Chemistry of hydrogen and its advancements

Chemistry of Hydrogen (1H)

• The first element of the periodic table.• Atomic Number = 1• Atomic weight = 1.0079• Electronic configuration = 1s1

Introduction

Isotopes of Hydrogen

1. Protium / Hydrogen

2. Deuterium

3. Tritium

Isotopes of Hydrogen1) Protium / Hydrogen (H)

It is the most commonly available isotope. It constitutes 99% of total hydrogen available in nature. The molecule of ordinary hydrogen is diatomic (H2)

The nucleus of atom consist of single proton & no neutron (mass number = 1).

It is represented by .H

1

1


D1

2

2) Deuterium / Heavy Hydrogen (D) Deuterium constitutes 0.016% of total hydrogen

occurring in nature. The molecule of deuterium or heavy hydrogen is

diatomic D2.

The nucleus of atom consist of single proton & a neutron (mass number = 2).

It is represented by .

Isotopes of Hydrogen3) Tritium (T)

It is formed in upper atmosphere by certain nuclear reaction induced by cosmic rays.

It constitutes 1 part in 1021 parts of total hydrogen available in nature.

The molecule of Tritium is diatomic T2.

The nucleus of atom consist of single proton & two neutron (mass number = 3).

It is represented by .


3) Tritium (T) It is radioactive in nature. Tritium decays by the loss of β particle to yield rare

but stable isotope of helium.

The half-life period for this decay is 12.4 years.

HeT2

3

1

3


3) Tritium (T) It can be obtained by bombarding neutron on

isotopes of Lithium.

nHeTnLi

HeTnLi

0

1

2

4

1

3

0

1

3

7

2

4

1

3

0

1

3

6

Importance of Isotopes

1) Use of deuterium & tritium in nuclear energy Continuous production of tritium from lithium is important

step in the future generation of energy from nuclear fusion. In fusion reactor, tritium & deuterium are heated to give a

plasma in which the nuclei react to produce a neutron & . Energy obtained per unit mass of deuterium & tritium nuclei is

about 4 times than that from fission of Uranium & 10 million times than from petrol.

He2

4

Nuclear Reaction of Deuterium & Tritium

MeVnHeTD 6.170

1

2

4

1

3

1

2


2) Heavy water (D2O) use as neutron moderator & Coolant for nuclear reactors:

Water containing deuterium instead of normal hydrogen is called as heavy water.

Ordinary water contains very small portion (about 1 part in 5000) of D2O.

Concentration of heavy water is increased by fractional distillation / prolong electrolysis of water.


2) Heavy water (D2O) use as neutron moderator & Coolant for nuclear reactors:

D2O is used as moderator in the nuclear power industry.

Neutrons are used for bringing about fission of Uranium atoms but for this purpose, their speed should be slower down.

This is done by passing them through heavy water. It is also used as coolant for nuclear reactors.


3) Kinetic Isotope effect: Differences in the properties which arise from the

difference in mass are called as isotope effect. Rates of reactions are measurable different for the process

in which E-H & E-D bonds are broken, made or rearranged (E – another element).

The detection of this kinetic isotope effect help to support a proposed reaction mechanism of many chemical reactions.


4) Isotope effect in detection of motion of hydrogen: Frequencies of molecular vibrations depends on the masses of

atoms.

As the masses of D & H are different, their frequencies of the molecular vibrations are different.

The heavier isotope (D) results in lower frequency.

This isotope effect can be studied by IR spectra of H & D substituted molecule to determine motion of H atom in the molecule.


5) Isotopes as tracers: The distinct properties of isotopes makes them

useful as tracers. The involvement of H & D through a series of

reactions can be followed by IR & mass spectroscopy.

Tritium can be detected by its radioactivity.


6) Use in NMR (Nuclear Magnetic Resonance) Spectroscopy: 1H-NMR detects the presence of hydrogen nuclei

in compound & is powerful method for structure determination of molecule, even like protein.

Heavy water (D2O) is used as one of the

references in NMR spectroscopy.


7) Tritium in self powered lighting devices. Tritium is used in specialized self powered lighting

devices.

The emitted electrons from radioactive decay of small

amount of tritium cause phosphors (A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence) to glow.


