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ARTICLE IN PRESSG ModelCATTOD-8714; No. of Pages 8Catalysis Today xxx (2013) xxx xxx

Contents lists available at ScienceDirect

Catalysis Today

jou rn al hom epage: www.elsev ier .com

Combin e membr

Shin-Kun yu Jong-Sooa Energy Mater 102 GDaejeon 305-3b Department o Vanco

a r t i c l

Article history:Received 29 JuReceived in reAccepted 1 NoAvailable onlin

Keywords:MethaneSynthesis gasCatalytic nickel membraneSteam and CO2 reforming of methaneGas to liquid (GTL)

team shor). Theigatedn was

with the increase in the CO2/H2O feed ratio at 923 K, while the inuence of the CO2/H2O feed ratio on CH4conversion was not signicant at temperatures 973 K. Unlikely CH4 conversion, the conversion of CO2increased with the increase in the CO2/H2O feed ratio over the temperature range of 9231023 K. Theconversion of CH4 and that of CO2 both increased with increasing temperature because the correspondingreactions are endothermic and remained nearly constant at temperatures 973 K. The H2/CO molar ratiocould be adjusted by the CO2/H2O feed ratio for downstream applications. No carbon deposition on thecatalytic nickel membrane was observed after the combined steam and dry reforming of methane tests

1. Introdu

With theingly been cenergy. Natverted to uindirect roupling of methe desiredwhich methwhile, the methane isCO) by steathese two rcomponentthe desired

SynthesiTropsch (FTpartial oxid

CorresponE-mail add

0920-5861/$ http://dx.doi.o this article in press as: S.-K. Ryi, et al., Combined steam and CO2 reforming of methane using catalytic nickel membrane for gas to) process, Catal. Today (2013), http://dx.doi.org/10.1016/j.cattod.2013.11.001

under all process conditions. 2013 Elsevier B.V. All rights reserved.

ction

depletion of liquid petroleum, natural gas has increas-onsidered one of the main resources for chemicals andural gas contains primarily methane and can be con-seful products by two different routes, i.e., direct andtes [15]. The direct routes include the oxidative cou-thane, in which methane is reacted with oxygen to give

product, and non-oxidative coupling of methane, inane is converted directly to the desired product. Mean-indirect route involves two-step processes whereby

rst converted to synthesis gas (a mixture of H2 andm reforming [5], CO2 reforming [6] or a combination ofeactions [68] and partial oxidation [6,7,9]; then, thes of the synthesis gas react with each other to produce

products.s gas is converted to synthetic fuels by the Fischer) process with a H2/CO ratio of 2 [10]. Although, theation of methane produces a suitable H2/CO ratio for FT

ding author. Tel.: +82 42 860 3155; fax: +82 42 860 3134.ress: [email protected] (S.-K. Ryi).

synthesis, it is difcult to control the operating temperature andrisk of explosion [11,12]. With the growing concerns about globalwarming, the dry reforming of methane for the utilization of CO2is garnering increasing attention. However, the dry reforming ofmethane is a highly endothermic reaction and requires very highoperating temperatures (8001000 C) to reach a high conversionof methane. These very high operating temperatures result incatalyst deactivation by coke deposition, mainly due to the deepcracking of methane, which is thermodynamically favored athigh temperature [13,14]. The steam reforming of methane is thedominant process to produce synthesis gas but is not suitable forFischerTropsch synthesis because of the very high H2/CO ratio(>3) associated with the process [15,16]. These problems of steamand dry reforming of methane can be overcome combining thesetwo reactions. This combination has two main advantages in theGTL process: (i) carbon formation is reduced due to the oxidationof the carbon precursor species and (ii) a desirable H2/CO ratiocan be obtained via the adjustment of the CH4/H2O/CO2 ratio inthe feed stream [68]. Environmentally, the combination of thesteam and dry reforming of methane utilizes greenhouse gases,i.e., methane and carbon dioxide, and produces useful chemicalproducts. Koo et al. investigated the combination of the steamand dry reforming of methane for the GTL process [17,18]. They

see front matter 2013 Elsevier B.V. All rights reserved.rg/10.1016/j.cattod.2013.11.001ed steam and CO2 reforming of methanane for gas to liquid (GTL) process

