- Email: [email protected]
Convenient synthesis of deuterated aluminium hydrides
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Scripta Materialia 59 (2008) 515–517 www.elsevier.com/locate/scriptamat
Convenient synthesis of deuterated aluminium hydrides Roland H. Pawelke, Michael Felderhoff, Claudia Weidenthaler and Ferdi Schu¨th* Max-Planck-Institut fu¨r Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mu¨lheim an der Ruhr, Germany Received 10 March 2008; revised 23 April 2008; accepted 27 April 2008 Available online 4 May 2008
We describe the ball-milling synthesis of alkali metal deuterides from commercial lithium aluminium deuteride. This reaction principle was exemplified by the mechanochemical synthesis of NaAlD4 and KAlD4. NaAlD4 was prepared on the multi-gram scale by this procedure and purified by standard wet-chemical separation. Pure NaAlD4 was obtained and used for the synthesis of Ca(AlD4)2. The formation of all products was verified by X-ray diffraction. Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Hydrogen storage; Complex aluminium deuterides; Mechanochemical synthesis; Ball milling
Vehicular onboard hydrogen storage is considered to be a major obstacle in the way of the economic use of hydrogen [1–3]. For this reason, scientific interest in complex aluminium hydrides has increased immensely over the last 10 years [4], since these materials have reached the most advanced development state. In order to fully understand such materials, structural characterization is mandatory. However, the poor X-ray diffraction (XRD) properties of hydrogen are a general problem for the characterization of hydrogen storage materials. Neutron diffraction provides an interesting alternative to XRD for structural studies. In order to take full advantage of this analysis method, though, the exchange of hydrogen by deuterium atoms is required, since hydrogen has a very high inelastic scattering cross-section and therefore strongly increases the background in the diffraction patterns. The use of the light metal complex hydride Ca(AlH4)2 for hydrogen storage has been discussed individually [5–7], or in combination with other materials [8]. The X-ray powder diffraction pattern of Ca(AlH4)2 has been calculated Løvvik [9], and non-deuterated Ca(AlH4)2 can be prepared by a wet-chemical metathesis procedure [10] according to Eq. (1): THF
2 NaAlH4 þ CaCl2 ! CaðAlH4 Þ2 þ 2 NaCl
been reported so far. When we tried to prepare Ca(AlD4)2 by an procedure analogous to the one given in Eq. (1), we had to substitute NaAlH4 with LiAlD4, since this is the only commercial [AlD4] source. This modification affected the course of the reaction dramatically; after separation of the insoluble residue, we then had to try to isolate the product from the filtrate. The addition of pentane did not lead to product precipitation. Instead, we observed the formation of a two-phase system, presumably containing mixed LiAlD4–Ca(AlD4)2–tetrahydrofuran (THF) aggregates [11]. With direct access to Ca(AlD4)2 from commercially available chemicals denied, the simple synthesis of large amounts of NaAlD4 became mandatory. Only two synthesis procedures for NaAlD4 have been described: one by Bastide et al. [12], the other by Kuznetsova et al. [13]. The former comprises the reaction of LiAlH4 and an alkali metal halide (preferably fluoride), which is solubilised as a Ziegler-type complex with AlEt3. Hauback et al. used this method for the preparation of NaAlD4 [14] and KAlD4 [15], corresponding to Eq. (2), although significant impurity (20%) from residual lithium fluoride is claimed: AlEt3
ð1Þ
Oddly enough, neither the synthesis of Ca(AlD4)2 nor any neutron scattering investigations on Ca(AlD4)2 have * Corresponding author. Tel.: +49 208 306 2373; fax: +49 208 306 2995; e-mail address: [email protected]
LiAlD4 þ MFM¼Na;K ! MAlD4 þ LiF
ð2Þ
