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Debesh Samanta
12I170014
Hydrolysis of Complex Hydrides
for Hydrogen Generation
Submitted by- Debesh Samanta
(Roll No. 12I170014)
Under guidance of
Professor Pratibha Sharma
Department of Energy Science & Engineering
INDIAN INSTITUTE OF TECHNOLOGY- BOMBAY
April, 2013
Introduction
Renewable energy carrier.
Hydrogen on combustion produces clean
exhaust.
Very high energy density (142MJ/kg , around
three times higher than that of petroleum, 47
MJ/kg).
2Slide of 25
Different types of possible hydrogen storage and
issues related to them.
Gaseous storage :
Very high pressure
Low volumetric storage density
Very high diffusivity of H2 amd metal embrittlement.
Liquid storage :
Very low boiling point of Hydrogen (20 k)
The refrigerator system is energy intensive process.
boil off losses.
3Slide of 25
Advantages of solid storage
The drastic decrease in safety risk.
Easy to initiate the reaction.
Long time storage.
4Slide of 25
Metal organic frameworks (MOF), carbon
nano-tubes, nonporous materials, Pd etc.
The metal hydrides alloys
like, MgH2, LaNi5, TiNi, NiFe.
Light metal complex hydrides
Solid hydrides used in hydrolysis
5Slide of 25
Why complex hydrides?
Advantage of light metal complex hydrides
low molecular weight.
capability of carrying up to 4H-
Solubility in water.
6Slide of 25
Why hydrolysis?
Thermolysis:
Advantage-Volumetric storage density is
higher
Limitation- Demands a very high temperature.
Hydrolysis:
Reaction starts even in room temperature.
7Slide of 25
DOE target
Target 2010
(new)
2010 (old) 2015
(new)
2015
(old)
Ultimate
Full Fleet
System
Gravimetric
Density
(% wt)
4.5
(1.5
kWh/kg)
6
(2.0
kWh/kg)
5.5
(1.8
kWh/kg)
9
(3
kWh/kg)
7.5
(2.5
kWh/kg)
System
Volumetric
Density
(g/L)
28
(0.9
kWh/L)
45
(1.5
kWh/L)
40
(1.3
kWh/L)
81
(2.7
kWh/L)
70
(2.3
kWh/L)
System Fill Time
for 5-kg fill,
min (Fueling
Rate, kg/min)
4.2 min
(1.2
kg/min)
3 min
(1.67
kg/min)
3.3 min
(1.5
kg/min)
2.5 min
(2.0
kg/min)
2.5 min
(2.0
kg/min)
Source: DOE targets for onboard Hydrogen storage systems for light-duty vehicles: current R&D focus is on 2015 targets with potential to meet
ultimate targets. http://www1.eere.energy.gov/hydrogenandfuelcells/storage/pdfs/targets_onboard_hydro_storage.pdf. accessed on 08-Apr-138Slide of 25
Hydrolysis of complex hydrides
NaBH4 hydrolysis
NaBH4 + 2H2O →NaBO2 + 4H2 ∆H = -75kJ/mol H2
If 1 gm of NaBH4 is fully ionized it produce 2.37 l of
hydrogen at STP.
GSD is 10.8wt% which is greater than the DOE
target.
9Slide of 25
NH3BH3 hydrolysis
NH3BH3 + 2H2O → NH4+ + BO2
- + 3H2
Gravimetric hydrogen densities -19.6 wt%
LiBH4 hydrolysis
LiBH4 + 4H2O → LiOH + H3BO3 + 4H2
LiBH4 + 2H2O → LiBO2 + 4H2
Gravimetric hydrogen densities -18.5 wt.%
Volumetric hydrogen densities -121 kg H2/m3
10Slide of 25
N2H4BH3 hydrolysis
N2H4BH3 + 2H2O catalyst N2H5BO2 + 3H2
Gravimetric hydrogen densities – 15.4 wt%
MgH2 hydrolysis
MgH2 + 2 H2O → 2 H2 + Mg(OH)2
Gravimetric hydrogen densities – 7.66%
LiAlH4 hydrolysis
LiAlH4 + 4 H2O → LiOH + Al(OH)3 + 4 H2
Gravimetric hydrogen densities – 10.6 wt%11Slide of 25
Catalytic research
The catalysts generally used in hydrolysis can
be classified as –
Transition metal or non-noble metal catalysts
Noble metal catalysts
12Slide of 25
Catalytic researches on NaBH4
Non-noble metal catalysts
Most effective
Cobalt (II) chloride followed by Nickel(II)
And Iron, Manganese Chloride.
