co2 reforming of methane

ww.sciencedirect.com

i n t e rn a t i o n a l j o u rn a l o f h y d r o g e n en e r g y x x x ( 2 0 1 4 ) 1e8

Available online at w

ScienceDirect

journal homepage: www.elsevier .com/locate/he

CO2 reforming of methane on Ni/g-Al2O3 catalystprepared by dielectric barrier discharge hydrogenplasma

Lijun Jin, Yang Li, Ping Lin, Haoquan Hu*

State Key Laboratory of Fine Chemicals, Institute of Coal Chemical Engineering, School of Chemical Engineering,

Dalian University of Technology, Dalian 116024, China

a r t i c l e i n f o

Article history:

Received 28 September 2013

Received in revised form

27 December 2013

Accepted 26 January 2014

Available online xxx

Keywords:

CO2 reforming of methane

Ni/g-Al2O3

Hydrogen

Dielectric barrier discharge

Plasma

* Corresponding author. Tel./fax: þ86 411 84E-mail address: [email protected] (H. Hu)

Please cite this article in press as: Jin L, edischarge hydrogen plasma, Internationa

0360-3199/$ e see front matter Copyright ªhttp://dx.doi.org/10.1016/j.ijhydene.2014.01.1

a b s t r a c t

Ni/g-Al2O3 catalyst was prepared by direct treatment of Ni(NO3)2/g-Al2O3 precursor with

dielectric barrier discharge (DBD) hydrogen plasma at different input powers, characterized

by XRD, H2-TPR, CO2-TPD, N2 adsorption and TEM, respectively, and used as the catalyst for

CO2 reforming of methane (CRM). The results showed that the input power obviously

affected the reduction degree and catalytic performances of catalysts. Low input power

under 40 W mainly resulted in the decomposition of nickel nitrate into Ni oxides. The

reduction degree, catalytic activity and stability increase with the input power. Similar

catalytic performances in CRM reaction can be obtained when the power exceeds 80 W.

Compared with the Ni/Al2O3 catalyst prepared by traditional method, Ni/g-Al2O3 samples

prepared by H2 DBD plasma exhibit better activities, stability and anti-carbon deposit

performances. It is mainly ascribed to smaller Ni particle size, more basic sites and weaker

basicity. The increase of Ni particle sizes due to the sintering at high temperature results in

the decrease of catalytic activities and coke formation.

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

reserved.

1. Introduction

CO2 reforming of methane (CRM) has attracted more

attention in the last few decades due to the effective

utilization of two greenhouse gases and its low H2/CO

ratio of nearly unit in the products [1,2]. Especially

considering the reaction stoichiometry, it is more profit-

able to make use of the gases with similar amounts of

CH4 and CO2 like biogas or some natural gas streams with

high CO2 content [3,4].

986157..

t al., CO2 reforming of ml Journal of Hydrogen E

2014, Hydrogen Energy P71

Nowadays, tremendous effects have focused on the

development of catalysts with high activity and stability for

CRM. Nickel-based and noble metal supported catalysts (Rh,

Ru, Pd, Pt, etc.) seem to be the promising catalysts [5,6].

Although the noble metal catalysts are proved to be less

sensitive to coking, it is more practical to develop improved

Ni-based catalysts considering high catalytic activity, prod-

ucts selectivity and low cost [7,8]. However, faster carbon de-

posit on nickel than noble metals makes it very necessary to

develop the coking-resistant Ni-based catalyst for the future

application.

ethane on Ni/g-Al2O3 catalyst prepared by dielectric barriernergy (2014), http://dx.doi.org/10.1016/j.ijhydene.2014.01.171

ublications, LLC. Published by Elsevier Ltd. All rights reserved.

mailto:[email protected]

www.sciencedirect.com/science/journal/03603199

www.elsevier.com/locate/he

http://dx.doi.org/10.1016/j.ijhydene.2014.01.171



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 x x x ( 2 0 1 4 ) 1e82

Recently, many studies found that the catalysts prepared

by use of plasma technologies, especially reduced by the

plasma, exhibited better lower temperature activity and

stability than the conventional catalyst [9e15], which is

mainly ascribed to the enhanced metal dispersion and

smaller Ni crystal size. Various kinds of non-equilibrium

plasmas with features of low temperature and many high-

energy electrons are used for the reduction of supported

metal catalysts. Halverson and Cocke prepared the Al2O3-

supported Ru catalyst with highly dispersed metallic parti-

cles as well as large metal aggregates by using the capaci-

tively coupled radio-frequency plasma of oxygen/water [10].

