1
34
N. Hamzah et al. / Applied Catalysis A: General 419–420 (2012) 133–141
3
alternative method to enhance acidic condition and also the activ-
ities of the catalyst. To the best of our knowledge, development of
supported Ru on two support materials for hydrogenolysis glycerol
in aqueous medium had not been report elsewhere.
under a He flow of 30 cm /ml. Dispersion values were calculated
from quantification of the desorbed hydrogen and the assumption
that the stiochiometry factor between chemisorbed hydrogen and
surface Ru equals H:Ru = 1:1.
The aim of this research was to use a combination of bentonite
and TiO2 as a support material in order to improve the conversion
and selectivity of glycerol hydrogenolysis to 1,2-propanediol under
a mild reaction condition. The effect of various ratios of bentonite
to TiO2 on the catalytic performance and the optimum reaction
parameters such as metal loading, glycerol concentration, reaction
temperature, reaction time and recyclability will be presented and
discussed in this paper.
The reduction characteristics of the catalysts were stud-
ied by a temperature programmed reduction (TPR) using the
same apparatus and pretreatment method as for the CO pulse
chemisorption-TPD measurements. After pretreatment, the tem-
◦
◦
◦
perature was raised from 30 C to 600 C at a rate of 10 C/min in a
3
10% H /He flow (30 cm /min).
2
The acidity properties of the catalytic materials was mea-
sured by a temperature-programmed desorption of ammonia. The
experiments were conducted on the same apparatus as the TPD
experiments described above. Prior to monitoring of the TPD-NH3
2
. Experimental
◦
profiles, the samples were heated in a helium flow at 150 C for
3
◦
0 min. After a cooling temperature of 70 C, the samples were
2.1. Materials and catalyst preparation
exposed to ammonia and flushed with a 50 ml/min helium for
6
1
0 min. The TPD measurement was carried out with a heating rate
0 C/min up to 750 C under a flowing helium (50 ml/min). The
Glycerol (99.9%), ruthenium trichloride (RuCl ), and support
3
◦
◦
materials (TiO , bentonite, SiO2 and Al O ) were purchased from
2
2
3
desorption of ammonia was monitored by a TCD.
◦
Sigma–Aldrich. The support materials were calcined in air at 500 C
for 3 h to remove moisture and organic impurities. Various ratios
(
wt%) of bentonite-TiO2 mixture were prepared by mixing both
2.3. Catalytic reaction and analysis of the reaction products
materials in acetone and left with stirring for an hour. Then, the
◦
resulting mixture was dried slowly in an oven at 65 C for 12 h. All
The catalytic hydrogenolysis reactions were carried out in
a 50 ml stainless-steel with Teflon liner autoclave, PARR reac-
tor equipped with an electronic temperature controller and a
mechanical stirrer. The reaction was normally conducted under the
Ru supported catalysts with 5 wt% metal loading were prepared
by impregnation method with some modifications using RuCl3 as
precursor for Ru metal. After impregnation, the slurry was stirred
at room temperature for several minutes and then sonicated for
0 min. The catalysts were then dried in the oven at 60 C during
◦
following standard conditions: 150 C temperature, 20 bar initial
◦
6
1
hydrogen pressure, 1.0 g catalyst, 23 ml of 20 wt% aqueous solution
of glycerol, 7 h reaction time and at a constant stirring speed at
200 rpm.
The reactor was cooled to room temperature and the liquid
phase products were separated from the catalyst by centrifugal
force at 4000 rpm for 15 min and then filtered. These products
were analysed by a gas chromatography using GC-Hewlett Packard
Model 6890N equipped with a flame ionisation detector (FID)
on a DB-WAX capillary column (30 m × 0.32 mm × 0.5 m) man-
ufactured by Angilent Technologies. Solutions of n-butanol and
◦
2 h. In the next step, the catalyst was calcined in N2 flow at 300 C
◦
for 2 h and further reduced to a hydrogen stream at 200 C for 2 h.
Then the catalysts were used directly for hydrogenolysis without
any further treatment.
2.2. Catalyst characterisation
The surface area of the supported Ru catalyst was measured
using the BET method (N2 adsorption) with a Gemini apparatus
Micromeritics 2010 Instrument Corporation). Transmission elec-
tron microscope (TEM) images for the determination of the particle
sizes were recorded with a CM12 instrument (Philips) and operated
at 200 kV. The samples were dispersed by a sonicator in ethanol
before placing them on Cu grids. The morphology and microstruc-
ture data for the samples were obtained from FESEM using LEO
1
,4-butanediol with known amounts were used as internal stan-
(
dards for quantification of various glycerol-derived compounds in
the product.
3. Results and discussion
1
450VP equipped with energy dispersive X-ray detector (EDX). All
3.1. BET surface area
the samples were analysed in a high-vacuum at 20 kV. The phase
structures of the catalysts were determined by an X-ray diffrac-
tion (XRD) using Bruker AXS D8 Advance diffractometer with Cu
K␣ (ꢀ = 0.15406 nm) at an angle of 2ꢁ = 20–80. The sample (2.0 g)
was grinded and the fine powder was pressed and placed on the
sample holder. The X-ray photoelectron spectrum (XPS) data of the
as-prepared samples were obtained using an XPS type Ultra from
Kratos. The samples were analysed at 3 × 10 mbar using C1s line
at 284.5 eV from adventitious carbon as a reference for the binding
energies.
The main physicochemical characteristics of the supports were
analysed by BET and found that the specific surface area of TiO ,
2
2
−1
2
−1
bentonite, SiO and AlO supports were as 8.8 m g , 101.3 m g
,
2
3
2
−1
2
−1
130.5 m g and 155.6 m g , respectively. TiO2 had the lowest
BET surface area while the rest of the supports had similar BET
2
−1
surface area that ranged from 101 to 155 m g . The BET surface
area of bentonite to TiO2 mixture revealed an interesting trend.
There was a 10-folds decrease in the surface area as the content of
the TiO2 increased from 1:0 to 1:3. However, at 1:1 ratio the sur-
face area was reduced to about half of the initial values (Table 1).
Overall, there was a decreasing trend in the surface area of the
support as the TiO2 content was increased except for the sample
with 1:1 ratio. The same decreasing surface area trend was also
−9
The dispersion of the catalysts was also measured with CO pulse
chemisorption and subsequent temperature programmed desorp-
tion of the chemisorbed CO. These experiments were performed in
a gas flow system equipped with a thermal conductivity detector
(
TCD). Typically, the catalyst sample (50–60 mg) was placed in a U-
observed for Ru/TiO -bentonite catalyst (5 wt% Ru). The highest
2
3
shaped quartz reactor and pretreated in flowing He (30 cm /min)
for 0.5 h at 150 C, and this was followed by cooling at room temper-
ature. Then, CO pulse chemisorption was performed at 100 C under
1
surface area was recorded for the catalyst with 1:1 bentonite to TiO
2
◦
2
−1
ratio (37.3 m g ). In general, the catalyst surface area decreased
about 3-folds with the same 3-fold increase in the amount of TiO2
in the support material except for the sample with 1:1 ratio. The
opposite trend was observed when the amount of bentonite was
◦
3
0%CO/He flow (30 cm /ml). The TPD experiments were performed
◦
◦
◦
by heating the samples at a rate of 10 C/min from 30 C to 500 C,
Hamzah, Noraini
