Hydrogen delivery through liquid organic hydrides potential technology

Hydrogen delivery through liquid organic hydrides:
Considerations for a potential technology
Anshu Shukla, Shilpi Karmakar, Rajesh B. Biniwale*
National Environmental Engineering Research Institute, Council of Scientific and Industrial Research, Environmental Materials Unit,
Nehru Marg, Nagpur, Maharashtra 440020, India
a r t i c l e i n f o
Article history:
Received 27 February 2011
Received in revised form
12 April 2011
Accepted 13 April 2011
Available online 17 May 2011
Keywords:
Hydrogen transportation
Cycloalkanes
Dehydrogenation
Clean energy
Catalysts
a b s t r a c t
Carrying hydrogen in chemically bounded form as cycloalkanes and recovery of hydrogen
via a subsequent dehydrogenation reaction is a potential option for hydrogen transport
and delivery. We have earlier reported a novel method for transportation and delivery of
hydrogen through liquid organic hydrides (LOH) such as cycloalkanes. The candidate
cycloalkanes including cyclohexane, methylcyclohexane, decalin etc. contains 6 to 8 wt%
hydrogen with volume basis capacity of hydrogen storage of 60e62 kg/m3
. In view of
several advantages of the system such as transportation by present infrastructure of
lorries, no specific temperature pressure requirement and recyclable reactants/products,
the LOH definitely pose for a potential technology for hydrogen delivery. A considerable
development is reported in this field regarding various aspects of the catalytic dehydro-
genation of the cycloalkanes for activity, selectivity and stability. We have earlier reported
an account of development in chemical hydrides. This article reports a state-of-art in LOH
as hydrogen carrier related to dehydrogenation catalysts, supports, reactors, kinetics,
thermodynamic aspects, potential demand of technology in field, patent literature etc.
Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights
reserved.
1. Introduction
In order to meet the ever increasing energy demand without
causing further damage to the environment, zero carbon
emission fuel such as hydrogen is required [1,2]. There is
consensus on the hydrogen as a clean energy option. An
efficient method for hydrogen storage, transportation and
delivery to point of usage is a prerequisite for any hydrogen-
fueled energy system [2]. Among wide variety of hydrogen
storage technologies liquid organic hydrides provide several
advantages such as relatively higher hydrogen capacity on
both the weight and volume basis [1,2]. The candidate liquid
organic hydrides reported comprise cyclic alkanes such as
methylcyclohexane, cyclohexane, decalin, etc. The physico-
chemical properties and hydrogen storage capacities for
cyclohexane, methylcyclohexane and decalin are listed in
Table 1.
Considering the boiling point and melting point, cyclo-
alkanesareinliquidphaseatambientconditionswithprevailing
temperature of 20e40
C. This facilitates the transportation of
cycloalkanes using simple transport means such as lorries.
Further, properties of methylcyclohexane, as one of the candi-
date media for hydrogen storage, (Table 2) are comparable to
that of gasoline and diesel which makes it possible to transport
using present fuel transportation methods.
Due to simple reaction mechanism, the dehydrogenation
reaction is considered as favorable process for hydrogen
abstraction from cycloalkanes. The mechanism involves
adsorption of cycloalkane over metal catalyst (particularly Pt)
with either simultaneous or rapid subsequent dissociation of
* Corresponding author. Tel.: þ91 712 2249885, þ91 9822745768(mobile).
E-mail address: rb_biniwale@neeri.res.in (R.B. Biniwale).
Available at www.sciencedirect.com
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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 3 7 1 9 e3 7 2 6
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doi:10.1016/j.ijhydene.2011.04.107

hydrogen atoms via pi-bond formation [3]. Dehydrogenation
results in formation of hydrogen and aromatic. The reaction is
highly selective over Pt catalysts and there have been reports for
formation of no by-products or partially dehydrogenated prod-
ucts. Dehydrogenation and its subsequent hydrogenation of
aromatics are easily reversible [1, 2, and 4]. A typical concept of
transportation of hydrogen from hydrogenproduction facility to
fueling station using methylcyclohexane is depicted in Fig. 1.
Thus, in view of this researchers are trying to demonstrate
hydrogen storage and supply using liquid organic hydrides
mainly cycloalkanes such as cyclohexane, methylcyclohex-
ane and decalin. Hodoshima and co-workers reported that the
decalin should be considered as a potential candidate for fuel
cell vehicles [5]. The advantages related to decalin are inves-
tigated by Lazaro and group as negligible evaporation loss, low
toxicity, no parallel reactions, low cost and low dehydroge-
nation energy which allows reaction to perform at relatively
low temperatures [6]. The methylcyclohexane exhibits similar
advantages as a candidate medium. The advantages expla-
ined by Oda and group include relatively high boiling point
and no carcinogenic products are formed [7]. Hodoshima and
co-workers also reported that the tetralin can be a potential
option over decalin due to 4e5 times higher reaction rate
under superheated liquid film condition [8].