Phillips et al. studied the supported Pd/C and Pd/Al2O3 cata-

lysts prepared by plasma torch [11]. Liu’s group investigated

many plasma-assisted catalysts, including Ni/Al2O3, Ir/Al2O3,

Ni/SiO2, Pd/HZSM-5 by vacuum glow discharge with/without

the following thermal calcination, and found the remarkable

enhancement in dispersion and low-temperature activity of

the catalysts [12e15]. But they also found that not all sup-

ported metal catalysts can be reduced by Ar glow discharge

plasma. Some supported Fe(NO3)3, Ni(NO3)2, and Co(NO3)2matters are just decomposed to the corresponding metal

oxides by non-hydrogen plasma, which is attributed to the

negative standard electrode potential of the Mnþ/M ions pair

[16]. Hu et al. observed that NiO supported Al2O3 cannot be

reduced by cold plasma jet under Ar atmosphere although

the discharged gas temperature is 467 �C at the discharge

voltage of 600 V, but quickly reduced at 10%H2/Ar atmosphere

[17]. Li et al. even found that the catalytic stability in partial

oxidation of methane was improved by preventing carbon

deposit on Ni catalyst when the reduced Ni/Al2O3 catalyst by

traditional method was further treated by using plateeplate

discharge model via a corona discharge [18]. Chu et al. used

the frequency plasma to prepare several glow discharge

plasma-assisted catalysts, such as FischereTropsch cobalt

catalyst, Ni/a-Al2O3, Pd/a-Al2O3, and developed a novel

plasma-assisted calcination and reduction method to pre-

pare novel Ni/SiO2 or Ni/Al2O3 catalysts for methane

reforming reaction [19,20]. The results showed that the Ni/g-

Al2O3 catalyst prepared by directly decomposed and reduced

by atmospheric pressure glow discharge plasma jet exhibited

high catalytic activity and good anti-carbon deposit perfor-

mance in CRM reaction. Although the temperature of catalyst

bed in discharge zone is 527 �C when 20 KHz AC voltage is

utilized for 10 min, the Ni particle size on the catalyst surface

is about 5 nm. They attributed the excellent low-temperature

activity and structure of the catalyst to short treatment time

of 10 min in plasma process instead of several hours in

conventionally decomposing and reducing the catalyst pre-

cursor of Ni(NO3)2/g-Al2O3, which effectively avoided the

sintering and aggregation of Ni particles.

Dielectric barrier discharge (DBD) plasma can be also used

to reduce the supported metal catalysts, such as Pt/g-Al2O3,

Co/g-Al2O3, Ni/MgO [21,22]. In this paper, the impregnated g-

Al2O3 with Ni(NO3)2 was directly treated by H2 DBD at different

input powers. The prepared samples were characterized by

XRD, H2-TPR, CO2-TPD, TEM, N2 adsorption/desorption and TG

techniques, respectively. Their catalytic performances in CO2

reforming of methane were examined and compared with the

catalyst prepared by conventional method.

Please cite this article in press as: Jin L, et al., CO2 reforming of mdischarge hydrogen plasma, International Journal of Hydrogen E

2. Experimental

2.1. Catalyst preparation

Ni(NO3)2/g-Al2O3 with 10 wt.% Ni was prepared by incipient

wetness impregnation. The support g-Al2O3 with surface area

of 260 m2/g (from Dalian Haixin Chemical industrial Co., Ltd.)

was crushed, sieved to 20e40mesh and dried at 120 �C for 12 h

before use. The desired aqueous solution of Ni(NO3)2 was

added and impregnated for 12 h at room temperature, then

the mixture was dried at 105 �C for another 12 h. The obtained

samples were divided into two parts and treated by conven-

tional method or DBD plasma of H2, respectively.

