Liquid Hydrocarbons1

7/29/2019 Liquid Hydrocarbons1

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Hydrogen Production by Catalytic Reforming of LiquidHydrocarbons

Dong Ju Moon

Published online: 6 November 2010 Springer Science+Business Media, LLC 2010

Abstract In this review, we are reporting the catalytic

reforming of liquid hydrocarbon fuels carried out in ourresearch group, covering the catalytic reforming of iso-

octane and toluene as surrogate of gasoline, gasoline fuel

processor system and steam reforming ofn-hexadecane and

decahydronaphthalene, main constituents of diesel. The

commercial ICI reforming catalyst is prone to be poisoned

by sulfur contained in iso-octane. We investigated various

supported transition metal formulations and developed Ni/

Fe/MgO/Al2O3 (KIST-5) catalyst with prolonged catalytic

stability ([760 h), higher activity and sulfur tolerance

ability over commercial ICI and HT catalysts for ATR

reaction of iso-octane. We found that the concentration of

CO can be reduced to\1,800 ppm by the gasoline fuel

processor system charged with KIST-5 reforming catalyst,

commercial HTS catalyst and KIST PtNi/CeO2 LTS cat-

alyst. The addition of Rh metal to spc-Ni/MgAl catalyst

as promoter was found to be very effective in inhibiting

the deactivation of spc-Ni/MgAl catalyst by sintering of

reduced Ni metal at high temperature during steam

reforming ofn-hexadecane. A 0.3 wt% Rh loading on spc-

Ni/MgAl catalyst was optimized to have the best perfor-

mance for steam reforming of n-hexadecane among the

prepared catalysts. The addition of Rh to spc-Ni/MgAl

catalyst also restricted the deactivation of the catalyst due

to carbon formation at high reaction temperature. In view

point of prolonged stability and higher activity, these

developed reforming catalysts have a good scope in the

reforming process of gasoline and diesel for hydrogen

station and fuel processor system applications.

Keywords Catalytic reforming Hydrogen production Fuel processor system Hydrogen station Steamreforming Gasoline Iso-octane Toluene N-hexadecane

1 Introduction

Hydrogen has the potential to offer cleaner, more-efficient

alternatives to the combustion of gasoline and other fossil

fuels. Though transition from a petroleum-based to a

hydrogen-based economy is expensive, in the long run it is

affordable. A total conversion to a hydrogen economy

society is possible in the near future. Limited petroleum-

based fuels resources, rising natural gas prices, dependency

on other countries for fuel, green house gas emissions are

the driving forces to shift towards hydrogen economy

society. Hydrogen economy will revolutionize the world in

energy crises. It is eco-friendly and produces no air pol-

lutants, green house gases when used in the fuel cells. It

can be produced using diverse domestic resources

including fossil fuels such as natural gas, liquid hydro-

carbons and coal, nuclear, biomass and other renewable

energy technologies, such as solar, wind and hydro-elec-

tric power [1].

Most of the hydrogen is now produced as an industrial

scale by the process of steam reforming of natural gas or as

a byproduct of petroleum refining and chemicals produc-

tion. Generally, it is produced by the following processes

such as steam reforming (SR), partial oxidation (POX) and

autothermal reforming (ATR) of hydrocarbons.

Steam reforming uses thermal energy to separate

hydrogen from the carbon components of hydrocarbons,

D. J. Moon (&)

Clean Energy Center, Korea Institute of Science and Technology

(KIST), 39-1, Hawolgok-dong, Sungbuk-ku, Seoul,

Republic of Korea

e-mail: [email protected]

123

Catal Surv Asia (2011) 15:2536

DOI 10.1007/s10563-010-9105-5


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and involves the reaction of these fuels with steam on

catalytic surfaces. The first step of the reaction is the

decomposition of the fuel into hydrogen and carbon mon-

oxide, followed by water gas shift reaction (WGS) of the

carbon monoxide and water to carbon dioxide and hydro-

gen [24]. Steam reforming is an endothermic process,

hence some of the fuel must be burned and the heat

transferred to the reformer via heat exchangers.Partial oxidation involves [5] the reaction of oxygen

with fuel to produce H2 and CO when the oxygen-to-fuel

ratio is less than that required for total combustion. Partial

oxidation can be conducted with a catalyst (catalytic partial

oxidation) or without a catalyst (non-catalytic partial oxi-

dation). The reaction rates are much higher for partial

oxidation than for steam reforming, but the H2 yield per

carbon in the fuel is lower.

Autothermal reforming involves the reaction of oxygen,

steam and fuel to produce H2 and CO, and can be viewed

as a combination of partial oxidation and steam reforming.

This reforming step generates gases which contain 812%CO besides H2, CO2, CH4 and air. This CO must be con-

verted with the help of steam to CO2 and hydrogen via

WGS reaction to enrich the hydrogen [612].

Hydrogen produced by catalytic reforming of hydro-

carbons such as methane, methanol, ethanol, liquid petro-

leum gas (LPG), gasoline, kerosene, diesel and other oil

derivatives can be used as fuel for fuel cell [1316].

Hydrogen contains less energy than gasoline or diesel on a

per-volume basis, so it is difficult to store enough hydrogen

onboard a vehicle to travel long distance. The lack of an

infrastructure for the production and distribution of H2 has

stimulated research in fuel processing, in particular, the

development of fuel processors for reforming of infra-

structured fuels such as natural gas, liquefied petroleum

gas, gasoline and diesel at the point of applications.

