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词条 Magnesium hydride
释义

  1. Preparation

  2. Structure and bonding

  3. Reactions

  4. Potential use for hydrogen storage

  5. References

{{redirect-distinguish|Magnesium dihydride|magnesium monohydride}}{{chembox
| Watchedfields = changed
| verifiedrevid = 450496080
| ImageFile = Magnesium-hydride-unit-cell-3D-balls.png
| ImageSize =
| ImageFile1 = Magnesium-hydride-xtal-3D-ionic-B.png
| IUPACName = Magnesium hydride
| OtherNames =
|Section1={{Chembox Identifiers
| InChI = 1/Mg.2H/rH2Mg/h1H2
| InChIKey = RSHAOIXHUHAZPM-HZAFDXBCAG
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 25107
| SMILES = [MgH2]
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/Mg.2H
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = RSHAOIXHUHAZPM-UHFFFAOYSA-N
| CASNo = 7693-27-8
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 107663
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID=16787263
| EINECS = 231-705-3
|Section2={{Chembox Properties
| Formula = MgH2
| MolarMass = 26.3209 g/mol
| Appearance = white crystals
| Density = 1.45 g/cm3
| MeltingPtC = 327
| MeltingPt_notes = decomposes
| Solubility = decomposes
| SolubleOther = insoluble in ether
}}
|Section3={{Chembox Structure
| CrystalStruct = tetragonal
}}
|Section5={{Chembox Thermochemistry
| DeltaHf = -75.2 kJ/mol
| DeltaGf = -35.9 kJ/mol
| Entropy = 31.1 J/mol K
| HeatCapacity = 35.4 J/mol K
|Section7={{Chembox Hazards
| MainHazards = pyrophoric[1]
| FlashPt =
| AutoignitionPt =
|Section8={{Chembox Related
| OtherFunction_label = Magnesium hydrides
| OtherFunction = Magnesium monohydride Mg4H6
| OtherCations = Beryllium hydride
Calcium hydride
Strontium hydride
Barium hydride
}}Magnesium hydride is the chemical compound with the molecular formula MgH2. It contains 7.66% by weight of hydrogen and has been studied as a potential hydrogen storage medium.[2]

Preparation

In 1951 preparation from the elements was first reported involving direct hydrogenation of Mg metal at high pressure and temperature (200 atmospheres, 500 °C) with MgI2 catalyst:[3]

Mg + H2 → MgH2

Lower temperature production from Mg and H2 using nano crystalline Mg produced in ball mills has been investigated.[4] Other preparations include:

  • the hydrogenation of magnesium anthracene under mild conditions:[5]

Mg(anthracene) + H2 → MgH2

  • the reaction of diethylmagnesium with lithium aluminium hydride[6]
  • product of complexed MgH2 e.g. MgH2.THF by the reaction of phenylsilane and dibutyl magnesium in ether or hydrocarbon solvents in the presence of THF or TMEDA as ligand.[1]

Structure and bonding

The room temperature form α-MgH2 has a rutile structure.[7] There are at least four high pressure forms: γ-MgH2 with α-PbO2 structure,[8] cubic β-MgH2 with Pa-3 space group,[9] orthorhombic HP1 with Pbc21 space group and orthorhombic HP2 with Pnma space group.[10] Additionally a non stoichiometric MgH(2-δ) has been characterised, but this appears to exist only for very small particles[11]
(bulk MgH2 is essentially stoichiometric, as it can only accommodate very low concentrations of H vacancies[12]).

The bonding in the rutile form is sometimes described as being partially covalent in nature rather than purely ionic;[13] charge density determination by synchrotron x-ray diffraction indicates that the magnesium atom is fully ionised and spherical in shape and the hydride ion is elongated.[14]

Molecular forms of magnesium hydride, MgH, MgH2, Mg2H, Mg2H2, Mg2H3, and Mg2H4 molecules identified by their vibrational spectra have been found in matrix isolated samples at below 10 K, formed following laser ablation of magnesium in the presence of hydrogen.[15] The Mg2H4 molecule has a bridged structure analogous to dimeric aluminium hydride, Al2H6.[15]

Reactions

MgH2 readily reacts with water to form hydrogen gas:

MgH2 + 2 H2O → 2 H2 + Mg(OH)2

At 287 °C it decomposes to produce H2 at 1 bar pressure,[16] the high temperature required is seen as a limitation in the use of MgH2 as a reversible hydrogen storage medium:[17]

MgH2 → Mg + H2

Potential use for hydrogen storage

Its potential as a reversible "storage" medium for hydrogen has led to interest in improving the hydrogenation and dehydrogenation reaction kinetics.[17][18] This can be partially achieved by doping or by reducing the particle size using ball milling.[19][20][21] An alternative approach under investigation is the production of a pumpable slurry of MgH2 which is safe to handle and releases H2 by reaction with water, with reprocessing of the Mg(OH)2 into MgH2.  An application (yet to be examined) for a US Patent (US 2010/0163434 A1)   has been made in respect of a hydrogen energy storage system using laser excitation to assist desorption of hydrogen gas from magnesium hydride.

