CO2 reforming

Fuel Processing Technology 114 (2013) 69–74

Contents lists available at SciVerse ScienceDirect

Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc

Influence of pore distribution on catalytic performance over inverse CeO2/Co3O4 catalysts for CH4/CO2 reforming Shanghong Zeng, Xiaojuan Fu, Tiezhuang Zhou, Xiaoman Wang, Haiquan Su ⁎ Inner Mongolia Key Laboratory of Chemistry and Physics of Rare Earth Materials, School of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot 010021, China

a r t i c l e

i n f o

Article history: Received 27 July 2012 Received in revised form 15 March 2013 Accepted 20 March 2013 Available online xxxx Keywords: CeO2/Co3O4 Molar ratio Double pore distribution CH4/CO2 reforming

a b s t r a c t A series of inverse CeO2/Co3O4 catalysts with different Ce loading was prepared via the hydrothermal process and microemulsion method, and characterized by XRD, BET, H2-TPR and TGA–DSC techniques. The catalysts exhibited high activity and moderate H2 and CO selectivity for CH4/CO2 reforming under atmospheric pressure and 750 °C. The results showed that the CeO2/Co3O4 catalysts with double pore distribution could provide more active sites as well as better gas circulation channels, which could reduce the internal diffusion resistance and improve the catalytic performance for CH4/CO2 reforming. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Carbon dioxide reforming of methane to synthesis gas, which is a crucial intermediary in the chemical industry, has attracted interests from industrial and environmental perspectives in recent years. This reaction consumes two harmful greenhouse gases (CO2 and CH4) to produce valuable synthesis gas with a H2/CO ratio of about 1, which is adequate for hydroformylation and carbonylation reactions, as well as for methanol and Fischer–Tropsch syntheses [1–3]. However, the major drawback of this catalytic process recently remains the rapid deactivation of catalysts originating from the sintering of the metal active sites as well as the carbon deposition at hightemperature operation [4,5]. The research showed that most of the group VIII metals (Rh, Ru, Ni, Pt, Pd, Ir, Co, Fe) are more or less effective for the CH4/CO2 reaction [6–14]. To date, two main kinds of catalysts are employed for this reaction: the Ni-based and the noble metal-based catalysts [8,11,12]. Although cobalt catalysts have not been a focus of attention until recently, it has been revealed that cobalt showed considerable activity for the CH4/CO2 reaction, which suggests that cobalt could be a suitable metal [6,7,15]. Moreover, the literatures reported that CeO2 can effectively improve catalytic performance in CH4/CO2 reforming reaction [1,15]. Moreno et al. [1] reported that because of the oxygen-storage capacity of CeO2, Ni catalysts with Ce tended to be in better activity and less coking formation. Damyanova et al. [15] examined the influence of pretreatment temperature and CeO2 concentration on the morphology of Pt particles. The results showed ⁎ Corresponding author. Tel.: +86 471 4995006; fax: +86 471 4992981. E-mail address: [email protected] (H. Su). 0378-3820/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fuproc.2013.03.040

that the high stability of Pt/CeO2–ZrO2 catalysts was related to the close contact between Pt and CeO2. Here a series of CeO2/Co3O4 catalysts was synthesized in order to study the influence of different Ce loading on the pore distribution, catalytic performance and carbon deposition. 2. Experimental 2.1. Catalyst preparation The surfactant PEG (20000, A Johnson Matthey Company) was added into 0.4 M Co(NO3)2·6H2O solution (99% purity, Medicine group chemical reagent Co, LTD). The mixture was precipitated gradually by the 1.0 M Na2CO3 solution until the precipitation was complete (pH = 9–10), then stirred for 30 min. The obtained solution was transferred into a stainless steel autoclave with 100 ml-capacity Teflon liner and heated for 16 h at 150 °C. The precipitate was collected by filtration, and washed several times with distilled water and absolute ethanol. After drying overnight, the Co3O4 was synthesized by heating the precipitate at rate of 5 °C/min and keeping at 500 °C for 3 h in an air atmosphere. The CeO2/Co3O4 catalysts with different Ce/Co molar ratio were synthesized by the microemulsion method. The triton, n-heptane and Hexanol were used to prepare the microemulsion A, with the above Co3O4 support and 0.25 M Ce(NO3)3 (nce:nco = 1:1, 1:2, 1:3, 1:4, 1:5, 1:6 and 1:8). The microemulsion B contained tetramethyl ammonium hydroxide, triton, n-heptane and hexanol in some distilled water. Then, the microemulsion B was added into A gradually, and stirred for 24 h in a glass reactor. The precipitates were collected and washed several times with distilled water and absolute ethanol.

