Advances in Ma terials Physics and Che mist ry, 2012, 2, 165-168
doi:10.4236/ampc.2012.24B043 Published Online December 2012 (htt p://www.SciRP.org/journal/ampc)
Hydrogen as Carbon Gasifying Agent During Gly c erol Steam
Reforming over Bimetallic Co-Ni Cataly st
Chin Kui C he ng, Rwi Hau Lim, Anabil Ub il , Sim Yee C hin, Jolius Gimbun
Faculty of Chemical & Natural Resources Engineering, Universiti Malaysia Pahang, Kuantan, Malaysia
Received 2012
ABSTRACT
Alumina-supported bimetallic cobalt-nickel catal yst h as been pr epared an d employed in a fixed-b ed reactor for the dir ect production
of synthesis gas from glycerol steam reforming. Physicochemical properties of the 5Co-10Ni/85Al2O3 catal yst were d eter mined fro m
N2-physisorption, H2-chemisorption, CO2 and NH3-temperature-programmed desorption measurements as well as X-ray diffraction
analysis. Both weak and s trong acid sit es are present on the catalyst sur face. The acidic: basic rat io is about 7. Carb on deposit ion was
evident at 923 K; addition of H2 however has managed to reduce the carbon deposition. Significantly, this has resulted in the incre-
ment of CH4 formation rate, consistent with the increased carbon gasification and methanation. Carbon deposition was almost
non-existent, particularly at 1023 K. In addition, the inclusion of hydrogen also has contributed to the decrease of CO2 and increase
of CO formation rates. This was attributed to the reverse water-gas-shift reaction. Overall, both the CO2:CO and CO2:CH4 ratios
decrease with the hydrogen parti al pressure.
Keywords: Carbon Deposition; Catalyst; Gasification; Glycerol; Steam Re forming
1. Introduction
The use of renewable feedstock is fast gaining attention in lieu
of the context of securing sustainable use of energy and pre-
serving the environment for the future generations. Considera-
ble effort has been devoted into applying green catalytic route
to co nvert renewable fe edstock su ch as biomass into commodi-
ty chemicals and clean bio-fuels. In particular, glycerol, also
known as 1,2,3-propanetriol, is produced in excess quantity in
the form of by-product during biodiesel synthesis. It constitutes
an approximately 10wt% of the total product. In an effort to add
value to glycerol as precursor for renewable and clean energy
production, it was steam-reformed at temperatures greater than
773 K to produce H2, CO and CO2 which are important ingre-
dients for the manufacture of a variety of industrial chemicals
[1,2]. The relevant r eactions are:
C3H8O3 + 3H2O → 3CO2 + 7H2 (1)
C3H8O3 → 3CO + 4H2 (2)
Carbon deposition is a perennial issue during glycerol steam
reforming. Cheng et al. [3] have reported a kinetic study of
carbon deposition during glycerol steam reforming over alumi-
na supported bimetallic Co-Ni catalyst. At least two types of
carbonaceo us sp ecies were depo sited on the cat alyst surface [ 3].
Sanchez and Comelli [4] published a paper on deactivation
process and regeneration technique during glycerol steam re-
forming over a Ni-alumina catalyst. A TPO characterized by a
main peak centered at 963 K was o btained [ 4] .
As a continuation to the previous works, this paper reports on
the adoption of H2 as co-reactant during glycerol steam re-
forming to encourage simultaneous carbon gasification. Results
on the effects of H2 addition towards carbon deposition and
product variation will be presented and elucidated in detailed.
2. Methodology
2.1. Catalyst Sy nthesis and Phy sic oche mical
Characterizat io n
Bimetallic 5Co-10Ni/85Al2O3 catalyst was prepared via co-
impregnation of cobalt and nickel nitrate solutions on γ-alumina
which has been preheated at 873 K for 6 h. Subsequently, the
slurry catalyst was oven-dried at 403 K for overnight and then
calcined at 873 K for 6 h to obtain oxide metals. For the physi-
cochemical char acteri zatio n , BE T surface area an d po re volume
were obtained from liquid N2 physisorption on the Quantach-
rome Autosorb-1 unit. The metal catalyst dispersion and sur-
face area were determined from Micromeritics ASAP 2000 via
H2-chemisorption technique. The crystallography of catalyst
was examined via XRD techni que via s can rate o f 4 o min-1 from
10o to 80o. Carbon content of collected samples post-reforming
reaction, was determined using a Shimadzu Solid Sample
Module (SSM-5000A) based on combustion at 1173 K.
2.2. Reaction Studies
Figure 1 shows the experimental set-up for the current experi-
mental work. Reaction runs were conducted in a stainless-steel
fixed bed reactor under minimal influence from physical trans-
port limitations. 60 wt% aqueous glycerol solution was pre-
pared and directly injected into a 10-mm diameter fixed-bed
reactor system using 50 mL syringe pump reacting at tempera-
tures between 923 and 1023 K. Prior to reaction, catalyst was
reduced in-situ using 50 ml min-1 of H2 for 2 h. Subsequently,
H2 was co-added to the reactor as gasifying reactant. Total
GHSV for the experiment was co ntro lled at 5×104 mL g-1 h-1.
