holes, and therefore improve the H
2
photo catalytic activity [130]. Boumaza et al. [13] reported that
the best catalytic performance over CuCr
2
O
4
for H
2
photoproduction was obtained in NaOH 0.5 M, Na
2
S
2
O
3
0.025 M with an average rate of 0.013 cm
3
h
1
mg catalyst and a quantum efficiency of 0.2 under polychromatic light.
2.2.1.2 Sulphur based thermo,chemical water splitting cycles
Thermochemical water splitting cycle is a promising process to produce hydrogen using solar
or nuclear energy [131]. Ginosar et al. [16] evaluated the activity and stability of several
complex metal oxides: two ABO
3
structures FeTiO
3
and MnTiO
3
and three AB
2
O
4
structures NiFe
2
O
4
, CuFe
2
O
4
, and NiCr
2
O
4
and copper chromite i.e., 2CuO.Cr
2
O
3
was also selected due to the high activities of Cr
2
O
3
and CuO [132] for the atmospheric decomposition of concentrated
sulfuric acid in sulfur based thermochemical water splitting cycles. Catalyst activity was determined
at temperatures from 725 to 900 C. Catalytic
stability was examined at 850 C for up to 1 week
of continuous operation. The results were compared to a 1.0 wt PtTiO
2
catalyst. Over the temperature range, the catalyst activity of the
complex oxides followed the general trend: 2CuO.Cr
2
O
3
CuFe
2
O
4
NiCr
2
O
4
.NiFe
2
O
4
MnTiO3. FeTiO3. Tagawa and Endo [132] observed the order of the activities for the decomposition of
sulfuric acid in thermochemical water splitting process at the initial concentration of SO
3
of 4.0 mol as follows: Pt ≈ Cr
2
O
3
Fe
2
O
3
CuO CeO
2
NiO Al
2
O
3
. The activity of Cr
2
O
3
above 700°C was nearly the same as the Pt catalyst.
2.2.2 Catalytic conversion of alcohols
In recent years, the catalytic decomposition reforming of alcohols has gained particular interest
due to growing environmental, economic, and political concerns regarding energy production
[133]. Safe and efficient in situ hydrogen generation from alcohols i.e. methanol, ethanol,
propanol, butanol can promote the use of fuel cells and other clean technologies as a source of energy
for mobile applications. Alcohols can serve as H
2
carriers that
are compatible
with current
infrastructures for liquid fuels and can be catalytically converted on site in order to minimize
energy input
requirements and
operating temperatures [134]. Methanol and ethanol have
the highest HC ratios among the alcohols and gasoline range alkanes e.g., heptane. That is,
more hydrogen can be extracted from their molecular
frameworks [135].
Production of
hydrogen from alcohols can be accomplished by their dehydrogenation and reforming processes.
2.2.2.1 Dehydrogenation of alcohols
Hydrogen as by product is obtained from dehydrogenation of alcohols over copper chromite
catalysts as discussed in section 2.1.2. The dehydrogenation of alcohols is a reversible and an
endothermic process which implies that heat must be supplied to the system. Of course very pure
hydrogen is obtained on dehydrogenation of ethanol over copper chromite catalyst [136].
2.2.2.2 Decomposition of methanol
Methanol is easy to transport over long distances and to store. The catalytic decomposition
of methanol to CO and H
2
can provide a clean and efficient fuel eqn. 25:
CH
3
OH ↔ CO + 2H
2
∆H = 90.2 kJmol 25 For example, methanol decomposition on board
of a vehicle Fig. 8 provide a fuel which is cleaner and 60 more efficient than gasoline and up to
34 better than undecomposed methanol [137 139]. Methanol decomposition is an endothermic
reaction. The reaction heat can be provided by the engine coolant and exhaust gas. This recovers the
waste heat and increases the heating value of the fuel. The decomposed methanol may also be used
as a clean fuel for gas turbines at times of peak demand of electricity [137 140]. Lean and complete
Copyright © 2011, BCREC, ISSN 1978 2993 Fig. 8. Methanol decomposition on board a vehicle
combustion will ensure low CO and formaldehyde emissions. NOx emission will be greatly reduced
because of lower combustion temperatures. Although
the po te ntial
gain from
implementation of methanol decomposition related technology is evident, successful development of
efficient catalysts and reaction processes is crucial for the implementation of the technology. Cu based
catalysts such as CuCrMn are active catalysts in the decomposition of methanol to CO and H
2
. Cheng et al. [138] concluded that CuCr based
catalysts are much more active than the conventional
CuZn catalysts
in methanol
decomposition. The acidic nature of the CuCr based catalysts, which leads to the decreased
selectivity, can be greatly reduced by passivating the catalysts with alkali metal ions such as
potassium.
2.2.2.3 Reforming of alcohols