In an earlier article we have given an account of chemical
hydrides in general and LOH in particular for hydrogen storage
and supply [2]. This article covers the state-of-art develop-
ment on several other aspects such as kinetics, thermody-
namics, patent-review regarding LOH technology.
2. Dehydrogenation catalysts
Several catalysts are reported for dehydrogenation of cyclo-
alkanes. Coughlan et al. in 1990 reported that the dehydrogena-
tionofcyclohexaneonnickelexchangedY-zeolitesproceededvia
series of consecutive dehydrogenation steps [9]. Kobayashi et al.
reported Pt/Al2O3 as an efficient catalyst for dehydrogenation of
iso-propanol [10]. In an early work related to this reaction, 3.82 wt
% Pt/PCC (Pt supported on petroleum coke carbon) catalyst was
studied for dehydrogenation of methylcyclohexane and decalin
by Kariya et al. [4]. They concluded that the major properties such
as hydrogen spillover and hydrogen-recombination to be taken
into consideration while selecting the catalysts. The same group
in 2003 reported methylcyclohexane dehydrogenation over 10 wt
% Pt/ACC (Pt supported on activated carbon cloth) wherein the
hydrogen evolution rate was reported as 0.52 mmol/gmet/min at
298
C [1]. They proved that the particle size of catalyst have
profound effect on dehydrogenation reaction. Hodoshima and
group in one of the report concluded shorter Pt distance with its
neighbor can affect dehydrogenation of decalin. They even
proposed tomodify catalystandstudytheeffectof alkalireagents
on catalytic activity and fine structure of Pt species [11].
Bi-metallic catalysts have shown considerably higher
activity for dehydrogenation than monometallic catalysts as
has been reported by Ichikawa and group [4]. They concluded
that PteMo/PCC, PteW/PCC and PteRe/PCC exhibit compara-
tively better hydrogen evolution rate than monometallic Pt/
PCC for cyclohexane dehydrogenation. They also suggested
that physical mixing of Pd/PCC and Pt/PCC improves catalytic
activity, since Pd helps in suppressing reverse reaction and Pt
helps in hydrogen-recombination ability. These conclusions
are based on the hydrogen evolution activity and there is no
evidence of arrangement of metal presence on support.
Hodoshima and co-workers explained catalyst selection is
based on its ability to CeH dissociation for alkane and inves-
tigated PteRe/AC (PteRe supported on activated carbon) to
have excellent activity for dehydrogenation of decalin with
nearly 100% conversion [12]. In the same year 2005, Hodosh-
ima et al. have reported dehydrogenation of tetralin over
carbon supported on NieRu and suggested that this can be
alternate catalyst to costly Pt. Biniwale et al. have reported an
Table 1 e Hydrogen storage capacities for cycloalkanes such as cyclohexane, methylcyclohexane and decalin and their
physical properties.
Sr. No. Properties Cyclohexane Methylcyclohexane Decalin
1. Melting point (
C) 6.5 À126.6 À30.4
2. Boiling point (
C) 80.74 100.9 185.5
3. Density (g/ml) 0.779 0.77 0.896
4. Standard formation enthalpy in
dehydrogenation of cyclic hydrocarbons (101.3 kPa) DH (kJ molÀ1
)
þ205.9 þ204.8 þ319.5
5. Theoretical hydrogen storage- weight basis (%) 7.2 6.2 7.3
6. Theoretical hydrogen storage evolume basis (1028
mol/m3
) 3.3 2.8 3.8
8. Product of dehydrogenation Benzene Toluene Naphthalene
Table 2 e Comparison of properties of methylcyclohexane with gasoline and diesel.
Sr. No. Properties Diesel Gasoline Methylcyclohexane
1. Reid vapor pressure (psi) 0.2 8e15 1.61
2. Auto ignition temperature (
F) 446 572 482
3. Flash point (
F) 165 À45 25
4. Peak flame temperature (
F) 3729 3591
5. Density (g/cc) 0.83 0.75 0.81
6. Flammable limit in air LELeUEL 1.3e6.0% 1.4e7.4% 1.1e6.7%

enhancement in the activity of catalyst by addition of a small
amount of Pt to the Ni based catalyst. Activated carbon was
used as the support with synergistic effect of NiePt catalysts
(with Ni:Pt ratio of 40:1 on the weight basis) [13].