S. Zeng et al. / Fuel Processing Technology 114 (2013) 69–74

CeO

(311) (220)

(511)

(400)

(111)

2

Co 3 O 4

(440)

Quantity Adsorbed (cm3/g STP)

70

1:8

Intensity(a.u.)

1:6 1:5 1:4 1:3 1:2 (111) (220)

(200)

(311)

(331)

1:8Ce/Co 1:6Ce/Co 1:5Ce/Co 1:4Ce/Co 1:3Ce/Co 1:2Ce/Co

1:1 10

1:1Ce/Co 20

30

40

50

60

70

80 0.0

2 Theta (deg.)

0.2

0.4

0.6

0.8

1.0

Relative Pressure (P/P0)

dV/dw (cm3/g.A)

Fig. 1. X-ray diffraction patterns (XRD) of the CeO2/Co3O4 catalysts.

Finally, the products were dried and calcined at 500 °C for 3 h in an air atmosphere. The samples were marked as CeO2/Co3O4 (1:1), CeO2/Co3O4 (1:2), CeO2/Co3O4 (1:3), CeO2/Co3O4 (1:4), CeO2/Co3O4 (1:5), CeO2/Co3O4 (1:6), CeO2/Co3O4 (1:7) and CeO2/Co3O4 (1:8), respectively. 1:1 1:2 1:3 1:4 1:5 1:6 1:8

2.2. Catalyst characterization X-ray diffraction (XRD) patterns of the samples were carried on a MAC Science diffractometer equipped with a CuKα source (λ = 0.15406 nm) and a power setting of 40 kV and 100 mA. The patterns were recorded at room temperature in the air with a 2θ range from 10 to 80°. The Brunauer–Emmett–Teller (BET) surface area and pore structure of the catalysts were determined by nitrogen physisorption at liquid nitrogen temperature using a Micromeritics Apparatus (Model ASAP2020). The fresh CeO2/Co3O4 catalysts were degassed at 200 °C under vacuum before analysis. The pore size distribution and average pore volume were analyzed using the desorption branch of the N2 isotherm. H2-TPR was performed in the 10% H2/Ar gas mixture on an AutoChem 2920 Automated Catalyst Characterization System. The flow rate of the gas was 50 ml/min and the heating rate was 10 °C/min. The carbon deposition analysis on the spent catalysts was performed via a STA 409PC thermal analysis device in an air stream from room temperature to 900 °C with a heating rate of 10 °C/min.

1:1 1:2 1:3 1:4 1:5 1:6 100

Pore Wid

th (A)

1:8 1000

Fig. 2. N2 adsorption–desorption isotherms and pore size distribution curves of the CeO2/Co3O4 catalysts.

