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H. Jang et al. / Journal of Molecular Catalysis A: Chemical 380 (2013) 57–60
Fig. 1. Conversion of lactic acid to propylene glycol.
CM-95 and CNFs from Carbon Nano-material Technology, and
graphite from Aldrich.
Prior to the impregnation of ruthenium, all carbon supports
were immersed overnight in a stirred mixture of nitric acid and
sulfuric acid (volume ratio of 3:1). After washing the resultant car-
bon in warm distilled water several times, the supports were placed
in an oven at 100 ◦C and left overnight.
The ruthenium catalysts supported on various carbons were
prepared using the incipient wetness impregnation method fol-
lowed by drying at 100 ◦C. The ruthenium loading was 5 wt% for
all the catalysts, and the dried powder was calcined at 500 ◦C for
4 h under flowing air. Prior to the reaction, all synthesized cata-
lysts were reduced under flowing hydrogen at 400 ◦C for 4 h. After
cooling, the catalysts were passivated in nitrogen for 30 min before
being exposed to air [14].
All the synthesized catalysts underwent detailed analyses. The
crystallinity of the synthesized samples was investigated using
X-ray diffraction analysis (Rigaku, D/max-2200). A transmission
electron microscope (JEOL/JEM2100F) was used to examine the sur-
face morphologies and ruthenium particle sizes. The surface areas
of the synthesized catalysts were determined using the BET method
(ASAP 2020), and both the pore volumes and average pore sizes
were calculated using the BJH model.
2.2. Hydrogenation of lactic acid
Liquid-phase catalytic hydrogenation of lactic acid to propylene
glycol was performed in a 150 mL batch reactor at various reaction
pressures (40–80 bar) and temperatures (110–170 ◦C).
Fig. 2. (a) X-ray diffraction pattern of 5 wt% Ru/CNTs, and (b) a TEM image of 5 wt%
A mixture of 1 M lactic acid solution (50 mL) and prepared cat-
alyst (0.5 g) was placed into the reactor and agitated at 700 rpm.
After purging the reactor with nitrogen for 5 min, the reactor was
heated under flowing hydrogen. When the temperature reached
the desired value, the hydrogen pressure was set to the specified
pressure (40–80 bar) and the reaction was left for 6 h. The prod-
ucts were analyzed using a gas chromatograph (HP 6890) equipped
with a flame-ionization detector. A free fatty-acid phase capillary
column was used for the separation of the reactants and products.
Ru/ketjen black.
the TEM images, are summarized in Table 1. Before impregnation
of ruthenium, all carbon supports were pretreated in a mixture of
nitric acid and sulfuric acid. Many types of functional groups, such
as hydroxyl groups, can form on the surface of carbon supports;
of ruthenium particles.
The BET surface areas, pore volumes, average pore sizes, and
average particle sizes of the various carbon-supported ruthenium
catalysts are listed in Table 1. Although the ruthenium particles
were observed to be finely dispersed on all the carbon supports,
the average particle size correlated remarkably with the surface
area of the carbon support. Ketjen-black – supported ruthenium
exhibited the highest surface area (1242.4 m2/g), highest pore vol-
ume (5.54 cm3/g), and smallest average ruthenium particle size
(1.6 nm) of the investigated catalysts. The surface area of ket-
jen black is reported to be 1423 m2/g, and this high surface area
was maintained after the impregnation of ruthenium. In con-
trast, graphite-supported ruthenium showed the lowest surface
area (17.2 m2/g) and the largest average ruthenium particle size
(10.4 nm), which is probably because of its high crystallinity and
dense structure. Overall, the supports with larger surface areas
exhibited smaller average ruthenium particle sizes. These results
can be explained by the presence of functional groups that form
on the surface of the carbon support during acid treatment. Larger
carbon surface areas result in the formation of more functional
3. Results and discussion
3.1. Characterization of supports and supported catalysts
X-ray diffraction analyses were performed on all samples; the
tion under hydrogen flow is shown in Fig. 2(a). For all the catalysts,
two broad and strong peaks are evident at 2ꢀ = ∼25◦ and 44◦, which
are assigned to the (0 0 2) diffraction of graphite carbon and the
diffraction of the (1 0 1) planes of metallic ruthenium, respectively
[15]. This indicates that the ruthenium in each catalyst was reduced
to metallic ruthenium during thermal treatment under hydrogen
flow.
Fig. 2(b) shows a TEM image of Ru/ketjen black after reduction
under hydrogen flow. The Ru/ketjen black catalyst exhibited fairly
uniform dispersion of small ruthenium species (less than 3 nm).
Fine dispersion was also observed for the other carbon supports,
and the average particle sizes of each catalyst, as measured from
Jang, Hyuk