Okada and co-workers reported 0.1 wt% k þ 0.6 wt% Pt/
Al2O3 catalyst with a view to perform the reaction at relatively
lower temperature [14]. The initial reactions were reported at
nearly 375
C to avoid coke formation on the catalyst surface.
They have investigated use of g-alumina as a support for Pt
and optimized pH for impregnation of Pt for preparation of the
catalyst. The catalyst was reported with relatively higher
hydrogen evolution rate of about 744 mmol/gmet/min. Further,
a hydrogen evolution rate of 958 mmol/gmet/min at 90 min
with 350
C was reported during dehydrogenation of methyl-
cyclohexane over a proprietary catalyst [15].
Dehydrogenation of methylcyclohexane on partially
reduced metal oxide namely MoO3 has been reported earlier
[16]. This can be a cost effective catalyst option for dehydro-
genation reaction, as the reaction is performed in absence of
noble metal catalyst. They have reported that the catalytic
dehydrogenation of methylcyclohexane prevails at relatively
higher temperatures of 300
C and 380
C. They report metal
sites present in MoO2(Hc)ac are responsible for the catalytic
dehydrogenation of methylcyclohexane.
Accordingly, Pt based catalysts are reported for having
higher activity and selectivity. The literature seems to drive
the catalyst’s search toward bi-metallic catalysts exploring
hydrogen spillover and recombination properties of two co-
existing different metals [17]. The attempts to use Pt in
combination with Ni, Pd etc. have been reported as the
potential catalysts. The benchmark activity of 744 mmol/g/
min in terms of hydrogen evolution rate and selectivity of
about 99% for catalyst is reported with use of a ﬁxed bed
reactor system and bi-metallic catalyst [14]. We have reported
a relatively higher activity in terms of hydrogen evolution rate
of 958 mmol/g/min [16].
Although, several efﬁcient bi-metallic catalysts have been
reported with their detailed characterization and possible
synergistic effects none of the reports describes the mecha-
nism by which dehydrogenation is improved over a particular
catalyst. There is a scope for fundamental and theoretical
studies providing direct evidences from characterization to
explain and guide the further designing of the catalysts.
3. Selection of supports for catalysts
Dehydrogenation reaction is particularly favorable on the
well-dispersed catalysts. When a reforming catalyst such as
Ni is used the lower dispersion may lead to side reactions
such as hydrogenolysis [13]. The supports used for disper-
sion of metal catalysts have a major role to play in the
dehydrogenation reactions. Various materials that can be
employed as supports for metal catalysts include carbon
materials, metal oxides, perovskites, zeolites, silica etc
[1,2,4,5,6,15,16,17,18,19]. Due to high surface area and
inertness to the side reaction carbon based supports such
as activated carbon granules and activated carbon cloth are
widely studied by various groups [1,2,5].
Kariya et al. and Biniwale et al. reported that the conduc-
tive support like alumite (alumina layer formed through
surface oxidation of aluminum using anodization) favors high
and uniform catalyst surface temperature [1,20]. Lazaro and
co-workers have reported that 0.25 wt% Pt/CNF is effective for
dehydrogenation of cyclohexane [6]. They have claimed that
similar activity and selectivity was exhibited by 0.25 wt% Pt/
CNF catalyst as compared to 1 wt% Pt/Al2O3. This can be
attributed to better dispersion on Pt and the open structure of
CNF/CNT which allows the liquid to have easy accessibility for
catalyst sites and desorption of product is favored.
Okada et al. reported that the deactivation of catalyst can be
suppressed by high dispersion of Pt on pore controlled g-Al2O3
[14]. They also reported that the pH for impregnation has to be
optimized for chloroplatinic acid. A pH swing method was
applied for controlled pore distribution of g-Al2O3. One of the
reports wherein, dynamics of hydrogen spillover on carbon
based materials is discussed. Reports suggest metal oxide
favors small energy barrier of H-migration from catalyst to
substrates and favors subsequent proton diffusion [15]. Belatel
et al. investigated determination of fermi level for explaining
metallic character of the catalyst for reduced MoO2 [17]. They
explained that the dissociation of hydrogen can take place on
reduced MoO2 which can also lead to formation of Bro¨nsted
MoeOH group. This mechanism is not favored in carbon based
materials and thus, hydrogen spillover is suppressed. A study
reports metal oxides as support for Pt favoring hydrogen
spillover and in turns lowers the thermodynamic equilibrium
and thus performs better that activated carbon [15]. Biniwale
and group studied various metal oxide supports for Pt. The
different metal oxides supports studied include TiO2, La2O3,
CeO2, ZrO2, Fe2O3, Al2O3, MnO2 and LaNiO3. Further, perovskite
type oxides have been used as support for Pt catalysts. They
found 1 wt% Pt/La0.7Y0.3NiO3 exhibit hydrogen evolution rate of
Fig. 1 e Concept for hydrogen transportation using
methylcyclohexaneetoluene pair.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 3 7 1 9 e3 7 2 6 3721

45 mmol/gmet/min during dehydrogenation of methyl-
cyclohexane at 350
C [15].