The latter procedure consists of an exchange reaction between NaH and LiAlD4 in diethyl ether following Reaction (3): Et2 O
LiAlD4 þ NaH ! NaAlD4 þ LiH
1359-6462/$ - see front matter Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2008.04.042
ð3Þ
516
R. H. Pawelke et al. / Scripta Materialia 59 (2008) 515–517
Although both methods are viable, we were interested in finding an alternative synthesis pathway that is easy and scalable to large amounts. In order to facilitate the substitution of lithium by higher alkali metal ions thermodynamically, the formation of lithium fluoride (DDHf LiF–NaF = 45 kJ mol1, DDHf LiF–KF = 51 kJ mol1) as per Reaction (4) seemed best. Such a scheme provides a high thermodynamic driving force for two reasons: lithium fluoride is the most stable alkali metal fluoride, while the stability of alkali metal alanates increases with atomic number B:M:
LiAID4 þ MFM¼Na;K ! MAlD4 þ LiF
ð4Þ
By conducting this step in a mechanochemical reaction, the phenomenon of incomplete lithium fluoride precipitation from solution is avoided while taking advantage of the simplicity of ball-milling procedures. All chemicals were obtained from Sigma–Aldrich (NaF and KF, anhydrous, 99.9+%; LiAlD4, 90%, 98 at.% D; CaCl2, anhydrous, 96+%). A Fritsch Pulverisette P7 classic line ball mill was used, with 12 ml vials made of steel and six balls of the same material (10 mm diameter). For the multi-gram assays, 45 ml steel vials with seven balls (15 mm diameter) were employed. Loading and extraction procedures were performed in an argon-filled glove box (O2 < 2 ppm, H2O < 1 ppm). THF was distilled from sodium/benzophenone. All treatments in solution were performed by standard Schlenk techniques; filtration steps were done on P4 frits. Depending on the chemical composition of the samples, the X-ray powder patterns for qualitative phase analysis were collected either on a Stoe STADI P transmission diffractometer with a primary monochromator (Mo Ka1) and a linear position sensitive detector or on a X’Pert Pro instrument (PANalytical company) (Cu Ka1) equipped with an X’Celerator detector. For the measurements, the samples were filled into glass capillaries (0.5 mm diameter) in a glove box, which were sealed to prevent contact with air. The measured patterns were evaluated qualitatively by comparison with entries from the PDF-2 powder pattern database. In a preliminary reaction, 235 mg (5.5 mmol) of LiAlD4 were mixed with a respective amount (5.0 mmol) of sodium or potassium fluoride in a 12 ml steel milling vial with six balls of 10 mm diameter. The ball-to-powder ratio was approximately 46:1. The reactants were subjected to 3 h of non-stop ball milling at 800 rpm. Loss due to the de-loading procedure was 100 mg. Powder-XRD analysis of the mixture showed NaAlD4 and KAlD4, LiF and a minor amount of elemental aluminium (Fig. 1). Concerns about fluoride induced decomposition [16] turned out to be unsubstantiated, although some pressure formation in the reaction vessels was observed. NaAlD4 was purified by dissolution in THF. LiF and other insoluble residues were filtered off and pure NaAlD4 was obtained in 80% yield (Fig. 2). With respect to the synthesis of Ca(AlD4)2, the synthesis of NaAlD4 was upscaled to a 50 mmol assay, using 45 ml steel vials with seven 15 mm diameter balls (ball-to-powder ratio 23:1).
Figure 1. Powder patterns of (a) NaAlD4 and (b) KAlD4. The open circles represent LiF impurities. Both datasets were collected using Cu Ka radiation.
Figure 2. Powder pattern of pure NaAlD4 (collected using Cu Ka radiation).
The synthesis of Ca(AlD4)2 and Mg(AlD4)2 according to Eq. (5) failed. Although the exchange was not supposed to be restricted by thermodynamics (DDHf 2LiF–MgF2 = 118 kJ mol1, DDHf 2 LiF–CaF2 = 24 kJ mol1), no reaction took place. This may be due to the single-step nature of the metathesis reaction. B.M.