Ryia,b,, Sung-Wook Leea, Jin-Woo Parka, Duck-K Parka, Sung Su Kimb

ials and Convergence Research Department, Korea Institute of Energy Research (KIER),43, South Koreaf Chemical and Biological Engineering, University of British Columbia, 2360 East Mall,

e i n f o

ly 2013vised form 14 October 2013vember 2013e xxx

a b s t r a c t

In this study, test on the combined salytic nickel membrane within a very(CO2/H2O feed ratio and temperatureH2/CO ratio in the products was investreforming of methane, CH4 conversio/ locate /ca t tod

using catalytic nickel

Oha,

ajeong-ro, Yuseong-Gu,

uver, BC, Canada V6T 1Z3

and dry reforming of methane were carried out over a cat-t residence time of 120 ms under different process conditions

effect of the molar ratio of CO2/H2O in the reactants on the at 9231023 K. In the reaction of the combined steam and dry

strongly inuenced by the CO2/H2O feed ratio and decreased


ARTICLE IN PRESSG ModelCATTOD-8714; No. of Pages 82 S.-K. Ryi et al. / Catalysis Today xxx (2013) xxx xxx

Fig. 1. Gas

determinedof CH4:H2Orate of cokecoke forma

In previobrane and methanatioow passagbrane is shoporous wallsized poresother gaseseffect was tive of this ssteam and dbrane for thactivity andmembrane CH2:H2O:C

2. Experim

2.1. Catalyt

A catalymethod. Tepressed widiameter omade presscompressedfor 2 h. NickInco Co. wawetness imincrease itseter and thi0.8 mm, resmounted ometal boltsThe preparein Fig. 2.

2.2. Combin

A schemis shown inwas heatedtemperatur

Fig.

lled bbly araned COeriesINICas ca2O mratiof theraturoduc) equl coted bment

arac

e siranes, Aec, Ois waranee caterized by SEM/EDX to verify coke formation.

ults and discussion ow passage and membrane effect in catalytic nickel membrane.

that a H2/CO ratio of 2 could be attained by a feed ratio:CO2 = 1:0.8:0.4. Even though they could reduce the

formation by ceria promotion on a Ni/Al2O3 catalyst,tion was not avoidable [17].us studies, we developed a novel catalytic nickel mem-examined the steam reforming of methane and then reaction for synthesis gas production [15,19]. The gase and membrane effect in the catalytic nickel mem-wn in Fig. 1. The reforming reactions take place on the

of the catalytic nickel membrane which has sub-micron. H2 passed the catalytic nickel membrane faster than

because of viscous and Knudsen ow. The membranedescribed in previous study in detail [15]. The objec-tudy was to examine the performance of the combinedry reforming of methane over a catalytic nickel mem-e GTL process. To obtain a desirable H2/CO ratio, the

stability of the combined process over a catalytic nickelwere investigated at various reaction temperatures andO2 ratios.

ental

ic nickel membrane

tic nickel membrane was created by the sintered metaln grams of alumina-modied nickel powder was com-thout a binder in a cylindrical metal mold with af 51 mm under a pressure of 70 MPa using a home-ure device described in a previous study [20]. The

powder was then sintered at 900 C under hydrogenel powder with an average particle size of 3 m froms pre-treated with an alumina coating by the incipient

controassemmembCH4 an5850 s(NS, Mtest wCO2/Hmolar effect otempeThe pr6890Nthermaseparaexperi

2.3. Ch

Pormembmeritic(Lazertanalysmembture, thcharac

3. Res this article in press as: S.-K. Ryi, et al., Combined steam and CO2 reformin) process, Catal. Today (2013), http://dx.doi.org/10.1016/j.cattod.2013.11.00

pregnation method, as described in previous studies, to thermal stability [21]. After heat treatment, the diam-ckness of the catalytic nickel membrane were 50.8 andpectively. The prepared catalytic nickel membrane wasn a plate-type metal module and tightened by eight

and nuts. A metal O-ring was used for gas tightness.d catalytic nickel membrane and assembly are shown

ed steam and dry reforming test

atic of the combined steam and dry reforming test Fig. 3. The gas tightened assembly shown in Fig. 2

in an electric furnace equipped with a programmablee controller. The temperature of the furnace was

3.1. Catalyt

Heterogcontrolled bfusion, surfAmong theto the pore tance on thshape and dis difcult tby measuripore area ogated by coand yellow2. Photograph of catalytic nickel membrane and assembly.

