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Structure and properties of porous mesostructured zirconium oxo- phosphate with cubic (Ia3d) symmetry
Studies in Surface Science and Catalysis 146 Park et al (Editors) © 2003 Elsevier Science B.V. All rights reserved
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Structure and properties of porous mesostructured zirconium oxophosphate witli cubic (Ia3d) symmetry Freddy Kleitz^^ Stuart J. Thomson^^, Zheng Liu*', Osamu Terasaki^ and Ferdi Schiith^* ^Max-Planck-Institut fiir Kohlenforschung 45470 Miilheim an der Ruhr, Germany. ^Japan Science and Technology Corporation (CREST) and Department of Physics, Tohoku University, Sendai 980-8578, Japan The synthesis and characterization of the first porous zirconium oxo-phosphate material structured on the nanoscale with a cubic Ia3d symmetry is described. The new ordered porous material was obtained in aqueous solution by the self-assembly of a simple cationic surfactant combined with the inorganic zirconium sulfate precursor. The cubic zirconium oxo-phosphate was characterized by X-ray diffraction (XRD), high resolution electron microscopy (HREM), N2 sorption and FTIR spectroscopy. 1. INTRODUCTION The developments in the field of non-siliceous mesostructured and mesoporous materials have recently been reviewed.''^ In particular, transition metal-based ordered mesoporous materials have been synthesized on the basis of titanium, zirconium, niobium or tantalum, most of them being either hexagonally ordered or rather disordered.''^ However, considerably less attention has been given to non-hexagonal structures,^ mainly due to the higher difficulty in achieving stable well-ordered porous solids."*'^ We previously reported the synthesis of mesoporous zirconium 0x0phosphates with 2-D hexagonal phase.^'^ These well-ordered and thermally stable zirconium oxo-phosphate materials, show relatively large adsorption capacity, high surface area, and Lewis and Bronsted acidity. The desire to create porous materials combining acid-base properties and the advantages of a well-defined 3-D structure led us to develop the synthesis of a cubic Ia3d mesoporous zirconium-based analogue.^ However, in the initial study we were not able to remove the template without structural collapse. By carefully examining the synthesis conditions and the method used for the template removal, we have now succeeded in removing the template without destroying the structure.^ The present report focuses on the characterization of this newly synthesized material. 'Author for correspondence. E-mail: [email protected] ^Present address: Center for Functional Nanomaterials, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea. ^Present address: Materials Division, Australian Nuclear Science and Technology Organisation (ANSTO) PMB 1, Menai, NSW, Australia, 2234. The European Community (project HPRN-CT-99-00025) and the Japan Science and Technology Corporation are gratefully acknowledged forfinancialsupports.
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2. EXPERIMENTAL SECTION The addition of an aqueous solution of Zr(S04)2«4H20 to N-benzyl-N,Ndimethyloctadecylammonium chloride in water leads to rapid formation of a zirconium sulfate-surfactant composite mesophase. The reactants molar ratio of the reagents used was Zr(S04)2: C18BDAC : H2O =\ I r I All. Two surfactant to zirconium sulfate molar ratios (r) were studied, r = 0.40 and r = 0.54. The mesostructured material obtained under acidic conditions was then hydrothermally aged (3 days) and subsequently posttreated with an aqueous solution of phosphoric acid (0.5 M), following a method described previously.^'' As a comparison, hexagonal analogous materials were synthesized, with r - 0.40 and r = 0.54, according to a method described previously.'' Template-free products were obtained after air calcination in a box furnace with a plateau at 300°C for 3 hours followed by 3 hours at 500°C. Slow heating rates (0.5°C/min) were used as this has been shown to have a critical effect on the mesostructure.*^'^ Full details of the syntheses and characterization procedures have been recently reported.^ 3. RESULTS AND DISCUSSION The XRD patterns of the assynthesized samples show reflections suggesting a cubic Ia3d symmetry (Fig. la and lb). Only reflections within 2-8 ° (20), which are due to the ordering of the pores, are observed. This indicates that no condensed crystalline phases arc present. The unit cell parameter of the cubic lattice, calculated from d(211), is generally about ao = 9.9 nm for assynthcsizcd materials. It has been shown previously that the surfactant to zirconium ratio range, where the cubic Ia3d mesophase with a well-resolved diffraction pattern is obtained, is rather 2 theta (•] 2 theta ['] narrow, between r = 0.40 and r = 0.67.