2 LiAlD4 + MF2M = Mg, Ca
M(AlD 4)2 + 2 LiF
ð5Þ
For the synthesis of Ca(AlD4)2, 14.40 g of NaAlD4/LiF mixture (calcd. NaAlD4 mass content 69% = 9.95 g (170 mmol)) was stirred in 600 ml of dry THF for 1 h. The reaction mixture was filtered onto 9.52 g (86 mmol) calcium chloride and stirred overnight (Reaction (6)). ð1:ÞTHF
NaAlD4 =LiF ! NaAlD4 =THF ð2:ÞFiltration
0:5 eq: CaCl2
! CaðAlD4 Þ2 þ 2 NaCl
ð6Þ
Sodium chloride was filtered off. Upon addition of 1.5 l of dry pentane to the filtrate, Ca(AlD4)2 precipitated as the THF adduct [12]. The colourless solid was isolated by filtration. The solvent was removed by drying 6 h at 120 °C in vacuo. Due to the decomposition of the THF adduct, the sample crystallinity was only moderate, but the XRD pattern is in very good agreement with the reference of Løvvik (Fig. 3) [9]. The isolated yield was 6.95 g (63 mmol, 73%).
R. H. Pawelke et al. / Scripta Materialia 59 (2008) 515–517
Figure 3. Pattern shown in (a) was calculated from the structure predicted by Løvvik. Diffraction pattern (b) represents the sample of Ca(AlD4)2 measured on the Mo Ka instrument.
The multi-gram availability of pure sodium and potassium aluminium deuteride as synthesis intermediates may help to extend the benefits of analytical methods requiring deuterium, e.g. neutron scattering, in hydrogen storage and alanate chemistry. Although this is not in the centre of our interest, a simple extension of this work would be the synthesis of the higher analogues RbAlD4 and CsAlD4. In addition to the basic funding by the Max-PlanckGesellschaft, this work was supported by General Motors Fuel Cell Activities.
517
[1] D.K. Ross, Vacuum 80 (2006) 1084. [2] B. Sakintuna, F. Lamari-Darkrim, M. Hirscher, Int. J. Hydrogen Energy 32 (2007) 1121. [3] M. Felderhoff, C. Weidenthaler, R. von Helmolt, U. Eberle, Phys. Chem. Chem. Phys. 9 (2007) 2643. [4] S.-i. Orimo, Y. Nakamori, J.R. Eliseo, A. Zu¨ttel, C.M. Jensen, Chem. Rev. 107 (2007) 4111. [5] C. Wolverton, V. Ozolins, Phys. Rev. B: Condens. Matter Mater. Phys. 75 (2007) 064101/1. [6] K. Komiya, N. Morisaku, Y. Shinzato, K. Ikeda, S. Orimo, Y. Ohki, K. Tatsumi, H. Yukawa, M. Morinaga, J. Alloys Compd. 446–447 (2007) 237. [7] M. Mamatha, B. Bogdanovic´, M. Felderhoff, A. Pommerin, W. Schmidt, F. Schueth, C. Weidenthaler, J. Alloys Compd. 407 (2006) 78. [8] S.V. Alapati, J.K. Johnson, D.S. Sholl, J. Phys. Chem. B 110 (2006) 8769. [9] O.M. Løvvik, Phys. Rev. B: Condens. Matter Mater. Phys. 71 (2005) 144111/1. [10] M. Fichtner, C. Frommen, O. Fuhr, Inorg. Chem. 44 (2005) 3479. [11] B.M. Bulychev, A.V. Golubeva, P.A. Storozhenko, Zh. Neorg. Khim. 29 (1984) 1948. [12] J.P. Bastide, J. Fl Hajri, P. Claudy, A. El Hajbi, Synth. React. Inorg. Met.-Org. Chem. 25 (1995) 1037. [13] S.F. Kuznetsova, N.T. Kuznetsov, S.I. Bakum, M.B. Bychkovskaya, Zh. Neorg. Khim. 32 (1987) 2293. [14] B.C. Hauback, H.W. Brinks, C.M. Jensen, K. Murphy, A.J. Maeland, J. Alloys Compd. 358 (2003) 142. [15] B.C. Hauback, H.W. Brinks, R.H. Heyn, R. Blom, H. Fjellva˚g, J. Alloys Compd. 394 (2005) 35. [16] L.-C. Yin, P. Wang, X.-D. Kang, C.-H. Sun, H.-M. Cheng, Phys. Chem. Chem. Phys. 9 (2007) 1499.