From the literature, the conclusion can be drawn that the
metal oxides are potential support for metal catalysts for dehy-
drogenation of methylcyclohexane. A strong metalesupport
interaction helps in better hydrogen spillover and therefore
improving forward rate of reaction. Further, metal oxides under
reduced conditions form additional active sites on the surface
for dehydrogenation reaction.
4. Kinetic aspects of dehydrogenation of
cycloalkanes
Ichikawa and co-workers reported that the rate of reaction
dehydrogenation of cycloalkanes varies profoundly with
change in temperature, supports, initial feeding rates and use
of bi-metallic catalysts [4]. They studied the rate constant (k)
for dehydrogenation of cyclohexane and decalin and found
increase in rate constant with increase in temperature. The
retardation constants (K) observed to be declining with
increase in temperature. They suggested that this was due to
reduced adsorption of aromatics (product) on catalytic surface
at higher temperature. They also studied the various Pt based
catalysts supported on PCC, CC, Al2O3, FSM-16, HZSM-5 for
estimating rate constants for dehydrogenation. The variations
in support for Pt catalyst suggest Pt/PCC and Pt/CC resulted in
higher value for (k) with the feed of cyclohexane at 1.2 and
1.10 ml. The value for (k) with Pt/PCC at 1.20 ml was observed
as 4.5 mmol/min. The rate constant (k) calculated for Pt/CC
with the reactant of 1.10 ml was 4.3 mmol/min. The use of
different active carbons results in variation in reaction rate
depending on their particle size distribution, pore size distri-
bution and surface area, etc. They also reported that there is
no specific co-relation between rate of reaction and nature of
carbon. Very low rate of reaction for Pt/FSM, Pt/HZSM-5 and
Pt/Al2O3 catalysts was observed. In context with reactant feed,
the initial feeding rate of cyclohexane and methylcyclohexane
has been reported to have profound effect on the reaction rate
constant. However, in the case of decalin initial feeding rate
was not found to have significant effect. Thus, retardation
constant data as explained by Ichikawa’s group; suggest dec-
alin have higher retardation constant (K) value than methyl-
cyclohexane and cyclohexane. This is because of naphthalene
adsorption property over catalytic surface. The adsorption of
naphthalene resulted in blockage of active catalytic sites.
Hodoshima and co-workers also found declination of the
reaction rate with use of decalin and gave same conclusion of
naphthalene adsorption over catalytic sites. Kariya et al.
reported Langmuir-type equation for reaction rate (ÀrA) and
rate constants (k) [1]. They discussed change in temperature of
the catalysts surface under alternate wet-dry reaction condi-
tions with conclusion that the major reason for decrease in
temperature is due to evaporation of liquid reactant droplets
on the catalysts surface. They reported negligible retardation
reaction rate (K) and suggested that the dehydrogenation
reaction to be first order reaction [1]. In an article Hodoshima
and group reported kinetics for dehydrogenation of tetralin in
superheated and liquid film state. They found higher value for
rate constant (k) and lower retardation constant (K) [12]. They
also suggested that higher reaction rates can be achieved by
sharp temperature gradient at catalystereactant interface.
The continuous removal of adsorbed hydrogen from catalysts
surface can also help in achieving higher forward rate of
reaction. Biniwale and co-workers, studied the dehydrogena-
tion of methylcyclohexane with Pt supported on different
metal oxides and reported reaction to be zero-order reaction
[15]. They found no difference in value of rate constant (k) for
Pt/LaNiO3 and Pt/La0.7Y0.3NiO3. The substitution of yittrium at
A-site of LaNiO3 has effect only on selectivity toward
hydrogen and toluene.
From the above discussions it can be concluded that higher
temperature of catalyst surface improves kinetics of the
reaction. The higher reaction temperature helps in rapid
removal of hydrogen from the surface of catalyst avoiding
blockage of active sites. The rate of reaction may be altered by
change in support used for the Pt catalyst.