2.3. Activity evaluation The CH4/CO2 reforming was performed in a packed-bed tubular reactor. The reactor temperature was measured via a thermocouple positioned at the middle of catalyst bed. The amount of catalyst used in the reaction was 0.05 g with the particle size in the range

Table 1 Particle sizes and textural properties of the catalysts. Catalyst

Ce/Co molar ratio

Particle size (nm) d (Co3O4)

CeO2/Co3O4 CeO2/Co3O4 CeO2/Co3O4 CeO2/Co3O4 CeO2/Co3O4 CeO2/Co3O4 CeO2/Co3O4 a b c

(1:1) (1:2) (1:3) (1:4) (1:5) (1:6) (1:8)

1:1 1:2 1:3 1:4 1:5 1:6 1:8

19.6 10.8 18.0 14.3 16.6 15.0 12.6

nm nm nm nm nm nm nm

a

(CeO2) 10.6 19.3 9.7 10.6 6.0 6.2 5.9

Calculated from the Scherer equation according to the [311] diffraction peaks of Co3O4. Calculated from the Scherer equation according to the [111] diffraction peaks of CeO2. According to the pore size distribution curves of catalysts.

b

nm nm nm nm nm nm nm

BET (m2/g)

Pore size distributionc (nm)

Pore volume (cm3/g)

91 98 86 63 76 72 65

14 nm 18 nm 10 nm, 30 nm 9 nm, 30 nm 7 nm, 28 nm 1 nm, 26 nm 9 nm, 25 nm

0.453 0.451 0.379 0.301 0.269 0.264 0.242

from 45 to 75 μm, and it was diluted with the quartz sand. The catalysts were reduced in situ using 10% H2 in Ar stream at 650 °C for 1 h, and then fed with the reactant gas mixture of CH4 and CO2 for 5 h at a −1 GHSV of 8000 ml·gcat ·h −1. The molar ratio of CH4 and CO2 was 1:1 and the reaction temperature was 750 °C. The products and reactants were analyzed with an online SP6890 gas chromatograph, and TDX-01 column was used to separate CO2, CH4, H2, and CO. 2.4. Calculation equations of conversion and selectivity The CH4 and CO2 conversion as well as H2 and CO selectivity (all calculated in units of mol %) were defined as follows:

71

H2 consumption (a.u.)

S. Zeng et al. / Fuel Processing Technology 114 (2013) 69–74

1:8 1:6 1:5 1:4 1:3 1:2

XCH4 ð% Þ ¼

XCO2 ð% Þ ¼

SH2 ð% Þ ¼

Fin  ICH4 ;in −Fout  ICH4 ;out

1:1

Fin  ICH4 ;in

100

300

400

500

600

700

800

900

Temperature (oC)

Fin  ICO2 ;in −Fout  ICO2 ;out Fin  ICO2 ;in

Fig. 4. TPR patterns of the CeO2/Co3O4 catalysts with different Ce/Co ratios.

Fout  IH2 ;out   2  Fin  ICH4 ;in −Fout  ICH4 ;out

3. Results and discussion 3.1. XRD analysis

Fout  ICO ;out    SCO ð% Þ ¼  Fin  ICH4 ;in −Fout  ICH4 ;out þ Fin  ICO2 ;in −Fout  ICO2 ;out where Fin/out was the flow rate in the feed or effluent of total components, and Ii was the molar fraction of component in the gaseous feed or effluent. Co0 active group

accumulation hole

CeO2

200

A

Co

gas channels

Co0 active group

accumulation hole

B

Co

Fig. 1 showed the XRD patterns of different CeO2/Co3O4 catalysts. After calcination at 500 °C the catalysts exhibited crystalline features of Co3O4 spinel and CeO2 fluorite. For Co3O4 supports, the 2θ values of reflections appeared at 19.03°, 31.28°, 36.95°, 45.05°, 59.36° and 65.21°, respectively corresponding to (111), (220), (311), (400), (511) and (440) planes of the spinel structure. For CeO2, the 2θ values of reflections were 28.57°, 33.01°, 47.56°, 56.24°, and 76.70°, respectively attributed to (111), (200), (220), (311) and (331) planes of the cubic fluorite structure. It was clear that the intensity of CeO2 peaks became weaker with the decrease of Ce/Co molar ratio. Table 1 listed a detailed analysis about the crystallite sizes calculated from the Scherer equation. The crystallite sizes of CeO2 and Co3O4 gradually decreased with the decrease of Ce/Co molar ratio, suggesting that the low Ce/Co molar ratio was favorable for the formation of small Co3O4 and CeO2 crystallites by the microemulsion method. In the pretreatment process, the Co3O4 was reduced into metallic cobalt, which was the key active component for CH4/CO2 reforming. 3.2. Textural property analysis