Scripta Materialia 59 (2008) 515–517 www.elsevier.com/locate/scriptamat
Convenient synthesis of deuterated aluminium hydrides Roland H. Pawelke, Michael Felderhoff, Claudia Weidenthaler and Ferdi Schu¨th* Max-Planck-Institut fu¨r Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mu¨lheim an der Ruhr, Germany Received 10 March 2008; revised 23 April 2008; accepted 27 April 2008 Available online 4 May 2008
We describe the ball-milling synthesis of alkali metal deuterides from commercial lithium aluminium deuteride. This reaction principle was exemplified by the mechanochemical synthesis of NaAlD4 and KAlD4. NaAlD4 was prepared on the multi-gram scale by this procedure and purified by standard wet-chemical separation. Pure NaAlD4 was obtained and used for the synthesis of Ca(AlD4)2. The formation of all products was verified by X-ray diffraction. Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Hydrogen storage; Complex aluminium deuterides; Mechanochemical synthesis; Ball milling
Vehicular onboard hydrogen storage is considered to be a major obstacle in the way of the economic use of hydrogen [1–3]. For this reason, scientific interest in complex aluminium hydrides has increased immensely over the last 10 years [4], since these materials have reached the most advanced development state. In order to fully understand such materials, structural characterization is mandatory. However, the poor X-ray diffraction (XRD) properties of hydrogen are a general problem for the characterization of hydrogen storage materials. Neutron diffraction provides an interesting alternative to XRD for structural studies. In order to take full advantage of this analysis method, though, the exchange of hydrogen by deuterium atoms is required, since hydrogen has a very high inelastic scattering cross-section and therefore strongly increases the background in the diffraction patterns. The use of the light metal complex hydride Ca(AlH4)2 for hydrogen storage has been discussed individually [5–7], or in combination with other materials [8]. The X-ray powder diffraction pattern of Ca(AlH4)2 has been calculated Løvvik [9], and non-deuterated Ca(AlH4)2 can be prepared by a wet-chemical metathesis procedure [10] according to Eq. (1): THF
2 NaAlH4 þ CaCl2 ! CaðAlH4 Þ2 þ 2 NaCl
been reported so far. When we tried to prepare Ca(AlD4)2 by an procedure analogous to the one given in Eq. (1), we had to substitute NaAlH4 with LiAlD4, since this is the only commercial [AlD4] source. This modification affected the course of the reaction dramatically; after separation of the insoluble residue, we then had to try to isolate the product from the filtrate. The addition of pentane did not lead to product precipitation. Instead, we observed the formation of a two-phase system, presumably containing mixed LiAlD4–Ca(AlD4)2–tetrahydrofuran (THF) aggregates [11]. With direct access to Ca(AlD4)2 from commercially available chemicals denied, the simple synthesis of large amounts of NaAlD4 became mandatory. Only two synthesis procedures for NaAlD4 have been described: one by Bastide et al. [12], the other by Kuznetsova et al. [13]. The former comprises the reaction of LiAlH4 and an alkali metal halide (preferably fluoride), which is solubilised as a Ziegler-type complex with AlEt3. Hauback et al. used this method for the preparation of NaAlD4 [14] and KAlD4 [15], corresponding to Eq. (2), although significant impurity (20%) from residual lithium fluoride is claimed: AlEt3
ð1Þ
Oddly enough, neither the synthesis of Ca(AlD4)2 nor any neutron scattering investigations on Ca(AlD4)2 have * Corresponding author. Tel.: +49 208 306 2373; fax: +49 208 306 2995; e-mail address: [email protected]
LiAlD4 þ MFM¼Na;K ! MAlD4 þ LiF
ð2Þ
The latter procedure consists of an exchange reaction between NaH and LiAlD4 in diethyl ether following Reaction (3): Et2 O