5. Thermodynamics aspects of
dehydrogenation of cycloalkanes
Okada et al. reported that the dehydrogenation of decalin is
comparatively easier than methylcyclohexane and cyclo-
hexane [14]. Methylcyclohexane with a side chain is easily
dehydrogenated than cyclohexane as reported by Okada and
co-workers. They suggested that for the same equilibrium
conversion the temperature required for decalin is less than
as required for methylcyclohexane and cyclohexane. They
also reported that 99% conversion of methylcyclohexane can
be obtained with temperature maintained around 330
C.
La´zaro et al. reported a relation of the theoretical thermody-
namic equilibrium compositions vs. reaction temperature
using Gibbs energy minimization method [6]. They reported
data on decalin conversion with respect to various tempera-
tures suggesting that the increase in reaction temperature
increases thermodynamic conversion. They have estimated
that a 90% conversion of decalin is achievable at temperature
of ca 265
C. As an optimum temperature they performed
dehydrogenation of decalin at ca 240
C. Since the dehydro-
genation of cycloalkanes is endothermic reaction it is favor-
able at higher temperatures and the equilibrium conversion is
achievable with reaction temperatures in the range of
250e375
C depending on the reactant, catalysts and reactor
system used.
6. Reactor systems
Dehydrogenation being endothermic reaction demands
supply of heat [1e2 and 4]. Thus, different reactor systems are
being developed and demonstrated by many groups. The
steady and unsteady state reactors have been studied for
dehydrogenation reaction. The advantages and disadvantages
for different reactor system employed for dehydrogenation of
cycloalkanes are shown in Table 3.
Initially a couple of studies reported steady state reactors
for dehydrogenation reactions [14,18]. Newson and co-
workers reported membrane reactor using Pd based catalyst
for hydrogen storage [5].

The unsteady state reaction mechanism as thin liquid film
was reported by Kameyama and co-workers for dehydroge-
nation of iso-propanol on Pt/Al2O3 at 95
C [10]. In order to
improve the conversion of cycloalkanes several attempts have
been reported employing unsteady state reactor systems.
In this context, Ichikawa and co-workers studied the
dehydrogenation of cycloalkanes using a spray-pulsed reactor
and reported optimization of parameters such as tempera-
ture, reactants, support, monometallic-bi-metallic catalyst,
and reactant/catalyst ratio [4]. Also, Bordeje and group
proposed a rotating monolithic reactor system so as to over-
come complexities of spray-pulse reactor system [6]. Ichikawa
and group reported use of wet-dry multiphase condition
wherein reactant and catalyst contact is effectively achieved
[4]. They also explained how this method is advantageous
over conventional method of reactant flow. The higher rate of
reaction for methylcyclohexane was reported as compared to
dehydrogen of decalin. It is explained that the dehydro-
genated product from decalin i.e. naphthalene requires higher
energy for removal from the catalyst surface due to its high
boiling point and affinity toward carbon. They proved efficacy
of reactant catalyst contact was improved, catalyst main-
tained a high temperature which helped in avoiding reverse
reaction. However, the rate of production of hydrogen was
dependent on reaction conditions like reactant feed rate,
temperature and catalyst support.
The same group studied the reaction with spray pulse
mode of reactant flow. The hydrogen production is dependant
on rate of reactant flow. Hodoshima and co-workers
concluded superheated liquid film conditions can be consid-
ered as better option than conventional batch process over
wide ranges of feed rate for decalin [17]. Roumanie et al.
demonstrated the development of silicon micro-structured
reactor for dehydrogenation of methylcyclohexane [19]. They
reported Pt/Al2O3 prepared by conventional method exhibited
better performance than that made by vapor deposition of
platinum film (PVD). They suggest the problem of elevated
endothermic heat of reaction can be resolved by proper design
of a micro-structured reactor with height in the range of
100 mm. The uniform temperature was successfully main-
tained at 400
C with a preheating zone at 80
C, using such
micro-reactor. Okada and co-workers reported the use of fixed
bed reactor with higher hydrogen evolution rates [14]. Ichi-
kawa and co-workers studied dehydrogenation of cyclo-
hexane with a different view of thermographic analysis [20].
Herein, they recorded the temperature profile of reaction
temperature and estimated heat transfer flux under transient
conditions. They investigated in wet-dry reaction condition of
reactant on catalyst surface, the catalyst surface experiences
phase change for reactant due to evaporation. This resulted in
better heat transfer due to alternate wet-dry conditions
formed on the surface with better solid-liquid contact. Lazaro
et al. reported successful dehydrogenation of decalin over Pt/
CNF (Pt supported on carbon) using fixed bed reactor and
proposed use of rotating monolithic reactor system [6]. Shukla
et al. reported the dehydrogenation of methylcyclohexane
with Pt supported on different metal oxides using spray pulse
mode of reactant flow [15]. In succeeding report, they reported
nearly 100% conversion of methylcyclohexane with consid-
erable high hydrogen evolution rate of about 968 mmol/gmet/
min [16]. A high purity hydrogen production using amorphous
silica membranes with membrane reactor was reported by
Oda et al. [7]. They reported one step method to produce
hydrogen from methylcyclohexane. In 2010, Oda et al.
demonstrated hydrogen generation with high purity of 99.95%
in absence of sweep gas or carrier gas using membrane
reactor. They reported the activity was almost similar to the
simulated data.
