] M.A. Drezdzon, Inorg. Chem. 27 (1988) 4628. [8] K. Chibwe, W. Jones, J. Chem. Soc., Chem. Commun. (1989) 926. [9] E.D. Dimotakis, T.J. Pinnavaia, Inorg. Chem. 29 (1990) 2393. [10] V.I. Iliev, V.I. Ileva, L.D. Dimitrov, Appl. Catal. A 126 (1995) 333. [11] L. Ruhlmann, A. Nakamura, J. Vos, J.-H. Fuhrhop, Inorg. Chem. 37 (1998) 6052. [12] K.A. Carrado, J.E. Forman, R.E. Botto, R.E. Winans, Chem. Mater. 5 (1993) 427. [13] I.Y Park, K. Kuroda, C. Kato, Chem. Lett. (1989) 2057. [14] G. Labat, J.L. Seris, B. Meunier, Angew. Chem., Int. Ed. Engl. 29 (1990) 1471.
Oxidation catalysis of a manganese(III)porphyrin intercalated in layered double hydroxide clays Zhiwei Tong a, Tetsuya Shichi a, Katsuhiko Takagi a,b,* a
Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Furocho, Chikusaku, Nagoya 464-8603, Japan b CREST, Japan Science and Technology (JST), Japan Received 26 June 2002; accepted 26 June 2002
Abstract Tetra( p-sulfonatophenyl)porphinatomanganese(III) anions, [Mn(III)TSPPCl]4 were intercalated into the interlayer spaces of Mg – Al-layered double hydroxide (LDH) and studied as a catalyst for the oxidation of 2,4,6-trichlorophenol (TCP). The Mn(III)TSPP anions could be efficiently intercalated into the LDH interlayers as a perpendicular Mn(III)TSPP/LDH complex by adsorbing the guest molecules, which is a characteristic for easy handling and a high catalytic activity. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Layered double hydroxide; Tetra( p-sulfonatophenyl)porphinatomanganese(III) anion; Intercalation; Catalysts; Nanocomposites
1. Introduction Metallo-porphyrins and -phthalocyanines and other macrocyclic complexes are capable of carrying out redox catalysis under ambient conditions [1 –5]. This property is of great interest for applications in the remediation of contaminated groundwater and industrial effluents. However, such metal complexes typically have only limited longevity due to the oxidative self-decomposition of the catalyst under the reaction conditions. Immobilization of the catalyst by attachment to an organic or inorganic polymer [1,6] has * Corresponding author. Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Furocho, Chikusaku, Nagoya 464-8603, Japan. Tel.: +81-52-7894501; fax: +81-52-789-3338. E-mail address: [email protected] (K. Takagi).
been reported to be one approach in reducing the degradation. This is assumed to be due to the suppression of the formation of A-oxo-dimer in the macrocyclic organometallic catalyst. In addition to the stability of the catalyst, it is advantageous because it is easily recovered from the reaction mixture. Layered double hydroxides (LDHs) possess an anion-exchange ability which is especially promising as a support for the organic materials under investigation. The formula for the LDH structure can be expressed as follows: [M2 +aM3 +b(OH)2a + 2b]X bH2O, Fig. 1; where M2 + and M3 + are the divalent and trivalent metal cations, respectively, and X is an exchangeable gallery anion. Catalytically active polyoxometallates can be intercalated as the X anions into the LDH structures by a variety of synthetic routes [7 – 9] The intercalated anionic macrocycle complex, cobalt(II) phthalocyaninetetrasulfonate, was orthogo-
0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-577X(02)01206-5
Z. Tong et al. / Materials Letters 57 (2003) 2258–2261
2259
Fig. 1. Schematic representation of the LDH structure.
nal to the LDH sheet, and was found to be active for the autoxidation of thiolate to disulfide [2,10]. The longevity of LDH-intercalated metallophthalocyanine and related macrocyclic complexes is of great significance, especially in cases where such materials are designed for the remediation of polluted aqueous environment. In the present work, we report on the catalytic oxidation of 2,4,6-trichlorophenol (TCP) by KHSO5 using a [MnTSPP]3 /LDH complex obtained by the intercalation of metalloporphyrins into the Mg – Al LDH clays through anion exchange.