2.1.1. H2 plasma methodFig. 1 shows the schematic diagram of the atmospheric pres-

sure DBD reactor used in our experiments. An inside stainless

steel rod with a diameter of 3 mm was used as high voltage

(HV) electrode. The coaxial stainless steel mesh, which was

wrapped around the corundum tube, served as the ground

electrode. The discharge gap of the DBD reactor is 2.5 mm.

Before discharge, about 1.0 g Ni(NO3)2/g-Al2O3 without

decomposition at elevated temperature was loaded into

discharge zone and fed with a 100 ml/min flow rate of H2 to

remove air for 10 min. Then different discharge voltage with a

sine wave was regulated by plasma generator (CTP-2000K,

Nanjing Suman Electronics Corp.) with the maximum voltage

40 kV and an adjustable frequency between 10 and 40 kHz to

treat the sample for 20 min. The total AC input power was

calculated by multiplying the input voltage by the corre-

sponding current. The temperature in the discharge zone was

measured quickly by a K-type thermocouple when the

discharge was stopped. The prepared catalysts were

expressed as P-x (x represents input power).

2.1.2. Conventional methodFor comparison, the Ni(NO3)2/g-Al2O3 sample was calcined at

700 �C for 6 h and reduced at 700 �C for 2 h with a 20%H2/N2

flow rate of 250 ml/min according to H2-TPR profile. The

resultant sample was denoted as C-700.

2.2. Characterizations

X-ray diffraction (XRD) patterns of the samples were ob-

tained on a D/Max2400 diffractor (Rigaku) with a Cu Ka ra-

diation at 40 kV and 40 mA. The mean size of nickel

crystallites was calculated from the broadening of Ni(111)

peak, according to ScherrereWarren equation [23].

Temperature-programmed reduction of hydrogen (H2-TPR)

measurement was performed in a conventional apparatus

equipped with a TCD detector. About 0.10 g catalyst was

pretreated at 300 �C for 30 min with a N2 flow rate of

60 ml/min before cooling down to 120 �C, then heated to

900 �C at a heating rate of 10 �C/min with a H2 flow rate of

60 ml/min. The basic properties of the catalysts were

measured by temperature-programmed desorption of CO2

(CO2-TPD) on the same apparatus as H2-TPR. The sample

(0.10 g) was first pretreated at 300 �C for 2 h in a N2 stream of

60 ml/min. After cooling down to 120 �C, the sample was




Fig. 1 e Schematic diagram of the apparatus for catalyst

preparation by H2 DBD (1. gas inlet; 2. gas outlet; 3. high

voltage electrode; 4. ground electrode; 5. catalyst sample).

i n t e rn a t i o n a l j o u rn a l o f h y d r o g e n en e r g y x x x ( 2 0 1 4 ) 1e8 3

exposed in CO2 atmosphere for 30 min. Then the sample

was purged with N2 until the baseline was steady. Finally,

the CO2-TPD was carried out with a ramp of 10 �C/min from

120 �C to 900 �C under the N2 flow rate of 60 ml/min. The

specific surface area and pore volume of the catalysts were

measured by N2 adsorption/desorption using ASAP 2010

Micromeritics instrument at �196 �C. The samples were

outgassed at 300 �C for 4 h prior to adsorption. Transmission

electron microscopy (TEM) images of the fresh and used

catalysts were acquired with FEI Tecnai G2 20 instrument.

The amount of carbon deposit on the spent catalysts was

measured by TG/DTG analysis on a Mettler Toledo TGA/

SDTA851e. About 20 mg of the sample was placed in a

ceramic crucible and heated from room temperature to

800 �C with a heating rate of 10 �C/min under air flow rate of

60 ml/min.

Table 1 e Temperatures in the discharge region underdifferent input power.a

Input Power (W) 20 40 60 80 100

Temperature (�C) 150 270 380 430 480

a Quickly measured by a K-type thermocouple when the discharge

is stopped.