Accordingly, a considerable improvement in the cata-
lytic reactors for carrying out endothermic dehydrogena-
tion reactions has been reported in the literature. Further
scope of improvement relates to minimizing the heat
requirement by improvement in heat transfer and
improving the surface area of the catalysts. Up-scaling of
reactor and its study for dehydrogenation of cycloalkanes
also need to be pursued.
Table 3 e The strengths and weakness for different reactor systems employed for dehydrogenation of cycloalkanes.
Sr. No. Reactors Strengths Weakness
1. Batch reactor High conversion is achieved Liquid reaction is favored
2. Fixed bed reactor Continuous product formation Favors reverse reaction and
liquid phase reaction
3. Wet-dry multiphase system
or spray pulse system
1) Efficiency of reactant supply is high Commercial feasibility process,
intensification of process is crucial,
considering available volume in vehicle or
portable device is very limited
2) Catalyst is kept at high temperature
3) Suppression of reverse reaction
4. Monolithic reactor system 1) Structured catalyst reactor No direct experimental data available
2) Avoidance of granular catalyst
3) High catalytic geometric surface area,
maximizing working volume
4) Alternate wet-dry condition and thin liquid film
5) Regeneration step can be included
6) Exploitation of observed initial
5. Micro-reactor 1) Compact design Complicated design
2) Overcomes heat transfer limitation
6. Membrane reactor Reaction and separation carried out in one step Higher cost and maintenance
7. Liquid-film state condition Suspension of liquid reactant
with catalyst can be avoided
Thin film liquid always covers the
catalyst surface and does not favor drying

7. Theoretical studies
There are limited theoretical studies wherein hydrogen
adsorption on different materials is reported. The hydrogen
spillover on to carbon based materials is well studied by
Cheng and co-workers. They concluded that the spillover of
hydrogen is favored onto nanostructured carbon materials
only if H-atom generated via dissociation by metal catalyst
remains physisorbed. They reported molecular dynamics
(MD) calculations revealed efﬁcacy of graphene materials can
be improved by using carbon materials with curved surfaces.
Chen et al. reported hydrogen spillover on the MoO3 in pres-
ence of Pt catalyst using periodic density functional theory
(DFT) [21]. They found relocation of adsorbed H-atom from Pt6
to MoO3 (010) to go through a transition from repulsive elec-
trostatic to attractive protoneoxygen interactions. There is
a need for understanding of catalytic dehydrogenation
phenomena at atomistic level.
8. Patents on hydrogen storage by chemical
hydrides
Various methods for hydrogen storage and delivery have
been patented. A summary of the patents available is listed in
Table 4. Patents have been claimed on the basis of dehydro-
genation catalyst, reactants, reactor system, and reaction
conditions. Patents claimed on various chemical hydrides as
reactants include the use of solid hydrides, liquid hydrides
and liquid organic hydrides. Various solid hydrides like
lithium hydride, magnesium hydride has been reported for
hydrogen storage, magnesium based alloys have been repor-
ted for storage of hydrogen [22].
A Japanese patent No. JP20001110437 describes catalytic
production of hydrogen from benzene, toluene, xylene,
mesitylene, naphthalene, anthracene, biphenyl, phenan-
threne and their alkyl derivatives by using Pt supported on
high surface area substrate as catalyst [23]. US Patent Appli-
cation 20050002857 explains the process where extended pi-
conjugated substrates are used to store and release
hydrogen by means of reversible catalytic hydrogenation [24].
These extended pi-conjugated substrates includes large
polycyclic aromatic hydrocarbons, polycyclic aromatic
hydrocarbons with nitrogen hetero-atoms, polycyclic
aromatic hydrocarbons with oxygen hetero-atoms, polycyclic
aromatic hydrocarbons with alkyl, alkoxy, nitrile, ketone,
ether or polyether substituent. The hydrogen storage capacity
was relatively low in these chemicals for their economical use.