8) Tritium in nuclear weapon:

Tritium is used as nuclear weapons to enhance efficiency & yield of fission bombs.

It is used in hydrogen bomb.

Methods of Preparation

1. Laboratory Scale Preparation

2. Industrial Production

3. From Solar Energy


A. From Aqueous acid It is based on the principle of displacement of hydrogen

from its solution which follow hydrogen in electrochemical series where metals are arranged in the order of increasing ease of reduction.

2 Na(s) + H3O+

(aq)2 2 Na+

(aq) + H2(g) + 2 H2O(l)


A. From Aqueous acid On laboratory scale , the usual method is reaction of Zn

with dil H2SO4 / dil HCl.

Zn(s) + H2SO4 ZnSO4 + H2(g)

Zn(s) + 2 HCl ZnCl2 + H2(g)


B. From alkali H2 can be prepared in laboratory scale by reaction of Al or

Si with hot alkali solution.

2 Al + 2 NaOH + 6 H2O Na[Al(OH)4] + 3 H2

2. Industrial Production of H2

A. Production from fossil sources Hydrogen is produced in large amount by steam

reforming process. Production of hydrogen is often integrated directly

into chemical process that require H2 as a feed stock.

Most of the H2 for industry is produced by high

temperature reaction of H2O with CH4 or with coke.


A. Production from fossil sourcesa) Steam Reforming of methane:

Hydrocarbons such as methane (from natural gas) is mixed with steam & passed over nickel catalyst at 700 – 1100oC to yield water gas (mixture of CO & H2).

Further reaction of water gas produces more H2 by water gas shift reaction.

CH4 + H2O CO + 3 H2


A. Production from fossil sourcesWater Gas Shift Reaction

The gases emerging from the steam reformer are then mixed with more steam cooled to 400oC & then are passes through shift converter – an iron copper catalyst.

The CO2 so formed is easily removed either by dissolving in water under pressure or reacting it with K2CO3 or by using aqueous solution of various amines to remove CO2 forming solid ammonium carbonate.

CO + H2O CO2 + H2


A. Production from fossil sourcesb) Steam Reforming of coke:

Coke is obtained by carbonization of coal – the process of heating coal to a high temperature in the absence of air to improve quality as a fuel.

Hydrogen is made cheaply & in large amount by passing steam over red hot coke. The product is water gas . The process takes place at 1000oC.

It is difficult to separate H2 from CO. To produce more H2, water gas is subjected to water gas shift reaction.

C + H2O CO + H2


A. Production from fossil sourcesc) Electrolysis of water

By electrolysis of water containing a small amount of acid or alkali, hydrogen (H2) is liberated at cathode while oxygen (O2) is liberated at anode.



Acidic medium:

H2SO4 2 H+ + SO4

-2

H2O H+ + OH

-



At Cathode:

At Anode:

2 H+ + 2e

- 2 H .

H + H H2

4 OH- 4 OH + 4 e

-

4 OH 2 H2O + O2

3. From Solar Energy:

Water splitting is the general term for a chemical reaction in which water is separated into oxygen & hydrogen.

Solar energy is utilized in several ways such as, wind turbines, photosynthesis & photovoltaic cells.

One such technology under development is high temperature solar H2 production.

High Temperature Solar H2 Production

Single step thermal decomposition of water requires temperature in excess of 4000oC, which is very high to achieve & practically unsuitable.

Sunbelt regions that receives solar power of about 1 kW/m2 are suitable for high temperature solar H2 production.

Solar power concentration reflect & focus solar radiation onto the receiver furnace, producing temperature in excess of 1500oC.

By using multistep process, it is possible to produce H2 at lower temperatures.

Reactions involved

2 Fe2O3(g) 6 FeO(s) + 1/2 O2(g)

H2O(l) + 3 FeO(s) Fe3O4(s) + H2(g)

Compounds of Hydrogen

1. Molecular hydrides

2. Saline hydrides

3. Metallic hydrides

4. Intermediate hydride

Compounds of Hydrogen

Molecular hydride

e.g. CH4 - methane, ammonia

NH3, water H2O, etc

Saline hydride

e.g. LiH, NaH, CaH2,

etc

Metallic hydride

e.g. Zirconium hydride, titanium

hydride, etc

Intermediate hydride

e.g. NaBH4, LiAlH4, etc

Molecular Hydrides

Molecular hydrides are the compounds of hydrogen

with p-block elements & beryllium.