CeO2 gas channels

Co0 active group CeO2 microparticle

accumulation hole

Table 1 summarized the textural properties of CeO2/Co3O4 catalysts. It was noted that the BET surface area and pore volume of catalysts all decreased with the decrease of Ce/Co molar ratio. Fig. 2 showed the N2 adsorption–desorption isotherms and pore size distribution curves of CeO2/Co3O4 catalysts. The isotherms were type-IV isotherms according to five kinds of isotherms from BDDT pore model, corresponding to

C Co Table 2 The coke deposition of the CeO2/Co3O4 catalysts.

CeO2 gas channels

Catalyst

Catalyst particles Reaction gas molecules Single active site Fig. 3. Schematic diagram of pore distribution over the CeO2/Co3O4 catalysts: (A) CeO2/Co3O4 (1:1 and 1:2); (B) CeO2/Co3O4 (1:3–1:6); (C) CeO2/Co3O4 (1:8).

CeO2/Co3O4 CeO2/Co3O4 CeO2/Co3O4 CeO2/Co3O4 CeO2/Co3O4 CeO2/Co3O4 CeO2/Co3O4

(1:1) (1:2) (1:3) (1:4) (1:5) (1:6) (1:8)

Total reduction degree of Co3O4

Reaction Temp. and time

Coke deposition (wt.%)

0.8938 0.9073 0.9662 0.9743 0.9350 0.9159 0.9526

750 750 750 750 750 750 750

40.84% 53.11% 61.21% 61.04% 68.62% 61.52% 47.33%

°C, °C, °C, °C, °C, °C, °C,

5 5 5 5 5 5 5

h h h h h h h

72

S. Zeng et al. / Fuel Processing Technology 114 (2013) 69–74

100

100

98 96

CO2 Conversion (%)

CH4 Conversion (%)

94 92 90 88 86

40 30

90

1:1 1:2

50

1:3

40

1:4

30

20

20 0

1

2

3

4

5

0

1

2

3

Time(h) 40

5

36

1:5

35

33

CO Selectivity(%)

H2 Selectivity (%)

4

Time(h)

30 25 20 15

CeO2

1:6

30

1:8

27 24 21 18

2 0

1

2

3

4

5

0

1

2

Time(h)

3

4

5

Time(h)

Fig. 5. Conversion and selectivity over the CeO2/Co3O4 catalysts at 750 °C reaction temperature.

3.3. TPR measurements TPR experiments were performed in the 10% H2/Ar gas mixture in order to study redox properties of the CeO2/Co3O4 catalysts. Pure Co3O4 has two reductive peaks at 300 °C and 357 °C, corresponding

1:8 1:6 1:5

DSC(mW/mg)

typical mesoporous solids. The pore structure was related to the shape of hysteresis loop on the adsorption–desorption isotherm. The hysteresis loop of CeO2/Co3O4 was H2 loop, a characteristic of porous materials with wide pore diameter. As shown in Fig. 2, it was evident that the pore size distribution curves gradually became wider with the decrease of Ce/Co molar ratio, indicating that the different size pores were formed with the change in crystallite sizes of CeO2 and Co3O4. The pore size distribution curves became double pore distribution from single pore distribution when the Ce/Co molar ratio decreased to 1:3–1:8 from 1:1 and 1:2. Fig. 3 presented the schematic diagram of pore distribution over the CeO2/Co3O4 catalysts. As mentioned in XRD measurements, the crystallite sizes of CeO2 and Co3O4 gradually decreased with the decrease of Ce/Co molar ratio, and TEM measurements showed that the CeO2 and Co3O4 particles were spherical in the catalysts, therefore the CeO2 and Co3O4 particles stacked the different size pores, which were closely related with the catalytic performance. The curves of CeO2/Co3O4 (1:1) and CeO2/Co3O4 (1:2) catalysts were single pore distribution (Fig. 3A), and the wide pore size was favorable for the gas diffusion. The curves of catalysts became double pore distribution when the Ce/Co molar ratio varying from 1:3 to 1:6 (Fig. 3B). The micropores could provide the more active sites, and the mesopores could offer the gas diffusion channels from the particle surface to the interior [16]. Further decreasing the Ce/Co molar ratio to 1:8, the interaction between CeO2 and Co3O4 became weaker in compare with the other catalysts.