In our previous review [1720], the hydrogen produc-

tion by catalytic reforming of gaseous hydrocarbons has

been reviewed. Liquid fuels can be used as the energy

carriers in many applications, especially residential power

generation (RPG) systems in remote areas and the auxiliary

power units (APU) based on solid oxide fuel cell (SOFC)

systems. Especially, diesel is an attractive fuel for the

production of hydrogen by reforming because of its high

gravimetric and volumetric hydrogen density and well-

established delivery infrastructure. Ahmed et al. [21] dis-

cussed the advantages of using liquid hydrocarbons for

portable and stationery fuel processors. The main problems

associated with the reforming of diesel are related to cat-

alyst degradation during the reaction due to the harsh

operating conditions such as high temperatures and high

H2O/C ratios, the necessary to obtain high yield of

hydrogen. Degradation may be due to poisoning of the

catalysts by sulfur, thermal sintering and extensive carbon

formation due to the low H/C ratio and the high molecular

weight of the molecules present in diesel fuel.

Recently, proton exchanged membrane (PEM) fuel

cells operating with hydrogen from hydrocarbon reform-

ing technologies are being increasingly accepted as the

most appropriate power source for future generation

vehicles. It has polymer electrolyte and operates at 80 C

with hydrogen as reformate, prepared externally. ForPEM fuel cells, the concentration of CO should be

reduced as it poisons an anode catalyst. Solid oxide fuel

cell is also gaining interest, though the operating tem-

perature is high (700900 C). It has ceramic electrolyte

and can use H2/CO2/CH4 reformate as fuel which can be

reformed internally or externally. It is tolerant to sulfur

and there is no CO poison effect as observed in PEM

fuel cells.

Presently, steam reforming of hydrocarbons, especially

of methane is the largest and generally the most econom-

ical way to make hydrogen and has been reported by many

researchers [1, 16, 17, 21]. However, little has beenreported on ATR of liquid hydrocarbon fuels [22]. The lack

of infrastructure for hydrogen production and distribution

as well as the current cost of hydrogen from nuclear or

renewable energy has led the car manufacturers and

researchers to consider on-board generation from various

hydrocarbons. ATR of n-octane was applied [23] recently

for developing on-board reformers for automotive appli-

cations. Ni-based catalysts had moderate activity in this

reaction than noble metal catalysts which also get deacti-

vated under reaction conditions [24]. A bimetallic NiPd

catalyst show high activity with good stability. Springmann

et al. [25] tested Rh-based catalyst deposited on metal

sheets in a monolithnic reactor for steam reforming and

ATR of liquid hydrocarbons such as iso-octane, hexane and

toluene.

Very little experimental data is available on liquid

hydrocarbon. Krumpelt et al. [26] also reported data on

pilot scale reformer of iso-octane. Catalytic partial oxida-

tion of higher hydrocarbons such as iso-octane, n-decane

and diesel fuel over Rh-coated monoliths with high yield of

H2 and CO (*80%) in autothermal millisecond reactors

have been reported [2729]. Addition of steam to the cat-

alytic partial oxidation of diesel and gasoline fuel and their

surrogates over precious and transition metal catalysts

increase H2 and CO2 and reduce CO levels at contact times

typically greater than milliseconds compared to dry con-

ditions [30], suggesting water gas shift and steam reform-

ing occur with the addition of steam to the reactor.

In this work, the catalytic reforming of liquid fuels

carried out in our research group will be reviewed covering

the catalytic reforming of iso-octane and toluene as a sur-

rogate of gasoline, the steam reforming of n-hexane as a

surrogate of diesel.

26 D. J. Moon

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2 Features of Catalysts

Generally, the composition of reforming catalyst typically

comprise of transition metals (Ni, Co, Fe, etc.) or noble

metals (Pt, Pd, Rh, etc.) deposited or incorporated into

carefully engineered supports such as thermally stabilized

alumina, doped alumina with promoters to accelerate car-

bon vaporization [31] and mixed metal oxides [32].

2.1 Hydrotalcites

Anionic clay-based hydrotalcites-like materials have been

extensively studied [3336] in last few decades for various

catalytic applications such as steam reforming, base-cata-

lyzed organic transformations, alcohol synthesis, alkylation

of phenol with alcohols, selective oxidation, isomerization

of allylic compounds and decomposition of nitrogen and

sulfur oxides. Hydrotalcite-derived mixed oxides are used

as ion exchangers, absorbers, catalysts and catalyst sup-

ports. They show interesting properties such as high sur-face area, phase purity, basic surface properties, structural

stability and memory effect [37]. Memory effect

allows the reconstruction of the original hydrotalcite

structure under mild conditions when contacting the

product of the thermal treatment with water solutions

containing various anions [37, 38]. Upon calcinations,

hydrotalcite-like compounds form a homogeneous mixture

of oxides with a very small crystal size, stable to thermal

treatment and upon reduction form small and thermally

stable metal crystallites [39].

Usually, supported metal catalysts used in the reforming

reactions of hydrocarbons are prepared by wet impregna-

tion of different supports. But this method has drawbacks

that it is not reproducible, gives inhomogeneity in metal

distribution on surface and also fine metal particles tend to

sinter at high temperature resulting in the catalyst deacti-

vation [40]. So solid phase crystallization (spc) method

giving stable and highly dispersed metal-supported catalyst

using pervoskite [41] and hydrotalcite [42] as precursor

have been reported.

2.2 Noble Metals Loaded Hydrotalcites

The reforming catalysts typically comprise of transition

metals (Ni, Co, Fe, etc.) or noble metals (Pt, Pd, Rh, etc.)

deposited or incorporated into carefully on the supports

[43].