2.3. Catalytic performance

The CRM reactionwas carried out in a stainless steel fixed-bed

reactor with an inner diameter of 8 mm at atmospheric

pressure. 0.40 g catalyst placed in the center of the reactor was

first heated to 700 �C under N2 of 200ml/min, then the gaseous

mixture of CO2 (80 ml/min), CH4 (80 ml/min) and N2 (200 ml/

min) with a volume ratio of 2/2/5 instead of N2 was fed into the

reactor, along with a total volumetric hourly space velocity

(VHSV) of 54,000 ml/(h gcat). The products were analyzed by

gas chromatograph (GC 7890Ⅱ) equipped with a thermal con-

ductivity detector (5 A molecular sieve packed column) and a

flame ionization detector (GDX 502 packed column). The

conversions of CH4 and CO2, and H2/CO ratio were calculated

according to the following equations:

Conversion of CH4 ð%Þ ¼ FCH4; in� FCH4; outFCH4; in

� 100% (1)


Conversion of CO2 ð%Þ ¼ FCO2; in� FCO2; outFCO2; in

� 100% (2)

H2=CO ratio ¼ Mol of H2 producedMol of CO produced

(3)

where FCH4; in, FCH4; out, FCO2; in and FCO2; out represent the

volume of CH4 and CO2 of the inlet and outlet, respectively.

3. Results and discussion

3.1. XRD and H2-TPR profiles of catalysts

The effect of input power on the structure and properties of P-

x catalysts prepared by H2 plasma treatment of Ni(NO3)2/g-

Al2O3 precursor was examined. The results showed that the

input power obviously affected the appearance color of the

samples (not shown in the paper). When the input power in-

creases from 20W to 40W, the sample changes from greenish

of P-20 to gray, which means that Ni(NO3)2 supported on the

Al2O3 has been partly decomposed to NiO under the effect of

plasma [24]. It can be seen from Table 1 that the temperature

of discharge region is about 270 �C, which is beneficial to the

decomposition of Ni(NO3)2. With further increasing input

power, the powder became black, meaning that parts of Ni

oxides were reduced to Ni metal by H2 plasma, which is

further confirmed by the XRD results in Fig. 2(a).

From the XRD patterns of P-x samples treated at different

input powers in Fig. 2(a), it can be seen that the P-20 sample

has obvious characteristic peaks of Al2O3 with 2q being 37.4�

and 67.3�, and small patterns ascribed to NiO species at 37.2�,43.5� and 62.9�. Nometal Ni phases (44.5�, 51.8� and 76.4�) were

identified, indicating that NiO was not reduced at low input

power. Additionally, weak peaks at 32.0� and 39.0� ascribed to

Ni2O3 species were also detected. With increasing the input

power, the peak of NiO at 37.2� becomes weaker and weaker,

while the intensity of Ni(111) peak at 44.5� gradually increases.

When the power increases to 120 W, the peak of Ni metal at

51.8� is also detected on P-120 catalyst, which means that

more Ni metals are reduced and the reduction degree of

sample increases with the input power.

H2-TPR profiles shown in Fig. 2(b) further verify the

reduction of nickel oxides on Al2O3 support. Sample P-20 has

two obvious peaks of H2 consumption. One is at 240 �Cascribed to the reduction of Ni2O3 species and another is at

560 �C due to NiO reduction [25]. With the increase of input

power, the peak at 240 �C disappears and the peak intensities

at high temperature gradually decrease, suggesting the in-

crease of input power leads to the enhancement of reduc-

ibility by H2 plasma, and many Ni oxides have been reduced.




Fig. 2 e XRD patterns (a) and H2-TPR profiles (b) of P-x catalysts treated by H2 DBD at different input power.


Shang et al. thought that higher input power can supplymany

high-energy electrons to activate the hydrogenmolecules and

promote the action between catalyst precursor and large

amount of H atoms in plasma process, further improving the

reduction degree [26]. Compared with the C-700 catalyst pre-

pared by traditional calcination and reduction of H2 at 700 �C,the P-120 sample demonstrates similar hydrogen consump-

tion peak below 500 �C. However, slightly more hydrogen

consumption at above 600 �C than that of C-700 suggests that

some NiO species are difficultly reduced owing to the inter-

action of NieO with the aluminum ions of the support. The

characterization results of XRD and H2-TPR suggest that

Ni(NO3)2/g-Al2O3 precursor can be directly decomposed and

further reduced to Ni/g-Al2O3 catalyst by use of H2 DBD

plasma at the appropriate input power.