^ No significant variations in Fig. 1: XRD patterns, a) and b) As-synthesized cubic zirconium oxo-phosphates. c) and d) As-synthesized the (211) d-spacing (d = ca. 4 nm) hexagonal zirconium oxo-phosphates. e) and f) Calcined is observed. However, even within cubic materials, g) and h) Calcined hexagonal materials. this r range only the two first The dashed lines materialized low angle scattering reflections, assigned to the cubic intensity cut by beam block. space group Ia3d, arc well defined. The higher order reflections appear with low signal-to-noise ratios. In contrast, materials obtained under the same synthetic conditions using CI STAB as a template, exhibit well-resolved XRD patterns of 2-D hexagonal p6mm phase (Fig. Ic and Id).^'^ This highlights the unique role of the surfactant molecular geometry to direct the final
223
mesophase structure. The unit cell parameter of the hexagonal phase is usually around 5.3 nm.^The HREM images of an as-synthesized sample synthesized in presence of Nbenzyl-N,N dimethyloctadecylammonium ions with r = 0.54 reveal domains of highlyordered mesostructure (Fig. 2). Images of the [111] and [100] zone axis are presented in Fig. 2a and 2d, respectively. In the electron diffraction (ED) pattern (Fig. 2b), only diffuse rings are observed indicating that the wall structure of the as-prepared samples is amorphous. Fig. 2c, which is the Fourier diffractogram obtained from the HREM image in Fig. 2a, suggests that the material is commensurate with Ia3d symmetry. As-prepared samples synthesized with r = 0.40 show similar features. In agreement with the XRD, the HREM investigations confirm that the architecture of the zirconium oxo-phosphate surfactant mesophase is characteristic of the cubic Ia3d phase.
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Fig. 2: Typical HREM image and electron diffraction (ED) pattern of an as-prepared sample with r = 0.54. Fig. 2a) HREM image taken along the [111] zone axis. Fig. 2b) Electron diffraction pattern. Fig. 2c) Fourier diffractograms obtained the area labeled by 1. Fig. 2d) HREM image taken along the [100] zone axis.
The samples were carefully calcined as described. Fig. le and If show the XRD patterns recorded for calcined samples synthesized with r = 0.40 and r = 0.54, respectively. Generally, the structure shrinks drastically and the (220) reflection appears only as a shoulder. No higher order reflections can be detected. The sample synthesized with r = 0.54 undergoes a larger shrinkage (about 30%, acaicined-o.54 = 7 nm) than that with r = 0.40 (about 25%, acaicined-o.4o = 7.5 nm). On the other hand, the shrinkage is slightly less pronounced for hexagonal phase materials (21% for r = 0.40, 25% for r = 0.54) and the reflections at higher 2 theta angles are retained. But a lower ordering is evidenced in all cases. The samples synthesized with less surfactant (r = 0.40) are more stable and undergo less contraction upon calcination. Although the X-ray diffraction patterns recorded for the calcined cubic materials are poorly resolved (Fig. le and If), the HREM image reveals large domains of highlyordered mesostructure (Fig. 3a and 3d). The HREM images presented in Fig. 3a and Fig. 3d are consistent with the Ia3d symmetry and show the uninterrupted channels along the observation direction. In the electron diffraction pattern (Fig.3b), one can observe diffuse electron diffraction rings, indicating that the walls remain amorphous after calcination. This is also supported by the absence of wide-angle reflections in the XRD pattern. The Fourier diffractogram (Fig. 3c) indicates that the zirconium oxophosphate material is also commensurate with the Ia3d symmetry after calcination. Therefore, Fig. 3 gives the clear evidence that the cubic Ia3d mesostructure is retained after the removal of the template by thermal treatment. The sample with r = 0.40, investigated by EM shows similar well-resolved cubic domains.
224
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Fig. 3: Typical HREM image and electron diffraction (ED) pattern of a sample with r = 0.54 after calcination at 500°C. Fig. 3a) HREM image taken along the [111] zone axis. Fig. 3b) Electron diffraction pattern. Fig. 3c) Fourier diffractograms obtained from the HREM image in Fig. 3a. Fig. 3d) HREM image taken along the [100] zone axis (inset is the ED pattern).