Takehira et al. [44] reported that Pt or Ru doped Ni-

based catalyst prepared from MgAl hydrotalcite-like

anionic clay with citrate method showed high and stable

activity for steam reforming of propane. Dreyer et al. [45]

studied autotherrmal steam reforming of higher hydrocar-

bons such as n-decane, n-hexadecane and JP-8 over

Rh-coated monolith. Noble metals, especially Rh catalysts

are active in the reforming of hydrocarbons to synthesis gas

and also they tolerate sulfur and prevent coke formation

unlike conventional nickel catalysts which are necessary

properties for any reforming catalyst used for commercial

application [46]. Commercial fuels contain sulfur as aro-

matic rings which cannot be removed completely [47].

Hence noble metals, especially Rh is preferred even thoughit is costly.

Moon et al. [17] reported the steam reforming of n-

hexadecane, a main constituent of diesel, over noble metal

(Rh) modified Ni-based hydrotalcite catalyst. The catalysts

were prepared by a co-precipitation and dipping methods.

The noble metal modified Ni-based hydrotalcite catalyst

displayed higher resistance for the sintering of active metal

than Ni-based hydrotalcite catalysts prepared by conven-

tional method. Rh modified Ni-based catalysts showed high

resistance to the formation of carbon compared to the

Ni-based catalysts.

2.3 Mixed Oxides and/or Noble Metal Loading

In the industrial production of H2 by steam-methane

reforming, Ni supported on modified alumina or mixed

metal oxides are most widely used [48]. Although other

Group VIII metals such as Co, Ru, Rh, Pd, Ir and Pt are

active for steam reforming. Among these Ni catalysts are

preferred because of their lower cost. The Ni catalysts are

prone to deactivation due to sulphur poisoning and coke

formation. Hence, the interest in using Rh-based reforming

catalysts for steam reforming is increasing, in spite of their

initial higher cost as they tend to inhibit coke formation

[49]. The role of oxide supports have been investigated on

the performance of Rh catalysts for the autothermal

reforming of gasoline and gasoline surrogates to hydrogen

[13, 50]. As a part of the development of a gasoline

reformer, the reforming of iso-octane, a model compound

for gasoline, over a Pt catalyst supported on a CeO2ZrO2mixed oxide support was investigated by Villegas et al.

[51]. They selected this support as its redox properties can

promote noble metals activity, whereas its basic character

limits carbon deposition in reforming reactions. They

found that the ceria-zirconia support plays an active role in

the transformation of the carbonaceous species, originating

from iso-octane decomposition into gaseous products and

hence, Pt/CeO2ZrO2 catalyst apparently does not get

poisoned by carbon deposition.

Kaila [52] used two bimetallic RhPt catalysts, with total

metal loading of not more than 0.5 wt%, prepared by co-

impregnation from Rh(NO3)3 and Pt(NH4)4(NO3)2 precur-

sors. The Rh to Pt molar ratios of the bimetallic catalysts

were 1.2 and 2.4 mol/mol. The performance of these

bimetallic catalysts in ATR of the n-dodecanetoluene

Hydrogen Production From Liquid Hydrocarbons 27

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mixture was compared with the performance of Rh, Pd, and

Pt catalysts and the ZrO2 support. They found that thermal

stability of Rh catalyst was improved when Rh was com-

bined with Pt in the bimetallic RhPt catalysts.

3 Catalytic Reforming of Liquid Hydrocarbons

Many researchers have reported Rh catalysts for partial

oxidation of CH4 and C2H6, steam reforming of CH4,

ethanol and propanol and dry reforming of CH4 [53],

however, little has reported on ATR of hydrocarbon fuels

[22]. Steam reforming of liquid hydrocarbons such as

gasoline, kerosene, diesel and other oil derivatives have

been reported [5456]. Liquid fuels can be used as the

energy carriers in many applications especially residential

power generation (RPG) systems in remote areas and the

auxiliary power units (APU) based on SOFC systems.

Especially, gasoline and diesel are attractive fuels for the

production of hydrogen by reforming because of their highgravimetric and volumetric hydrogen density and well

established infrastructure.

3.1 Catalytic Reforming of Gasoline

The overall POX reforming reaction (autothermal reform-

ing, ATR) of iso-octane, as a main component of gasoline

(Eq. 1) is given by,

C8H18 x O2 3:76 N2 16 2x H2O! 8CO2 25 2x H2 3:76 x N2 1

where x is a ratio of oxygen/fuel.During POX reforming of iso-octane and toluene, the

heat of reaction and the amount of carbon formed were

calculated by the Gibbs free energy minimization method

[57] were reported. Figure 1 shows the effect of O/C ratio

on the heat of reaction in POX reforming reaction of iso-

octane at 700 C and feed molar ratios H2O/C = 3 and 1.

The heat of reaction for the gross-reaction is dependent on

the molar ratio of oxygen/fuel, the molar ratio of H2O/fuel

and the reaction temperature. There is gradual change from

endothermic at sufficiently low O/C molar ratio to exo-

thermic at high O/C molar ratio, 0.6. By advantage of being

able to tune the reaction heat by properly varying O/C

molar ratio makes POX reforming superior to steam

reforming. Hence for low energy requirement, an O/C

molar ratio ofC0.6 is favorable for POX reforming ofiso-

octane.

The amount of carbon formed as a function of temper-

ature for five reforming reactions ofiso-octane and toluene

are presented in Fig. 2. If the feed consists of iso-octane

(1 gmol/h) and air at O/C = 1, more than 1 9 10-9

mmol h-1 of coke would form in the partial oxidation of

iso-octane at temperatures up to 950 C. If the feed consists

of iso-octane (1 gmol/h) and H2O a t H2O/C = 1, more

than 1 9 10-9 mmol h-1 of coke would occur in the steam

reforming of iso-octane at temperatures up to 800 C. If

water is added with molar ratio of H2O/C = 1 while

maintaining the O/C ratio = 1, the reactor temperature in

the POX reforming ofiso-octane can be lowered to 560 C

before carbon formation occurs. It was found that the

carbon formation temperature was increased until 600 C

when the ATR reaction of toluene was carried out under

the same reaction conditions ofiso-octane.