y a K-type thermocouple placed on the outside of thend the temperature at the bottom of the catalytic nickel

was monitored to determine the reaction temperature.2 were supplied by mass ow controller (MFC, Brooks) and liquid water was supplied by a micro liquid pumpHEMI PUMP). The combined steam and dry reformingrried out at a (H2O + CO2)/CH4 molar ratio of 3. Theoral ratio was varied from 0 to 1.0 to adjust the H2/CO

to create a system designed for GTL processing. The feed molar ratio on the H2/CO ratio was probed over thee range of 9231023 K. The residence time was 120 ms.t gases were analyzed by a gas chromatograph (Agilentipped with HP-MOLSIV and HAYESEP D columns andnductivity detectors (TCD). Water in the products wasy a cold trap before analyzing the product gases. Theal conditions and the results are summarized in Table 1.

terization of catalytic nickel membrane

ze, pore volume and porosity of catalytic nickel were investigated using mercury porosimeter (Micro-utoPore IV 9520) and color confocal microscopeptics H1200). X-ray photoelectron spectroscopy (XPS)s conducted to investigate the oxidation state of Ni on

surface. When testing was completed at each tempera-talytic nickel membrane was cooled under nitrogen andg of methane using catalytic nickel membrane for gas to1

ic nickel membrane

eneous catalysis using porous material is generallyy the following factors: external diffusion, internal dif-ace reaction, internal diffusion and external diffusion.se factors, internal diffusion resistance is closely relatedstructure and size. The effect of internal diffusion resis-e porous material can be assessed based on the poreiameter of the material. Since the tortuosity of the poreo measure, the effect of internal diffusion was examinedng the average pore diameter or porosity. The surfacef the catalytic nickel membrane which was investi-lor confocal microscope is shown in Fig. 4. Dark spots

spots are nickel grains and surface pores, respectively.


ARTICLE IN PRESSG ModelCATTOD-8714; No. of Pages 8S.-K. Ryi et al. / Catalysis Today xxx (2013) xxx xxx 3

Table 1The effect of te

Temp. [K]

923

973

1023

Table 2Pore propertie

Average porTotal pore arTotal pore voPorosity (%)

The averagwas 5 mThis value porosimetenickel memarea of 0.83

The avera powder csized pore ihas large siz this article in press as: S.-K. Ryi, et al., Combined steam and CO2 reformin) process, Catal. Today (2013), http://dx.doi.org/10.1016/j.cattod.2013.11.00

Fig. 3. Schematic of experimental set-up for the combined steam

mperature and feed ratios on activity and productivity.

Feed [CH4:H2O:CO2] XCH4 [%] H2/CO rat

1.0:3.0:0 84.2 11.0 1.0:2.7:0.3 80.6 7.5 1.0:2.25:0.75 75.8 4.6 1.0:1.5:1.5 69.3 2.3

1.0:3.0:0 95.8 8.1 1.0:2.7:0.3 94.1 5.7 1.0:2.25:0.75 93.4 3.7 1.0:1.5:1.5 92.7 2

1.0:3.0:0 96.0 7.5 1.0:2.7:0.3 94.5 5.3 1.0:2.25:0.75 93.6 3.4 1.0:1.5:1.5 92.9 1.8

s of the catalytic nickel membrane measured by mercury porosimeter.

e diameter (nm) 390ea (m2 g1) 0.83lume (cm3 g1) 0.08

39.90

e surface pore area of the catalytic nickel membrane2. The porosity calculated by the pore area was 40.2%.is similar with the one (39.9%) analyzed by mercuryr shown in Table 2. As shown in Table 2, the catalyticbrane has average pore diameter of 390 nm, total pore

m2 g1 and total pore volume of 0.08 cm3 g1.age pore diameter is considerably high compared withatalyst. Generally, the catalyst that has relatively smalls more affected by internal diffusion than the one whiched pores. Therefore, the catalytic membrane which has

lager pore sthe internacatalytic msize is gettiresistance. and pore sizThe averagesize [22], faamount of t

3.2. Activity

The comout by intralytic nickemaintainina temperatug of methane using catalytic nickel membrane for gas to1

and dry reforming of methane.

io Production rate of Syn. gas (H2 + CO) [N m3 h1]

4.57 1024.45 1024.27 1024.02 102

5.43 1025.39 1025.46 1025.42 102

5.52 1025.56 1025.67 1025.68 102

ize has an advantage in mass transfer when consideringl diffusion resistance. However, it should be noted thatembrane may lose the function of membrane if poreng higher and higher to decrease the internal diffusionTherefore, it is very important to control the porositye for ensuring the performance of catalytic membrane.

pore size and porosity can be controlled by the powderbrication conditions such as molding pressure [20] andhe loaded alumina on the nickel powder [21].

of combined steam and dry reforming

bined steam and dry reforming of methane was carriedoducing a mixture of CH4, H2O and CO2 over the cat-l membrane at different CO2/H2O ratios (01.0), whileg a (H2O + CO2)/CH4 ratio of 3.0 in the feed stream overre range of 9231023 K and a residence time of 120 ms.