The N2 sorption isotherms are similar to Type I isotherms characteristic for microporous materials, and likely correspond to pore sizes in the upper micropore range or lower mesopore range.^ In general, the total nitrogen adsorption capacity decreases rapidly with increasing surfactant-to-zirconium sulfate ratio. The highest adsorption capacity is measured for r = 0.40. This cubic zirconium oxo-phosphate sample exhibits total nitrogen adsorption capacity of up to 130 cm^/g and has a pore volume of up to 0.20 cmVg. In addition, the physisorption data indicate a smaller pore size for the cubic zirconium oxo-phosphate compared to Wavenumber [cm^] the corresponding hexagonal phase Fig. 4: Typical FTIR spectra recorded on a material.^ zirconium-based cubic mesophase. a) Zirconium The FTIR spectra recorded on a cubic sulfate mesophase. b) As-synthesized zirconium zirconium-based mesophase (r = 0.40), oxo-phosphate. c) Calcined zirconium oxoprior to and after the phosphation step, phosphate. Samples in KBr. Offset is for clarity. and after removal of the template by calcination, are detailed in Fig. 4a, 4b and 4c, respectively. The broad unresolved peak observed for all synthesis stages at about 3200-3600cm'' is characteristic of hydrogenbonding from 0-H groups. The peak observed at 1630-1640 cm'^ is due to the bending mode of water adsorbed on the sample surface, which also contributes to the broad 0-H stretching band above 3200 cm"'.'''^ The absorption bands observed around 1470 cm"' and 2800-3000 cm', in Fig. 4a and 4b, originate from the surfactant species and are due the C-H hydrocarbon deformation and stretching modes, respectively. In addition, the weak absorption bands observed around 3065 cm' originate from the aromatic ring of the surfactant head group. All these bands disappear after calcination (Fig. 4c).'^Several absorption bands attributed to the sulfate groups in the zirconium sulfate-surfactant mesophase are observed between 900-1300 cm' (Fig. 4a). After phosphation of the sample, an intense broad
225
band centered at 1040-1060 cm"^ assigned to the stretching region of phosphates^ ^''^ is observed at the same frequency range (Fig. 4b). Furthermore, the spectrum in Fig. 4a exhibits medium intensity peaks around 610-650 cm"'. After phosphation, these signals are reduced (611 cm'^ Fig. 4b), and a new absorption band appears at ca. 515 cm'. After thermal treatment at 500°C, the bands at 610-650 cm' seem to vanish, while the band at ca. 515 cm'' is retained. The appearance of all peaks in the phosphated sample in Fig. 4b likely suggests therefore the presence of both sulfate and phosphate species, which may act to increase the disorder in the zirconium-based fi-amework.^ In addition, a weak absorption peak is observed around 742 cm"' for the calcined zirconium oxophosphate (Fig. 4c), and might be due to the presence of pyrophosphate groups"''^ (P0-P bending) suggesting phosphate condensation during calcination. The intensity around 2440 cm"' is probably due to overtone and combination bands. Pyridine sorption followed by IR spectroscopy shows that the samples contain both Bronsted and Lewis acid sites, the concentrations of which depend on the synthesis parameters.^ In terms of relative peak intensities, the largest Bronsted : Lewis (B : L) peak ratio, determined using the ratio of the 1540 cm"' (B) and the 1446 cm' (L) peak, was observed in the 0.54 sample. The sample with r = 0.40 has more Bronsted acidic bridging OH groups. This sample has the highest pore volume (0.20 cmVg), and the highest thermal stability. 4. CONCLUSIONS The cubic structure inferred from XRD is confirmed for the template free materials by HREM, which enables precise structure assignment. The porous zirconium oxophosphate described is therefore one of the first transition metal-based analogues of MCM-48-type materials. The zirconium oxo-phosphate exhibits total nitrogen adsorption capacity of up to 130 cm^/g and has a pore volume of up to 0.20 cmVg, with pore sizes reaching the upper micropore range. Pyridine sorption followed by IR spectroscopy shows that the samples contain both Bronsted and Lewis acid sites. As prospects, it could be expected that such high surface area ordered porous zirconium oxo-phosphates could find interest as metal or metal sulfide catalyst supports for hydrotreatment processes'^ or low-temperature methanol decomposition reactions.'