References

1. ^1 {{cite journal | doi = 10.1021/om00042a055| title = Synthesis of magnesium hydride by the reaction of phenylsilane and dibutylmagnesium| journal = Organometallics| volume = 11| issue = 6| pages = 2307–2309| year = 1992| last1 = Michalczyk| first1 = Michael J}}
2. ^{{cite journal | doi = 10.1002/anie.198502621| title = Catalytic Synthesis of Organolithium and Organomagnesium Compounds and of Lithium and Magnesium Hydrides - Applications in Organic Synthesis and Hydrogen Storage| journal = Angewandte Chemie International Edition in English| volume = 24| issue = 4| pages = 262–273| year = 1985| last1 = Bogdanovic| first1 = Borislav}}
3. ^{{cite journal|authors=Egon Wiberg, Heinz Goeltzer, Richard Bauer|year=1951|title=Synthese von Magnesiumhydrid aus den Elementen (Synthesis of Magnesium Hydride from the Elements)|journal=Zeitschrift für Naturforschung B|volume=6b|page=394|url=http://zfn.mpdl.mpg.de/data/Reihe_B/6/ZNB-1951-6b-0394_n.pdf}}
4. ^{{cite journal | doi = 10.1016/S0925-8388(99)00073-0| title = Nanocrystalline magnesium for hydrogen storage| journal = Journal of Alloys and Compounds | volume = 288| issue = 1–2| pages = 217–225| year = 1999| last1 = Zaluska| first1 = A| last2 = Zaluski| first2 = L| last3 = Ström–Olsen| first3 = J.O}}
5. ^{{cite journal | doi = 10.1002/anie.198008181| title = Catalytic Synthesis of Magnesium Hydride under Mild Conditions| journal = Angewandte Chemie International Edition in English| volume = 19| issue = 10| pages = 818| year = 1980| last1 = Bogdanovi?| first1 = Borislav| last2 = Liao| first2 = Shih-Tsien| last3 = Schwickardi| first3 = Manfred| last4 = Sikorsky| first4 = Peter| last5 = Spliethoff| first5 = Bernd}}
6. ^{{cite journal | doi = 10.1021/ja01154a025| title = The Preparation of the Hydrides of Zinc, Cadmium, Beryllium, Magnesium and Lithium by the Use of Lithium Aluminum Hydride1| journal = Journal of the American Chemical Society| volume = 73| issue = 10| pages = 4585| year = 1951| last1 = Barbaras| first1 = Glenn D| last2 = Dillard| first2 = Clyde| last3 = Finholt| first3 = A. E| last4 = Wartik| first4 = Thomas| last5 = Wilzbach| first5 = K. E| last6 = Schlesinger| first6 = H. I}}
7. ^{{cite journal | doi = 10.1107/S0365110X63000967 | title = Neutron diffraction study of magnesium deuteride | journal = Acta Crystallographica | volume = 16 | issue = 5 | pages = 352 | year = 1963 | last1 = Zachariasen | first1 = W. H | last2 = Holley | first2 = C. E | last3 = Stamper | first3 = J. F }}
8. ^{{cite journal | doi = 10.1016/S0925-8388(99)00028-6| title = Structure of the high pressure phase γ-MgH2 by neutron powder diffraction| journal = Journal of Alloys and Compounds| volume = 287| issue = 1–2| pages = L4–L6| year = 1999| last1 = Bortz| first1 = M| last2 = Bertheville| first2 = B| last3 = Böttger| first3 = G| last4 = Yvon| first4 = K}}
9. ^{{cite journal | doi = 10.1103/PhysRevB.73.224102| title = Structural stability and pressure-induced phase transitions inMgH2| journal = Physical Review B| volume = 73| issue = 22| pages = 224102| year = 2006| last1 = Vajeeston| first1 = P| last2 = Ravindran| first2 = P| last3 = Hauback| first3 = B. C| last4 = Fjellvåg| first4 = H| last5 = Kjekshus| first5 = A| last6 = Furuseth| first6 = S| last7 = Hanfland| first7 = M| bibcode = 2006PhRvB..73v4102V}}
10. ^{{cite journal | doi = 10.1143/JPSJ.75.074603| title = Structural Phase Transition of Rutile-Type MgH2at High Pressures| journal = Journal of the Physical Society of Japan| volume = 75| issue = 7| pages = 074603| year = 2006| last1 = Moriwaki| first1 = Toru| last2 = Akahama| first2 = Yuichi| last3 = Kawamura| first3 = Haruki| last4 = Nakano| first4 = Satoshi| last5 = Takemura| first5 = Kenichi| bibcode = 2006JPSJ...75g4603M}}