A process describing a hydrogen generation system including
an energy system have been stated in United States Patent
Application 20030014917, wherein they have used a group of
chemical hydride solute consisting of: NaBH4, LiBH4, KBH4,
RbBH4 to react with water in the presence of a catalyst (Ru, Co,
Pt or alloy thereof) to generate hydrogen [25]. The chemical
hydride has a shelf life under alkali conditions where alkaline
additive used is 0.1%NaOH and the chemical hydrides can be
stored as well [26]. Another patent on liquid organic hydrides
made to US Patent No. 6,074,447 describes a process of dehy-
drogenation of methylcyclohexane, decalin, dicyclohexyl, and
cyclohexane to toluene, naphthalene, biphynl and benzene,
respectively, in the presence of particular iridium based
molecular complex catalyst at preferably 190
C or higher [27].
In an attempt to design reactors for endothermic dehydro-
genation reaction US patent application no. 20060143981
describes the use of micro channel catalytic reactor for dehy-
drogenation of liquid fuel for hydrogen generation. They have
used reactants including hydrogenated form of extended pi-
Table 4 e Summary of patents available for hydrogen storage, transportation and delivery using chemical hydrides.
Month/year Patent no. Title
Jan 2010 US 2010/0010280 A1 Catalyst for dehydrogenation of hydrocarbon
May 2009 US 2009/0118557 A1 Reactant dehydrogenation of alkyl aromatics
April 2008 US 7351395 B1 Hydrogen storage by reversible hydrogenation of pi-conjugated substrates.
Sep 2008 US 7429372 B2 Hydrogen storage by reversible hydrogenation of pi-conjugated substrates.
June 2006 US 2006/0135831 A1 Dehydrogenation process
July 2006 US 2006/0143981 A1 Dehydrogenation of liquid fuel in micro channel catalytic reactor
Jan 2006 US 2006/0009668 A1 Process for the dehydrogenation of an unsaturated hydrocarbon.
Sep 2006 US 7,101,530 B2 Hydrogen storage by reversible hydrogenation of pi-conjugated substrates.
Jan 2005 US patent application 2005002857 A1 Hydrogen storage by reversible hydrogenation of pi-conjugated substrates
June 2005 US 2005/0119515 A1 Partial dehydrogenation method using continuous heterogeneous catalyst
Oct 2004 US patent application 20040199039 Dehydrogenation reactions in narrow reaction chambers and integrated reactors
April 2004 US patent application 20040074759 Catalytic process for the treatment of organic compounds.
Jan 2003 US patent application 20030014917 Chemical hydride hydrogen generation system and an energy system
incorporating the same
May 2003 US patent application 20030091876 Chemical hydride hydrogen generation system and fuel cell stack incorporating
a common heat transfer circuit
May 2003 US patent application 20030091879 Chemical hydride hydrogen generation system and an energy system
incorporating the same
June 2003 US patent application 20030113259 Chemical hydride hydrogen reactor and generation system
May 2002 JP-2002134141 Hydrogen storage and supply system and liquid organic hydrogen storage
and supply body.
April 2001 JP-2001110437 Hydrogen fuel supply system for fuel cell.

conjugatedsubstratewith hetro-atomsother than nitrogen, pi-
conjugated monocyclic substrates with multiple nitrogen
hetro-atoms, pi-conjugated organic polymers and oligomers
and ionic pi-conjugated substrate and polycyclic aromatic
hydrocarbon [28]. The reaction temperature reported for
dehydrogenation in this patent was in the range of 60e300
C.
The process described involves reversible catalytic hydroge-
nation and dehydrogenation of the liquid organic compound
followed by separation of the liquid phase dehydrogenated
organic compound and gaseous hydrogen and their recovery.
Many catalysts are reported to be used as hydrocarbon
conversion catalyst like Pt (0.1e5 wt%)-second metal alloy
(second metal may be Co, Ni, Fe, Cu, Sn, Pd, Cd, Ir, Rh, Ru, Ag, Bi,
Hg, Pb) supported on a refractory support by impregnation or
ion exchange technique. They have been employed for dehy-
drogenation of C3eC25 hydrocarbons and the patent relates to
platinum containing catalyst and their use for the catalytic
conversion of hydrocarbons [29]. A Japanese patent JP-
2002134141 describes catalytic dehydrogenation of aromatic
derivatives and hydrogenation of the respective aromatic by
catalyst containing at least one metal from Ni, Pd, Pt, Rh, Ir, Ru,
Mo, Re, W, V, Os, Cr, Co and Fe [30]. A US patent application No.
20100010280 demonstrates a stationary or fluid bed catalyst for
dehydrogenation of hydrocarbons containing an alumina
carrier, with chromium and alkali metals consisting of only
sodium and potassium oxides, added as promoters [31]. US
Patent Application 20040199039, reports reactor configuration
for dehydrogenation of propane and isobutane to propylene
and isobutene, respectively in narrow reaction chamber and
integrated reactors [32]. Whereas another US Patent Applica-
tion 20050013767 describes a method of delivering a reversible
hydrogenstorage to a mobileor stationaryapplicationusingpi-
conjugated substrate [33].