Fig. 4. Surface color confocal microscope image of catalytic nickel membrane: darkspots are nickel grains and yellow spots are pores. (For interpretation of the ref-erences to color in gure legend, the reader is referred to the web version of thearticle.)

The conversby the steagenerally a(2)). Syntheaccording t

CH4 + H2O

CO + H2O

CH4 + CO2 Fig. 5(a)

tion tempethe conversremained nof CH4 reacreactants. TCH4 converbrane is mo

923 K, the results showed a strong inuence of the CO2/H2O feedratio on the CH4 conversion, while the inuence of the CO2/H2Ofeed ratio on the CH4 conversion was not signicant at tempera-tures 973 K. These phenomena are illustrated in Fig. 5(b), whichshows the conversion of CH4 as a function of the CO2/H2O feedratio at different temperatures. These effects are due to the lowerendothermic nature of steam reforming compared with that ofdry reforming meaning that the activation energy for both the dryreforming and steam reforming of methane is sufcient at temper-atures 973 K, while the activation energy for the dry reforming isnot high enough to attain a sufciently high conversion of methaneat 923 K. Above 973 K, very high CH4 conversion (92.796%) isattained over the range of all CO2/H2O feed ratios (01.0) becauseCH4 becomes the limiting reactant and is consumed in both steamand dry reforming. Similar results were reported in thermody-namic and experimental studies of the combined dry and steamreforming of methane over different types of catalysts [8,23,24]. Itwas reported that the addition of extra steam to the feed streamof a 50CH4 + 50CO2 mixture increased the conversion of methaneconsiderably, especially at temperatures below 1073 K. Choudharyet al. reported the opposite results when they carried out the com-bined steam and dry reforming of methane at 1123 K [7,25]. Theyconcluded that the increase in CH4 conversion with the increase inthe CO2/H2O feed ratio is due to the higher activity of their catalyst

refo cond COrature of ns inn sune d

C )) aning, ns, an anreactinvere valactioperaperion of methane into synthesis gas is usually carried outm reforming of methane according to Eq. (1), which isccompanied by the water-gas shift reaction (WGS, Eq.sis gas can be produced by the dry reforming of methaneo Eq. (3).

CO + 3H2 H = 206 kJ mol1 (1)

CO2 + H2 H = 41 kJ mol1 (2)

2CO + 2H2 H = 247 kJ mol1 (3) shows the conversion of CH4 as a function of the reac-rature over a catalytic nickel membrane. As expected,ion of CH4 increased with increasing temperature andearly constant at temperatures 973 K. The conversionhed 96% at 1023 K when CO2 was not included in the

for dryThe

ture antempebecausreactioreactiometha(2CO (Eq. (2reformreactioreactioCO2 is In the positiveach reas temthe tem this article in press as: S.-K. Ryi, et al., Combined steam and CO2 reformin) process, Catal. Today (2013), http://dx.doi.org/10.1016/j.cattod.2013.11.00

he addition of CO2 to the steam led to a decrease in thesion. This result indicates that the catalytic nickel mem-re active for steam reforming than for dry reforming. At

the dominaacted as comethane, C

Fig. 5. Conversion of CH4 as a function of the reaction temperature (a) and the CO2g of methane using catalytic nickel membrane for gas to1

rming compared to that for steam reforming.version of CO2 as a function of the reaction tempera-2/H2O feed ratio is shown in Fig. 6(a) and (b). At lowe, CO2 does not seem to be a reagent, but a productnegative value of CO2 conversion. There are many side

the combined steam and dry reforming of methanech as steam reforming (Eq. (1)), dry reforming (Eq. (3)),ehydrogenation (CH4 2H2 C), Boudouard reaction