11. ^{{cite journal | doi = 10.1021/ja051508a| pmid = 16218629| title = Hydrogen Cycling of Niobium and Vanadium Catalyzed Nanostructured Magnesium| journal = Journal of the American Chemical Society| volume = 127| issue = 41| pages = 14348| year = 2005| last1 = Schimmel| first1 = H. Gijs| last2 = Huot| first2 = Jacques| last3 = Chapon| first3 = Laurent C| last4 = Tichelaar| first4 = Frans D| last5 = Mulder| first5 = Fokko M}}
12. ^{{cite journal|last=Grau-Crespo|first=R.|author2=K. C. Smith |author3=T. S. Fisher |author4=N. H. de Leeuw |author5=U. V. Waghmare |title=Thermodynamics of hydrogen vacancies in MgH2 from first-principles calculations and grand-canonical statistical mechanics|journal=Physical Review B|year=2009|volume=80|pages=174117|doi=10.1103/PhysRevB.80.174117|issue=17|arxiv=0910.4331|bibcode=2009PhRvB..80q4117G}}
13. ^{{Cotton&Wilkinson6th}}
14. ^{{cite journal | doi = 10.1016/S0925-8388(03)00104-X| title = Charge density measurement in MgH2 by synchrotron X-ray diffraction| journal = Journal of Alloys and Compounds| volume = 356-357| pages = 84–86| year = 2003| last1 = Noritake| first1 = T| last2 = Towata| first2 = S| last3 = Aoki| first3 = M| last4 = Seno| first4 = Y| last5 = Hirose| first5 = Y| last6 = Nishibori| first6 = E| last7 = Takata| first7 = M| last8 = Sakata| first8 = M}}
15. ^1 {{cite journal | doi = 10.1021/jp046410h| title = Infrared Spectra of Magnesium Hydride Molecules, Complexes, and Solid Magnesium Dihydride| journal = The Journal of Physical Chemistry A| volume = 108| issue = 52| pages = 11511| year = 2004| last1 = Wang| first1 = Xuefeng| last2 = Andrews| first2 = Lester| bibcode = 2004JPCA..10811511W}}
16. ^{{cite book |title=Hydrogen and Energy |edition=illustrated |first1=T. R. |last1=McAuliffe |publisher=Springer |year=1980 |isbn=978-1-349-02635-7 |page=65 |url=https://books.google.com/books?id=71OuCwAAQBAJ}} [https://books.google.com/books?id=71OuCwAAQBAJ&pg=PA65 Extract of page 65]
17. ^1 {{cite journal | doi = 10.1038/35104634| pmid = 11713542| title = Hydrogen-storage materials for mobile applications| journal = Nature| volume = 414| issue = 6861| pages = 353| year = 2001| last1 = Schlapbach| first1 = Louis| last2 = Züttel| first2 = Andreas }}
18. ^J Huot Hydrogen in Metals (2002) in New Trends in Intercalation Compounds for Energy Storage, Christian Julien, J. P. Pereira-Ramos, A. Momchilov, Springer, {{ISBN|1-4020-0594-6}}
19. ^{{cite journal|last=Sakintuna|first=B.|author2=F. Lamaridarkrim |author3=M. Hirscher |title=Metal hydride materials for solid hydrogen storage: A review|journal=International Journal of Hydrogen Energy|year=2007|volume=32|issue=9|pages=1121–1140|doi=10.1016/j.ijhydene.2006.11.022}}
20. ^{{cite journal|last1=Smith|first1=Kyle|last2=Fisher|first2=Timothy|last3=Waghmare|first3=Umesh|last4=Grau-Crespo|first4=Ricardo|title=Dopant-vacancy binding effects in Li-doped magnesium hydride|journal=Physical Review B|volume=82|issue=13|pages=134109|year=2010|issn=1098-0121|doi=10.1103/PhysRevB.82.134109|arxiv=1009.4806|bibcode=2010PhRvB..82m4109S}}
21. ^{{cite journal|last1=Liang|first1=G.|last2=Huot|first2=J.|last3=Boily|first3=S.|last4=Van Neste|first4=A.|last5=Schulz|first5=R.|title=Catalytic effect of transition metals on hydrogen sorption in nanocrystalline ball milled MgH2–Tm (Tm=Ti, V, Mn, Fe and Ni) systems|journal=Journal of Alloys and Compounds|volume=292|issue=1–2|year=1999|pages=247–252|issn=0925-8388|doi=10.1016/S0925-8388(99)00442-9}}
{{Magnesium compounds}}

2 : Magnesium compounds|Metal hydrides
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