1:4 1:3 1:2 1:1

200

300

400

500

600

700

Temperature (oC) Fig. 6. DSC curves of the spent catalysts under air atmosphere.

S. Zeng et al. / Fuel Processing Technology 114 (2013) 69–74

to the reduction of Co3O4 to CoO and CoO to Co [17]. Pure ceria is reduced at 480 °C and 750 °C, which are attributed to the reduction of surface ceria and bulk ceria, respectively [18]. Fig. 4 showed H2-TPR profiles of the CeO2/Co3O4 catalysts. The reduction peaks of Co3O4 to CoO named as α peaks appeared at 260–280 °C, indicating that the interaction between CeO2 and Co3O4 promoted the first step reduction of Co3O4 [4]. The overlapping peaks between 280 °C and 500 °C (β peaks) were attributed to the reduction of CoO to Co and surface ceria. The γ peaks at about 700 °C corresponded to the reduction of bulk ceria. The total reduction degree of Co3O4 via the calculation of separating peaks was listed in Table 2. It was noteworthy that most of Co3O4 was transformed into the metallic cobalt before pretreatment temperature of 650 °C and the total reduction degree of Co3O4 was higher than 90% except CeO2/Co3O4 (1:1), which could supply the active sites for CO2 reforming of CH4. Furthermore, the reduction degree of CeO2 over the CeO2/Co3O4 (1:1), CeO2/Co3O4 (1:2) and CeO2/Co3O4 (1:3) catalysts before 650 °C was 36.25%, 16.25% and 8.06%, respectively, indicating the presence of Ce3+/Ce4+ cycle for the samples with high CeO2 content, which could promote CO2 adsorption as well as C oxidation [1,2]. 3.4. Catalytic performance Fig. 5 showed the catalytic performance of CeO2/Co3O4 catalysts. The catalysts exhibited high activity and moderate H2 and CO selectivity, but ceria has weak catalytic performance, suggesting that the Co0 particles were the key active sites for CO2 reforming of CH4. CO2 conversion was higher than CH4 conversion, which was attributed to the occurrence of reverse water gas-shift reaction and elimination carbon reaction (C + CO2 → 2CO) during CO2/CH4 reforming, leading to the decrease of H2 selectivity. As shown in Fig. 5, the CeO2/Co3O4 (1:3), CeO2/Co3O4 (1:4), CeO2/Co3O4 (1:5) and CeO2/Co3O4 (1:6) catalysts presented better catalytic performance because they were double pore distribution (Fig. 3B) and could give more active sites as well as better gas diffusion channels. It was consistent with the results of textural property analysis, and it was similar with the report about bimodal silica [16]. 3.5. Carbon deposition analysis Table 2 listed the coke deposition of CeO2/Co3O4 catalysts from TG results. It was clear that the amount of coke deposition was not only related to the activity of catalysts, but also had a close connection with the pore size distribution of catalysts. The higher concentration of active sites could easily form carbon deposition. On the contrary, the good gas diffusion which promoted CO2 molecules to react with C coming from CH4 dissociation could resist the carbon deposition of active sites [19]. When the Ce/Co molar ratio was equal to 1:1 and 1:2, the addition of high content CeO2 could effectively prevent carbon deposition because CeO2/Ce2O3 participated in the redox reactions with surface carbon (TPR measurements), making a low carbon formation [7]. The catalysts with double pore distribution possessed more active sites which were close to each other over the Co 0 particle active group when the Ce/Co molar ratio varying from 1:3 to 1:6, resulting in a high carbon deposition. For CeO2/Co3O4 (1:8), the weakest activity led to the lower carbon deposition compared with the other catalysts. Furthermore, as shown in Fig. 6, there was an exothermic peak on the DSC curve of the spent catalysts under air atmosphere, which was the weight loss of carbon combustion, indicating that there was one kind of deposition carbon on the catalysts. It was different from the report of literatures about active carbon (low temperature) and inert carbon (high temperature) [3,4,20]. The CeO2/Co3O4 catalysts still maintained high activity after 5 reaction hours in spite of the large amount of carbon deposition, as shown in Table 2, indicating

