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Catalytic oxidative steam reforming of bio-ethanolfor hydrogen production over Rh promotedNi/CeO2eZrO2 catalyst

Tarak Mondal a, Kamal K. Pant a,*, Ajay K. Dalai b

a Department of Chemical Engineering, Indian Institute of Technology Delhi, HauzKhas, New Delhi, 110016, Indiab Department of Chemical and Biochemical Engineering, University of Saskatchewan, Saskatoon, SK, S7N5C5,

Canada

a r t i c l e i n f o

Article history:

Received 3 September 2014

Received in revised form

12 December 2014

Accepted 17 December 2014

Available online 12 January 2015

Keywords:

Oxidative steam reforming

Hydrogen production

Bio-ethanol

Rh promoted Ni/CeO2eZrO2 catalyst

Catalyst characterization

* Corresponding author.E-mail address: kkpant@chemical.iitd.ac.

http://dx.doi.org/10.1016/j.ijhydene.2014.12.00360-3199/Copyright © 2014, Hydrogen Ener

a b s t r a c t

Catalytic steam reforming of bio-ethanol in presence of oxygen for hydrogen production

was studied over Ni/CeO2eZrO2 and RheNi/CeO2eZrO2 catalysts. The catalysts were pre-

pared by an impregnation-co-precipitation method and characterized by various charac-

terization techniques. Characterization results revealed that addition of ZrO2 improves the

oxygen storage capacity of CeO2 which improves catalytic activity. The effects of temper-

ature, ethanol/water/oxygenmolar ratio, and space time on ethanol conversion and product

selectivities were investigated using a tubular fixed bed reactor at atmospheric pressure.

Complete ethanol conversion was achieved at 600 �C with a maximum hydrogen yield of

4.6 mol/mol on the 1%Rhe30%Ni/CeO2eZrO2 catalyst. Ethanol conversion and H2 selectivity

were increased with increasing contact time, while CO and CH4 selectivity decreased.

Investigation revealed Rh promoted catalyst exhibited better catalytic activity than 30%Ni/

CeO2eZrO2 catalyst for oxidative steam reforming of ethanol, indicating that addition of Rh

improved the catalytic activity significantly by promoting water gas shift reaction.

Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

Introduction

Hydrogenproduction from fossil fuels has been investigated for

many years. However, fossil fuels are not sustainable energy

sources and are expected to become scarce in the coming de-

cades. In contrast, renewable energy sources are clean and will

not run out in the foreseeable future. Because of their consis-

tent long-termavailability, renewable energy resources are also

inherently more stable in price than fossil fuels. As a new en-

ergy source, biomass has receivedmuch attention, because it is

in (K.K. Pant).70gy Publications, LLC. Publ

renewable and carbon neutral. Hydrogen production from

renewable sources such as biomass, is gaining attention as a

CO2 neutral energy supply because CO2 produced during the

conversion process gets consumed by the biomass growth.

Among various renewable feedstock alternatives for H2

production, bio-ethanol is very attractive because of its rela-

tively high hydrogen content, availability, non-toxicity, stor-

age, ease of handling and safety. Bio-ethanol can be produced

by fermentation of biomass resources, such as sugar, starch or

cellulose contained in energy plants, agro-industrial wastes,

ished by Elsevier Ltd. All rights reserved.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 0 ( 2 0 1 5 ) 2 5 2 9e2 5 4 42530

forestry residues, and the organic fraction of municipal solid

waste.

Steam reforming of ethanol (SRE), partial oxidation (POX),

and oxidative steam reforming (OSR) are effective routes for

producing hydrogen from bio-ethanol. Among these, steam

reforming is the most studied route since it produces the

highest hydrogen yield. SRE generates a high H2/CO ratio but

has the disadvantage of high endothermicity and catalyst

deactivation due to carbon deposition. Whereas POX allevi-

ates the problem of energy consumption since it is

exothermic, its pitfall is a lower H2/CO ratio than steam

reforming. OSR, being a combination of endothermic SRE and

exothermic POX, can produce a suitable H2/CO ratio without

external energy consumption. Furthermore, it can present a

viable route for attenuating coke deposition [1e4].

The steam reforming process is summarized as follows:

CH3CH2OH þ 3H2O/6H2 þ 2CO2; DH0298 ¼ 174 kJ=mol (1)

However, there are several reaction pathways that could

occur in the ethanol steam reforming process depending on

the catalysts used [1,2,4].

The ethanol decomposition reaction leads to generation of

CO and CH4:

CH3CH2OH/COþ CH4 þH2; DH0298 ¼ 49 kJ=mol (2)

Ethanol reforming to synthesis gas:

CH3CH2OHþH2O/2COþ 4H2; DH0298 ¼ 256 kJ=mol (3)

Ethanol dehydrogenation leads to formation of

acetaldehyde:

CH3CH2OH/CH3CHOþH2; DH0298 ¼ 68 kJ=mol (4)

Coke formation is mainly due to dehydration of ethanol

and Boudouard reactions:

CH3CH2OH/C2H4 þH2O; DH0298 ¼ 45 kJ=mol (5)

2CO#CO2 þ C; DH0298 ¼ �171:5 kJ=mol (6)

Methane also forms due to the methanation reaction

which is the reverse of methane steam reforming:

3H2 þ CO#CH4 þH2O; DH0298 ¼ �206 kJ=mol (7)

4H2 þ CO2#CH4 þ 2H2O; DH0298 ¼ �165 kJ=mol (8)

Water gas shift(WGS) and reversewater gas shift reactions:

COþH2O#CO2 þH2; DH0298 ¼ ±41 kJ=mol (9)

The presence of oxygen in the feed can also lead to other

possible reactions [5] as follows:

CH3CH2OHþ 1:5O2/3H2 þ 2CO2; DH0298 ¼ �552 kJ=mol (10)

CH3CH2OHþ 2H2Oþ 0:5O2/5H2 þ 2CO2; DH0298 ¼ 4:4 kJ=mol

(11)

H2 þ 12O2#H2O; DH0

298 ¼ �241:8 kJ=mol (12)

COþ 12O2#CO2; DH0

298 ¼ �283 kJ=mol (13)

CH4 þ 2O2#CO2þ2H2O; DH0298 ¼ �802:2 kJ=mol (14)

The steam reforming of ethanol has been investigated over a

wide variety of supported metal catalysts in the literature.

Transitionmetals involvingNi, Co, Pt andPdhavebeen reported

to show good activity and selectivity for ethanol steam reform-

ing reactions [6e11]. Among these, Ni is widely used because of

its highactivity forCeCbondbreakingand its relatively lowcost

[8,9]. However, it is also reported that Ni has a high affinity to-

wards coke formation and metal sintering thus lowers the

catalystperformance for longtermoperations [12,13]. Inorder to

minimize the problem of coke deposition, the concept of bime-

tallic catalysts has been investigated; Zhang et al. [14] and Pant

et al. [15] have reported that NieCu and NieCo bimetallic cata-

lysts have high H2 selectivity as well as good coke resistance.

Observations from literature indicate that among the twomain

categories of active phases (noble and non-noble metal), Rh

exhibited the best performances in terms of bio-ethanol con-

version and hydrogen yield [16e18]. Although, the role of Rh is

not well established, it has been reported that it shows high

activity for steam reforming due to its vacant f-orbital, which

imparts excellent redoxbehaviour, i.e., exhibiting simultaneous

oxidation-reduction during intermediate complex formation.

Bespalko et al. [19] and Virginie et al. [20] have concluded that

addition of small amount of Rh improves catalytic performance

and reduces carbon deposition. The nature of the support also

plays an important role towards product selectivity and the

deactivationbehaviourof thecatalyst.Acidicsupports likeAl2O3

are more prone to deactivation on account of coke formation

[21]. Suitable basic supports, like MgO, ZnO, CeO2 and La2O3 or

mixed oxides, can inhibit carbon deposition to some extent

[8,22,23]. CeO2 is an effective support due to its high oxygen

storage capacity (OSC) and ability to store and release oxygen

during reactions (redox properties). The addition of ZrO2 further

enhances its OSC, thermal and mechanical stability and pro-

motes the water gas shift reaction [24,25]. Fornasiero et al. [26]

reported that an optimum composition like Ce0.5Zr0.5O2 (molar

ratio of Ce:Zr ¼ 1:1) has a high OSC and redox property.