The compounds are formed by covalent bonds.

The bond polarity varies depending on the electron

activity of the atoms to which H2 is attached.

Molecular hydrides

Electron precise

e.g. CnH2n+2 hydrocarbons, silane SiH4,

germane GeH4, etc

Electron rich

e.g. ammonia & water

Electron deficient

e.g. diborane B2H6

Molecular Hydrides

A. Hydrocarbons1. Methane

Molecular Hydrides


• It is the simplest hydrocarbon.• At room temperature & standard pressure, it is colourless,

odorless & flammable gas.• It undergo combustion reaction as

• Apart from this combustion reaction, it is not very reactive.

CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g)

Molecular Hydrides


Occurrence• It is the major component of natural gas about 87% by

volume.• Apart from gas fields, methane can be obtained via biogas

generated by fermentation of organic matter including manure, wastewater sludge, etc under anaerobic conditions.

• It is created near the earth’s surface, primarily by microorganisms by the process of methanogenesis.

Molecular Hydrides


Preparationa) Laboratory scale preparation• Methane can be produced by the destructive distillation

of acetic acid in presence of soda lime.

• Acetic acid is decarboxylated in this process.

Molecular Hydrides


Preparationa) Industrial scale preparation1. Methane can be produced by hydrogenating CO2 through

the Sabatier process.The process involves reaction of H2 & CO2 at elevated temperature & pressure in the presence of Ni-catalyst to produce methane & water.

CO2 + 4 H2 CH4 + 2 H2O

Molecular Hydrides


Preparationb) Industrial scale preparation2. Methane is also side products of hydrogenation of CO in

Fischer-Topsch process.It involves collection of chemical reactions that convert the mixture of CO & H2 into hydrocarbons.

CO + 2 H2 CH4 + H2O

Molecular Hydrides


Applicationsa) It is used as domestic & industrial fuel. Methane in the form of

compressed natural gas is used as vehicular fuel. It is a clean burning fuel. It may be transported as a refrigerated liquid.

b) It is important for electrical generation by burning it as a fuel in a gas turbine or steam engine.

c) Chemical feedstock – in chemical industries, methane is converted to synthesis gas, a mixture of CO & H2, by steam reforming.

Molecular Hydrides

A. Hydrocarbons1. Ethane

Molecular Hydrides


• It is aliphatic hydrocarbon.• At STP, it is colourless, odorless gas.• It undergo combustion reaction as

• It occurs in traces in earth’s atmosphere & sea.

2 C2H6 + 7 O2 4 CO2 + 6 H2O

Molecular HydridesA. Hydrocarbons

1. EthanePreparation

a) Laboratory scale preparation• Ethane can be prepared by Kolbe’s electrolysis, In this

technique an aqueous solution of acetate salt is electrolyzed.• At anode acetate is oxidized to produce CO2 & methyl radical

& highly reactive methyl radicals combine to produce ethane.

Molecular Hydrides


Preparation

CH3COO- CH3 + CO2 + e

-.

CH3 + CH3 C2H6

. .

Molecular Hydrides


Preparationa) Industrial scale preparation

Ethane Is the second largest component of natural gas.It is separated from methane by liquefying at cryogenic temperatures, where gaseous methane can be separated out.Heavier hydrocarbons are separated by distillation.

Molecular Hydrides


Applicationsa) It is mainly used in chemical industries in the production

of ethylene by steam cracking. It is a raw material for polymer formation.

b) It can be used as a refrigerant in cryogenic refrigeration system.

c) In scientific research, liquid ethane is used in cryo-electron microscopy.

Molecular Hydrides

B. Silane

Molecular Hydrides

B. Silane1. Silanes are saturated hydrosilicons in which Si atoms is

bonded to four other hydrogen atom by covalent bond, thus having a tetrahedral structure. It is a colorless gas.

2. Silanes are much more reactive than alkanes. SiH4 is spontaneously flammable in air, reacts violently with hydrogens & hydrolyzed in contact with water. The increase reactivity as compared to hydrocarbons is attributed to large atomic size of Si.