LiAlD4 þ NaH ! NaAlD4 þ LiH
1359-6462/$ - see front matter Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2008.04.042
ð3Þ
516
R. H. Pawelke et al. / Scripta Materialia 59 (2008) 515–517
Although both methods are viable, we were interested in finding an alternative synthesis pathway that is easy and scalable to large amounts. In order to facilitate the substitution of lithium by higher alkali metal ions thermodynamically, the formation of lithium fluoride (DDHf LiF–NaF = 45 kJ mol1, DDHf LiF–KF = 51 kJ mol1) as per Reaction (4) seemed best. Such a scheme provides a high thermodynamic driving force for two reasons: lithium fluoride is the most stable alkali metal fluoride, while the stability of alkali metal alanates increases with atomic number B:M:
LiAID4 þ MFM¼Na;K ! MAlD4 þ LiF
ð4Þ
By conducting this step in a mechanochemical reaction, the phenomenon of incomplete lithium fluoride precipitation from solution is avoided while taking advantage of the simplicity of ball-milling procedures. All chemicals were obtained from Sigma–Aldrich (NaF and KF, anhydrous, 99.9+%; LiAlD4, 90%, 98 at.% D; CaCl2, anhydrous, 96+%). A Fritsch Pulverisette P7 classic line ball mill was used, with 12 ml vials made of steel and six balls of the same material (10 mm diameter). For the multi-gram assays, 45 ml steel vials with seven balls (15 mm diameter) were employed. Loading and extraction procedures were performed in an argon-filled glove box (O2 < 2 ppm, H2O < 1 ppm). THF was distilled from sodium/benzophenone. All treatments in solution were performed by standard Schlenk techniques; filtration steps were done on P4 frits. Depending on the chemical composition of the samples, the X-ray powder patterns for qualitative phase analysis were collected either on a Stoe STADI P transmission diffractometer with a primary monochromator (Mo Ka1) and a linear position sensitive detector or on a X’Pert Pro instrument (PANalytical company) (Cu Ka1) equipped with an X’Celerator detector. For the measurements, the samples were filled into glass capillaries (0.5 mm diameter) in a glove box, which were sealed to prevent contact with air. The measured patterns were evaluated qualitatively by comparison with entries from the PDF-2 powder pattern database. In a preliminary reaction, 235 mg (5.5 mmol) of LiAlD4 were mixed with a respective amount (5.0 mmol) of sodium or potassium fluoride in a 12 ml steel milling vial with six balls of 10 mm diameter. The ball-to-powder ratio was approximately 46:1. The reactants were subjected to 3 h of non-stop ball milling at 800 rpm. Loss due to the de-loading procedure was 100 mg. Powder-XRD analysis of the mixture showed NaAlD4 and KAlD4, LiF and a minor amount of elemental aluminium (Fig. 1). Concerns about fluoride induced decomposition [16] turned out to be unsubstantiated, although some pressure formation in the reaction vessels was observed. NaAlD4 was purified by dissolution in THF. LiF and other insoluble residues were filtered off and pure NaAlD4 was obtained in 80% yield (Fig. 2). With respect to the synthesis of Ca(AlD4)2, the synthesis of NaAlD4 was upscaled to a 50 mmol assay, using 45 ml steel vials with seven 15 mm diameter balls (ball-to-powder ratio 23:1).
Figure 1. Powder patterns of (a) NaAlD4 and (b) KAlD4. The open circles represent LiF impurities. Both datasets were collected using Cu Ka radiation.
Figure 2. Powder pattern of pure NaAlD4 (collected using Cu Ka radiation).
The synthesis of Ca(AlD4)2 and Mg(AlD4)2 according to Eq. (5) failed. Although the exchange was not supposed to be restricted by thermodynamics (DDHf 2LiF–MgF2 = 118 kJ mol1, DDHf 2 LiF–CaF2 = 24 kJ mol1), no reaction took place. This may be due to the single-step nature of the metathesis reaction. B.M.