In the present study, Ni based CeO2eZrO2 supported cata-

lysts were prepared for hydrogen production via catalytic

oxidative steam reforming of ethanol (OSRE). Incorporation of

small amount of Rh (1wt.%) as a promoter to the Ni/

CeO2eZrO2 catalyst was done with the aim to improve the

catalytic performance for the water gas shift reaction and to

reduce carbon deposition. The catalysts were characterized by

BET, XRD, TPR, TPD, chemisorption, TGA, SEM-EDX and TEM

techniques. The effects of process variables such as temper-

ature, space time, steam to ethanol ratio, oxygen to ethanol,

and run time on ethanol conversion, hydrogen yield and

product distribution were investigated.

Experimental

Catalyst preparation

The CeO2eZrO2 support was prepared by a co-precipitation

method, taking the CeO2/ZrO2 in the weight ratio of 1.0.

Cerium (III) nitrate hexahydrate [Ce(NO3)3.6H2O], zirconyl

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 en e r g y 4 0 ( 2 0 1 5 ) 2 5 2 9e2 5 4 4 2531

nitrate hydrate [ZrO(NO3)2.xH2O] supplied by Central Drug

House Pvt. Ltd., New Delhi, India were used as precursors for

ceria and zirconia. The mixed aqueous solution of cerium (III)

nitrate and zirconyl nitrate was stirred continuously for 1 h at

50 �C. Liquid ammonia was added drop wise to maintain the

solution pH at 10, which facilitates precipitation of cerium and

zirconium ions as their hydroxides. The precipitate thus ob-

tained was aged overnight, washed several times using de-

ionized water, followed by drying overnight at 110 ± 3 �C.The dried precipitate was calcined at 750 ± 5 �C for 6 h to form

mixed oxides of CeO2eZrO2. Ni/CeO2eZrO2 and RheNi/

CeO2eZrO2catalysts were prepared by a wet impregnation

method using nickel nitrate hexahydrate [Ni(NO3)2.6H2O]

supplied by Merck Specialities Pvt. Ltd., Mumbai, India and

rhodium (III) trichloride [RhCl3.xH2O] supplied by Loba

Chemie, Mumbai, India.

Characterization of catalysts

BET surface areaThe BET surface areas and pore volume of the catalysts and

supports were determined by standard nitrogen phys-

isorption at liquid nitrogen temperature on a Micromeritics

ASAP 2020 instrument. All the samples were degassed under

vacuum at 150 �C for 4 h prior to the measurements.

ICP-MS and EDXThe amount of Ni loading on the final catalysts after calcina-

tion was determined by inductively coupled plasma mass

spectrometry (ICP-MS) and energy dispersive X-ray (EDX)

techniques. For ICP-MS, approximately 50 mg of the sample

was dissolved in a mixture of 2 ml of concentrated hydroflu-

oric acid and 3 ml concentrated nitric acid in a Teflon beaker.

Then, the resulting solutionwas heated at 80 �C for 30min and

diluted with de-ionized water prior to analysis.

H2 chemisorptionThe amount of H2 chemisorbed was measured by using a

Micromeritics ASAP 2020 system. Prior to adsorption mea-

surements, samples were reduced in situ under 5% H2 in He, at

the desired reduction temperature (450 �C) for 2 h, followed by

evacuation to 10 mm Hg and cooling down to 35 �C. The

adsorption isotherms were measured at equilibrium pres-

sures between 200 and 400 mmHg. The first adsorption

isotherm was established by measuring the amount of H2

adsorbed as a function of pressure. Then the system was

evacuated for 1 h at 10 mm Hg absolute and the second

adsorption isotherm was obtained. The amount of the probe

molecule chemisorbedwas calculated by taking the difference

between the two isothermal adsorption amounts.

Temperature programmed reduction (TPR) and temperatureprogrammed desorption (TPD)Temperature programmed reduction (TPR) was performed to

determine the reduction behaviour of the catalysts as well as

supports. The experiments were performed on an Autosorb

(Automated gas sorption analyser) Quantachrome instrument

using 100mg of sample. Prior to the reduction, the samplewas

pre-treated under a N2 flow of 30 ml/min at 250 �C for 1 h and

then cooled to room temperature. Subsequently, a H2eN2

mixture (3% H2 by volume) was introduced to the sample at a

flow rate of 30 ml/min and the temperature was increased

linearly from ambient to 650 �C at a rate of 10 �C min�1. The

hydrogen consumption was continuously monitored by a

thermal conductivity detector (TCD). The degree of reduction

of Ni was calculated by taking the ratio of actual H2 con-

sumption to theoretical H2 requirement to reduce all the Ni

species present in the sample by assuming constant degree of

reduction of support material in all the cases.

NH3-TPD measurements were also performed by using the

Quantachrome instrument. For this, the samples were treated

at 250 �C for 1 h under a N2 flow of 30 ml/min and then cooled

to room temperature. Adsorption of NH3 was carried out at

50 �C using a NH3eN2 mixture (3% NH3 by volume) at a flow

rate of 30 ml/min for 1 h. Prior to desorption, physisorbed NH3

was purged for 1 h under N2 flow rate of 30 ml/min. Then,

desorption of chemisorbed NH3 was carried out from 50 �C to

650 �C at a heating rate of 10 �C/min and the concentration of

NH3 in the exit gas was continuously monitored by a thermal

conductivity detector (TCD).

X-ray diffraction (XRD)The bulk crystalline structures of the catalysts were deter-

mined by the X-ray Diffraction (XRD) technique. The XRD

measurements were performed using a D8 diffractometer

manufactured by Bruker AXS, USA, employing Ni filtered Cu

Ka radiation (l¼ 1.5406Å) with a scanning angle (2q) of 10e90�,scanning speed of 1�/min operated at 40 kV voltage and 40mA

current. The average crystallite sizes (‘d’, nm) of NiO were

determined using the Scherrer equation from the half-widths

of the XRD peaks corrected for instrumental broadening.

TGAThermogravimetric analyses (TGA) were performed to mea-

sure the weight loss, the rate of weight loss and the amount of

coke removal from catalysts surface as a function of temper-

ature. The change in mass is then related to the changes

taking place in the catalyst during calcination. The analysis

was performed with TGA-Q500 instrument (supplied by Wa-

ters LLC, USA) with a N2 or air flow of 40 ml/min from 25 �C to

700 �C at a heating rate of 10 �C/min.

Temperature programmed oxidationThe carbon deposit formed during the steam reforming of

ethanol was analysed by temperature programmed oxidation

(TPO) method. About 50 mg of used catalyst sample was

heated up from room temperature to 800 �C at 10 �C min�1 in

an oxidising atmosphere (5 vol% O2 in helium). The amount of

oxygen consumption during the oxidation process was

continuously monitored by a thermal conductivity detector

(TCD).

Scanning electron microscopy (SEM) and transmission electronmicroscopy (TEM)The morphology of as prepared calcined catalyst powders

were analysed using a Zeiss EVO 50 field emission scanning

electron micrographs (SEM) equipped with energy dispersive

X-ray (EDX) analyser and SEM images were obtained. The

surface morphology of fresh calcined and used catalysts were

analysed using a JEMeEVO transmission electron microscope

Fig. 1 e Schematic diagram of experimental set-up.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 0 ( 2 0 1 5 ) 2 5 2 9e2 5 4 42532

operated at 200 kV and the images were recorded. Samples

were prepared by dispersing powder in ethanol, placing in an

ultrasonic bath, then putting droplets onto 3 mm copper grids

coated with amorphous carbon film followed by drying in air

at room temperature.

