(583dz) Evaluation of Surface Oxidized SUS304 As Tetradecane CO2 Reforming Catalyst

Evaluation of
Surface Oxidized SUS304 as Tetradecane CO₂ Reforming Catalyst

de la Rama, S.R.^a, Yamada,
H.^b, and Tagawa, T.^c

Department of
Chemical Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan

Introduction

Continuous
research in improving the economic, environmental and energy aspects of
catalysis has led to better revenues, waste-management, and efficiency.  Catalytic
dry methane reforming (DMR) provides an avenue of producing renewable energy
from biomass while using two of the most harmful greenhouse gases.  At present,
this technology was reported to be applied in a nearly industrial scale [1]. 
Also, supported nickel catalysts are being intensively studied and improved as
a substitute to the scarce and expensive noble metal catalysts.  However, supported
nickel catalysts are highly sensitive towards coke poisoning and sintering [2, 3,
4]; thus, developing a catalyst with high coke resistant and strong mechanical
strength is important. 

The
most common support for nickel catalysts is Al₂O₃ [5]; however
the formation of the catalytically inactive NiAl₂O₄ phase
[2] led to the development of other support materials and doping with alkali [4],
alkaline-earth [2,6] and basic iron-containing minerals [7] were reported to
prevent coking and promote reforming.  Further, O₂ pretreated
Ni/β-SiC showed higher activity and complete inhibition of carbon
nanofilaments [8].  In addition, Ni particle size [6], dispersion [2, 6] and a
strong nickel-support interaction [2, 7, 9] are also important in designing a
catalyst that is resistant towards sintering and carbon formation.  It was also
reported that upon oxidation of nickel-containing alloys, reducible nickel is
optimally dispersed on its surface which renders the alloy active towards
reforming reaction [10, 11].

As
reported in our screening tests, surface-oxidation pretreatment had rendered
Ni-containing alloys active towards hydrocarbon reforming [12, 13].  In this study,
surface-oxidized austenitic SUS304 (Ni: 10-14 wt%, Cr: 18-20 wt%, Fe: balance)
was tested as a CO₂ reforming catalyst.  Upon oxidation, the less
noble components of an alloy form a protective metal oxide scale that was
hypothesized to function both as a support material and a reaction precursor
while preventing carbon formation.  In addition, the catalytically active metal
was predicted to be highly dispersed on the metal oxide matrix while
maintaining a strong interaction between the support material and the dispersed
metal.  Tetradecane, a simple straight chain hydrocarbon, was selected as a
model compound of biomass gasification products and used to evaluate the
catalytic activity of the alloy for CO₂ reforming. 

Experimental Procedure

The
continuous flow reactor used in this study is shown consisted of an evaporator,
a quartz reactor (inner diameter: 1cm), an electrically heated furnace and a
temperature control system.  The upper end of the quartz reactor was connected
to the feed inlet while the lower end was connected to a gas sampling valve and
a condenser.

Surface
oxidation of SUS304 (outer diameter: 1/4in, length: 35cm) was conducted in O₂
for 2 hours at 3 different temperatures: 600, 730, and 1000°C.  For each
sample, 1 cm was cut, pressed, and subjected to surface analyses.  X-ray
diffraction patterns of the untreated, pretreated, and spent alloy tubes were
collected using RINT-2500TTR with CuKα while changes in morphology of the oxidized
tubes were determined using a scanning electron microscope (JSM-6330F).

To
compare the effects of oxidation temperatures on the catalytic activity of
SUS304, CO₂ reforming was conducted for 2 hours at 600,700 and 800°C
with tetradecane (1.0 μmol/s) and CO₂ (70.0 μmol/s) being automatically
pumped into the evaporator. 

After
determining the ideal oxidation and reaction temperatures, the effect of CO₂
concentration on the amount of carbon formed was examined; C₁₄H₃₀-CO₂
molar ratios of 1/14, 1/42, and 1/70 were specifically compared.  For both
steps, GC-TCD (GL Sciences GC-3200) was used to quantify H₂, CO, CO₂
and CH₄ in the product gas using Ar as carrier gas.