2 LiAlD4 + MF2M = Mg, Ca
M(AlD 4)2 + 2 LiF
ð5Þ
For the synthesis of Ca(AlD4)2, 14.40 g of NaAlD4/LiF mixture (calcd. NaAlD4 mass content 69% = 9.95 g (170 mmol)) was stirred in 600 ml of dry THF for 1 h. The reaction mixture was filtered onto 9.52 g (86 mmol) calcium chloride and stirred overnight (Reaction (6)). ð1:ÞTHF
NaAlD4 =LiF ! NaAlD4 =THF ð2:ÞFiltration
0:5 eq: CaCl2
! CaðAlD4 Þ2 þ 2 NaCl
ð6Þ
Sodium chloride was filtered off. Upon addition of 1.5 l of dry pentane to the filtrate, Ca(AlD4)2 precipitated as the THF adduct [12]. The colourless solid was isolated by filtration. The solvent was removed by drying 6 h at 120 °C in vacuo. Due to the decomposition of the THF adduct, the sample crystallinity was only moderate, but the XRD pattern is in very good agreement with the reference of Løvvik (Fig. 3) [9]. The isolated yield was 6.95 g (63 mmol, 73%).
R. H. Pawelke et al. / Scripta Materialia 59 (2008) 515–517
Figure 3. Pattern shown in (a) was calculated from the structure predicted by Løvvik. Diffraction pattern (b) represents the sample of Ca(AlD4)2 measured on the Mo Ka instrument.
The multi-gram availability of pure sodium and potassium aluminium deuteride as synthesis intermediates may help to extend the benefits of analytical methods requiring deuterium, e.g. neutron scattering, in hydrogen storage and alanate chemistry. Although this is not in the centre of our interest, a simple extension of this work would be the synthesis of the higher analogues RbAlD4 and CsAlD4. In addition to the basic funding by the Max-PlanckGesellschaft, this work was supported by General Motors Fuel Cell Activities.
517
[1] D.K. Ross, Vacuum 80 (2006) 1084. [2] B. Sakintuna, F. Lamari-Darkrim, M. Hirscher, Int. J. Hydrogen Energy 32 (2007) 1121. [3] M. Felderhoff, C. Weidenthaler, R. von Helmolt, U. Eberle, Phys. Chem. Chem. Phys. 9 (2007) 2643. [4] S.-i. Orimo, Y. Nakamori, J.R. Eliseo, A. Zu¨ttel, C.M. Jensen, Chem. Rev. 107 (2007) 4111. [5] C. Wolverton, V. Ozolins, Phys. Rev. B: Condens. Matter Mater. Phys. 75 (2007) 064101/1. [6] K. Komiya, N. Morisaku, Y. Shinzato, K. Ikeda, S. Orimo, Y. Ohki, K. Tatsumi, H. Yukawa, M. Morinaga, J. Alloys Compd. 446–447 (2007) 237. [7] M. Mamatha, B. Bogdanovic´, M. Felderhoff, A. Pommerin, W. Schmidt, F. Schueth, C. Weidenthaler, J. Alloys Compd. 407 (2006) 78. [8] S.V. Alapati, J.K. Johnson, D.S. Sholl, J. Phys. Chem. B 110 (2006) 8769. [9] O.M. Løvvik, Phys. Rev. B: Condens. Matter Mater. Phys. 71 (2005) 144111/1. [10] M. Fichtner, C. Frommen, O. Fuhr, Inorg. Chem. 44 (2005) 3479. [11] B.M. Bulychev, A.V. Golubeva, P.A. Storozhenko, Zh. Neorg. Khim. 29 (1984) 1948. [12] J.P. Bastide, J. Fl Hajri, P. Claudy, A. El Hajbi, Synth. React. Inorg. Met.-Org. Chem. 25 (1995) 1037. [13] S.F. Kuznetsova, N.T. Kuznetsov, S.I. Bakum, M.B. Bychkovskaya, Zh. Neorg. Khim. 32 (1987) 2293. [14] B.C. Hauback, H.W. Brinks, C.M. Jensen, K. Murphy, A.J. Maeland, J. Alloys Compd. 358 (2003) 142. [15] B.C. Hauback, H.W. Brinks, R.H. Heyn, R. Blom, H. Fjellva˚g, J. Alloys Compd. 394 (2005) 35. [16] L.-C. Yin, P. Wang, X.-D. Kang, C.-H. Sun, H.-M. Cheng, Phys. Chem. Chem. Phys. 9 (2007) 1499.