Thermodynamic analysis of oxidative steam reforming ofethanol

Prior to the experiment, a thermodynamics analysis of the

oxidative steam reforming of ethanol was carried out using

ProII 8.1 software and SRK (Soave-Redlich-Kwong)

thermodynamics fluid package. The thermodynamic analysis

was conducted to improve the understanding of the viability

of reaction-product model systems and develop relationships

between process variables (i.e., temperature, steam to

ethanol ratio (S/E), oxygen to ethanol ratio (O/E)), and the

product distribution [27,28]. For this, reactor temperature was

varied from 300 to 1000 �C at atmospheric pressure for

different molar ratios of steam to ethanol and oxygen to

ethanol in the feed. The standard Gibbs' free energy mini-

mization technique was used to estimate the product com-

positions. The species under consideration were hydrogen,

carbonmonoxide, methane, carbon dioxide and carbon along

Table 1 e BET surface area, pore size and pore volume of support and catalyst.

Catalyst SBET (m2/g) Combined surface area (m2/g)a Pore volume (cm3/g) Avg. Pore diameter (nm)

CeO2eZrO2 35.8 ± 0.8 e 0.065 ± 0.005 5.2 ± 0.2

15% Ni/CeO2eZrO2 27.5 ± 0.5 30.7 ± 0.5 0.054 ± 0.001 5.6 ± 0.1

30% Ni/CeO2eZrO2 20.6 ± 0.5 26.5 ± 0.5 0.048 ± 0.001 6.3 ± 0.1

1%Rhe 30%Ni/CeO2eZrO2 14.9 ± 0.5 25.4 ± 0.5 0.035 ± 0.001 6.2 ± 0.1

a Calculated by taking linear combination of surface area of metal and support.

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 en e r g y 4 0 ( 2 0 1 5 ) 2 5 2 9e2 5 4 4 2533

with unreacted ethanol and water based on preliminary

experiments.

Catalytic test

Oxidative steam reforming of ethanol was carried out using a

fixed-bed reactor made of stainless steel (i.d. ¼ 8 mm)at

different temperatures, ethanol to water feed ratios and space

times. Prior to the reactions, catalysts were reduced in situ

under a flowingmixture of H2/N2 (H2 volume fraction of 0.5) at

550 �C for 6 h. The water and ethanol mixture was pumped

into a vaporizer at 0.4 ml/min by a liquid pump and heated up

to 250 �C and thenmixedwith 30ml/minN2. Then themixture

was passed through the reactor containing 1 g of catalyst. The

catalyst pellets were made from the fine catalysts powder

using an automatic pelletizing press (Techno Search AP-15)

and subsequently crushed and sieved to a particle size of

0.5 ± 0.1 mm. These pellets were placed in the centre of the

reactor and diluted with SiC (same particle size range) at a

volume ratio of 1:1 to avoid adverse thermal effects such as

hot-spots, and to distribute heat more evenly across the

catalyst bed. Reaction products were passed through a

condenser maintained at ~ 3 �C. The gas products were ana-

lysed using a gas chromatograph (GC) equipped with thermal

conductivity detector (TCD) and using Porapak T and molec-

ular sieve (13X) columns in series. The liquid products were

analysed using a gas chromatograph (GC) containing packed

column (10% FFAP) with a flammable ignition detector (FID).

The schematic diagram of the experimental set-up is shown

in Fig. 1. Preliminary runs were carried out to eliminate

external mass transfer and internal diffusion resistance. The

plug flow conditions were maintained by providing catalyst

bed height (L) to catalyst particle size (dp) ratio, L/dp � 50 and

using an internal diameter of reactor (D) to catalyst particle

size (dp) ratio, D/dp� 30 to avoid backmixing and channelling

[21]. The experiments were performed at atmospheric pres-

sure for a feedmixture with ethanol to watermolar ratio of 1:9

and oxygen to ethanol molar ratio of 0.35 over a temperature

range of 400e700 �C by varying feed flow rate in the range of

0.4e1 ml/min.

Ethanol conversion (XEtOH), hydrogen yield (YH2 ) and prod-

ucts selectivities (Si) were calculated according to equations

(15e18), as used in another study [29].

Ethanol Conversion ½XEtOH ð%Þ� ¼ moles of ethanol in�moles of et

moles of ethanol in

H2 yield ðYH2Þ ¼ moles of hydrogen produced

moles of ethanol reacted(16)

Product selectivityðSi� ¼ moles of gaseous product imoles of all gaseous product

� 100

(17)

WHST

�WFA0

�¼ weightof catalystethanolflowrateinfeed

ðKgcat:h=Kgmol½EtOH� Þ

(18)

where, WHST ¼ weight hourly space time.

Results and discussion

Catalyst characterization

BET surface areaThe BET surface area, pore volume and the average pore

radius of the support (CeO2eZrO2), Ni/CeO2eZrO2 and RheNi/

CeO2eZrO2 catalysts are given in Table 1. The surface area of

the support CeO2eZrO2 was 35.8 m2/g and decreased after

metal impregnation. The surface area and pore volume of

metal impregnated catalysts were in the range of

12.7e27.5 m2/g and 0.032e0.054 cm3/g, respectively. The sur-

face areas of metal impregnated catalysts were found to be

lower than their combined values. These results suggest that

the incorporation of metal significantly reduced the surface

area and pore volume of the support, presumably because of

partial blockage of pore surface by metal oxide particles [29].

ICP-MS and EDXThe compositions of the calcined catalysts as prepared were

determined by ICP-MS and Energy Dispersive X-ray (EDX)

techniques and are shown in Table 2. As can be seen from

Table 2, the estimated compositionswere close to initial metal

loading.

H2 chemisorptionThe metal dispersion and crystallite size of CeO2eZrO2 sup-

ported catalysts were obtained by H2 pulse chemisorption. It

can be seen from Table 3, the nickel based catalyst exhibited a

hanol out(15)

Table 2 e Metal loading on various catalysts.

Catalyst IntendedNi loading

(wt.%)

Niloadinga

(wt.%)

Ni loadingb

(wt.%)

15% Ni/CeO2eZrO2 15 14.9 16.3

30% Ni/CeO2eZrO2 30 27.7 28.9

1%Rhe 30%Ni/CeO2eZrO2 30 26.7 30.9

a Determined by ICP-MS.b Determined by EDX analysis.

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low dispersion (~1e2%) probably due to high Ni loading which

is desired for breaking CeC bond of ethanol molecules to

promote the steam reforming reaction [29]. The metal

dispersion decreased from 1.7% to 1.2% with an increasing

metal loading from 15 to 30% on themixed oxide support. The

maximum dispersion was obtained with 1%Rhe30%Ni/

CeO2eZrO2 catalyst. These results suggest that the presence of

Rh in the catalyst formulations improves Ni dispersion and

decreases the NiO crystallite size. The dispersion values ob-

tained in this study, were slightly higher than those reported

by Dong et al. [30] and Biswas et al. [31].

Temperature programmed reduction (TPR) and temperatureprogrammed desorption (TPD)The reduction features of the support as well as catalyst were

analysed by TPR. The TPR plots of CeO2eZrO2 support and

CeO2eZrO2 supported Ni catalysts are shown in Fig. 2(a), and

are summarized in Table 4.

The TPR profile of CeO2 shows peaks at two different

temperature ranges, two at low temperature range from 300 to

550 �Cwhich are assigned to the reduction of surface CeO2 and

another peak at a higher temperature of 760 �C, which is due

to the reduction of bulk CeO2. Similar reduction behaviour of

pure CeO2 was reported in literatures whereas pure ZrO2 does

not easily reduce at temperatures below 1000 �C [32]. In

contrast, the reduction profile of CeO2eZrO2 support showed

only a broad peak at 560 �C which is assigned to the reduction

of Ce4þ to Ce3þ. It shows that the reduction peak of CeO2 in

CeO2eZrO2 support shifted towards lower temperatures,

suggesting that the presence of ZrO2 promotes the reduction

of bulk CeO2 by increasing lattice defect as Zr4þ has smaller

ionic radii than Ce4þ. The reduction of Ce4þ to Ce3þ is

enhanced due to the formation of defect-associated OH

groups on ceria as well as by vacancy formation. The TPR

profile of NiO shows a board peak at 370 �Cwhich indicates the

complete reduction of NiO. In contrast, the TPR profiles of Ni

Table 3 e Metal dispersion and crystallite size.