^ 5. REFERENCES 1. A. Sayari, Chem Mater., 8 (1996) 1840. 2. F. Schuth, Chem. Mater., 13 (2001) 3184. 3. P. Yang, D. Zhao, D.I. Margolese, B.F. Chmelka and G.D. Stucky, Chem. Mater., 11 (1999) 2813. 4. D.M. Antonelli, A. Nakahira and J.Y. Ying, Inorg. Chem., 35 (1996) 3126. 5. H. Hatamaya, M. Misono, A. Tagushi and N. Mizuno, Chem. Lett., (2000) 884. 6. U. Ciesla, S. Schacht, G.D. Stucky, K.K. Unger and F. Schuth, Angew. Chem. Int. Ed. Engl., 35 (1996)541. 7. U. Ciesla, M. Fr6ba, G.D. Stucky and F. Schuth, Chem. Mater., 11 (1999) 227. 8. F. Schuth, U. Ciesla, S. Schacht, M. Thieme, Q. Huo and G. Stucky, Mater. Res. Bull., 34 (1999) 483. 9. F. Kleitz, S.J. Thomson, Z. Liu, O. Terasaki and F. Schuth, Chem. Mater., in press. 10. F. Kleitz, W. Schmidt and F. Schuth, Microporous Mesoporous Mater., 44-45 (2001) 95. 11. D.E.C. Corbridge and E.J. Lowe, J. Chem. Soc, (1954) 493. 12. K. Segawa, Y. Kurusu, Y. Nakajima and M. Kinoshita, J. Catal., 94 (1985) 491. 13. M.S. Wong and J.Y. Ying, Chem. Mater., 10 (1998) 2067. 14. Y. Sun, P. Afanasiev, M. Vrinat and G. Coudurier, J. Mater. Chem., 10 (2000) 2320. 15. M. Ziyad, M. Rouimi and J.L. Portefaix, Appl. Catal. A, 183 (1999) 93 16. M.P. Kapoor, Y. Ichihashi, W.-J. Shen and Y. Matsumura, Cata. Lett., 76 (2001) 139.
221
Structure and properties of porous mesostructured zirconium oxophosphate witli cubic (Ia3d) symmetry Freddy Kleitz^^ Stuart J. Thomson^^, Zheng Liu*', Osamu Terasaki^ and Ferdi Schiith^* ^Max-Planck-Institut fiir Kohlenforschung 45470 Miilheim an der Ruhr, Germany. ^Japan Science and Technology Corporation (CREST) and Department of Physics, Tohoku University, Sendai 980-8578, Japan The synthesis and characterization of the first porous zirconium oxo-phosphate material structured on the nanoscale with a cubic Ia3d symmetry is described. The new ordered porous material was obtained in aqueous solution by the self-assembly of a simple cationic surfactant combined with the inorganic zirconium sulfate precursor. The cubic zirconium oxo-phosphate was characterized by X-ray diffraction (XRD), high resolution electron microscopy (HREM), N2 sorption and FTIR spectroscopy. 1. INTRODUCTION The developments in the field of non-siliceous mesostructured and mesoporous materials have recently been reviewed.''^ In particular, transition metal-based ordered mesoporous materials have been synthesized on the basis of titanium, zirconium, niobium or tantalum, most of them being either hexagonally ordered or rather disordered.''^ However, considerably less attention has been given to non-hexagonal structures,^ mainly due to the higher difficulty in achieving stable well-ordered porous solids."*'^ We previously reported the synthesis of mesoporous zirconium 0x0phosphates with 2-D hexagonal phase.^'^ These well-ordered and thermally stable zirconium oxo-phosphate materials, show relatively large adsorption capacity, high surface area, and Lewis and Bronsted acidity. The desire to create porous materials combining acid-base properties and the advantages of a well-defined 3-D structure led us to develop the synthesis of a cubic Ia3d mesoporous zirconium-based analogue.^ However, in the initial study we were not able to remove the template without structural collapse. By carefully examining the synthesis conditions and the method used for the template removal, we have now succeeded in removing the template without destroying the structure.^ The present report focuses on the characterization of this newly synthesized material. 'Author for correspondence. E-mail: [email protected] ^Present address: Center for Functional Nanomaterials, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea. ^Present address: Materials Division, Australian Nuclear Science and Technology Organisation (ANSTO) PMB 1, Menai, NSW, Australia, 2234. The European Community (project HPRN-CT-99-00025) and the Japan Science and Technology Corporation are gratefully acknowledged forfinancialsupports.
