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 & EngineeringINDIAN 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.

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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

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Why complex hydrides?

Advantage of light metal complex hydrides

low molecular weight.

capability of carrying up to 4H-

Solubility in water.

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Why hydrolysis?

Thermolysis:

Advantage-Volumetric storage density is

higher

Limitation- Demands a very high temperature.

Hydrolysis:

Reaction starts even in room temperature.

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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.

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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

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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.

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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.

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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

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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

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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

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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

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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

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