Catalyst Metaldispersiona

(%)

Metaldispersionb

(%)

NiOcrystalliteb

size (nm)

15% Ni/CeO2eZrO2 1.7 3.0 32.6

30% Ni/CeO2eZrO2 1.2 2.7 35.7

1%Rhe 30%Ni/CeO2eZrO2 1.9 3.8 25.5

a Calculated from H2 chemisorption data.b Calculated from XRD patterns using Scherrer equation.

impregnated catalysts showed two distinct reduction peaks.

The peak obtained at ~400 �C on Ni impregnated catalysts,

were associated with the reduction of bulk NiO (NiO to Ni�) aswell as the reduction of support promoted by the formation of

metal particles and the peak above 500 �C were attributed to

the partial reduction of Ce4þ to Ce3þ [33]. The amount of

hydrogen consumed by the Ni impregnated catalysts was

higher than that required for complete reduction of NiO, as

the degree of reduction of Ni for these catalysts was greater

than 100%, which indicates that small amount of support was

also reduced in addition to NiO. These results indicate that the

presence of Ni enhanced the reducibility of CeO2 in the sup-

port. The intensity of the first peak increased with an increase

in metal loading from 15% to 30% due to increasing NiO con-

tent. The reduction temperatures also increased with metal

loading, suggesting decreasing NiO reducibility at higher

loading as can be seen from Table 4 [33]. The TPR profile of Rh

promoted Ni/CeO2eZrO2 catalyst showed a low temperature

reduction peak at 190 �C, which is assigned to reduction of

Fig. 2 e (a)TPR profiles of (a) CeO2 (b) CeO2eZrO2, (c) 15Ni

%/CeO2eZrO2, (d) 30Ni%/CeO2eZrO2, (e) 1%Rhe30%Ni/

CeO2eZrO2, and (f) NiO catalysts (b)TPD profiles of (a) 30Ni

%/CeO2eZrO2, and (b) 1%Rhe30%Ni/CeO2eZrO2 catalysts.

Table 4 e Summary of temperature programmed reduction results.

Catalyst Reductiontemperature (�C)

H2 consumption[mL H2/gcat]

H2 consumption[mmol H2/gcat]

Degree of reductionCeO2 (%)a

Degree ofreduction Ni (%)a

CeO2 390(22), 520(32), 760(46) 22.9 1.1 38.6 e

CeO2eZrO2 560 5.7 0.3 17.4 e

15% Ni/CeO2eZrO2 410(80), 460(20) 65.8 3.0 e 115

30% Ni/CeO2eZrO2 420(60), 540(40) 133.5 6.0 e 110

1%Rhe 30%Ni/CeO2eZrO2 190(10), 390(90) 165.3 7.4 e 144

NiO 370 272.5 12.2 e 91.4

Numbers within brackets indicate the relative contribution to H2 consumed.a Calculated by Actual H2 consumption/Theoretical H2 consumption.

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 en e r g y 4 0 ( 2 0 1 5 ) 2 5 2 9e2 5 4 4 2535

Rh2O3 to Rh� and a higher temperature reduction peak at

390 �C, assigned to the reduction of bulk NiO as well as the

support [34]. It can be noted that the temperature for the

reduction of bulk NiO decreased and the degree of reduction of

Ni increased significantly than that of unpromoted Ni cata-

lysts, indicating the presence of Rh enhanced the reducibility

of Ni and the support.

The acid-base nature of the catalysts was analysed by the

technique of ammonia desorption. Ammonia desorption

profiles of the catalysts are shown in Fig. 2(b). The desorption

temperatures, amount of total desorbed ammonia, and total

acid site concentration of the catalysts are presented in

Table 5. The TPD profiles (Fig. 2(b)) of 30%Ni/CeO2eZrO2 and

1%Rhe30%Ni/CeO2eZrO2 catalysts showed ammonia desorp-

tion peak in the temperature range of 300e500 �C which im-

plies that they both had moderate acidic sites. It can be seen

from Table 5, the total concentration of acidic sites increased

from 0.83 to 2.41 mmol of NH3 per g of catalyst after Rh

impregnation on 30%Ni/CeO2eZrO2 catalyst. This increased

acidity is probably due to the type of precursor (RhCl3) used for

the impregnation of the noble metal and better dispersion of

metal on the support [35,36].

X-ray diffraction (XRD)The XRD patterns of calcined CeO2eZrO2 support and Ni/

CeO2eZrO2 catalysts are shown in Fig. 3(a). The XRD patterns

of pure CeO2 showed peaks corresponding to (111), (200), (220),

(311), (400) and (331) crystal planes of cubic fluorite structure.

On the other hand, the diffraction patterns of pure ZrO2

resulted a number of peaks corresponding to (110), (�111),

(111), (200), (220), and (022) crystal planes, which can be

assigned to monoclinic structure of ZrO2. For the CeO2eZrO2

support, the XRD pattern showed peaks corresponding to

(111), (200), (220), and (311) crystal planes of cubic-fluorite

Table 5 e Acidity of the catalysts from temperature-programmed desorption of NH3.

Catalyst Temperature(�C)

Totalvolumedesorbed(mLNH3 /gcat

@STP)

Totalacid site

concentration[mmolNH3 /gcat]

30% Ni/CeO2eZrO2 149, 372, 561 18,693 0.83

1%Rhe

30%Ni/CeO2eZrO2

138, 313, 430 53,986 2.41

structure of cerium (IV) zirconium oxide [(Ce0.91Zr0.09)O2].

However, some additional peaks at 29.59, 34.61, and 49.66�

observed, which can be assigned due to the appearance of

tetragonal phase of zirconia [24]. The characteristic peaks of

CeO2 shifted towards higher degree, which suggests that the

incorporation of ZrO2 into CeO2 lattice increases the lattice

Fig. 3 e (a)XRD patterns of (a) CeO2, (b) CeO2eZrO2, (c) 15Ni

%/CeO2eZrO2, (d) 30Ni%/CeO2eZrO2, and (e) ZrO2 catalysts

(b)XRD patterns of (a) 30Ni%/CeO2eZrO2, and (d) 1%Rhe30Ni

%/CeO2eZrO2 catalysts.

Fig. 4 e (a)TGA profiles of pre-calcined 30%Ni/CeO2eZrO2

fresh catalyst (b)TGA profiles of used 30%Ni/CeO2eZrO2

catalyst after 36 h of reaction.

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defect. The diffraction peaks of ZrO2 were not found in the

CeO2eZrO2 support which indicates that CeO2 forms a solid

solution with ZrO2 [33]. The XRD patterns of Ni impregnated

catalysts showed the characteristic peaks of NiO corre-

sponding to (222), (400), (440), (622) and (444) crystal planes.

The peaks corresponding to NiO intensified with an increase

in nickel loading from 15wt.% to 30wt.%.

The XRD patterns of Rh promoted Ni/CeO2eZrO2 catalyst is

also shown in Fig. 3(b). It exhibited the characteristic peaks of

NiO corresponding to (222), (400), (440), (622) and (444) crystal

planes and peaks corresponding to (111), (200), (220), and (311)

crystal planes of cerium (IV) zirconium oxide [(Ce0.91Zr0.09)O2].

However, the diffraction lines for Rh were not observed due to

low concentration of Rh. The 30%Ni/CeO2eZrO2 catalyst

exhibited sharp NiO peak with high intensity, whereas 1%

Rhe30%Ni/CeO2eZrO2 showed relatively less intense NiO

peak as compared to the mixed oxide phase. This indicates a

better dispersion of NiO crystallites in Rh promoted Ni/

CeO2eZrO2 catalyst.

TGA-DTAThe changes conferred on the catalysts during calcination

were studied through TGA-DTA analysis and their profiles are

shown in Fig. 4(a).