Results and Discussion

The
XRD patterns showed that metal oxide formation (α-Fe₂O₃)
took place when oxidation temperature was increased to 730°C; at 1000°C Cr₂O₃
and γ FeNi were also formed.  The SEM micrograph of SUS304 oxidized at
1000°C showed a porous structure with no distinguishing shape for the different
metal oxides formed.

Based
on the CO production rates, no reforming reaction took place at all reaction
temperatures using unoxidized SUS304 (Figure 1a) and SUS304 oxidized at 600°C
(Figure 1b) and 730°C (Figure 1c), respectively.  However, the presence of CH₄
and H₂ suggested that hydrocarbon cracking occurred at higher
reaction temperatures.  While SUS304 oxidized at 1000°C showed increasing
activity with increasing reaction temperature (Figure 1d).  Specifically, low
and unstable reactions were observed when at 600 and 700°C; while at 800°C good
and stable activity was observed.  Although hydrocarbon cracking also took
place, it was in a relatively minimal rate.  When the CO₂ flowrate
was respectively decreased to 42 and 14μmol/s, catalyst deactivation was observed;
however, the production rate of CH₄ remained stable.  This indicated
that CO₂ reforming and hydrocarbon cracking have different active
sites.

From
data gathered, it was confirmed that CO₂ flowrate is directly
proportional to CO production rate and stability.

	Legend:   ◆-CO   ■-H2   ●-CH4

 

Figure
1. Production rates of primary gases generated during CO₂ reforming
of C₁₄H₃₀ catalyzed with SUS304 that was a)untreated
b)oxidized at 600°C c)oxidized at 730°C and d)oxidized at 1000°C

References

[1]
I. Fechete, Y. Wang, J. Védrine, Catalysis Today, 189, 2-27 (2012)

[2] S.
Damyanova, B. Pawelec, K. Arishtirova, J.L.G. Fierro, International Journal of Hydrogen
Energy, 37, 15966-15975 (2012)

[3] S.
Sivasangar and Y.H. Taufiq-Yap, Advanced Materials Research, 364, 519-523
(2012)

[4] K.
Kang, H. Kim, I. Shim, H. Kwak, Fuel Processing Technology, 92, 1236-1243
(2011)

[5] J.
Gou, H. Lou, H. Zhao, D. Chai, X. Zheng, Applied Catalysis A: General, 273,
75-82 (2004)

[6] T.
Hayakawa, S. Suzuki, J. Nakamura, T. Uchijima, S. Hamakawa, K. Suzuki, T.
Shishido, K. Takehira, Applied Catalysis A: General, 183, 273-285 (1999)

[7] C.
Courson, L. Udron, D. Świerczyński, C. Petit, A Kiennemann, Catalysis
Today, 76, 75-86 (2002)

[8] D.L.
Nguyen, P. Leroi, M.J. Ledoux, C. Pham-Huu, Catalysis Today, 141, 393-396
(2009)

[9] Z.
Xu, Y. Li, J. Zhang, L. Chang, R. Zhou, Z. Duan, Applied Catalysis A: General,
210, 45-53 (2001)

[10] N.
Chikamatsu, T. Tagawa, S. Goto, Journal of Material Science, 30, 1367-1372
(1995)

[11] T.
Tagawa, S.R. de la Rama, S. Kawai, H. Yamada, 15^th International
Congress on Catalyst, Germany, 107-7377, July,2012

[12] S.R.
de la Rama, S. Kawai, H. Yamada, T. Tagawa, International Symposium on EcoTopia
Science '11, 10A03-13(7072), December, 2011

Acknowledgement

e-mail address: ^asrdelarama@yahoo.com, ^byamada@nuce.nagoya-u.ac.jp,

^ctagawa@nuce.nagoya-u.ac.jp