222
2. EXPERIMENTAL SECTION The addition of an aqueous solution of Zr(S04)2«4H20 to N-benzyl-N,Ndimethyloctadecylammonium chloride in water leads to rapid formation of a zirconium sulfate-surfactant composite mesophase. The reactants molar ratio of the reagents used was Zr(S04)2: C18BDAC : H2O =\ I r I All. Two surfactant to zirconium sulfate molar ratios (r) were studied, r = 0.40 and r = 0.54. The mesostructured material obtained under acidic conditions was then hydrothermally aged (3 days) and subsequently posttreated with an aqueous solution of phosphoric acid (0.5 M), following a method described previously.^'' As a comparison, hexagonal analogous materials were synthesized, with r - 0.40 and r = 0.54, according to a method described previously.'' Template-free products were obtained after air calcination in a box furnace with a plateau at 300°C for 3 hours followed by 3 hours at 500°C. Slow heating rates (0.5°C/min) were used as this has been shown to have a critical effect on the mesostructure.*^'^ Full details of the syntheses and characterization procedures have been recently reported.^ 3. RESULTS AND DISCUSSION The XRD patterns of the assynthesized samples show reflections suggesting a cubic Ia3d symmetry (Fig. la and lb). Only reflections within 2-8 ° (20), which are due to the ordering of the pores, are observed. This indicates that no condensed crystalline phases arc present. The unit cell parameter of the cubic lattice, calculated from d(211), is generally about ao = 9.9 nm for assynthcsizcd materials. It has been shown previously that the surfactant to zirconium ratio range, where the cubic Ia3d mesophase with a well-resolved diffraction pattern is obtained, is rather 2 theta (•] 2 theta ['] narrow, between r = 0.40 and r = 0.67.^ No significant variations in Fig. 1: XRD patterns, a) and b) As-synthesized cubic zirconium oxo-phosphates. c) and d) As-synthesized the (211) d-spacing (d = ca. 4 nm) hexagonal zirconium oxo-phosphates. e) and f) Calcined is observed. However, even within cubic materials, g) and h) Calcined hexagonal materials. this r range only the two first The dashed lines materialized low angle scattering reflections, assigned to the cubic intensity cut by beam block. space group Ia3d, arc well defined. The higher order reflections appear with low signal-to-noise ratios. In contrast, materials obtained under the same synthetic conditions using CI STAB as a template, exhibit well-resolved XRD patterns of 2-D hexagonal p6mm phase (Fig. Ic and Id).^'^ This highlights the unique role of the surfactant molecular geometry to direct the final
223
mesophase structure. The unit cell parameter of the hexagonal phase is usually around 5.3 nm.^The HREM images of an as-synthesized sample synthesized in presence of Nbenzyl-N,N dimethyloctadecylammonium ions with r = 0.54 reveal domains of highlyordered mesostructure (Fig. 2). Images of the [111] and [100] zone axis are presented in Fig. 2a and 2d, respectively. In the electron diffraction (ED) pattern (Fig. 2b), only diffuse rings are observed indicating that the wall structure of the as-prepared samples is amorphous. Fig. 2c, which is the Fourier diffractogram obtained from the HREM image in Fig. 2a, suggests that the material is commensurate with Ia3d symmetry. As-prepared samples synthesized with r = 0.40 show similar features. In agreement with the XRD, the HREM investigations confirm that the architecture of the zirconium oxo-phosphate surfactant mesophase is characteristic of the cubic Ia3d phase.
®D
202
' o6o 121 ]
•fl
' 2nm'^
0.2nm"^
Fig. 2: Typical HREM image and electron diffraction (ED) pattern of an as-prepared sample with r = 0.54. Fig. 2a) HREM image taken along the [111] zone axis. Fig. 2b) Electron diffraction pattern. Fig. 2c) Fourier diffractograms obtained the area labeled by 1. Fig. 2d) HREM image taken along the [100] zone axis.