The TGA profiles of pre-calcined fresh catalysts are very

similar. They each have three distinct weight loss stages in the

temperature ranges between 25 and 120 �C, 120e230 �C and

230e350 �C. The first and second weight loss stages are

attributed to the removal of water and volatile matter present

in the sample respectively. The third weight loss stage is

associated with a strong exothermic peak centred at around

300 �C corresponding to decomposition/oxidation of nitrates

and precursor materials from the catalysts [37]. The TGA-DTA

profiles of spent catalyst after 36 h of reaction are also shown

in Fig. 4(b), and exhibited maximal weight loss in the

~500e600 �C temperature range, indicating the loss of a large

amount of carbon which was deposited on the surface of

catalysts [38]. DTA curve shows a sharp positive peak at 550 �Cindicating the exothermic nature of carbon combustion [39].

Scanning electron microscopy (SEM) and transmission electronmicroscopy (TEM)SEM images of the prepared catalysts are shown in Fig. 5. SEM

images show that metal particles with spherical shapes are

deposited on comparatively larger irregular shaped

CeO2eZrO2 solid particles. It was also observed that the metal

particles are uniformly dispersed on support particles [40].

TEM images of the prepared and used catalysts are shown

in Fig. 6. TEM images show that the NiO crystallite sizes in the

prepared (fresh) catalysts are in the range of 50e100 nmwhich

is in agreement with that obtained from XRD data. TEM im-

ages of used catalyst after 36 h of run shows agglomerated

carbon deposition on the catalyst surface [19]. No significant

difference in NiO crystallite size was observed by comparing

the TEM images of fresh and used catalysts indicating that

catalyst sintering was insignificant. This result indicates that

the catalyst deactivation occurred mainly due to carbon

deposition on the catalyst surface which reduced the avail-

ability of active sites for reaction.

Thermodynamics analysis of oxidative steam reforming ofethanol

The thermodynamics analysis (Fig. 7) reveals that hydrogen

selectivity increases with increasing temperature and de-

creases with increasing oxygen content in the feed at a con-

stant steam to ethanol molar ratio due to the increase in

production of CO and H2O under oxygen enriched conditions.

Higher oxygen in the feed also reduces the hydrogen selec-

tivity as part of hydrogen consumed by partial oxidation

process (Rxn-12). The CO selectivity increases with tempera-

ture over the entire range of temperatures and it decreases

with increasing O/E molar ratio at temperature greater than

500 �C due to total oxidation of CO to CO2. As a result, CO2

selectivity decreases with increasing temperature and in-

creases with increasing O/E molar ratio. The increase in oxy-

gen content in the feed stream decreases methane selectivity,

probably due tomethane combustion (Rxn-14). The selectivity

to methane decreases rapidly with rise in temperature as the

methane steam reforming reaction (Rxn-7, 8) is favoured at

higher temperatures. According to thermodynamic analysis,

at a constant S/E molar ratio high hydrogen selectivity with

minimum CO selectivity can be obtained with lower oxygen

content (O/E molar ratio of ~0.3) in the feed [41,42].

Fig. 5 e SEM images of prepared catalysts: (a) CeO2eZrO2, (b) 30%Ni/CeO2eZrO2, and (c & d) 1%Rhe30%Ni/CeO2eZrO2.

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For the range of feed composition (S/Emolar ratio from 1 to

10) analysed (Fig. 8), hydrogen yield and selectivity increases

with temperature. Each curve for hydrogen yield vs temper-

ature passed through a maxima and the maxima occurs at

lower temperature for progressively higher S/E ratios.

Methane selectivity decreases as the amount of water in the

feed increases over the entire range of temperatures, since

larger water content promotes the consumption of methane

by the steam reforming reaction. For all feed conditions, CO

selectivity increases with rise in reaction temperature, but

reduces with greater water proportions in the feed; a phe-

nomenon which can be explained by greater favourability of

the water gas shift (WGS) reaction (Rxn-9) on increasing the

amount of water. All the curves representing carbon dioxide

selectivity except that for S/E equal to 1, exhibit a point of

inversion at a temperature around 550 �C, which is attributed

to the reversibility of thewater gas shift reaction. It shows that

at <550 �C, CO2 selectivity is high as the water gas shift reac-

tion being exothermic favour at low temperatures and it de-

creases with increasing water content. While at higher

temperatures (>550 �C), it decreases sharply with increasing

temperatures whereas it increases with increasing water

content in the feed as high water content promotes WGS. The

results from carbon yield vs S/E molar ratio (graph not shown)

confirm that the formation of carbon is favoured at steam to

ethanol ratio below 4 at all temperatures and O/E ratios

studied [42].

Results of thermodynamic analysis reveal that higher

steam to ethanol molar ratio in the feed favours hydrogen

production, as it promotes steam reforming, the water gas

shift reaction and suppresses coke formation. However, a

large amount of water in the feed increases reactor loading,

therefore trade-off between these two variables is desired.

Higher oxygen content in the feed also reduces hydrogen

selectivity as part of the hydrogen is consumed by partial

oxidation reactions. Therefore, based on these results, the

catalytic performance was investigated only at selected

conditions.

Evaluation of catalyst performance

Effect of temperatureThe effect of temperature on catalytic activity and selectivity

of 30%Ni/CeO2eZrO2 catalyst was examined at a constant

space time (W/FAO ¼ 9.17 Kgcat h/Kg mol[EtOH]) using EtOH/

H2O/O2 molar ratio equal to 1:9:0.35 (Fig. 9).

It was found that ethanol conversion increased with tem-

perature and reached to completion (99%) at 600�C. The

hydrogen yield increased from 2.5 to 3.5 mol/mol as the

reactor temperature was increased from 500 to 600�C.

Fig. 6 e TEM images of prepared catalysts: (a) 1%Rhe30%Ni/CeO2eZrO2 (fresh) and used catalysts (b) 30%Ni/CeO2eZrO2, and

(c) 30%Nie1%Rh/CeO2eZrO2.

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Hydrogen yield decreased at higher temperature (T > 600 �C)due to the ethanol decomposition reaction (Rxn-2). The

maximum hydrogen yield of approximately 3.5 mol of H2/mol

of ethanol fed, was obtained at 600 �C as compared to the

thermodynamic value of 5. With increasing temperature from

500 to 600�C hydrogen selectivity increased from 63% to 65%

and CO2 selectivity increased from 18% to 19%, while a

decreasing trendwas found in the case of CH4 selectivity. Such

selectivity trends in the temperature range investigated can

be explained by the steam reforming reactions (Rxn-1, 7 and 8)

that favoured the formation of H2 and CO2. CO2 selectivity

increased due to the contribution of the water-gas shift reac-

tion below 600 �C, while the role of reverse water gas shift

reaction was exhibited by an increase in CO selectivity, and

decrease in CO2 selectivity above 600 �C. Therefore, 600 �Cwas

chosen as an optimum temperature for further experiments

as at this temperature highest hydrogen selectivity and lesser

CO selectivity were obtained.

Effect of weight hourly space time (WHST)The WHST was varied from 3.67 to 9.17 Kgcat h/Kg mol[EtOH]

by changing the ethanol feed rate over a fixedmass of catalyst.

The effects of space time on ethanol conversion and product

distribution on 30%Ni/CeO2eZrO2 catalyst are shown in

Fig. 10.

As expected, it was found that ethanol conversion

increased with increasing contact time. As the value of W/FAOincreased from 3.67 to 9.17 Kgcat h/Kg mol[EtOH], ethanol

conversion increased from 78% to 96%. The selectivity of

steam reforming product, i.e. H2 and CO2 increased to 66% and

23% from 53% to 19%, respectively, while CO and CH4 selec-

tivity decreased from 11% to 8% and 12%e7%, respectively by

increasing space time from 4.59 to 9.17 Kgcat h/Kg mol[EtOH].

This suggests that higher space time tends to increase selec-

tivity of H2 and CO2, and decreases the selectivity of undesired

gases such as CO and CH4. This is because of ethanol

decomposion which is favoured more than that of steam

reforming reaction at lower space time [21].