3.2. Catalytic performance of P-x catalysts

CO2 reforming of methane on the P-x catalysts prepared with

different input powers was investigated and the results are

shown in Fig. 3. It can be seen from Fig. 3(a) that P-20 and P-40

catalysts have low and similar methane conversions, which is

mainly related with lower reduction degree. When increasing

the input power to 80W, the initial methane conversion of the

catalyst increases although it is lower than the thermody-

namic conversion (80.6%) and the stabilities are also

enhanced. However, when further increasing the input power,

Fig. 3 e Catalytic activity of catalysts prepared by H2 plasma at d

velocity: 54,000 ml/h gcat).


the P-100 and P-120 catalysts have similar but lower methane

conversion than P-80 sample despite high reduction degree.

From the conversion of CO2 in Fig. 3(b), the P-80 catalyst has

high conversion and good stability. It is analyzed that, at high

input power (e.g.100 W), the temperature of the electrons

themselves is far away from 480 �C (see Table 1) of discharge

region measured by thermocouple, which not only results in

the enhancement of reduction degree, but also accelerates the

sintering of active metallic Ni. Considering catalytic perfor-

mances and economy aspects, in the following studies, 80 W

was chosen as the input power for the preparation of catalyst.

3.3. Comparison of catalytic performances on P-80 andC-700 sample

To compare the catalytic performances of the catalysts pre-

pared by H2 DBD plasma and traditional method, P-80 and C-

700 samples were chosen and used in the CRM reaction at

different temperature. The results in Fig. 4 show that the

conversions of CH4 and CO2 increase with the reaction tem-

perature because CO2 reforming of methane is an endo-

thermic reaction. The conversion of CO2 is always higher than

that of CH4, suggesting that the reverse wateregas shift re-

action occurs [22,27]. However, at the same reaction temper-

ature, the P-80 catalyst treated by H2 plasma at 80 W always

exhibited higher catalytic activities and better stability (see

Fig. 5) than C-700 catalyst. It can be seen from Fig. 5(c) that H2/

ifferent input power (700 �C; CH4:CO2:N2 [ 2:2:5(vol.); space




Fig. 4 e Conversions of CH4 (a) and CO2 (b) of C-700 and P-80 samples at different temperature (CH4/CO2/N2 [ 2/2/5(vol.);

space velocity [ 54,000 ml/h gcat; Ni loading 10%).

Fig. 5 e Conversions of CH4 (a) and CO2 (b) and H2/CO ratio (c) of C-700 and P-80 catalysts at 700 �C (CH4:CO2:N2 [ 2:2:5(vol.);

space velocity [ 54,000 ml/h gcat; Ni loading 10%).


CO ratio on two catalysts is less than the theoretic value of

unit, further confirming the occurrence of reverse wateregas

shift reaction in CRM. Compared with C-700, the P-80 exhibi-

ted higher H2/CO ratio.

To explore the reasons for different catalytic perfor-

mances, two catalysts were characterized by N2 adsorption,

XRD, CO2-TPD and TEM analyses. The results by N2 adsorption

in Table 2 show that P-80 sample has slight larger surface area

and similar pore volume than C-700 catalyst. From the XRD

patterns in Fig. 6(a), it can be seen that P-80 catalyst exhibits

broader andweaker characteristic peaks ascribed to themetal

Ni phasewith 2q being 44.5�, 51.8� and 76.4� than C-700 sample

Table 2 e eTextural properties and Ni particle sizes of P-80 an

Catalysts Textural properties

SBET (m2 g�1) Vtot (cm3 g�1) Redu

P-80 179 0.397 4

C-700 141 0.396 10

a Calculated from the Ni(111) peak of XRD patterns according to Scherreb Reaction at 600 �C for 6 h.c 650 �C for 6 h.d 700 �C for 6 h.e 700 �C for 32 h.


in the XRD patterns, indicating smaller Ni size and better

dispersion on P-80 catalyst [22,25]. Table 2 shows that the

mean Ni particle size of the P-80 catalyst treated by H2 DBD is

4.4 nm, which is near to the size about 5 nm of Ni/g-Al2O3

prepared by plasma-assisted calcination and reduction

method with atmospheric high frequency cold plasma jet

[20,26], but obviously smaller than 10.3 nm of C-700 reduced

by traditional method, which is well accordant with the re-

sults by TEM images in Fig. 7. Compared with C-700 sample,

the fresh P-80 catalyst shows smaller size of nickel particle

and higher Ni dispersion (see Fig. 7(a) and (b)). Shang et al. [26]

thought that small Ni metal size was ascribed to short

d C-700 catalysts.