Various transition metal formulations, M(active)/MgO/

Al2O3, M(active)/MgO/SiO2Al2O3, Ni(major)/M(minor)/MgO/

Al2O3, Mo(major)/M(minor)/MgO/Al2O3 and Ni/Ce/ZrO2used for ATR of toluene and iso-octane and their

Oxygen / Carbon Ratio

-0.5 0.0 0.5 1.0 1.5 2.0 2.5

HeatofReaction(Kcal/moliso-octane)

-400

-200

0

200

400

600

800

H2O/C = 1

H2O/C = 3

Fig. 1 The effect of O/C ratio on the heat of reaction in POX

reforming reaction ofiso-octane at 700 C and feed molar ratios H2O/

C = 3 and 1

Temperature( oC)400 600 800 1000 1200

Carbon(mmol/hr)

1e-11

1e-10

1e-9

1e-8

1e-7

1e-6

1e-5

1e-4

1e-3

1e-2

1e-1

1e+0

1e+1

1e+2

iso-octaneH2O/C=1

O/C=1

TolueneH2O/C=1

O/C=1

iso-octaneO/C=1

iso-octaneH2O/C=1

iso-octaneH

2O/C=0.5

O/C=0.5

Fig. 2 Reaction temperature required to prevent the formation of

carbon during the reforming process of iso-octane and toluene,

assuming thermodynamic equilibrium

28 D. J. Moon

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characterization are summarized in Table 1. Where M is a

component selected from Ni, Co, Fe and Mo.

3.1.1 Autothermal Reforming of Toluene

The autothermal reforming of n-dodecane, toluene and

their mixtures has been studied by Reeta K. Kaila et al. [52]

over monometallic (Rh, Pd, Pt) and bimetallic (Rh/Pt)

noble metal zirconia catalysts at 700900 C. The Rh-

containing catalysts were more active toward ATR reac-

tions than the other noble metal catalysts (Pt and Pd) on

zirconia. It has been reported [58] that the addition of ZrO2to ceria leads to improvements in redox property, thermal

resistance and catalytic activity for ATR at lower

temperatures.

Figure 3 shows the comparison of the product compo-

sition and coke deposition temperature for the ATR ofiso-octane and toluene. Equilibrium conversion and carbon

formation temperature for ATR reaction ofiso-octane and

toluene were estimated by POR II simulation program,

assuming thermodynamic equilibrium at 700 C, feed

molar ratios of H2O/C = 3 and O/C = 1. The carbon

formation in the ATR reaction of iso-octane occurred at

less than 620 C, however, it was also found that it

occurred at less than 640 C in the ATR reaction of tolu-

ene. The results suggest that the selection of reasonablereforming temperature is important for the reforming of

mixed hydrocarbons such as gasoline because of higher

reforming temperature of toluene than that ofiso-octane. It

was found that Ni/Fe/MgO/Al2O3 catalyst showed better

activity and sulfur tolerance over the commercial Haldor

Topsoe (HT) catalyst and can be applied as ATR catalyst of

gasoline fuel processor application.

3.1.2 Autothermal Reforming of Iso-Octane

Catalytic partial oxidation of hydrocarbons for generating

hydrogen has gained much attraction in recent years owingto its direct application in proton exchange membrane fuel

cells for generating clean electrical energy. It has been

widely accepted as the most promising process to meet the

efficiency, volume and cost goals of the transportation

applications [59]. For vehicle applications, the advantage

of catalytic POX reforming over SR is a low energy

requirement, sulfur tolerance of a catalyst and more rapid

and controlled response to the transient power require-

ments [5, 60]. The use of commercial SR catalyst for POX

reforming of aliphatic and aromatic hydrocarbon liquids

has been done by some researchers [19, 61]. However,

number of problems was identified including the tendencyof deactivation of the catalyst due to formation of nickel

aluminate spinnels, excessive coking and susceptibility

to sulfur poisoning which limit their use for vehicle

applications.

The problem of catalyst deactivation by carbon depo-

sition and sulfur poisoning in the POX reforming reaction

of iso-octane over commercial reforming catalyst was

reported previously [19, 62]. Based on the experience

of our previous research [1720], we found the ideal

Table 1 Characteristics of the prepared and the commercial catalysts used for ATR of iso-octane and toluene

Catalyst code Catalyst composition BET surface areaa (m2/g) Total pore volumea (cc/g) Ave. pore diametera (A)

KIST-1 Ni/MgO/Al2O3 29 0.207 286.0

KIST-2 Fe/MgO/Al2O3 88 0.228 103.7

KIST-3 Co/MgO/Al2O3 66 0.305 185.6

KIST-4 Mo/MgO/Al2O3 88 0.294 134.1

KIST-5 Ni/Fe/MgO/Al2O3 74 0.212 115.1

KIST-6 Ni/Co/MgO/Al2O3 62 0.172 111.8

KIST-7 Ni/Mo/MgO/Al2O3 72 0.259 124.4

ICI Ni/CaO/Al2O3 35 0.085 96.26

a Derived from N2 physisorption using Quantachrome Co

I so -o ct an e To lu en e

ProductDistribution(%)

0

20

40

60

80

100

CarbonFormation

Temperature(oC)

500

550

600

650

700

750

H2

CO

CO2

CH4

Carbon formation temp.