Effect of metal loadingIn order to evaluate the effect of Ni loading, ethanol conver-

sion and hydrogen yield obtained on prepared catalysts were

compared (see Fig. 11). Ethanol conversion increased from90%

to 95% on increasing metal loading from 15% to 30%. A further

Fig. 7 e Effects of O2/EtOH molar ratio on thermodynamic selectivity of product at different temperatures (S/E ¼ 9 and

P ¼ 1 atm).

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increase in metal loading did not improve the conversion

significantly. A similar trend was observed for hydrogen yield

which increased from 3 to 3.5 mol/mol of ethanol as the

loading was increased from 15% to 30%. This result indicates

that catalyst activity improves with increased Ni loading, and

is also consistent with the findings of Yan et al. [43] for steam

reforming of bio-oil aqueous fractions over Ni/CeO2eZrO2

catalysts.

Effect of steam to ethanol (S/E) ratioThe effect of feed concentration (i.e. steam to ethanol ratio)

was investigated taking three different feed stocks having 3:1,

6:1, and 9:1 as S/E ratio. As S/E ratio increased from 3:1 to 9:1,

ethanol conversion and hydrogen yield increased from 91% to

95% and 2.8e3.6 mol/mol, respectively. The effect of S/E ratio

on product distribution is shown in Fig. 12.

Hydrogen selectivity increased from 59% to 67% as S/E ratio

changed from 3:1 to 9:1. This indicates that hydrogen selec-

tivity increases with increasing water content in the feed for a

given temperature. Excess water content in the feed promotes

both ethanol steam reforming (Rxn-1, 11) as well as the

methane reforming reaction (Rxn-7, 8) [44]. On the other hand,

CO selectivity decreased from 12% to 6% and CO2 selectivity

increased from 18% to 21% with increasing S/E ratio from 3:1

to 9:1 as excess water in feed promotes the water gas shift

reaction in the forward direction. Methane selectivity

decreased from 11 to 7%with increasing water content in feed

as methane reforming reaction is favoured at this condition.

Effect of oxygen to ethanol (O/E) ratioThe effect of oxygen addition on product distribution was

investigated by varying O/E ratios ranging from 0.1 to 1 mol of

oxygen/mol of ethanol for a constant S/E ratio in the feed on

30%Ni/CeO2eZrO2 catalyst at 600�C and at a fixedW/FAO value

of 9.17 Kgcat h/Kg mol[EtOH].

When O/E ratio was changed from 0.1 to 0.2, conversion

increased from 90% to 95%. Complete conversion of ethanol

was observed at an O/E ratio of 0.35 at 600 �C. The variation in

product selectivity with varying O/E ratios at constant tem-

perature is shown in Fig. 13.

The hydrogen selectivity decreased from 63.0% to 60.8% as

the O/E ratios increased from 0.1 to 0.35 mol/mol and

decreased further withmore oxygen input. At higher values of

O/E ratio, hydrogen selectivity decreased due to the oxidation

of CO and CH4 which leads to higher CO2 content in the

product stream. The selectivity to CO and CH4 decreased from

Fig. 8 e Effects of H2O/EtOH molar ratio on thermodynamic selectivity of product at different temperatures (S/E ¼ 9 and

P ¼ 1 atm).

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15% to 11% and 7.5%e4.3%, respectively while CO2 selectivity

increased from 15% to 29% with addition of oxygen due to CO

and CH4 oxidation reactions. A moderate value of H2 selec-

tivity (61%) and lowCO selectivitywere obtained at O/E ratio of

Fig. 9 e Effects of temperature on ethanol conversion,

product selectivity and H2 yield at P ¼ 1 atm, molar ratio

EtOH/H2O/O2 ¼ 1:9:0.35, W/FAO ¼ 9.17 Kgcat h/Kg mol

[EtOH] (Catalyst: 30%Ni/CeO2eZrO2).

Fig. 10 e Effects of space time on ethanol conversion,

product selectivity, and H2 yield at T ¼ 600 �C, P ¼ 1 atm,

molar ratio EtOH/H2O/O2 ¼ 1:9:0.35, W/FAO ¼ 3.67, 4.59,

6.11 & 9.17 Kgcat h/Kg mol[EtOH], [Catalyst: 30%Ni/

CeO2eZrO2].

Fig. 11 e Effects of metal loading on ethanol conversion

and H2 yield at 600 �C, P ¼ 1 atm, molar ratio EtOH/H2O/

O2 ¼ 1:9:0.35; W/FAO ¼ 9.17 Kgcat h/Kg mol[EtOH].

Fig. 13 e Effects of O/E ratio on product selectivity at 600 �C,P ¼ 1 atm, molar ratio EtOH/H2O ¼ 1:9; W/FAO ¼ 9.17

Kgcat h/Kg mol[EtOH], [Catalyst: 30%Ni/CeO2eZrO2].

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0.35 at 600 �C. It is desirable to run the reaction close to ther-

mally neutral state (ATR) or auto-thermal statewhich requires

minimum external energy.

Effect of addition of noble metal on ethanol conversion andproduct selectivityFig. 14 shows the ethanol conversion, product selectivities and

hydrogen yield on 30%Ni/CeO2eZrO2 catalyst and 1%Rhe30%

Ni/CeO2eZrO2 at constant EtOH/H2O/O2 molar ratio of

1:9:0.35 at 600 �C and space time of 9.17 Kgcat h/Kgmol[EtOH].

It was observed that ethanol conversion and hydrogen yield

(3.5e4.6 mol/mol) increased significantly due to addition of

noble metal (1wt.%Rh) on 30%Ni/CeO2eZrO2 catalyst. The

product composition of the outlet stream improved as

hydrogen selectivity increased from 60% to 71% and selectivity

to CO and CH4 reduced to approximately 4% and 3%,

Fig. 12 e Effects of S/E ratio on ethanol conversion and

product selectivity at 600 �C,P ¼ 1 atm, molar ratio EtOH/

O2 ¼ 1:0.35; W/FAO ¼ 9.17 Kgcat h/Kg mol[EtOH], [Catalyst:

30%Ni/CeO2eZrO2].

respectively. The improved hydrogen yield and selectivity can

be attributed to the ability of Rh to promote the water gas shift

reaction and methane steam reforming which leads to a

suppression of the undesirable by-products. Based on this

study, it can be concluded that 1%Rhe30%Ni/CeO2eZrO2 ex-

hibits better catalytic performance than the unpromoted

catalyst in the OSRE reaction under similar reaction

conditions.

Effect of run time on ethanol conversion and product selectivityThe effects of run time on ethanol conversion and product

distribution were studied for 36 h at 600 �C with the feed

having 9:1 steam to ethanol ratio at a constant space time of

9.17 Kgcat h/Kgmol[EtOH]. The time on stream (TOS) study on

both the catalysts (30%Ni/CeO2eZrO2 and 1%Rhe30%Ni/

CeO2eZrO2) is shown in Fig. 15.

Fig. 14 e Effects of noble metal on ethanol conversion and

product selectivity at 600 �C, P ¼ 1 atm, molar ratio EtOH/

H2O/O2 ¼ 1:9:0.35; W/FAO ¼ 9.17 Kgcat h/Kg mol[EtOH].

Fig. 15 e Time on stream study at T ¼ 600 �C, P ¼ 1 atm,

molar ratio EtOH/H2O/O2 ¼ 1:9:0.35, W/FAO ¼ 9.17 Kgcat.h/

Kgmol[EtOH], [( ) EtOH conversion, and ( ) H2; ( )

CO; ( ) CH4; ( ) CO2 selectivity for 1%Rhe30%Ni/

CeO2eZrO2 Catalyst ( ) EtOH conversion, and ( ) H2;

( ) CO; ( ) CH4; ( ) CO2 selectivity for 30%Ni/CeO2eZrO2

Catalyst].