Molecular Hydrides

B. Silane Preparation

1. Laboratory scale preparationa) Silane can be prepared by heating sand with Mg-powder

to produce Mg-silica which is then poured into 20% non-aqueous solution of HCl to produce silane.4 HCl + Mg2Si SiH4 + 2MgCl2

Molecular Hydrides


1. Laboratory scale preparationb) Silane can be prepared by reducing SiCl4 with LiAlH4, the

method gives better yield.

SiCl4 + LiAlH4 SiH4 + AlCl 3 + LiCl

Molecular Hydrides


2. Industrial Scale Preparationa) Commercially silane is prepared by the reaction of SiO2 with Al

under high pressure of hydrogen in a molten salt mixture of NaCl & AlCl3

6 H2(g) + 3 SiO2(s) + 4 Al 3 SiH 4(g) + 2 Al2O3(s)

Molecular Hydrides


2. Industrial Scale Preparationb) Industrial method for preparation of very high purity silane, suitable

for use in semiconductor starts with metallurgical grade silicon (Si), H2 & SiCl4. It involves a complex series of redistribution reaction (in which byproducts are recycled in process) & distillations.

6 H2(g) + 3 SiO2(s) + 4 Al 3 SiH 4(g) + 2 Al2O3(s)

Molecular Hydrides


2. Industrial Scale Preparationb) ---- Si + 2 H2 + 3 SiCl4 4 SiHCl3

2 SiHCl3 SiH2Cl2 + SiCl4

2 SiH2Cl2 SiHCl3 + SiH3Cl

2 SiH3Cl SiH4 + SiH2Cl2

Molecular Hydrides


2. Industrial Scale Preparationc) It can also be prepared by the reaction of LiH with silicon

tetrachloride via Sundermeyer process.

4 LiH + SiCl4 4 LiCl + SiH4

Molecular HydridesB. Silane

Preparation2. Industrial Scale Preparationd) Silane can be produced from metallurgical grade silicon in

two step process.In 1st step, powdered Si is reacted with HCl at 300oC to produce trichlorosilane along with H2 gas.

.In 2nd step, trichlorosilane is then boiled on resinous bed containing of silane.

Si + 3 HCl HSiCl 3 + H2

4 HSiCl3 SiH4 + 3 SiCl4

Molecular Hydrides

B. SilaneApplications1. Silane is used in the production of semiconductor

devices such as solar cells. Silanes are used in applying polycrystalline silicon layers on silicon wafers while manufacturing semiconductors.

2. Low cost solar panels can be prepared by using silane which is used for depositing amorphous silicon on glass or other tubes.

3. It can be used as water repellants.

Molecular Hydrides

B. SilaneApplications4. Silanes are used in masonry protection.5. It is used as sealants.6. It is used as coupling agents to adhere glass fibres to

a polymer matrix stabilizing the composite material.

Molecular Hydrides

C. Germane

It has applications in semiconductor industry.

Molecular Hydrides

C. Germane1. It is the simplest germanium hydride & is the most

useful compound of Germanium.2. It is having similar tetrahedral structure as that of

methane & silane. It is a colourless gas.3. It burns in air to give GeO2 & water. They are similar

to silane, but are less volatile, less flammable & are unaffected by water or aqueous acid or alkali.

Molecular Hydrides

C. Germane Preparation

1. Laboratory scale preparationOn laboratory scale, germane can be prepared by reaction of Na2GeO3 with sodium borohydride.

Na2GeO3 + NaBH4 + H2O GeH4 + 2NaOH + NaBO2

Molecular Hydrides


2. Industrial Scale Preparationa) Chemical reduction method

By the action of reducing agent GeCl4 or GeO2 converts to GeH4.

GeO2 + NaBH4 GeH4 + NaBO2

GeCl4 + LiAlH4 GeH4 + LiCl + AlCl 3

Molecular Hydrides


2. Industrial Scale Preparationb) Electrochemical reduction method

It uses Ge metal as cathode & Mo or Cd as anode immersed in aqueous electrolyte solution.

Ge & H2 gases evolve from cathode, while anode reacts to form molybdenum oxide or cadmium oxide.