For fixed-bed reactor operation with no recycle stream,
Levenspiel [5] s hows that the reaction rate is go verned by:

C. K. CHENG ET AL.
166
-rA = (yA,feed × Ffeed × X)/ m (3)
where −rA = reaction rate of reactant A (mol s-1 gcat-1)
yA, feed = mole fraction of component A in the reactant
stream
Ffeed = tot al molar flowrat e (mol s-1)
X = conversi on of species A
m = mass of catalyst (gcat)
For the purpose of comparison with other catalysts, specific
activity, defined as the rate of reaction per unit active area of-
fers a better index. Thus, for metal-catalysed reactions such as
steam reforming, the weight-based rate was divided by the ac-
tive metal area (obtained from H2-chemisorption) to give the
specific reaction rate of the catalyst. H ence,
i
i
calc
r
rSA
∧
=
(4)
where
i
r
∧
= specific reactio n rate of species i (mol m-2 s-1)
ri = reaction rate of sp ecies i (mol s-1 gcat-1)
SAcalc = metal surface area (m2 gcat-1)
3. Results and Discussion
3.1. Physicochemical Properties of Fresh Catalysts
As shown in Table 1, fresh cal cined catalyst exhibits BET sur-
face area and pore volume of 166 m2 gcat-1 and 0.57 cm3 gcat-1
respectively. The dispersion of metal was rather low, probably
due to the high metal loading (15 wt%) employed in the current
study. H2-chemisorption analysis revealed that the average
particl e diameter was 1 36.0 nm with metal sur face area of 0 .74
m2 gcat-1. NH3- and CO2-TPD measurements revealed the exis-
tence of two peaks, representing both strong and weak acid/
basic sites (cf. Table 2). Overall, the concentration of acid site
was higher than the basic site in ratio ranging from 7.0 to 7.3.
The diffractogram shown in Figure 2 for calcined catalyst
ind icates t he pres ence o f Co3O4 and NiCo2O4 at 2θ = 33 .0o, and
an overlapped peak consisting of CoAl2O4 and NiAl2O4 at 38.0o.
In addition, the two peaks at 2θ of 44.0o and 46.5o for the bi-
metallic catalyst may be attributed to the existence of NiO,
NiAl2O4 and CoAl2O4. The small peak at 2θ = 59.0o represents
NiAl2O4 and CoAl2O4 phase. Furthermore, another small dif-
fractio n peak at 2θ of 62.0o is attributed to NiO. The peak at 2θ
= 65.0o corresponds to the presence of composites of Co3O4 and
CoAl2O4 while the diffraction peak at 68.0o is assigned to Ni-
Al2O4.
3.2. Reaction Studies
Reaction results in Figure 3 show that with the addition of H2,
the CO2 and CO formation rates varied in reverse trend sug-
gesting that the presence of H2 in the feed encouraged the re-
verse water-gas-shift, viz. H2 + CO2 ↔ CO + H2O. In addition,
it seems that the CH4 formation rates increased with Phydrogen
ind icating an increase in methane p r oduction activit y.
Figure 1. Experimental set up for glycerol steam reforming.
Table 1. Physicochemical attribute of calcined bimetallic Co-Ni/
Al2O3 catalyst.
Properties 5Co-10Ni/85Al2O3
BET surface area (m2 gcat-1) 166
Pore v o l ume (cm3 gcat-1) 0.57
Dispersion (%) 0.74
Metal surface area (m2 gcat-1) 0.74
Active part i cle di ameter (nm) 136.0
Tabl e 2. Acid/ base properties of fresh Co-Ni/Al2O3 catalyst.
Properti es 5Co-10Ni/85Al2O3
NH3 heat of desorption, (kJ mol-1) 35.5
87.3
CO2 heat of desorption, (kJ mol-1) 62.4
56.0
Acid concentration (µmol m-2) 1.50
2.90
Basic concentration (µmol m-2) 0.21
0.42

C. K. CHENG ET AL.
167
Subsequently, the product ratios (CO2:CO, CO2:CH4 and
CO:CH4) as a function of Phydrogen showed that the CO2:CO
ratio is practically constant with Phydrogen as a result of re-
verse-water-gas-shift reaction (cf. Figure 4). The ratio was
lower than unity indicating that CO formation rate was higher
than CO2 as the latter was being consumed to produce the for-
mer. CO2:CH4 decr eas ed with P hydrogen du e to th e increased CH4
formation rate, whilst the ratio CO:CH4 decreased because the
increase in CH4 formation rate was higher than the increase
recorded for CO formation rate.
3.3. Carbon Deposition
Figure 5 suggests a decr ease in carb on deposition rate with H2
partial pressure, in part icular at 923 K. This observation is con-
sistent with the increase in CH4 formation rate indicating that
both methanation and carbon gasification contributed to the
increase i n CH4 formatio n. However, t emperatu re see ms to play
an increasingly dominant role in reducing carbon laydown than
adding H2 gasifyi ng reactan t at temperatu res ≥ 973 K. At 1023
K, deposition of carbon was essentially zero.
Figure 2. X RD patt ern of cal cined Co-Ni/Al2O3 catalyst.
Figure 3. Effect of Phydrogen on product formation rates at 973 K.
Figure 4. Effect of Phydrogen on pro duct ratios at 973 K.
Figure 5. Effect of Phydrogen on carbon laydown as function of tem-
perature.
4. Conclusions
The effects of adding H2 gasifying reactant during the glycerol
steam reforming have been examined. Reaction data revealed
that H2 addition led to the increased CH4 formation which can
be attributed to the gasification of carbon and methanation. In
addition, the product formation rate of CO2 decreased due to
reverse wat er-gas-shift.
5. Acknowledgements
Authors would like to thank Universiti Malaysia Pahan g for the
provision of short-term grant to fund this project.
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C. K. CHENG ET AL.
168
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