The samples were carefully calcined as described. Fig. le and If show the XRD patterns recorded for calcined samples synthesized with r = 0.40 and r = 0.54, respectively. Generally, the structure shrinks drastically and the (220) reflection appears only as a shoulder. No higher order reflections can be detected. The sample synthesized with r = 0.54 undergoes a larger shrinkage (about 30%, acaicined-o.54 = 7 nm) than that with r = 0.40 (about 25%, acaicined-o.4o = 7.5 nm). On the other hand, the shrinkage is slightly less pronounced for hexagonal phase materials (21% for r = 0.40, 25% for r = 0.54) and the reflections at higher 2 theta angles are retained. But a lower ordering is evidenced in all cases. The samples synthesized with less surfactant (r = 0.40) are more stable and undergo less contraction upon calcination. Although the X-ray diffraction patterns recorded for the calcined cubic materials are poorly resolved (Fig. le and If), the HREM image reveals large domains of highlyordered mesostructure (Fig. 3a and 3d). The HREM images presented in Fig. 3a and Fig. 3d are consistent with the Ia3d symmetry and show the uninterrupted channels along the observation direction. In the electron diffraction pattern (Fig.3b), one can observe diffuse electron diffraction rings, indicating that the walls remain amorphous after calcination. This is also supported by the absence of wide-angle reflections in the XRD pattern. The Fourier diffractogram (Fig. 3c) indicates that the zirconium oxophosphate material is also commensurate with the Ia3d symmetry after calcination. Therefore, Fig. 3 gives the clear evidence that the cubic Ia3d mesostructure is retained after the removal of the template by thermal treatment. The sample with r = 0.40, investigated by EM shows similar well-resolved cubic domains.
224
[ ^
202 .
0^0
-121
^^ 2nm"'
I 0.2nrn"^
Fig. 3: Typical HREM image and electron diffraction (ED) pattern of a sample with r = 0.54 after calcination at 500°C. Fig. 3a) HREM image taken along the [111] zone axis. Fig. 3b) Electron diffraction pattern. Fig. 3c) Fourier diffractograms obtained from the HREM image in Fig. 3a. Fig. 3d) HREM image taken along the [100] zone axis (inset is the ED pattern).
The N2 sorption isotherms are similar to Type I isotherms characteristic for microporous materials, and likely correspond to pore sizes in the upper micropore range or lower mesopore range.^ In general, the total nitrogen adsorption capacity decreases rapidly with increasing surfactant-to-zirconium sulfate ratio. The highest adsorption capacity is measured for r = 0.40. This cubic zirconium oxo-phosphate sample exhibits total nitrogen adsorption capacity of up to 130 cm^/g and has a pore volume of up to 0.20 cmVg. In addition, the physisorption data indicate a smaller pore size for the cubic zirconium oxo-phosphate compared to Wavenumber [cm^] the corresponding hexagonal phase Fig. 4: Typical FTIR spectra recorded on a material.^ zirconium-based cubic mesophase. a) Zirconium The FTIR spectra recorded on a cubic sulfate mesophase. b) As-synthesized zirconium zirconium-based mesophase (r = 0.40), oxo-phosphate. c) Calcined zirconium oxoprior to and after the phosphation step, phosphate. Samples in KBr. Offset is for clarity. and after removal of the template by calcination, are detailed in Fig. 4a, 4b and 4c, respectively. The broad unresolved peak observed for all synthesis stages at about 3200-3600cm'' is characteristic of hydrogenbonding from 0-H groups. The peak observed at 1630-1640 cm'^ is due to the bending mode of water adsorbed on the sample surface, which also contributes to the broad 0-H stretching band above 3200 cm"'.'''^ The absorption bands observed around 1470 cm"' and 2800-3000 cm', in Fig. 4a and 4b, originate from the surfactant species and are due the C-H hydrocarbon deformation and stretching modes, respectively. In addition, the weak absorption bands observed around 3065 cm' originate from the aromatic ring of the surfactant head group. All these bands disappear after calcination (Fig. 4c).'^Several absorption bands attributed to the sulfate groups in the zirconium sulfate-surfactant mesophase are observed between 900-1300 cm' (Fig. 4a). After phosphation of the sample, an intense broad