Molecular Hydrides


2. Industrial Scale Preparationc) Plasma synthesis method

It involves bombarding Ge metal with H2 atoms that are generated using high frequency plasma to produce germane.

Molecular Hydrides

D. Ammonia

Molecular Hydrides

D. Ammonia1. Ammonia or azane has a pyramidal structure.2. Nitrogen undergoes sp3 hybridization. 3 of 4 hybrid

orbitals are used in forming 3 N-H bonds, while the fourth is occupied by lone pair of electrons.

3. Due to larger lone pair-bond pair repulsion than bond pair-bond pair repulsion, the molecule gets little distorted.

4. It is a colorless gas with a characteristic pungent smell.

Molecular Hydrides

D. Ammonia5. Boiling point of NH3 is abnormally high as compared

to corresponding group elements which can be attributed to the association of its molecule through hydrogen bonding.

6. Nitrogen has lone pair of electrons which makes ammonia basic in nature.

7. The shape makes it polar. The molecules polarity & ability to form hydrogen bond, makes it miscible with water.

Molecular Hydrides

D. Ammonia Preparation

1. Laboratory scale preparationOn laboratory scale, ammonia is prepared by heating on intimate mixture of NH4Cl & dry slapped line (CaO).

2 NH4Cl + CaO CaCl2 + H2O + 2 NH3

Molecular Hydrides

D. Ammonia Preparation

2. Industrial Scale PreparationOn industrial scale, ammonia is prepared by Haber’s process.

N2 + 3 H2 2 NH3

Molecular Hydrides

D. AmmoniaApplications1. About 75% of ammonia is used as fertilizer as its salts

or as a solution.2. It is directly or indirectly the precursor to most

nitrogen containing compounds. Like for preparing HNO3.

3. Ammonium hydroxide is used as general purpose cleaner for many surfaces such as glass, porcelain, stainless steel, etc

Molecular Hydrides

D. AmmoniaApplications4. 16-25% solution of ammonia is used in fermentation

industry as a source of nitrogen for microorganisms & to adjust pH during fermentation.

5. It has been used as the cooling liquid in refrigerator.6. Liquid ammonia is often used as a cheaper & more

convenient way of transporting H2 than cylinders of compressed H2 gas.

Saline Hydrides

These are formed by metals which are more

electropositive than hydrogen. Such metals are of

group I & group II except Be & Mg.

These are formed by transfer of electrons from

metal to hydrogen atom contains H- ions.

e.g. LiH, NaH, CaH2, etc

Saline Hydrides

A. Lithium hydride1. It is a colourless solid with high melting point.2. It is insoluble in any solvent with which it does not

react.3. It reacts rapidly with moist air forming Li(OH)2, LiO2 &

Li2CO3.

4. It can ignite in air when heated slightly below 200oC.5. LiH reacts with water vigorously, explosively

producing LiOH & H2.

Saline HydridesA. Lithium hydride

It is prepared by direct heating of lithium metal with hydrogen gas at temperature above 600oC.

Increase in temperature or pressure, addition of carbon upto 0.003%, increases the yield upto 98%.

2 Li + H2 2 LiH

Saline Hydrides

A. Lithium hydrideApplications1. As it contains highest percentage of hydrogen, it is

used for storage of hydrogen but this application is restricted because of high stability. Removal of H2 requires high temperature above 700oC.

2. It rarely acts as reducing agent except synthesis of silanes & it can be used in the production of variety of reagents like LiAlH4.

3. LiH is used for shielding in nuclear reactors.

Saline Hydrides

B. Sodium hydride1. It is a colorless solid with high melting point.2. It is insoluble in organic solvent.3. It can ignite in air.4. It gives explosively violent reaction with water.

Saline Hydrides

B. Sodium hydrideIt is prepared by direct heating of sodium

metal with hydrogen gas at high temperature close to 700oC.

2 Na + H2 2 NaH

Saline Hydrides

B. Sodium hydrideApplications1. It acts as a strong reducing agent reducing various

compounds.2. It can be used to dry some organic solvents because of

its quick & irreversible reaction with water.3. NaH pellets when crushed in the presence of water

releases H2. Therefore NaH is proposed for H2 storage for the use in fuel cell vehicles.

