6.1 Introduction
63
2NH 4 Cl + Mg → MgCl 2 + 2NH 3 + H 2
Similarly, different hydrides like sodium borohydride are also capable of generating the sustainable hydrogen. Hydrides of metals liberate hydrogen when decomposed thermally. A striking characteristic of hydrides is that they can be generated
again in a reversible reaction. However, the hydrides have very small percentage
of hydrogen production. The hydrides of magnesium-based alloys exhibit higher
percentage of hydrogen production, at considerably high temperatures, hence making
their use impractical for generation of hydrogen. Another major problem of the
hydrides when used as the source of hydrogen is high air sensitivity. The general
chemical reaction of hydrogen liberation from hydrolysis of hydrides can be understood by the following reaction using sodium borohydride (NaBH 4 ) as the hydrogen
source:
NaBH 4 + H 2 O → NaBO 2 + 4H 2
NaBH 4 is one of the important hydrides of boron. The compound is stable in
dry air and is easy to handle as compared to the other chemicals of such nature.
Hydrogen can be generated by the action of catalysts or by hydrolysis of sodium
borohydride. Sodium borohydride is commonly employed hydride for the generation of hydrogen because of its several advantages over the others such as the
solutions of the compound are non-flammable; the chemical reactions liberate environmentally benign products, the reactions of sodium borohydride allow the rate
control of H 2 production, the by-product of the reaction NaBO 2 can be easily recycled, and the reactions occur at comparatively low temperatures. In the hydrolysis of
the sodium borohydride, the amount of hydrogen released is 10.8 wt.%, where half
of the hydrogen comes from the water [15]. Different catalysts have been reported
for the generation of hydrogen with NaBH 4 . Ru(acac) 3 was used as the catalyst for
hydrolysis of NaBH 4 , Keceli et al. [16]. Silica-supported ferromagnetic compounds
have also been found to assist the hydrolysis of the compound as catalysts [17].
Transition metals like Ni, Pt/C, and Ru/C also serve as the important catalysts of the
reaction [18–20]. Other than NaBH 4 important hydrides like LiBH 4 and KBH 4 are
also employed for the generation of hydrogen [21].
Hydrous hydrazine is also used as the raw material for the generation of hydrogen.
It is a derivative of ammonia. Hydrous hydrazine is a compound in liquid state at
room temperature. It has high contents of hydrogen. About 8.0 wt.% of hydrogen
can be obtained from the decomposition of hydrazine at mild conditions of reaction.
The compound only generates nitrogen as the by-product on complete dissociation.
The chemical equation for the reaction can be given as [22].
N 2 H 4 → N 2 + 2H 2
The use of the suitable catalyst is an absolute necessity for obtaining hydrogen
form hydrazine because the reaction is capable of proceeding in more than one
pathway. For instance, if the decomposition is not controlled by appropriate catalysts
63
2NH 4 Cl + Mg → MgCl 2 + 2NH 3 + H 2
Similarly, different hydrides like sodium borohydride are also capable of generating the sustainable hydrogen. Hydrides of metals liberate hydrogen when decomposed thermally. A striking characteristic of hydrides is that they can be generated
again in a reversible reaction. However, the hydrides have very small percentage
of hydrogen production. The hydrides of magnesium-based alloys exhibit higher
percentage of hydrogen production, at considerably high temperatures, hence making
their use impractical for generation of hydrogen. Another major problem of the
hydrides when used as the source of hydrogen is high air sensitivity. The general
chemical reaction of hydrogen liberation from hydrolysis of hydrides can be understood by the following reaction using sodium borohydride (NaBH 4 ) as the hydrogen
source:
NaBH 4 + H 2 O → NaBO 2 + 4H 2
NaBH 4 is one of the important hydrides of boron. The compound is stable in
dry air and is easy to handle as compared to the other chemicals of such nature.
Hydrogen can be generated by the action of catalysts or by hydrolysis of sodium
borohydride. Sodium borohydride is commonly employed hydride for the generation of hydrogen because of its several advantages over the others such as the
solutions of the compound are non-flammable; the chemical reactions liberate environmentally benign products, the reactions of sodium borohydride allow the rate
control of H 2 production, the by-product of the reaction NaBO 2 can be easily recycled, and the reactions occur at comparatively low temperatures. In the hydrolysis of
the sodium borohydride, the amount of hydrogen released is 10.8 wt.%, where half
of the hydrogen comes from the water [15]. Different catalysts have been reported
for the generation of hydrogen with NaBH 4 . Ru(acac) 3 was used as the catalyst for
hydrolysis of NaBH 4 , Keceli et al. [16]. Silica-supported ferromagnetic compounds
have also been found to assist the hydrolysis of the compound as catalysts [17].
Transition metals like Ni, Pt/C, and Ru/C also serve as the important catalysts of the
reaction [18–20]. Other than NaBH 4 important hydrides like LiBH 4 and KBH 4 are
also employed for the generation of hydrogen [21].
Hydrous hydrazine is also used as the raw material for the generation of hydrogen.
It is a derivative of ammonia. Hydrous hydrazine is a compound in liquid state at
room temperature. It has high contents of hydrogen. About 8.0 wt.% of hydrogen
can be obtained from the decomposition of hydrazine at mild conditions of reaction.
The compound only generates nitrogen as the by-product on complete dissociation.
The chemical equation for the reaction can be given as [22].
N 2 H 4 → N 2 + 2H 2
The use of the suitable catalyst is an absolute necessity for obtaining hydrogen
form hydrazine because the reaction is capable of proceeding in more than one
pathway. For instance, if the decomposition is not controlled by appropriate catalysts