Fig. 3 The comparison of the product composition and coke

deposition temperature for the ATR of iso-octane and toluene,

respectively. Reaction temperature = 700 C; feed molar ratios of

H2O/C = 1 and O/C = 1


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operating conditions for POX-reforming reactions as:

temperature 700 C, feed molar ratio of H2O/C = 3 and

O/C = 1. KIST-5 catalysts showed a little higher H2selectivity than commercial ICI catalyst. Selectivity of H2and CO progressively increased with increasing reaction

temperature. Hydrogen selectivity over KIST-5 and ICI

catalysts were 65 and 64% at 700 C, respectively and CO

selectivity was 11.3 and 13.4%, respectively.POX reforming of iso-octane was carried [60] over

various catalyst formulations (Table 1) for gasoline fuel

processor applications. The effect of sulfur impurities on

the stability of each catalyst was also investigated in the

POX reforming reaction ofiso-octane. The performance of

prepared catalysts was compared with that of the com-

mercial ICI catalyst. Generally the reforming of hydro-

carbons always has potential to form coke. If the reactor is

not properly designed or operated, coking is inclined to

occur. So the reactor temperature required to prevent the

formation of carbon during the reforming process of

iso-octane was estimated by PRO-II simulation program,assuming thermodynamic equilibrium [1720].

Overall, Ni/M/MgO/Al2O3 catalysts are more active

than M/MgO/Al2O3 catalysts. Especially, the catalytic

formulations using Ni as a major active component with a

minor active component such as Fe or Co are found to be

more active than the other catalytic formulations. The

KIST-5 catalysts before and after the POX reforming

reaction ofiso-octane have not shown any major change in

XRD phase patterns. Also, no metallic carbide such as

nickel carbide and ferric carbide was formed during POX

reforming of iso-octane at 700 C for 24 h. Modified

Ni/(Co or Fe)/MgO/Al2O3 system can be considered as

an alternative option to the commercial reforming catalyst

for POX reforming of iso-octane.

Figure 4 shows the comparison of the KIST-5 catalyst

with the commercial ICI catalyst for the product distribu-

tion in the POX reforming of iso-octane. It was identified

that KIST-5 catalyst showed similar activity to commercial

ICI catalyst. To elucidate the effect of sulfur impurities

on the catalytic deactivation, we investigated the POX

reforming reaction of iso-octane containing 100 ppm sul-

fur. Figure 5 represents the comparison of the KIST-5

with commercial ICI catalyst for sulfur tolerance in the

POX reforming of iso-octane at 700 C space veloc-

ity = 8,776 h-1, feed molar ratios of H2O/C = 3 and

O/C = 1. KIST-5 catalyst displayed better activity and

sulfur tolerance than commercial ICI catalyst, even though

none of the systems were found to be completely sulfur

resistant. Table 2 gives characteristics of the commercial

ICI catalyst and KIST-5 catalysts before and after ATR of

iso-octane under tested conditions.

Long term stability for the KIST-5 catalyst in the ATR

reaction ofiso-octane containing sulfur less than 5 ppm at

700 C, space velocity = 8,776 h-1, feed molar ratio of

H2O/C = 3 and O/C = 1 is shown in Fig. 6. The KIST-5

catalyst was found to be stable more than 800 h under the

tested conditions. Ferrandon and Krause found out [34]

superior activity and stability of Rh/LaAl2O3 for long

term tests of monoliths samples for the ATR of sulfur-free

gasoline. But KIST-5 catalyst comprising of Ni/Fe/MgO/

Al2O3 proved to be the best in the ATR ofiso-octane with

long term stability of more than 800 h and also economical

unlike the noble metal based catalyst.

3.1.3 Gasoline Fuel Processor System

The successful development of a fuel cell system is

dependent on the development of a fuel processor.

Hydrogen is an ideal fuel for proton exchange membrane


0

10

20

30

40

50

60

70

ICI

KIST 5

H2 CO CO2CH4

Fig. 4 The comparison of the KIST-5 with the commercial ICI

catalyst for the product distribution in the POX reforming of iso-

octane. Reaction temperature = 700 C; space velocity = 8,776 h-1;

feed molar ratios of H2O/C = 3 and O/C = 1

Time (h)

0 5 10 15 20 25


0

20

40

60

80

100

KIST 5 - H2KIST 5 - CH

4

KIST 5 - CO

KIST 5 - CO2

ICI - H2

ICI - CH4

ICI - CO

ICI - CO2

Fig. 5 Sulfur tolerance for the KIST-5 (Ni/Fe/MgO/Al2O3) and

commercial ICI catalysts in the POX reforming of iso-octane

containing sulfur (Cs = 100 ppm). Reaction temperature = 700 C;

space velocity = 8,776 h-1; feed molar ratios of H2O/C = 3 and

O/C = 1

30 D. J. Moon

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fuel cell because it simplifies system integration and hence

being increasingly accepted as the most appropriate power

source. Since there is no hydrogen infrastructure, the

development of fuel processor and hydrogen station has

been hot issue for commercialization of fuel cell system.

The lower efficiency of gasoline in comparison with

methanol can be compensated by the much higher energydensity of gasoline compared to methanol and also by the

well-developed infrastructure for gasoline [61]. Due to the

favorable factors required for the on board generation of

H2 in the fuel cell system, POX reforming of gasoline

attracts much attention primarily because of low energy

requirement.

It is reported [61] that the fuel cell performance was

progressively degraded by CO poisoning of Pt anode cat-

alyst. Therefore, many researchers studied [6, 63, 64] high

temperature water gas shift (HTS) and low temperature

water gas shift (LTS) reactions and/or preferential partialoxidation (PROX) to reduce the CO concentration within

the tolerance limit of the Pt anode catalyst. Especially, the

WGS reaction is a critical step during the fuel processing

since CO poisons the PEM electro-catalyst and LTS cata-

lyst was prone to be deactivated by sulfur poisoning and

thermal cycling [64]. The WGS reactors charged with

currently available commercial HTS and LTS catalysts

constitute about a third of the mass, volume and cost of the

fuel processor system.