Fig. 2. Powder X-ray diffraction patterns of (a) MnTSPP/LDH and (b) LDH before intercalation: shows remaining peaks of LDH.
.
Cl0.3xH2O by means of ICP elemental analysis. The X-ray powder diffraction patterns of LDH and MnTSPP/LDH are shown in Fig. 2. The basal spacing of MnTSPP/LDH was estimated to be 2.37 nm. Con-
2. Experimental The LDH employed in this study, Alcamack, manufactured by Kyowa Chemical, contains chloride ions as the exchangeable anions in its interlayers, i.e., [Al2Mg4.5(OH)13]Cl4H2O with an anion exchange capacity (AEC) of 350 meq/100 g. The MnTSPP was prepared according to previous literature [11]. The MnTSPP/LDH hybrid was prepared by an anion exchange method as follows: 0.1 g of LDH dispersed into 20 ml of distilled water was added to aqueous Na4[MnTSPPCl], the amount of which was eight times AEC of the LDH. The suspended mixture was sonicated for several minutes, stirred at 70 jC for a week and finally passed through a membrane filter.
3. Results and discussion The composition of the LDH composite, MnTSPP, was observed to be [Mg3.7Al2.3(OH)12](MnTSPPCl)0.5-
Fig. 3. Orientation of [MnTSPP]3
anions in LDH interlayers.
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Z. Tong et al. / Materials Letters 57 (2003) 2258–2261
Scheme 1. MnTSPP/LDH-catalyzed oxidation of 2,4,6-trichlorophenol (TCP) to 2,6-dichlorobenzoquinone (DCQ).
Fig. 4. IR spectra of (a) MnTSPP/Mg – Al intercalation compound, (b) MnTSPP in KBr.
sidering the original brucite layer thickness of 0.48 nm, the MnTSPP complex was seen to expand the interlayer space up to 1.89 nm, a value close to the van der Waals width (1.8 1.8 nm) of the sulfonated por-
Fig. 5. The UV – visible diffuse reflectance spectra of (a) MnTSPP/ Mg – Al intercalation compound, visible absorption of (b) MnTSPP in water.
phyrin ring. Therefore, MnTSPPCl is assumed to be intercalated almost perpendicularly to the LDH layers and can be referred to as an ‘‘edge on’’ alignment, as shown in Fig. 3. This ‘‘edge on’’ alignment has been proposed by Carrado et al. [12] for a Cu-phtharocyanine/LDH inclusion compound with a similar basal spacing (2.3 nm) and XRD patterns. The IR spectra of the MnTSPP alone and its LDHintercalated hybrid were observed to have almost unchanged each other, as shown in Fig. 4. The SO3H absorption bands of the hybrid in KBr disk at 1040 – 1037 cm 1 shifted slightly to lower frequency regions than those of the guest molecules. It was suggested that an interaction of the intercalated guest anions with the host hydroxide layers occurred [13]. The blue-colored MnTSPP-intercalated LDH powder showed a visible diffuse reflectance spectrum similar to the guest molecules in water (Fig. 5).
Fig. 6. Catalyst recycling in repetitive oxidation of 2,4,6trichlorophenol (TCP) by MnTSPP-KHSO5 homogeneous system ( , n) and MnTSPP/LDH-KHSO5 suspended system (o, 5). The moral ratios of the catalysts are 0.25% ( , o) and 1% (n, 5) based on TCP.
.
.