4. It is used for preparing NaBH4.

Storage of

Hydrogen

A. Chemical Storage: In the form of metal hydride as Sodium Alanates

B. Physical Storage: via compression, liquification, adsorption on porous carbon materials.

Storage of Hydrogen

For stationary storage of hydrogen, it is consumed in refineries & chemical plants where it is produced.

For the use of hydrogen as a fuel in vehicles, ‘on board’ storage of hydrogen has been the main challenge.

A. Chemical Storage

Alanates are complex metal hydrides, which have a potential for a high hydrogen capacity. Sodium alanate (NaAlH4) is a promising material for H2 storage with capacity of 5.5 wt %. It is one of the known complex hydride with favorable thermodynamics & acceptable gravimetric storage capacity for use in PEM fuel cell which operates at about 80oC.

A. Chemical Storage

It is released from NaAlH4 in the following steps:1. As 1 atm pressure, the first reaction between thermodynamically favorable at temperature above 33oC & release 3.7 wt % H2.

NaAlH4(s) Na3AlH6(s) + 2 Al (s) + 3 H2(g)

A. Chemical Storage

2. The 2nd reaction takes place above 110oC & can release 1.8 wt % H2.

Reversibility kinetics of NaAlH4 is improved upon addition of Ti &/or Zr dopants which causes in primary crystal size.

Rehydrogenation is preferably done at 10 MPa pressure & temperature slightly above 100oC

2 Na3AlH6(s) 6 NaH(s) + 2 Al (s) + 3 H2(g)

Limitations of Sodium Alanates

1. It contains low H2 capacity, slow uptake.

2. H2 release proceeds in stages which is not ideal for applications.

It helps for fundamental understanding, designing & developing improved types of complex metal hydrides.

B. Physical Storage

Physical adsorption of H2 on porous carbon material is one of the main methods being considered for automobile applications. It can be done in several forms of carbon like amorphous activated carbon, graphite, nanotubes, etc. e.g. Based on surface area of single graphene sheet (1315 m2/g), the storage capacity of hydrogen adsorbed on graphene is about 3.3 % by weight at cryogenic temperature.

B. Physical Storage

Carbon nanomaterials possesses small size, high surface area, porosity & low density. Carbon nanomaterials can be discussed in different forms as:

1. Fullerene2. Single walled carbon nanotubes3. Multiwalled carbon nanotubes4. Carbon & Graphite nanofibres

1. Fullerenes

Fullerenes are closed cage carbon molecules composed of sp2 hybridized carbon atoms. Spherical fullerene (C60) are often referred to as ‘bucky balls’ consisting of 20 hexagon & 12 pentagons. C60 can be hydrogenated & dehydrogenated reversibly. C60H36 contains approximately 5 wt % hydrogen. H2 can also be stored within fullerene framework.

1. Fullerenes

2. Single walled carbon nanotubes (SWNT)

SWNT’s is like single rolled sheet of graphene. It has a narrow porous size which makes them attractive as adsorbents of H2. H2 uptake increases with surface area which increases with tube diameter. Under 1 atm pressure, the amount of H2

adsorbed in SWNT’s is small (< 1 wt %) where as, under cryogenic conditions from 1 – 2.4 wt %.

2. Single walled carbon nanotubes (SWNT)

3. Multiwalled carbon nanotubes (SWNT)

MWNT’s consist of layers of concentric cylinders of graphene with hollow center. The spacing between each cylinder is similar to the interplanar distance in graphite, with number of cells varying from 2 to 50. MWNT’s are inactive for H2 storage, but alkali doped MWNT’s can store H2 of 7.2 wt %.

3. Multiwalled carbon nanotubes (MWNT)

4. Carbon & Graphite Nanofibres

Carbon nanofibres (CNF’s) are layered graphitic nanostructures.

The reported values of hydrogen storage capacity of such structures ranged from < 1 wt % to several tens of weight percentage at moderate temperature & pressure.

4. Carbon Nanofibres

4. Carbon & Graphite Nanofibres

Graphite nanofibres (GNF’s) consists of the stacks of graphene plates & cones, have plenty of open edges that can favor H2 adsorption.

GNF produced by pyrolysis of acetylene adsorb 6.5 wt % H2.

4. Graphite Nanofibres

Education

Chemistry of hydrogen and its advancements