Ni particle size (nm)a

ced Usedb Usedc Usedd Usede

.4 5.3 5.5 5.2 9.3

.3 13.4 12.2 13.6 14.2

reWarren equation.




Fig. 6 e XRD patterns (a) and CO2-TPD profiles (b) of C-700 and P-80 samples.


treatment time in plasma process instead of several hours in

conventional decomposing and reducing the catalyst precur-

sor of Ni(NO3)2/g-Al2O3, which effectively avoided sintering

and aggregation of Ni particles. However, it can be seen from

Table 2 that the active Ni metal size increases with the reac-

tion time even at low reaction temperature of 600 �C. Afterreaction of 32 h, the mean particle sizes of P-80 and C-700

samples increased from 4.4 nm to 9.3 nm and 10.3 to 14.2 nm,

respectively, which can also be confirmed by the TEM images

Fig. 7 e TEM images of fresh C-700 (a), fresh P-80 (b) a


in Fig. 7(c)e(d). After 6 h, the Ni size of spent P-80 sample

almost has no obvious increase, and well dispersed on the

Al2O3 support. However, the particle size increased to near

10 nm after 32 h, although it is still smaller than that of fresh

C-700 catalyst. Therefore, it can be concluded that the

decrease of catalytic activities is mainly attributed to the

sintering of metallic Ni to form larger Ni particles. Higher

catalytic activities and better stability of P-80 are mainly

related with smaller Ni sizes.

nd spent P-80 catalysts after 6 h (c) and 32 h (d).




Fig. 8 e TG-DTG curves of C-700 and P-80 catalysts after reaction time of 6 h (a) and 32 h (b) at 700 �C.


The basic properties of the Ni-based catalysts are also one

of the important factors for different catalytic performances.

Fig. 6(b) shows the CO2-TPD profiles of two catalysts. Gener-

ally, it is considered that the profiles can be differentiated both

in the integral area of the profiles and the shift of peak tem-

perature. The former corresponds to the amount of basic sites

and the latter indicates the strength of the basic sites. CO2

molecules adsorbed on weaker basic sites are easily desorbed

at low temperature and those adsorbed on strong basic sites

require high desorbed temperature. It can be found from

Fig. 6(b) that both catalysts show three desorption peaks,

indicating that there are three kinds of basic sites. Comparing

with C-700 sample, P-80 catalyst has more total basic amount.

Moreover, the peak temperature of C-700 catalyst prepared by

traditional method is above the reaction temperature of

700 �C, meaning that the reactant CO2 adsorbed on these sites

is relative difficultly desorbed in the reaction. However, the

temperature of 660 �C attributed to strong basic sites on P-80

catalyst is below 700 �C, which indicates that CO2 molecules

absorbed on the catalyst can be desorbed in the reaction

process, facilitating the CO2 reforming of methane. In addi-

tion, the adsorption of methane and carbon monoxide can be

also hindered for the competitive adsorption with CO2, and

will reduce the carbon deposit via carbon monoxide dispro-

portionation and methane decomposition. Thus, the carbon

deposit can be restrained, which can be confirmed by the TG

analysis in Fig. 8.

Fig. 8 shows the TG/DTG curves of C-700 and P-80 catalysts

after reaction for 6 h and 32 h at temperature of 700 �C. Theweight loss at the temperature region of 200e800 �C is

ascribed to combustion of deposited carbon [24]. It can be seen

from Fig. 8(a) that the P-80 catalyst has better anti-carbon

deposit performance in the first 6 h reaction. The amount of

coke is just 2.6%, obviously less than 16.2% of C-700 sample.