Z. Tong et al. / Materials Letters 57 (2003) 2258–2261
The selective oxidation of 2,4,6-trichlorophenol (TCP) by KHSO5 into 2,6-dichloroquinone (DCQ) could be accomplished by the present LDH-intercalated MnTSPP(MnTSPP/LDH), with a significant improvement over the less-effective catalytic conversions by homogeneous and polymer-supported MnTSPP [14], as shown in Scheme 1. Fig. 6 provides the conversion of TCP for homogeneous and LDH-intercalated catalysts. The reactions were carried out in aqueous media of 1 10 3 mol/dm 3 TCP and 5 10 3 mol/dm 3 KHSO 5 adjusted to pH 7.3 by the addition of a buffer solution. The oxidation was seen to proceed efficiently in the presence of the LDH-intercalated MnTSPP catalyst, and which was more effective than with a homogeneous catalyst without LDH. Assuming that the reaction of TCP with KHSO5 proceeds bimolecularly, the reaction rates for both the homogeneous and LDHintercalated catalysts were estimated to be 0.66 and 1.38 M 1 s 1 (MnTSPP/TCP = 0.25 mol%), and 2.73 and 5.36 M 1 s 1 (MnTSPP/TCP = 1%), respectively, in contrast to the control experiments, showing that the conversion of TCP was negligible in the absence of the catalyst. The metalloporphyrin-catalyzed oxidation of TCP is assumed to proceed on the basis of a mechanism proposed by Meunier et al. [14]. That is, MnTSPP may be oxidized to a high-valent metal-oxo intermediate, MnVj O, which reacts with TCP to form aryloxy radicals and MnIV –OH. The resulting aryloxy radical is oxidized to DCQ with MnIV – OH, as the MnTSPP species is immobilized in the interlayers. In the LDH-intercalated catalyst, the first oxidation step from TCP to aryloxy radical is immediately followed by the second oxidation step to DCQ. Moreover, the remarkable enhancement of the catalytic activity by intercalation can be explained by the immobilization of the MnTSPP species. In summary, LDH-immobilized metalloporphyrin complexes were found to possess high catalytic efficiencies for the oxidation of 2,4,6-trichlorophenols.
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Furthermore, since these solid catalysts can be recovered easily by filtration, LDH-supported catalysts have great potential for the actual applications in the remediation of polluted groundwater or industrial effluents.
Acknowledgements This work was supported by a Grant-in-Aid Fund from the Ministry of Education, Culture, Sports, Science and Technology, and by the Industrial Technology Research Grant Program for ’01 of the New Energy and Industrial Technology Development Organization (NEDO). We would like express our thanks for their support.
References [1] D.C. Sherrington, Pure Appl. Chem. 60 (1988) 401. [2] M.E. Perez-Bernal, R. Ruano-Casero, T.J. Pinnavaia, Catal. Letters 11 (1991) 55. [3] A. Sorokin, J.L. Seris, B. Meunier, Science 268 (1995) 1163. [4] L. Barloy, J.P. Lallier, P. Battioni, D. Mansuy, Y. Piffard, M. Tournoux, J.B. Valim, W. Jones, New J. Chem. 16 (1992) 71. [5] H.C. Sacco, Y. Iamamoto, J.R. Lindsay Smith, J. Chem. Soc., Perkin Trans. 2 (2001) 181. [6] N. Herron, G.D. Stucky, C.A. Tolman, J. Chem. Soc., Chem. Commun. (1986) 1521. [7] M.A. Drezdzon, Inorg. Chem. 27 (1988) 4628. [8] K. Chibwe, W. Jones, J. Chem. Soc., Chem. Commun. (1989) 926. [9] E.D. Dimotakis, T.J. Pinnavaia, Inorg. Chem. 29 (1990) 2393. [10] V.I. Iliev, V.I. Ileva, L.D. Dimitrov, Appl. Catal. A 126 (1995) 333. [11] L. Ruhlmann, A. Nakamura, J. Vos, J.-H. Fuhrhop, Inorg. Chem. 37 (1998) 6052. [12] K.A. Carrado, J.E. Forman, R.E. Botto, R.E. Winans, Chem. Mater. 5 (1993) 427. [13] I.Y Park, K. Kuroda, C. Kato, Chem. Lett. (1989) 2057. [14] G. Labat, J.L. Seris, B. Meunier, Angew. Chem., Int. Ed. Engl. 29 (1990) 1471.