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Almost complete ethanol conversion was achieved on the

1%Rhe30%Ni/CeO2eZrO2 catalyst up to a period of 16 h and

then it decreased slightly. The observed deactivation of the

catalyst is primarily due to coke formation on the catalyst'ssurface. The selectivities of gaseous products, i.e. H2, CO, CH4,

and CO2 in the outlet stream were found to be approximately

70%, 4%, 2% and 20%, respectively over the period under

consideration and no significant drop in selectivity was

observed indicating that deactivation did not attenuate cata-

lyst activity. On the other hand, 93% ethanol conversion was

achieved on the 30%Ni/CeO2eZrO2 catalyst and it decreased

slightly with time. The products (i.e. H2, CO, CH4, and CO2)

Fig. 16 e TPO profiles of used catalysts.

selectivities were found to be remained constant approxi-

mately at 60%, 12%, 10% and 18%, respectively over the period.

A similar trend was reported by Patel et al. [29] for steam

reforming of ethanol over a Ni-based ceria-zirconia catalyst.

This high stability and activity of the catalyst is supported by

the high oxygen storage-release capacity of CeO2eZrO2 sup-

port, which helps in gasifying the carbon deposited on the

catalyst during the reaction and thus avoids a possible route of

deactivation via carbonaceous deposits. In addition, the

incorporation of ZrO2 in CeO2 support enhances its lattice

defect and the improved defect densities promote dissociation

of water by forming bridging OH group as well as help to

dissociate adsorbed ethanol molecules by forming Type II

ethoxy species.

The amount of carbon deposited on the catalysts after 36 h

of run time was measured using thermogravimetric analysis.

It was observed that 86.8 and 42.3 mg C/g catalyst/h deposited

on 30%Ni/CeO2eZrO2 catalyst for steam reforming and

oxidative steam reforming, respectively. In case of 1%Rhe30%

Ni/CeO2eZrO2 catalyst, these values decreased to 61.5 and

14.2 mg C/g catalyst/h, respectively. These results indicate

that the carbon deposition decreases for both catalysts during

the oxidative steam reforming reaction due to oxidation of

deposited carbon in the presence of oxygen which leads to

lower deactivation of the catalysts.

The nature of the carbon deposits formedwas investigated

by TPO analysis of used catalysts after reaction and is shown

in Fig. 16. The TPO profiles of used catalysts show two

different oxidation zones: a small peak at low temperature

range (300e400 �C) and a large peak observed at high tem-

perature range (550e650 �C). These two peaks are attributed to

the presence of two different type of carbon deposition on the

surface of the catalysts. The peak at low temperature was

assigned to the oxidation of amorphous carbon deposit on

catalysts surface and whereas the peak at higher temperature

was due to the oxidation of graphitic carbon [45]. These indi-

cate that catalysts deactivation occurred due to formation of

both amorphous and graphitic carbon on the catalysts.

Fig. 17 e Comparison of product selectivity and hydrogen

yield at 600 �C,P ¼ 1 atm, molar ratio EtOH/H2O/

O2 ¼ 1:9:0.35; W/FAO ¼ 9.17 Kgcat h/Kg mol[EtOH] for SRE

and OSRE[Catalyst: 30%Ni/CeO2eZrO2].

Fig. 18 e Heat of reaction as a function of oxygen content in

the feed.

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Comparison of SRE and OSRE on product selectivity andhydrogen yieldBoth steam reforming and oxidative steam reforming of

ethanol over 30%Ni/CeO2eZrO2 catalyst were investigated at

optimum operating conditions and the comparative results

are shown in Fig. 17.

The selectivity to hydrogen in the gaseous product was 62%

in OSRE compared to 66% obtained from SRE. This can be

explained by the fact that the hydrogen oxidation reaction

being favoured more in the presence of oxygen. But this

decreased hydrogen yield is compensated over the advantage

of small energy requirement in case of oxidative steam

reforming. The overall heat of reaction was estimated with

varying oxygen content in the feed to check the effect of ox-

ygen on the nature (endothermic/exothermic) of the ethanol

steam reforming reaction. The standard heats of formation of

reactants and products were used to calculate the overall heat

of reaction. As can be seen from Fig. 18, that the heat of re-

action for SRE is 174 kJ/mol and it decreases with increasing

oxygen content in the feed. At O/E molar ratio equal to 0.36,

the reaction becomes autothermal and sustains itself without

requiring heat from an external source. However, with greater

O/E ratios, the reaction becomes exothermic, indicating that

introduction of only a small amount of oxygen in the feed is

optimal, leading to the choice of O/E ¼ 0.35 for conducting

experiments.

Conclusions

The catalytic oxidative steam reforming of ethanol (OSRE) for

hydrogen production over Ni based CeO2eZrO2 supported

catalystswas studied. 30%Ni loading is found to be optimumat

600 �C with EtOH/H2O/O2 molar ratio of 1:9:0.35 and space time

of 9.17 Kgcat h/Kg mol[EtOH] for this reaction. It was observed

that doping of noble metal (1wt.%Rh) on 30%Ni/CeO2eZrO2

catalyst improves both ethanol conversion (91e100%) and

hydrogen yield (3.5e4.6mol/mol) significantly due to the ability

of Rh to promote water gas shift reaction and methane steam

reforming. Almost complete conversion of ethanol with stable

product distributionwas observed on 1%Rhe30%Ni/CeO2eZrO2

catalyst up to a period of 36 h which indicates its high thermal

stability and activity and supported by the high oxygen

storage-release capacity of CeO2eZrO2 support. The compari-

son of steam reforming and oxidative steam reforming under

similar reaction conditions revealed that OSRE, despite having

slightly lesser hydrogen selectivity, is the better reforming

route to undertake since energy requirements are minimised

and there is much greater catalyst longevity due to gasification

of carbon deposits. Small amount of oxygen is found to be

beneficial for steam reforming of ethanol.

Acknowledgements

The authors acknowledge the financial support from Centre

for Fire, Explosive& Environment Safety (CFEES), Ministry of

Defence CFEES/ESG/CARS/003/10-11, India for conducting this

research. Author, TarakMondal, conveys his sincere thanks to

Graduate Student Exchange Program (GSEP) Canada for

providing financial support for his visit to University of Sas-

katchewan, Saskatoon, Canada for conducting part of this

research.

r e f e r e n c e s

[1] Bshish A, Yaakob Z, Narayanan B, Ramakrishnan R,Ebshish A. Steam reforming of ethanol for hydrogenproduction. Chem Pap 2011;65:251e66.

[2] Ni M, Leung DYC, Leung MKH. A review on reforming bio-ethanol for hydrogen production. Int J Hydrogen Energy2007;32:3238e47.

[3] Vaidya PD, Rodrigues AE. Insight into steam reforming ofethanol to produce hydrogen for fuel cells. Chem Eng J2006;117:39e49.

[4] Haryanto A, Fernando S, Murali N, Adhikari S. Current statusof hydrogen production techniques by steam reforming ofethanol: a review. Energy Fuel 2005;19:2098e106.

[5] Klouz V, Fierro V, Denton P, Katz H, Lisse JP, Mauduit S, et al.Ethanol reforming for hydrogen production in a hybrid electricvehicle: process optimization. J Power Sources 2002;105:26e34.

[6] Srisiriwat N, Therdthianwong S, Therdthianwong A.Oxidative steam reforming of ethanol over Ni/Al2O3 catalystspromoted by CeO2, ZrO2 and CeO2eZrO2. Int J HydrogenEnergy 2009;34:2224e34.

[7] Freni S, Cavallaro S, Mondello N, Spadaro L, Frusteri F. Steamreforming of ethanol on Ni/MgO catalyst: H2 production forMCFC. J Power Sources 2002;108:53e7.

[8] Comas J, Mari~no F, Laborde M, Amadeo N. Bio-ethanol steamreforming on Ni/Al2O3 catalyst. Chem Eng J 2004;98:61e8.

[9] Aupretre F, Descorme C, Duprez D. Bio-ethanol catalyticsteam reforming over supported metal catalyst. CatalCommun 2002;3:263e7.

[10] Batista MS, Santos RKS, Assaf EM, Assaf JM, Ticianelli EA.Characterization of the activity and stability of supportedcobalt catalysts for the steam reforming of ethanol. J PowerSources 2003;124:99e103.