73

that the deposition carbon was the active carbon which could be removed from the surface of active sites via the elimination carbon reaction during CO2/CH4 reforming. Furthermore, the Co0 active groups with large size could prevent effectively the oxidation of metal particles and slow down the deactivation of CeO2/Co3O4 catalysts. 4. Conclusions The inverse CeO2/Co3O4 catalysts were used for CH4/CO2 reforming. From XRD, The crystallite sizes of CeO2 and Co3O4 gradually decreased with the decrease of Ce/Co molar ratio, suggesting that the low Ce/Co molar ratio was favorable for the formation of small Co3O4 and CeO2 crystallites by the microemulsion method. TPR showed that most of Co3O4 was transformed into metallic cobalt under the pretreatment temperature of 650 °C. The activity data and TG results indicated that the deposition carbon was the active carbon which could be removed from the surface of active sites via the elimination carbon reaction during CO2/CH4 reforming. Furthermore, the Co0 active groups with large size could prevent effectively the oxidation of metal particles and slow down the deactivation of CeO2/Co3O4 catalysts. In conclusion, the CeO2/Co3O4 catalysts with double pore distribution could give more active sites as well as better gas circulation channels, which could reduce the internal diffusion resistance and improve the catalytic performance for CH4/CO2 reforming. Acknowledgments The authors would like to acknowledge the National Natural Science Foundation of China (grant no. 21061008) and the Natural Science Foundation of Inner Mongolia (grant nos. 2010ZD01, 2010BS0202). References [1] M.S. Moreno, F. Wang, M. Malac, T. Kasama, C.E. Gigola, I. Costilla, M.D. Sánchez, Electron microscopy study of CeOx–Pd/α-Al2O3 catalysts for methane dry reforming, Journal of Applied Physics 105 (2009), (083531-083531-6). [2] G.S. Gallego, J.G. Marín, C. Batiot-Dupeyrat, J. Barrault, F. Mondragón, Influence of Pr and Ce in dry methane reforming catalysts produced from La1 − xAxNiO3 − δ perovskites, Applied Catalysis A: General 369 (2009) 97–103. [3] S. Damyanova, B. Pawelec, K. Arishtirova, J.L.G. Fierro, C. Sener, T. Dogu, MCM-41 supported PdNi catalysts for dry reforming of methane, Applied Catalysis B: Environmental 92 (2009) 250–261. [4] S.Y. Foo, C.K. Cheng, T.H. Nguyen, A.A. Adesina, Kinetic study of methane CO2 reforming on Co–Ni/Al2O3 and Ce–Co–Ni/Al2O3 Catalysts, Catalysis Today 164 (2011) 221–226. [5] K. Takanabe, K. Nagaoka, K. Nariai, K. Aika, Influence of reduction temperature on the catalytic behavior of Co/TiO2 catalysts for CH4/CO2 reforming and its relation with titania bulk crystal structure, Journal of Catalysis 230 (2005) 75–85. [6] K. Omata, N. Nukui, T. Hottai, Y. Showa, M. Yamada, Strontium carbonate supported cobalt catalyst for dry reforming of methane under pressure, Catalysis Communications 5 (2004) 755–758. [7] Ş. Özkara-Aydınoğlu, A.E. Aksoylu, Carbon dioxide reforming of methane over Co–X/ZrO2 catalysts (X = La, Ce, Mn, Mg, K), Catalysis Communications 11 (2010) 1165–1170. [8] B. Fidalgo, A. Arenillas, J.A. Menéndez, Mixtures of carbon and Ni/Al2O3 as catalysts for the microwave-assisted CO2 reforming of CH4, Fuel Processing Technology 92 (2011) 1531–1536. [9] M.V. Sivaiah, S. Petit, J. Barrault, C. Batiot-Dupeyrat, S. Valange, CO2 reforming of CH4 over Ni-containing phyllosilicates as catalyst precursors, Catalysis Today 157 (2010) 397–403. [10] A.J. Zhang, A.M. Zhu, B.B. Chen, S.H. Zhang, C.T. Au, C. Shi, In-situ synthesis of nickel modified molybdenum carbide catalyst for dry reforming of methane, Catalysis Communications 12 (2011) 803–807. [11] S. Therdthianwong, C. Siangchin, A. Therdthianwong, Improvement of coke resistance of Ni/Al2O3 catalyst in CH4/CO2 reforming by ZrO2 addition, Fuel Processing Technology 89 (2008) 160–168. [12] N. Wang, W. Chu, L.Q. Huang, T. Zhang, Effects of Ce/Zr ratio on the structure and performances of Co–Ce1 − xZrxO2 catalysts for carbon dioxide reforming of methane, Journal of Natural Gas Chemistry 19 (2010) 117–122. [13] Y.H. Hu, Solid-solution catalysts for CO2 reforming of methane, Catalysis Today 148 (2009) 206–211. [14] V.M. Gonzalez-Delacruz, F. Ternero, R. Pereñíguez, A. Caballero, J.P. Holgado, Study of nanostructured Ni/CeO2 catalysts prepared by combustion synthesis in dry reforming of methane, Applied Catalysis A: General 384 (2010) 1–9.