CO2), carbon gasication (C 2H2O CO2 2H2), WGSd reverse-WGS. Among them, CO2 is a reactant in dryCO generation (reverse-Boudourd) and reverse-WGSnd a product in WGS and carbon gasication. If WGSd carbon gasication are faster than the reactions whereant, the conversion of CO2 indicates the negative value.se case, denitely, the conversion of CO2 should be theue. The magnitude of CO2 participation as a reactant inn is heavily dependent on the reaction conditions, suchture and partial pressure of reactants and products. Asature increased, the conversion of CO2 increased due toting dry reforming reaction. Because both CO2 and H2O-oxidants in the combined steam and dry reforming ofH4 reacted with H2O instead of CO2 at low temperature

/H2O feed ratio (b) for catalytic nickel membrane.



Fig. 6. Conversion of CO2 as a function of the reaction temperature (a) and the CO2/H2O feed ratio (b) for catalytic nickel membrane.

due to the higher stability of CO2. Like the conversion of CH4, theconversion of CO2 is nearly constant at temperatures 973 K due tothe limitation of CH4 as reactant. As shown in Fig. 6(b), the conver-sion of CO2 increased with the increase in the CO2/H2O feed ratio.The negative values of the conversion of CO2 at low CO2/H2O feedratios indicthe water-ga consideraing, insteadreforming o

The H2/Ca function oH2/CO molacially at lowis explainedtion increasby the highat elevatedthermodynthe contrarnot signicbecause theditions is re

The effeand dry refothe increaseproduct str

Table 3H2/gases selectivities of the catalytic nickel membrane.

H2/CO H2/CO2 H2/CH4

Selectivity 2.78 2.75 1.85

molafeed

2.0 lar trwere, reses a

the srvedd CH

that d 1.mem

ratioor ofe COprodn proction produces a H2/CO molar ratio of 3. It is expected thatediate H2/CO ratios would be produced upon combining theate that the dry reforming of methane is suppressed byas shift reaction. The increase of CO2 content causedble increase in the conversion of CO2 by dry reform-

of the water-gas shift reaction related to the steamf methane.O molar ratios for this catalytic nickel membrane asf reaction temperature are displayed in Fig. 7(a). Ther ratios decrease with increasing temperature, espe-

CO2/H2O molar ratios in the feed stream. This result by the fact that the effect of the water-gas shift reac-es at low temperature, while the H2/CO ratio is affectedly endothermic steam and dry reforming of methane

temperature because the water-gas shift reaction isamically unfavorable at elevated temperature [26]. Ony, the effect of temperature on the H2/CO molar ratio isantly at high CO2/H2O molar ratios in the feed stream

effect of the water-gas shift reaction under these con-duced.ct of the CO2/H2O molar ratio on the combined steamrming is shown in Fig. 7(b). The gure shows that with

in the CO2/H2O feed ratio, the H2/CO molar ratio in theeam decreased appreciably. As shown in Table 1, the

H2/COin the 3.7 andA simiratios and 1.0produc(>7) inis obseCO2 anshows2.75 annickel H2/CObehavithat thin the reactioing reainterm this article in press as: S.-K. Ryi, et al., Combined steam and CO2 reformin) process, Catal. Today (2013), http://dx.doi.org/10.1016/j.cattod.2013.11.00

Fig. 7. H2/CO molar ratios for the catalytic nickel membrane as a function of reactior ratio could be adjusted by the ratio of CH4:H2O:CO2stream. At 973 K, the H2/CO molar ratios were 8.1, 5.7,for CO2/H2O ratios of 0, 0.11, 0.33 and 1.0, respectively.end was observed at 1023 K, where the H2/CO molar

7.5, 5.3, 3.4 and 1.8 for CO2/H2O ratios of 0, 0.11, 0.33pectively. The stoichiometric steam reforming reactionH2/CO molar ratio of 3. However, a very high H2/CO ratioteam reforming alone, i.e., for a CO2/H2O feed ratio of 0,. Gas permeation tests were carried using pure H2, CO,4 at 373 K and pressure difference of 100 kPa. Table 3the selectivities of H2/CO, H2/CO2 and H2/CH4 were 2.78,85 respectively. It means that H2 passed the catalyticbrane faster than other gases. The very high value of

in the steam reforming alone is due to the H2 selective the catalytic nickel membrane [15]. It is not surprising2/H2O feed ratio strongly affects the H2/CO molar ratiosuct stream because the stoichiometric dry reformingduces a H2/CO molar ratio of 1, while the steam reform-g of methane using catalytic nickel membrane for gas to1

n temperature (a) and the CO2/H2O feed ratio (b).