However, the P-80 exhibits quick increase of carbon deposit

rate in the following 26 h, which is from 2.6% to 12.5%, higher

than that from 16.2% to 21.2% of C-700 sample.What results in

the difference of carbon deposit rate? It is thought that the

increase of Ni particle sizes is maybe the main reason. Osaki

et al. [28] thought that the carbon formation proceededmainly

on larger Ni ensemble than 9.1 nm in CRM. From Table 2 and

Fig. 7(c), it is found that the Ni size of P-80 is obviously smaller

than the required ensemble of 9.1 nm after the reaction of 6 h

despite slight increase to 5.2 nm, so the amount of carbon

deposit is quite little. However, after 32 h of reaction, the Ni


particle increases to near 10 nm (see Fig. 7(d)) due to the sin-

tering at high temperature, which is beneficial to the carbon

formation and results in the quick increase of carbon deposit

on P-80 catalyst. As to the fresh C-700 catalyst, the average Ni

size of 10.3 nmmakes it higher carbon deposit even in the first

6 h. Nevertheless, the total amount of coke on P-80 sample is

still less than that on C-700 catalyst after 32 h. More basic sites

and weaker basicity of P-80 catalyst than C-700 sample are

probably another reason for better anti-carbon deposit

performance.

4. Conclusions

The Ni/g-Al2O3 catalyst for CRM reaction was prepared by

direct treatment of Ni(NO3)2/g-Al2O3 with DBD H2 plasma at

atmospheric pressure. The input power has an obvious effect

on the reduction degree and catalytic activities of Ni/g-Al2O3

catalysts. When the power is below 40 W, nickel nitrate was

just decomposed into Ni oxides without obvious reduction.

The reduction degree increases and the catalytic activities and

stability can be improvedwith increasing input power. But the

catalyst prepared at input power of above 80Whas the similar

catalytic performance. Compared than C-700 catalyst pre-

pared by traditional calcination and reductionmethod, the Ni/

g-Al2O3 sample prepared by H2 DBD plasma exhibits better

activity, stability and anti-carbon deposit performances,

which are mainly ascribed to smaller Ni particle size, more

basic sites andweaker basicity of P-80 catalyst. The increase of

Ni particle size at high temperature results in the decrease of

catalytic activities and the carbon deposit.

Acknowledgments

This work was supported by the Natural Science Foundation

of China (No. 20906009, 21176042), the National Basic

Research Program of China (973 Program), the Ministry of

Science and Technology, China (No. 2011CB201301), Inter-

national S&T cooperation and exchange programs of Min-

istry of S&T (No.2013DFG60060), Liaoning Province Education

Administration Fund (No. L2013028) and the Fundamental

Research Funds for the Central Universities (No.

DUT12JN05).





r e f e r e n c e s

[1] Liu CJ, Ye JY, Jiang JJ, Pan YX. Progresses in the preparation ofcoke resistant Ni-based catalyst for steam and CO2 reformingof methane. ChemCatChem 2011;3:529e41.

[2] Fan MS, Abdullah AZ, Bhatia S. Catalytic technology forcarbon dioxide reforming of methane to synthesis gas.ChemCatChem 2009;1:192e208.

[3] Muradov N, Smith F, T-Raissi A. Hydrogen production bycatalytic processing of renewable methane-rich gases. Int JHydrogen Energy 2008;33:2023e35.

[4] Ross JRH. Natural gas reforming and CO2 mitigation. CatalToday 2005;100:151e8.

[5] Garcıa-Dieguez M, Pieta IS, Herrera MC, Larrubia MA,Alemany LJ. Nanostructured Pt- and Ni-based catalysts forCO2-reforming of methane. J Catal 2010;270:136e45.

[6] Richardson JT, Garrait M, Hung JK. Carbon dioxide reformingwith Rh and Pt-Re catalysts dispersed on ceramic foamsupports. Appl Catal A-Gen 2003;28:69e82.

[7] Jang WJ, Jeong DW, Shim JO, Roh HS, Son IH, Lee SJ. H2 andCO production over a stable NieMgOeCe0.8Zr0.2O2 catalystfrom CO2 reforming of CH4. Int J Hydrogen Energy2013;38:4508e12.

[8] Daza CE, Moreno S, Molina R. Co-precipitated Ni-Mg-Alcatalysts containing Ce for CO2 reforming of methane. Int JHydrogen Energy 2011;36:3886e94.

[9] Liu CJ, Zou JJ, Yu KL, Cheng DG, Han Y, Zhan J, et al. Plasmaapplication for more environmentally friendly catalystpreparation. Pure Appl Chem 2006;78:1227e38.

[10] Halverson DE, Cocke DL. Ruthenium impregnation of plasmagrown alumina films. J Vac Sci Technol 1989;7:40e8.