[11] Llorca J, Homs N, Sales J, Piscina PR. Efficient production ofhydrogen over supported cobalt catalysts from ethanolsteam reforming. J Catal 2002;209:306e17.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 0 ( 2 0 1 5 ) 2 5 2 9e2 5 4 42544

[12] Sehested J. Four challenges for nickel steam reformingcatalysts. Catal Today 2006;111:103e34.

[13] Mari~no F, Boveri M, Baronetti G, Laborde M. Hydrogenproduction from steam reforming of bioethanol using Cu/Ni/K/g-Al2O3 catalysts. Effect of Ni. Int J Hydrogen Energy2001;26:665e8.

[14] Zhang L, Liu J, Li W, Guo C, Zhang J. Ethanol reforming overNi-Cu/Al2O3-MyOz (M ¼ Si, La, Mg, and Zn) catalysts. J NatGas Chem 2009;18:55e65.

[15] Pant KK, Mohanty P, Agarwal S, Dalai AK. Steam reforming ofacetic acid for hydrogen production over bifunctional Ni-Cocatalysts. Catal Today 2013;207:36e43.

[16] Kugai J, Subramani V, Song C. Low temperature reforming ofethanol over CeO2-supported Ni-Rh bimetallic catalysts forhydrogen production. Catal Lett 2005;101:255e64.

[17] Liguras DK, Kondarides DI, Verykios XE. Production ofhydrogen for fuel cells by steam reforming of ethanol oversupported noble metal catalysts. Appl Catal B Environ2003;43:345e54.

[18] Cavallaro S, Chiodo V, Freni S, Mondello N, Frusteri F.Performance of Rh/Al2O3 catalyst in the steam reforming ofethanol: H2 production for MCFC. Appl Catal A Gen2003;249:119e28.

[19] Bespalko N, Roger AC, Bussi J. Comparative study of NiLaZrand CoLaZr catalysts for hydrogen production by ethanolsteam reforming: effect of CO2 injection to the gas reactants.Evid Rh Role as a Promot Appl Catal A Gen 2011;407:204e10.

[20] Virginie M, Araque M, Roger A, Vargas J, Kiennemann A.Comparative study of H2 production by ethanol steamreforming onCe2Zr1.5Co0.5O8-d and Ce2Zr1.5Co0.47Rh0.07O8-

d :evidence of the Rh role on the deactivation process. CatalToday 2008;138:21e7.

[21] Sahoo DR, Vajpai S, Patel S, Pant KK. Kinetic modeling ofsteam reforming of ethanol for the production of hydrogenover Co/Al2O3 catalyst. Chem Eng J 2007;125:139e47.

[22] Fatsikostas AN, Verykios XE. Reaction network of steamreforming of ethanol over Ni-based catalysts. J Catal2004;225:439e52.

[23] Freni S, Cavallaro S, Mondello N, Spadaro L, Frusteri F.Production of hydrogen for MC fuel cell by steam reformingof ethanol over MgO supported Ni and Co catalysts. CatalCommun 2003;4:259e68.

[24] Diagne C, Idriss H, Pearson K, Garcia MAG, Kiennemann A.Efficient hydrogen production by ethanol reforming over Rhcatalysts. Effect of addition of Zr on CeO2 for the oxidation ofCO to CO2. CR Chim 2004;7:617e22.

[25] Dave CD, Pant KK. Renewable hydrogen generation by steamreforming of glycerol over zirconia promoted ceria supportedcatalyst. Renew Energ 2011;36:3195e202.

[26] Fornasiero P, Monte RD, Rao GR, Kaspar J, Meriani S,Trovarelli A, et al. Rh-loaded CeO2-ZrO2 solid solutions ashighly efficient oxygen exchangers: dependence of thereduction behavior and the oxygen storage capacity on thestructural properties. J Catal 1995;151:168e77.

[27] Vasudeva K, Mitra N, Umasankar P, Dhingra SC. Steamreforming of ethanol for hydrogen production:thermodynamic analysis. Int J Hydrogen Energy1996;21:13e8.

[28] Garcı́a EY, Laborde MA. Hydrogen production by the steamreforming of ethanol: thermodynamic analysis. Int JHydrogen Energy 1991;16:307e12.

[29] Patel M, Jindal TK, Pant KK. Kinetic study of steam reformingof ethanol on Ni-based ceria-zirconia catalyst. Ind Eng ChemRes 2013;52:15763e71.

[30] Dong WS, Roh HS, Jun KW, Park SE, Oh YS. Methanereforming over Ni/Ce-ZrO2 catalysts: effect of nickel content.Appl Catal A Gen 2002;226:63e72.

[31] Biswas P, Kunzru D. Oxidative steam reforming of ethanolover Ni/CeO2-ZrO2 catalyst. Chem Eng J 2008;136:41e9.

[32] Trovarelli A, Zamar F, Llorca J, Leitenburg C, Dolcetti G,Kiss JT. Nanophasefluorite-structured CeO2eZrO2 catalystsprepared by high-energy mechanical milling. J Catal1997;169:490e502.

[33] Biswas P, Kunzru D. Steam reforming of ethanol forproduction of hydrogen over Ni/CeO2eZrO2 catalyst: effect ofsupport and metal loading. Int J Hydrogen Energy2007;32:969e80.

[34] Kugai J, Subramani V, Song C, Engelhard MH, Chin YH. Effectof nano crystalline CeO2 support on the properties andperformance of Ni-Rh bimetallic catalysts for oxidativesteam reforming of ethanol. J Catal 2006;238:430e40.

[35] Vagia EC, Lemonidou AA. Investigations on the properties ofceria-zirconia supported Ni and Rh catalysts and theirperformance in acetic acid steam reforming. J Catal2010;269:388e96.

[36] Aupretre F, Descorme C, Duprez D, Casanave D, Uzio D.Ethanol steam reforming over MgxNi1�xAl2O3 spinel oxide-supported Rh catalysts. J Catal 2005;233:464e77.

[37] Akande A, Idem R, Dalai A. Synthesis, characterization andperformance evaluation of Ni/Al2O3 catalysts for reformingof crude ethanol for hydrogen production. Appl Catal A Gen2005;287:159e75.

[38] Li M, Wang X, Li S, Wang S, Ma X. Hydrogen production fromethanol steam reforming over nickel based catalyst derivedfrom Ni/Mg/Al hydrotalcite-like compounds. Int J HydrogenEnergy 2010;35:6699e708.

[39] Alberton AL, Souza MMVM, Schmal M. Carbon formation andits influence on ethanol steam reforming over Ni/Al2O3

catalysts. Catal Today 2007;123:257e64.[40] Kamacz A, Pawlyta M, Dobrzanski LA, Krzaton A.

Characterization of the structure features of CeZrO2 and Ni/CeZrO2 catalysts for tar gasification with steam. Arch Mat SciEng 2011;48:89e96.

[41] Liu S, Zhang K, Fang L, Li Y. Thermodynamic analysis ofhydrogen production from oxidative steam reforming ofethanol. Energy Fuel 2008;22:1365e70.

[42] Alvarado FD, Gracia F. Steam reforming of ethanol forhydrogen production: thermodynamic analysis includingdifferent carbon deposits representation. Chem Eng J2010;165:649e57.

[43] Yan CF, Cheng FF, Hu RR. Hydrogen production fromcatalytic steam reforming of bio-oil aqueous fraction over Ni/CeO2-ZrO2catalysts. Int J Hydrogen Energy 2010;35:11693e9.

[44] Srivastava A, Pant KK. Oxidative steam reforming ofbioethanol over Rh/CeO2-Al2O3 catalyst for hydrogenproduction. J Thermodyn Catal 2013;4:119.

[45] Fang W, Paul S, Capron M, Dumeignil F, Duhamel LJ.Hydrogen production from bioethanol catalyzed byNixMg2AlOy ex-hydrotalcite catalysts. Appl Catal B Environ2014;152:370e82.