As compared to articles reported in journals, patent liter-
ature covers a more comprehensive class of potential
aromatic compounds which can be used as a hydrogen carrier
in the hydrogenated form. It is obvious to cover as many as
potential candidates in the patent literature in order to protect
the commercial interest. However, a systematic data on
reactions kinetics, thermodynamics and catalyst activity for
these extended potential reactants is not available.
Based on the patent literature available following are the
claims related to various aspects of hydrogen storage through
chemical hydrides or liquid organic hydrides.
Reactant: methylcyclohexane, cyclohexane, decalin, pi-
conjugated substrates.
Catalyst: Pt and Pt based catalyst with second metal
(second metal may be Co, Ni, Fe, Cu, Sn, Pd, Cd, Ir, Rh, Ru,
Ag, Bi, Hg, Pb)
9. LOH state-of-art
Considerably high evolution rate of about 3800 mmol/gmet/
min was reported Ichikawa and co-workers by dehydrogena-
tion of cyclohexane at 375
C with Pt/alumite as catalyst [1]. In
the same year the hydrogen evolution rate ranging from 1500
to 500 mmol/gmet/min was reported by several researchers.
However, these rates are for initial several minutes of the
reactions, typically for 5e20 min. Whereas, reports for time on
series data for a considerably longer period in several hours
are rare.
Considering hydrogen demand for PEMFC, Hodoshima and
co-workers demonstrated 50 kW of dehydrogenation system
using superheated liquid film condition as a feasible option for
practical purpose. They have achieved 70% conversion of
cycloalkanein one pass level having reactionarea ofabout 1 m2
.
There are several reports on high performance of dehy-
drogenation catalyst establishing the potential of the method
of hydrogen delivery using LOH for practical application,
Okada et al. reported methylcyclohexane conversion of 95%
with 99% selectivity toward toluene with stability upto 6000 h.
The hydrogen production cost of 64.7 U/Nm3
of H2 was
reported by Okada et al. A feasibility study by Biniwale and
group estimated the hydrogen production cost at 7.57 USD/kg
of hydrogen. They have reported the catalyst stability up to
200 h with conversion of ca 60% in a single step [16].
Many research groups in collaboration with industries
anticipated in demonstrating liquid organic hydrides system.
The first organic hydride vehicle was successfully driven by
Japanese based industries and Prof. Masaru Ichikawa from
Hokkaido University in 2008 [34]. They demonstrated fuel
efficiency was improved by 30% and CO2 emission was
reduced by 30% as compared to the base line emissions of
vehicle using only gasoline as fuel. In this experiment they
have used gasoline for initial period of drive and then
switched over to hydrogen. The use of gasoline in initial cold-
engine conditions attributed to emissions from the vehicle. If
a fuel cell vehicle is used by using hydrogen obtained from on-
board dehydrogenation of LOH then it is expected to result
into zero tail-pipe emissions.
Although emphasis is on transportation sector application
for hydrogen economy however, it is apparent that there are
several other potential markets of liquid organic hydride for
near future. Several potential applications for LOH technology
to meet hydrogen supply include;
Use of hydrogen in industrial applications such as float
glass, sorbital manufacture etc.
Auxiliary power generation units for remote application
such as telephone towers.
Hydrogen for electrolysers.
Large reforming units.
Hydrogen in transportation.
Use of hydrogen in IC engines.
10. Conclusions
Based on the literature and our groups studies it is evident
that LOH is a potential technology for transportation and
delivery of hydrogen. The advantages related to the LOH
systems include relatively higher hydrogen storage capacity,
possibility of hydrogen transportation at near ambient
conditions and using simple lorries. In order to realize the
hydrogen transportation by LOH system considerable devel-
opment have been reported in dehydrogenation catalysts,

heat transfer in reactor systems, use of unsteady states etc.
Nearly equilibrium conversion with relatively lower temper-
ature requirement has been reported. However, challenges
regarding minimizing heat losses, use of renewable energy for
providing heat for dehydrogenation, minimizing evaporative
losses, effective separation of products particularly liquid
product/unreacted reactant are need to be resolved as
a prerequisite for a step toward up-scaling of the technology.
Acknowledgment
The part of the work was carried out under the project spon-
sored by Ministry of New and Renewable Energy, New Delhi.
One of the author Ms. Anshu Shukla acknowledged a Senior
Research fellowship supported by CSIR, New Delhi.
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