74

S. Zeng et al. / Fuel Processing Technology 114 (2013) 69–74

[15] S. Damyanova, B. Pawelec, K. Arishtirova, M.V.M. Huerta, J.L.G. Fierro, The effect of CeO2 on the surface and catalytic properties of Pt/CeO2–ZrO2 catalysts for methane dry reforming, Applied Catalysis B: Environmental 89 (2009) 149–159. [16] A.Y. Khodakov, W. Chu, P. Fongarland, Advances in the development of novel cobalt Fischer–Tropsch catalysts for synthesis of long-chain hydrocarbons and clean fuels, Chemical Reviews 107 (2007) 1692–1744. [17] H.Q. Su, S.H. Zeng, H. Dong, Y. Du, Y.L. Zhang, R.S. Hu, Pillared montmorillonite supported cobalt catalysts for the Fischer–Tropsch reaction, 46 (2009) 325–329.

[18] S.H. Zeng, L. Zhang, X.H. Zhang, H. Pan, M. Zhang, H.Q. Su, Study on catalytic performance of Ni/CexZr1 − xO2 catalysts for carbon dioxide reforming of methane, Journal of Rare Earths 29 (2011) 422–427. [19] T. Huang, W. Huang, J. Huang, P. Ji, Methane reforming reaction with carbon dioxide over SBA-15 supported Ni–Mo bimetallic catalysts, Fuel Processing Technology 92 (2011) 1868–1875. [20] K. Tomishige, O. Yamazaki, Y.G. Chen, Development of ultra-stable Ni catalysts for CO2 reforming of methane, Catalysis Today 45 (1998) 35–39.