Please cite rming of methane using catalytic nickel membrane for gas toliquid (GTL .11.001


dry reforming and steam reforming of methane. These intermedi-ate values indicate that more CO and less H2 are formed by the dryreforming of methane upon increasing CO2/H2O ratio as shown inFig. 8, which depicts the composition of the products as a functionof the CO2/H2O ratio at 1023 K. It can be concluded that it is pos-sible to modify the H2/CO ratio by varying the CO2/H2O ratio inthe feed stream and temperature, depending on the downstreamapplication [10,27].

Fig. 9(a) and (b) shows the total ow rate (H2, CO, CO2, andCH4) of the production stream and the syngas gas ow rate (H2and CO) in the products after steam removal by cold trap, respec-tively. The results show the effect of the CO2/H2O ratio on the driedtotal ow rate of the production stream. With the increase in theCO2/H2O ratio, the dried total ow rate of the production stream isincreased at all temperatures of 923, 973 and 1023 K. For the GTLprocess, the syngas (H2 and CO) production rate is more importantthan the total product ow rate because H2 and CO are convertedto synthetic fuels by the FischerTropsch (FT) synthesis. Except at Fig. 8. Composition of products as a function of CO2/H2O ratio at 1023 K.

Fig. 9. Total ow rate (H2, CO, CO2, and CH4) of production stream (a) and the syngas gas ow rate (H2 and CO) (b) in the products after steam removal.

Fig. 10. Surfac combined steam and dry reforming of methane as a function of the CO2/H2Oratio: (a) and ( this article in press as: S.-K. Ryi, et al., Combined steam and CO2 refo) process, Catal. Today (2013), http://dx.doi.org/10.1016/j.cattod.2013

e (ac) and cross-sectional (df) SEM images of catalytic nickel membrane after the d) are at 923 K, (b) and (e) 973 K (c) and (f) 1023 K.



923 K, as thsyngas prodof 00.33. T5.68 102in the syngthe dry reforeaction anat low temp

3.3. SEM/ED

After theat each temfrom the mFig. 10 showafter the coCO2/H2O raand f), respspherical buder size of 3nickel memcombined sand (3), 2 mbined steamratio of oxidcarbon depratio of 3 tocontinued deactivationthere is no

3.4. XPS an

XPS anaof Ni on meand Ni0, resof catalytic methane teface, while

is main species. This result implies the surface of catalytic mem-brane can be changed reversibly, and thus the membrane can havea function participated in reforming reaction. XPS is surface anal-ysis and reforming reaction in this paper is also surface reaction.

rd toconsiengter, frn surch si

clus

folloy refopowd

convand e reancreersioteamong iwas ratio

97conv

dueerato thepossi

in ths we23 Kngasr ratnd a arborvedry rFig. 11. XPS spectrum of catalytic nickel membrane.

e CO2/H2O ratio increased, an increasing trend for theuction rate is observed over the CO2/H2O ratio rangehe syngas production rate is almost at and reachesN m3 h1 at 1023 K at a CO2/H2O ratio of 1.0. A decreaseas production rate was observed at 923 K. While bothrming and steam reforming reactions are endothermicd are favored at high temperature, the WGS is favorederature because it is an exothermic reaction.

X analysis

combined steam and dry reforming of methane testsperature, the catalytic nickel membrane were removedembrane assembly and characterized by SEM/EDX.s surface (ac) and cross-sectional (df) SEM imagesmbined steam and dry reforming of methane with a

It is hawhen ical strHowevstate oand su

4. Con

Theand drnickel

The ture in th

The iconvfor s

A strsion feed tures

The aturetempdue t

It is ratioratioat 10

A symola1.0 a

No cobseand d this article in press as: S.-K. Ryi, et al., Combined steam and CO2 reformin) process, Catal. Today (2013), http://dx.doi.org/10.1016/j.cattod.2013.11.00

tio of 1.0 at 923 (a and d), 973 (b and e) and 1023 K (cectively. As shown in Figs. 10, the nickel powder wast possessed an undulating shape with an average pow-

m. The SEM and EDX analysis of the tested catalyticbrane showed no sign of any carbon deposition after theteam and dry reforming of methane tests. From Eqs. (1)ol of CH4 needs 2 mol of oxidants (CO2 H2O) for com-

and dry reforming of methane reaction. In general, theants/CH4 in the reforming reactions is kept 1 to avoidosition. In this study, we used a (H2O CO2)/CH4 molar

prevent carbon deposition. The reforming tests were50 h at each temperature. There was no indication of

during the test period. The SEM analysis shows thatdeformation of the catalytic nickel membrane.