225
band centered at 1040-1060 cm"^ assigned to the stretching region of phosphates^ ^''^ is observed at the same frequency range (Fig. 4b). Furthermore, the spectrum in Fig. 4a exhibits medium intensity peaks around 610-650 cm"'. After phosphation, these signals are reduced (611 cm'^ Fig. 4b), and a new absorption band appears at ca. 515 cm'. After thermal treatment at 500°C, the bands at 610-650 cm' seem to vanish, while the band at ca. 515 cm'' is retained. The appearance of all peaks in the phosphated sample in Fig. 4b likely suggests therefore the presence of both sulfate and phosphate species, which may act to increase the disorder in the zirconium-based fi-amework.^ In addition, a weak absorption peak is observed around 742 cm"' for the calcined zirconium oxophosphate (Fig. 4c), and might be due to the presence of pyrophosphate groups"''^ (P0-P bending) suggesting phosphate condensation during calcination. The intensity around 2440 cm"' is probably due to overtone and combination bands. Pyridine sorption followed by IR spectroscopy shows that the samples contain both Bronsted and Lewis acid sites, the concentrations of which depend on the synthesis parameters.^ In terms of relative peak intensities, the largest Bronsted : Lewis (B : L) peak ratio, determined using the ratio of the 1540 cm"' (B) and the 1446 cm' (L) peak, was observed in the 0.54 sample. The sample with r = 0.40 has more Bronsted acidic bridging OH groups. This sample has the highest pore volume (0.20 cmVg), and the highest thermal stability. 4. CONCLUSIONS The cubic structure inferred from XRD is confirmed for the template free materials by HREM, which enables precise structure assignment. The porous zirconium oxophosphate described is therefore one of the first transition metal-based analogues of MCM-48-type materials. The zirconium oxo-phosphate exhibits total nitrogen adsorption capacity of up to 130 cm^/g and has a pore volume of up to 0.20 cmVg, with pore sizes reaching the upper micropore range. Pyridine sorption followed by IR spectroscopy shows that the samples contain both Bronsted and Lewis acid sites. As prospects, it could be expected that such high surface area ordered porous zirconium oxo-phosphates could find interest as metal or metal sulfide catalyst supports for hydrotreatment processes'^ or low-temperature methanol decomposition reactions.'^ 5. REFERENCES 1. A. Sayari, Chem Mater., 8 (1996) 1840. 2. F. Schuth, Chem. Mater., 13 (2001) 3184. 3. P. Yang, D. Zhao, D.I. Margolese, B.F. Chmelka and G.D. Stucky, Chem. Mater., 11 (1999) 2813. 4. D.M. Antonelli, A. Nakahira and J.Y. Ying, Inorg. Chem., 35 (1996) 3126. 5. H. Hatamaya, M. Misono, A. Tagushi and N. Mizuno, Chem. Lett., (2000) 884. 6. U. Ciesla, S. Schacht, G.D. Stucky, K.K. Unger and F. Schuth, Angew. Chem. Int. Ed. Engl., 35 (1996)541. 7. U. Ciesla, M. Fr6ba, G.D. Stucky and F. Schuth, Chem. Mater., 11 (1999) 227. 8. F. Schuth, U. Ciesla, S. Schacht, M. Thieme, Q. Huo and G. Stucky, Mater. Res. Bull., 34 (1999) 483. 9. F. Kleitz, S.J. Thomson, Z. Liu, O. Terasaki and F. Schuth, Chem. Mater., in press. 10. F. Kleitz, W. Schmidt and F. Schuth, Microporous Mesoporous Mater., 44-45 (2001) 95. 11. D.E.C. Corbridge and E.J. Lowe, J. Chem. Soc, (1954) 493. 12. K. Segawa, Y. Kurusu, Y. Nakajima and M. Kinoshita, J. Catal., 94 (1985) 491. 13. M.S. Wong and J.Y. Ying, Chem. Mater., 10 (1998) 2067. 14. Y. Sun, P. Afanasiev, M. Vrinat and G. Coudurier, J. Mater. Chem., 10 (2000) 2320. 15. M. Ziyad, M. Rouimi and J.L. Portefaix, Appl. Catal. A, 183 (1999) 93 16. M.P. Kapoor, Y. Ichihashi, W.-J. Shen and Y. Matsumura, Cata. Lett., 76 (2001) 139.