[11] Phillips J. Plasma generation of supported metal catalysts. US5989648, 1999.

[12] Zou JJ, Zhang YP, Liu CJ. Reduction of supported noble-metalions using glow discharge plasma. Langmuir2006;22:11388e94.

[13] Pan YX, Liu CJ, Shi P. Preparation and characterization ofcoke resistant Ni/SiO2 catalyst for carbon dioxide reformingof methane. J Power Sources 2008;176:46e53.

[14] Zhu XL, Huo PP, Zhang YP, Cheng DG, Liu CJ. Structure andreactivity of plasma treated Ni/Al2O3 catalyst for CO2

reforming of methane. Appl Catal B-Gen 2008;81:132e40.[15] Zhao Y, Pan YX, Xie YB, Liu CJ. Carbon dioxide reforming of

methane over glow discharge plasma-reduced Ir/Al2O3

catalyst. Catal Commun 2008;9:1558e62.


[16] Wang ZJ, Zhao Y, Cui L, Du HY, Yao P, Liu CJ. CO2 reformingof methane over argon plasma reduced Rh/Al2O3 catalyst: acase study of alternative catalyst reduction via non-hydrogen plasmas. Green Chem 2007;9:554e9.

[17] Hu SJ, Long HL, Xu Y, Shang SY, Yin YX. Reductionmechanism of Ni/Al2O3 catalyst reduced by cold plasma jetfor carbon dioxide reforming of methane. Chin J Catal2011;32:340e4.

[18] Li ZH, Tian SX, Wang HT, Tian HB. Plasma treatment of Nicatalyst via a corona discharge. J Mol Catal A-Chem2004;211:149e53.

[19] Liu GH, Li YL, Chu W, Shi XY, Dai XY, Yin YX. Plasma-assisted preparation of Ni/SiO2 catalyst using atmospherichigh frequency cold plasma jet. Catal Commu2008;9:1087e91.

[20] Chai XY, Shang SY, Liu GH, Tao XM, Li X, Bai MG, et al.Characterization of Ni/g-A1203 catalyst prepared byatmospheric high frequency cold plasma jet for CO2

reforming of CH4. Chin J Catal 2010;31:353e9.[21] Kim SS, Lee H, Na BK, Song HK. Plasma-assisted reduction of

supported metal catalyst using atmospheric dielectric-barrier discharge. Catal Today 2004;89:193e200.

[22] Hua W, Jin LJ, He XF, Liu JH, Hu HQ. Preparation of Ni/MgOcatalyst for CO2 reforming of methane by dielectric-barrierdischarge plasma. Catal Commun 2010;11:968e72.

[23] Hou ZY, Yashima T. Small amounts of Rh-promoted Nicatalysts for methane reforming with CO2. Catal Lett2003;89:193e7.

[24] Cheng DG, Zhu XL, Ben YH, He F, Cui L, Liu CJ. Carbon dioxidereforming of methane over Ni/Al2O3 treated with glowdischarge plasma. Catal Today 2006;115:205e10.

[25] Zhang Y, Chu W, Cao WM, Luo CR, Wen XG, Zhou KL. Aplasma-activated Ni/a-Al2O3 catalyst for the conversion ofCH4 to syngas. Plasma Chem Plasma P 2000;20:137e44.

[26] Shang SY, Liu GH, Chai XY, Tao XM, Li X, Bai MG, et al.Research on Ni/g-Al2O3 catalyst for CO2 reforming of CH4

prepared by atmospheric pressure glow discharge plasmajet. Catal Today 2009;148:268e74.

[27] Meshkani F, Rezaei M. Ni catalysts supported onnanocrystalline magnesium oxide for syngas production byCO2 reforming of CH4. J Nat Gas Chem 2011;20:198e203.

[28] Osaki T, Mori T. Role of potassium in carbon-free CO2

reforming of methane on K-promoted Ni/Al2O3 catalyst.J Catal 2001;204:89e97.


http://refhub.elsevier.com/S0360-3199(14)00251-1/sref1

























































































































































co2 reforming of methane

Documents

n t e rn

co2 reforming of methanenig

t i o n

ising catalysts

practicalnibased catalysts

r t i c

e i n f oconsidering

edischarge hydrogen