Gasoline fuel processor system consists of six sections:

feed supply section, evaporator, POX reforming reactor,

HTS reactor, LTS reactor and GC analysis sections. As apart of the development of gasoline fuel processor system

for integration with PEM fuel cell, we investigated [65, 66]

POX reforming reaction of iso-octane with/without

100 ppm sulfur over a commercial reforming catalyst. We

also investigated HTS reaction over Fe3O4Cr2O3 com-

mercial catalyst and LTS reaction over Cu/ZnO/Al2O3commercial catalysts to remove CO from the hydrogen

rich-stream produced by POX reforming reaction. Table 3

lists the characteristics of KIST reforming catalyst, com-

mercial HTS and KISTLTS catalysts used in gasoline fuel

processor system. It was found that the commercial

reforming catalyst was prone to be poisoned by sulfurcontained in iso-octane, but there is no coke deposition at

700 C under the tested conditions. The product distribu-

tion data from three different reaction stages over the KIST

reforming catalyst (KIST-5), commercial HTS catalyst and

KIST-LTS catalyst are shown in Fig. 7. The H2 and CO2concentrations after the gases passed through HTS and LTS

reactors increased while those of CO and CH4 decreased.

The concentration of CO can be reduced to\1,800 ppm

when KIST-5 reforming catalyst, HTS catalyst and LTS

Table 2 Comparison of the characteristics of KIST catalyst with commercial ICI catalyst before and after ATR reaction of iso-octane

Catalyst BET surface

areaa (m2/g)

Total pore

volumea (cc/g)

Active metal

S. A. (m2/g)bCarbon

contentc (wt%)

Sulfur

contentc (wt%)

ICI Before the reaction 35.3 0.085 0.789 0.01 0.003

After the reaction of iso-octane

(Cs\ 5 ppm)

26.7 0.069 0.543 5.8 0.004

After the reaction of iso-octane(Cs = 100 ppm) 19.9 0.049 0.397 25.7 0.006

KIST-5 Before the reaction 73.6 0.212 1.906 0.01 0.003


(Cs\ 5 ppm)

61.9 0.185 1.528 4.9 0.004


(Cs = 100 ppm)

49.4 0.166 1.397 19.6 0.005

a Derived from N2 Physisorption using Quantachrome Cob Derived from CO chemisorption using Micromeritics Coc Measured by Elemental Analyzer

Reaction Time (h)

0 100 200 300 400 500 600 700


0

20

40

60

80

100

H2CO

CO2CH

4

Fig. 6 Long term stability for the KIST-5 catalyst in the ATR

reaction of iso-octane containing sulfur less than 5 ppm. Reaction

temperature = 700 C; space velocity = 8,776 h-1; feed molar

ratios of H2O/C = 3 and O/C = 1


123


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(PtNi/CeO2) catalyst are charged with the gasoline fuel

processor system. In our previous work [65, 66], it was

reported that the concentration of CO can be reduced to

3,000 ppm when commercial ICI, HTS and LTS catalysts

were charged in gasoline fuel processor system.

The partnership for a new generation of vehicles

(PNGV) has a set a goal to reduce the weight of the shift

reactors to 75%. For integration with PEM fuel cell, the

preferential PROX reactor and the development of new

high performance catalysts with sulfur and coke-resistance

are needed.

3.2 Catalytic Reforming of Diesel

In previous paper [65], we reported high and stable activity

of Ni-loaded catalysts prepared from MgAl hydrotalcite-

like anionic clay for steam reforming of LPG. The con-

centration of H2 after 5 h was nearly same over spc-Ni/

MgAl and ICI catalysts for SR of LPG. The concentration

of H2 was maintained during reaction time (186 h) at

800 C, GHSV = 20,000 h-1 with H2O/C = 2. However,

it decreased over commercial ICI catalyst due to the for-

mation of carbon. Memory effect property of hydrotal-

cite-like support allows the reconstruction of the original

hydrotalcite structure under mild conditions when con-

tacting the product of the thermal treatment with water

which minimizes the degradation of the catalyst during

steam reforming reaction.

Steam reforming of LPG over nickel-based and noble

metals modified nickel based catalysts using (different Ni

to Mg ratio) hydrotalcite-like support is reported [17, 38,

42] recently. A spc-Ni/MgAl catalyst was prepared by co-

precipitation method and later also modified with noble

metals (Ru, Rh) by dipping method. Among the non

impregnated Ni-based catalysts, spc-Ni/MgAl catalyst

shows good performance up to 186 h for steam reforming

of LPG, though the activity was found to be declined at

800 C, H2

O/C = 2 and GHSV = 20,000 h-1. Figure 8

shows the XRD patterns of hydrotalcite (MgAl) and

0.3 wt% Rh spc-Ni/MgAl catalysts prepared by dipping

method. XRD pattern (a) is typical hydrotalcite peak pat-

tern taken after drying at 60 C for 12 h in air. Then after

calcining at 850 C for 5 h, hydrotalcite structure changed

to MgNiO crystalline form (b). When Rh modified spc-

Ni/MgAl catalyst was prepared using spc-Ni/MgAl by

dipping method followed by drying at 80 C for 6 h, Mg

NiO structure was found to reconstitute to hydrotalcite by

memory effect (c). XRD pattern (d) shows loaded Rh forms

Rhx

Ox

on the surface of Rh modified spc-Ni/MgAl catalyst

prepared by dipping method. Figure 9 shows the productdistribution of noble metal modified Ni-based catalysts for

steam reforming reaction with time on stream up to 53 h

at reaction conditions: temperature= 700 C, GHSV =

20,000 h-1 and H2O/C = 1.0. Ru modified spc-Ni/MgAl

catalyst showed H2: 64*66%, CH4: 5*7%, CO:

18*21%, CO2: 6*10% product distribution by vol(%)

whereas Rh modified spc-Ni/MgAl catalyst formed H2:

67%, CH4: 4.9%, CO: 19%, CO2: 8% by vol(%). It was

found that Rh loaded catalyst showed stable performance

Table 3 Characteristics of catalysts used in gasoline fuel processor system

Catalysts Reaction BET surface areaa (m2/g) Total pore volumea (cc/g) Active metal surface areab (m2/g) Maker

Ni/Fe/MgO/Al2O3 ATR 74 0.212 0.213 KISTc

Fe3O4Cr2O3 HTS 57 0.073 0.127 ICId

PtNi/CeO2 LTS 78 0.049 0.086 KISTc

a Derived from N2 physisorption using Quantachrome Cob Derived from CO chemisorptions using Micromeritics Coc KIST-Korea Institute of Science and Technology, South Koread ICI-Imperial Chemical Industries Co

Fig. 7 The product distribution from three different reaction stages

over the KIST-5 catalyst system (ATR: Ni/Fe/MgO/Al2O3; HTS:

Fe3O4Cr2O3; LTS: PtNi/CeO2). The ATR over KIST catalyst was

carried out at reaction temperature 700 C, space velocity =

8,776 h-1

, molar ratios H2O/C = 3 and O/C = 1. HTS and LTSreactions were carried out at 450 C and 250 C, respectively

32 D. J. Moon

123


9/12

for SR of LPG without fluctuation in product distribution

under severe reaction conditions: temperature= 700 C,

GHSV = 20,000 h-1, H2O/C = 1.0.

Moon et al. reported that the TEM images and TGA

profiles of 0.3 wt% Ru spc-Ni/MgAl and 0.3 wt% Rh spc-

Ni/MgAl catalysts before and after the reaction [17]. It was

found that plenty of carbon was formed on Ru spc-Ni/

MgAl catalyst, during the reaction, compared to Rh spc-Ni/

MgAl catalyst. The TGA profiles also show more weight

loss for Ru spc-Ni/MgAl catalyst compared to Rh spc-Ni/

MgAl catalyst which agrees well with TEM data. This

infers that Ru metal is not effective for inhibition of carbon

formation. This concludes that the addition of Rh metal to

spc-Ni/MgAl enhanced the reforming activity of LPG as

well as constrain to the carbon deposition. Also 0.3 wt%

Rh spc-Ni/MgAl catalyst was found to have prolonged

stability up to 1,100 h in the steam reforming of LPG as

shown in Fig. 10. These results draw a conclusion that

0.3 wt% Rh spc-Ni/MgAl catalyst is desirable LPG SR

catalyst for application in hydrogen station and fuel pro-

cessor systems. The spc-Ni/MgAl catalyst displayed better

activity than ICI commercial CH4 SR catalyst, but was

having tendency to coke formation even though carbon

formed did not affect adversely in this reaction. It wasfound that 0.3 wt% Rh spc-Ni/MgAl catalyst showed the

strong restraint of carbon formation compared to 0.3 wt%

Ru spc-Ni/MgAl catalyst.

The overall POX reforming of n-hexadecane as a sur-

rogate of diesel is given in Eqs. (24) [6771].

C16H34 32 H2O ! 49 H2 16CO2DH 2336 kJ=mol

2

C16H34 16 O2 ! 17 H2 16CO2DH 5694 kJ=mol

3

C16H34 16 H2O 8 O2 ! 33 H2 16CO2DH 1739 kJ=mol 4

The main problems associated with the reforming of

diesel are related to catalyst degradation during the reaction

due to the harsh operating conditions (high temperature and

H2O/C ratio) used to obtain high hydrogen yield. It is

mainly caused due to the poisoning of catalyst by sulfur,

thermal sintering and extensive carbon formation due to the

low H/C ratio and high molecular weight of the molecules

present in diesel fuel. Generally, reforming catalyst

Fig. 8 XRD patterns of prepared catalyst: (a) spc-Ni/MgAl-hydro-

talcite; (b) after calcination at 850 C for 5 h; (c) after dipping (b) in

an aqueous solution of Rh(III) chloride and drying; (d) after

calcination of 0.3 wt% RhNi/MgAl catalyst; filled circle, MgNi

O; open square, NiAl2O4; filled square, hydrotalcite

Time (h)

0 5 10 15 20 25 30 35 40 45 50 55

OutgasVol%

0

10

20

30

40

50

60

70

80

90

100

H2

CO

CH4

CO2

Fig. 9 Out gas distribution for SR of LPG over 0.3 wt% RhNi/

MgAl catalyst for 53 h (S/C = 1.0, GHSV = 20,000 h-1,

temperature = 700 C)

Time (h)

0 100 200 300 400 500 600 700 800 900 1000 1100

Outg

asvol.%

0

20

40

60

80

100

H 2CO

CH4CO2

Fig. 10 Out gas distribution for SR of LPG over 0.3 w%t RhNi/

MgAl catalyst for 1,100 h (S/C = 3.0, GHSV = 20,000 h-1,

temperature = 800 C)


123


10/12

comprise of transition metals (Ni, Co, Fe, etc.) or noble

metals (Pt, Pd, Ru, Rh, etc.) deposited or incorporated

on supports such as thermally stabilized alumina, doped

alumina with promoters to accelerate reforming ofhydrocarbon [72].