Cobalt mainly alloy with boron.
13Slide of 25
Effect of introduction of other materials
Introduction of other elements into Co-B
catalysts increases its activity.
Reason(s)
An increase in electron density of the
metallic Co active site.
Surface area increases because the additive
metals inhibit Co agglomeration.
14Slide of 25
Stability of Catalyst
Example
a filamentary Ni catalyst is studied over 200
catalytic cycles, and retained 76% of its initial
activity.
Reason:
Gradual formation of a film, consist of
hydrated borax (Na2B4O7.10H2O) and boron
oxide (B2O3), on the catalyst surface.15Slide of 25
Noble metal catalyst
Higher concentration of NaOH stabilizer in
solution decreases the activity of Ru. So Ru-based
catalysts may not be the most ideal choice.
The Pt catalyst loaded on LiCoO2 - one of the
most efficient catalysts for NaBH4 hydrolysis.
The most active catalyst reported is Rh loaded on
TiO2
16Slide of 25
Catalytic research on NH3BH3
Non-noble metal catalyst
1. Co, Ni and Cu supported catalyst- the mostcatalytically active.
2. supported Fe is catalytically inactive.
3. the amorphous Fe nano-particles form in situ inpresence of NaBH4 show exceptionally highcatalytic activity .
Reasons(3)
much greater structural distortion
much higher concentration of active sites for thecatalytic reaction 17Slide of 25
• Noble metal-based catalysts
The 20 wt% Pt/C catalyst shows the super high
activity and the reaction is completed in less
than 2 min.
Reason
reduction of Ptn+ (n = 4, 6) to Pto during the
course of the reaction,
Rh[(1,5-COD)(μ-Cl)]2 and Pd black have
lower activity and some noble metal oxides
(RuO2, Ag2O, Au2O3, IrO2) are almost inactive.
18Slide of 25
Issues related with hydrolysis
Water handling
Catalytic cycle
Reversibility of the reaction
Heat management
19Slide of 25
NaBH4 + 2H2O → NaBO2 + 4H2 + heat
NaBH4 + (2 + x) H2O → NaBO2·xH2O + 4H2 + heat
where x is the hydration factor.
In practice, the hydrated by-product is usuallyeither NaBO2·2H2O or NaBO2·4H2O, whichrequires an excess of water.
Water handling
20Slide of 25
The activity loss in case of noble metal catalyst is
very much lower than that of non-noble metal
catalysts.
Reason of decrease in activity:
In case of NaBH4 it is the gradual formation of a
film, consist of hydrated borax (Na2B4O7.10H2O)
and boron oxide (B2O3), on the catalyst surface.
Catalytic cycle
21Slide of 25
More the reversibility of the reaction cost of the
hydrolysis will be lower.
NaBO2 + 2MgH2 NaBH4 + 2MgO
NaBO2 + 2CH4 NaBH4 + 2CO + 2H2
Reversibility of the reaction
22Slide of 25
NaBH4 + (2 + x) H2O → NaBO2·xH2O + 4H2 + heat
Issues at a glance
23Slide of 25
Issue:
Cost
Issues:
Catalytic reactivity
Catalytic durability
Catalyst cost
Issues:
Recycling
Solubility
Issues:
Excess water
Storage capacity
Issue:
Heat
management
Boron based compound are dominating in the process
of hydrogen generation.
• low molecular weight.
• capability of carrying up to 4Hd-
The non-noble metal catalysts have been developed
with activity of similar level of noble metal catalysts.
A lower-cost alternative.
There are other issues like water handling, recovery of
reactant etc.
Hydrolysis of NaBH4 - exothermic process and the heat
must be controlled.
Conclusion
24Slide of 25
25Slide of 25
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