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Aluminum Hydride: the organometallic approach
Project ID # ST 034
This presentation does not contain any proprietary, confidential, or otherwise restricted information
Chengbao Ni, W.M. Zhou and J. Wegrzyn Brookhaven National Laboratory
05/14/2013
Overview Timeline • Project start date: FY10 • Project end date: Continuing
Budget • Funding received in FY12 – $250K (DOE)
• Planned Funding for FY13 – TBD (DOE)
Barriers MYPP Section 3.3.4.2.1 On-Board Storage Barriers:
- Weight & Volume - Efficiency - Durability/Operability - Charge/Discharge Rates
Target Material development for meeting the packaging, safety, cost and driving range (greater than 300 miles) DOE performance targets for the PEM hydrogen fuel vehicle.
Hydrogen storage materials:
Chem. Soc. Rev. 2009, 38, 73; Angew. Chem. Int. Ed. 2012, 51, 6074.
physical adsorption/weak interaction; low H2 weight percentage; (high mass of the MOF) low temperature (such as 77 K).
Metal-Organic Frameworks (MOF):
Amine-Borane Compounds:
high H2 percentage (19.6% vs. 14.2%); dehydrogenation well-studied (catalysis); rehydrogenation remains challenging.
LiH, MgH2, AlH3, LiAlH4, and others; most of the hydrides are quite stable; rehydrogenation is challenging.
Metal-Hydrides:
H3N-BH3 polyborazylene {BNH}x
BH2
NH2
BN
H
H
Ti lowers the activation energy of the decomposition reaction;
AlH3 is completely unstable at Ti concentrations ≥ 0.1 mol%.
Aluminum hydride (alane, AlH3):
Al + H2AlH332
J. Alloys Compd. 2007, 446, 271.
Synthesis of AlH3:
J. Alloys Compd. 2007, 446, 271.
3 LiAlH4 + AlCl3
Et2O
3 LiCl + 4 AlH3(Et2O)n
AlH3(Et2O)n
filtration
AlH3 polymorph
desolvation/crystallization
Crystallization
Al + H232 AlH3?Direct hydrogenation:
Conventional synthesis:
Too expensive!
Morphology
The organometallic approach:
The 3-step regeneration process:
The “Parodox” and challenges:
Phys. Rev. B. 2006, 74, 214114; Chem. Soc. Rev. 2009, 38, 73.
Al + 2 amine1 + H2
+ amine2
(1)
(2)
(3)
catalyst
+ 2 amine1vacuumheat
vacuumheat
AlH3 + amine2
⋅AlH3(amine1)2 ⋅AlH3amine2
⋅AlH3amine2
⋅AlH3(amine1)232Hydrogenation:
Transamination:
Decomposition:
N N
N
N
NTMA DMEA TEDA quinuclidine
NN
N
N
hexamineAmine1:
Strong amines, type I structure; Facilitate hydrogenation; Decomposition to Al metal
directly.
Weak amines, type II or III structures; Decomposes to AlH3 (with Al contamination; Does not facilitate hydrogenation.
H
Al
HH
NR3Al
H
H H
R3N NR3H
Al AlH
NR3
R3N H
HHH
(I) (II) (III)
NR3 is an amine.
Common amine·alane structural types:
N
TEAAmine2:
NN
N
TEA
N
DMEA
N
DEMA
increasing basicity
NO
NO
N
N
piperidine morpholine pyrrolidine
N
TMA
Approaches to the project: Tune the Lewis Basicity of amines:
Objectives: 1. Search for an amine that facilitate both hydrogenation and decomposition:
• Reduce energy input and chemical costs • Increase the efficiency of the process
2. Optimize the transamination and thermal decomposition steps:
Al + 2 amine1 + H2catalyst ⋅AlH3(amine1)2
32
vacuumheat
AlH3 + 2 amine1
⋅AlH3TEAvacuum
heatAlH3 + TEA
• Suppress Al formation and alane evaporation • Increase the yield and purity of AlH3
vacuumheat
vacuumheat
Al + TEA + H2
Evaporation unpublished results ROI filed/manuscripts manuscript accepted
Synthesis of alane adducts:
Al
H
H H
NN
Nex.
Nex.
Hydrogenation:
Al*
Al* No Reaction
• Reactor set-up: • H2 pressure: ~ 1000 psi; • Temperature: 0 ~ 25Á
C;• Chemicals: Et2O (80 mL) and amine (20 mL); • Al*: Ti doped Al metal, ~ 2.0 g.
Al
H
H HH
Al
HH
NNNN
γ-AlH3
N1 2
Al
H
H HH
Al
HH
NNN
N
γ-AlH3
N1 2
Direct synthesis:N
N
N-methylpyrrolidine (NMPy)
N-ethylpyrrolidine (NEPy)
J. Phys. Chem. C. Just accepted; DOI: 10.1021/jp310848u
Characterization (NMR, IR, and XRD):
alane adduct
Calculation Experiment Type I Type II Type III
NMPy 1700 1789 1598, 1793 1709 (2:1), 1773 (1:1) NEPy 1700 1789 1598, 1793 1773 (1:1)
Al-H stretching frequencies (cm-1):
(NMPy)2∙AlH3
H
Al
HH
NR3
Al
H
H H
R3N NR3
HAl Al
H
NR3
R3N H
HHH
(I)
(II)
(III)
Theoretical calculations:
alane adduct Binding Free Energy in Et2O with BSSE Correction (kcal∙mol-1)
Type I Type II Type III NMPy -19.91 -22.11 -18.57 NEPy -14.72 -19.49 -15.94 Et2O -13.24 -15.92 -13.77
H
Al
HH
NR3
Al
H
H H
R3N NR3
HAl Al
H
NR3
R3N H
HHH
(I)
(II)
(III)
Reversible formation of (NMPy)2·AlH3:
Hydrogenation Decomposition
2 NMPy + Al* + H2Et2O
(NMPy)2⋅ΑlH3heat32
Reversible formation of (NMPy)2∙AlH3 in the reactor (~ 60% yield); Low temperature enhances the reaction rate, but not the final yields;
Thermal decomposition Studies:
Hydrogenation coupled with decomposition with LiH:
XRD IR in KBr pellets
Al* + 2 NMPyEt2O
(NMPy)2⋅ΑlH3 vacuum, 50°C LiAlH4 + 2 NMPy1.0 eq LiH1000 psi H2
Al + 2 NMPy + H2(NMPy)2⋅ΑlH3322 NMPy + AlH3
Role of LiH: (NMPy)2⋅ΑlH3 + LiHdecomposition ?
Summary:
Department of Energy Office of Basic Energy Sciences Contract No. DE-AC02-98CH10886
Department of Energy Office of Fuel Cell Technologies Contract No. DE-AC02-98CH10886
Acknowledgements Liu Yang, James Muckerman, Jason Graetz; Yusuf Celebi, John Johnson, James Reilly; Christine Brakel, Kimberley Elcess; Pat Looney, Sabrina Parrish, Lori Happich; All other sustainable energy technologies personnel; The Chemistry department (the NMR instrument).
N
N
NMPy
NEPy
Steric effects:
LiAlH4 regeneration: Al* AlH
H H
NNhydrogenationH2, NMPy, Et2O
vacuum, 50°C
+ LiH
LiAlH4- NMPy
Al
H
H H
NN γ-AlH3
N2Al
H
H H
NNN2
Al
H
H H
NNex.
Al*N Nex.
No Reaction
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