Recently, the works on steam reforming ofn-hexadecane

(n-C16H34) as a main constituentof diesel have been reported

[17, 73, 74] over spc-Ni/MgAl and noble metal (Rh) modi-

fied Ni-based catalysts listed in Table 4. The spc-Ni/MgAl

catalyst derived from hydrotalcite precursor was prepared

by co-precipitation method and RhNi/MgAl catalyst was

made by dipping method. The steam reforming of n-hexa-

decane over these catalysts carried out at 900 C,

GHSV = 10,000 h-1and feed molar ratio of H2O/C = 3.

Catalytic performances of these catalysts after the reaction

for 5 h and 53 h are compared in Fig. 11. The H2 concen-tration and the product distribution for the steam reforming

ofn-hexadecane over 0.3 wt% Rh spc-Ni/MgAl catalyst was

maintained constant during steam reforming. However, H2concentration over spc-Ni/MgAl catalyst was decreased due

to drastic shrinkage in the metal dispersion and increase in

active metal particle size [39]. The addition of Rh metal to

the spc-Ni/MgAl catalyst as a promoter very effectively

inhibited the sintering of Ni metal under tested conditions.

The SR ofn-hexadecane on spc-Ni/MgAl and Rh spc-Ni/

MgAl catalysts was carriedout at 900 C, feed molar ratioof

H2O/C = 3 and GHSV of 10,000 h-1 for 53 h to confirm the

role of Rh metal with restraint of Ni metal sintering.Figure 12 represents the product distribution with time on

stream over 0.3 wt% Rh spc-Ni/MgAl catalyst for 53 h. The

initial activityfromstart up to 5 h overspc-Ni/MgAl catalyst

was found to be similar to 0.3 wt% Rhspc-Ni/MgAl catalyst.

However, activity of 0.3 wt% Rhspc-Ni/MgAl was constant

during the SR ofn-hexadecane. On the other hand, activity of

spc-Ni/MgAl catalyst decreased slowlywith enhancement in

degree of deactivation from 45 h after the commencement of

the reaction. The SR of decahydronaphthalene as a second

constituent of diesel onspc-Ni/MgAl catalyst wascarried out

at 900 C, feed molar ratio of H2O/C = 3 and GHSV of

10,000 h-1 [75, 76]. Figure 13 shows the product distribu-

tion with time on stream overspc-Ni/MgAl catalyst for 53 h.

The concentration of CO was slowly decreased with

increasing CO2 and carbon formation. This result may be

consideredthat the deactivation of catalyst was caused by the

carbon formation by Boudart reaction (Reaction 5) under the

tested conditions.

2CO ! CO2 C 5

4 Conclusions and Future Directions

This is a review on the works carried out on the production

of hydrogen by catalytic reforming of liquid hydrocarbon

fuels namely a main surrogate of gasoline and diesel.

Table 4 Characteristics of the modified spc-Ni/Mg/Al based catalysts before and after steam reforming of n-hexadecane

Catalyst BETa (m2/g) Before the reaction After the reaction

Dispersionb (%) Active metal particle

size (nm)

Dispersionb (%) Active metal particle

size (nm)Before After Ni Ni ? Rh Ni Ni ? Rh

spc-Ni/MgAl 198 42 17.12 6.33 0.25 401.73

RhNi/MgAlA 105 12.16 8.34 1.04

c

93.23

c

1.54 66.03

RhNi/MgAlB 107 13.53 7.50 2.75 36.89

RhNi/MgAlC 106 13.80 7.37 3.13 32.41

a Measured by N2 physisorption using Quantachrome Cob Measured by CO chemisorption using Micromeritics Coc After SR of n-hexadecane for 53 h at 950 C

after 5h

H2inoutgas(vol%)

0

20

40

60

80

100

after 53h after 5h after 53h

H2

CO

20wt% Ni/MgAl 0.3wt% Rh-Ni/MgAl

Fig. 11 The comparison of concentrations of H2 and CO in the SR of

n-hexadecane over spc-Ni/MgAl and 0.3 wt% RhNi/MgAl catalysts

for 53 h (S/C = 3.0, GHSV = 10,000 h-1, temperature = 900 C)

34 D. J. Moon

123


11/12

We investigated various supported transition metal for-

mulations for reforming of gasoline and compared to

commercial ICI catalyst. We found that Ni/Fe/MgO/Al2O3(KIST-5) catalyst showed higher catalytic activity and

sulfur tolerance than commercial ICI and HT catalysts. We

suggested that Ni/Fe/MgO/Al2O3 catalyst can be an alter-

native option to the commercial ATR reforming catalyst

for fuel cell system. As a part of the development of the

gasoline fuel processor system for integration with the

PEM fuel cell, we investigated the POX reforming reaction

of iso-octane over KIST reforming catalyst(KIST-5),

commercial HTS (Fe3O4Cr2O3) catalyst and KIST-LTS

(PtNi/CeO2) catalyst. The concentration of CO was found

to be reduced to\1,800 ppm in this system. We found that

commercial reforming catalyst was prone to be poisoned

by sulfur contained in iso-octane.

We investigated modified hydrotalcite based formula-

tions for the reforming of diesel and compared to spc-Ni/

MgAl catalyst. The addition of Rh metal to the spc-Ni/

MgAl catalyst also acts as a promoter, inhibiting the sin-tering of Ni metal particles during catalytic reforming of

n-hexadecane, a surrogate of diesel under tested conditions.

For applications in commercial process studies on the

catalytic reforming over structured catalyst by the modifi-

cation of the developed catalysts in this work will be

needed in near future.

Acknowledgments Author would like to thank our coworkers for

their valuable research contributions in reforming of liquids hydro-

carbons summarized in this review. The author would also like to

acknowledge financial support from KIST to carry out this research in

Clean Energy Center, Korea Institute of Science and Technology

(KIST).

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