alysis

lysis was conducted to investigate the oxidation statembrane surface. 856 and 853.3 eV is assigned to Ni2+

pectively [28]. As shown in Fig. 11, the XPS spectrummembrane after combined steam and dry reforming ofst reveals that Ni2+ species are dominant on the sur-the spectrum after the pretreatment shows metallic Ni

Acknowled

This worDevelopme(KIER) (B3-

References

[1] J.R.H. Ros193199

[2] M.T. Rava[3] J.H. Lunsf[4] Y. Xu, X. B[5] A. Holme[6] V.R. Chou[7] V.R. Chou[8] M.A. Sori

Hydrogen[9] A. Raee,

[10] M.R. Rahi[11] Y. Zeng, S

Sci. 58 (2[12] A.C.W. Ko

gen Ener[13] P. Gronch

227234[14] J. Ni, L. Chg of methane using catalytic nickel membrane for gas to1

insist that bulk valence of the membrane is reversibledering the analysis limitation (only surface), mechan-h of membrane and unique characteristics of catalysis.om the XPS result, it is obvious that a change in valenceface can function in the reforming reaction as a catalysttes are reversible.

ions

wing results were obtained from the combined steamrming tests using a catalytic nickel membrane made ofer with different CO2/H2O ratios as the oxidant:

ersion of CH4 was increased with increasing tempera-reached 96% at 1023 K when the CO2 was not includedctants.ase in the CO2/H2O ratio leads to a decrease in the CH4n because the catalytic nickel membrane is more active

reforming than for dry reforming.nuence of the CO2/H2O feed ratio on the CH4 conver-observed at 923 K, while the inuence of the CO2/H2O

on the CH4 conversion was not signicant at tempera-3 K.ersion of CO2 was increased with increasing temper-

to the dominating dry reforming reaction at highure and was nearly constant at temperatures 973 K

limitation of CH4 as the reactant.ble to modify the H2/CO ratio by varying the CO2/H2Oe feed stream and the temperature. The H2/CO molarre 8.1, 5.7, 3.7 and 2.0 at 973 K and 7.5, 5.3, 3.4 and 1.8

for CO2/H2O ratios of 0, 0.11, 0.33, 1.0 and respectively. production rate of 5.68 102 N m3 h1 at a H2/COio of 1.8 was obtained at 1023 K at a CO2/H2O ratio ofresidence time of 120 ms.n formation on the catalytic nickel membranes was

by the SEM and EDX analysis after the combined steameforming of methane tests.

gement

k was conducted under the framework of Research andnt Program of the Korea Institute of Energy Research2461-6).

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148155.[23] S. Ozkara-Aydinoglu, Int. J. Hydrogen Energy 35 (2010) 1282112828.[24] M.A. Al-Nakoua, M.H. El-Naas, Int. J. Hydrogen Energy 37 (2012) 75387544.[25] V.R. Choudhary, A.M. Rajput, Ind. Eng. Chem. Res. 35 (1996) 39343939.[26] B. Liu, A. Goldbach, H. Xu, Catal. Today 171 (2011) 304311.[27] W.-H. Chen, B.-J. Lin, Appl. Energy 101 (2013) 551559.[28] F. Pompeo, D. Gazzoli, N.N. Nichio, Int. J. Hydrogen Energy 34 (2009) 22602268. this article in press as: S.-K. Ryi, et al., Combined steam and CO2 refo) process, Catal. Today (2013), http://dx.doi.org/10.1016/j.cattod.2013g of methane using catalytic nickel membrane for gas to1

Combined steam and CO2 reforming of methane using catalytic nickel membrane for gas to liquid (GTL) process1 Introduction2 Experimental2.1 Catalytic nickel membrane2.2 Combined steam and dry reforming test2.3 Characterization of catalytic nickel membrane

3 Results and discussion3.1 Catalytic nickel membrane3.2 Activity of combined steam and dry reforming3.3 SEM/EDX analysis3.4 XPS analysis

4 ConclusionsAcknowledgementReferences

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