Selective hydrogenation of d-mannose to d-mannitol using NiO-modified TiO2 (NiO-TiO2) supported ruthenium catalyst

Article abstract of DOI:10.1016/j.apcata.2012.11.042

NiO-modified TiO₂ (NiO-TiO₂) supported ruthenium catalyst Ru/(NiO-TiO₂) is prepared by simple impregnation method and characterized by using energy dispersive X-ray analysis (EDX/EDS), temperature- programmed reduction (TPR), inductively coupled plasma (ICP) mass spectrometry, transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and CO chemisorption. The catalyst Ru/(NiO-TiO₂) is evaluated in d-mannose hydrogenation and hydrogenation experiments to produce a selective product d-mannitol were carried out batch wise in a three-phase laboratory scale reactor. A tentative mechanism for reduction of d-mannose is presented. The kinetics of d-mannose hydrogenation to d-mannitol using catalyst Ru/(NiO-TiO₂) was studied. The kinetic data were modeled by zero, first and second-order reaction equations. A set of four experiments was also carried out to test the deactivation of the catalyst. For affording maximum d-mannose conversion, yield and selectivity to d-mannitol, the reaction conditions are optimized.

Full text of DOI:10.1016/j.apcata.2012.11.042

Applied Catalysis A: General 453 (2013) 13–19
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Selective hydrogenation of d-mannose to d-mannitol using
NiO-modified TiO2 (NiO-TiO2) supported ruthenium catalyst
Dinesh Kumar Mishra, Jin-Soo Hwang∗
Bio-refinerery Research Center, Korea Research Institute of Chemical Technology (KRICT), Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 August 2012
Received in revised form 25 October 2012
Accepted 28 November 2012
Available online 14 December 2012
NiO-modified TiO2 (NiO-TiO2) supported ruthenium catalyst Ru/(NiO-TiO2) is prepared by simple impreg-
nation method and characterized by using energy dispersive X-ray analysis (EDX/EDS), temperature-
programmed reduction (TPR), inductively coupled plasma (ICP) mass spectrometry, transmission elec-
tron microscopy (TEM), X-ray powder diffraction (XRD) and CO chemisorption. The catalyst Ru/(NiO-TiO2)
is evaluated in d-mannose hydrogenation and hydrogenation experiments to produce a selective product
d-mannitol were carried out batch wise in a three-phase laboratory scale reactor. A tentative mechanism
for reduction of d-mannose is presented. The kinetics of d-mannose hydrogenation to d-mannitol using
catalyst Ru/(NiO-TiO2) was studied. The kinetic data were modeled by zero, first and second-order reac-
tion equations. A set of four experiments was also carried out to test the deactivation of the catalyst. For
affording maximum d-mannose conversion, yield and selectivity to d-mannitol, the reaction conditions
are optimized.
Keywords:
d-mannose
d-mannitol
Kinetics
Hydrogenation
Ruthenium
NiO-modified TiO2
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
pressure and a high temperature. However, very little attention
is paid for direct hydrogenation of d-mannose to d-mannitol
Several attempts were made by researchers earlier to develop
the catalysts based on nickel as an active metal (the catalysts, Raney
Ni or supported/promoted nickel catalysts) [1–5] in hydrogenation
of sugars to their corresponding sugar alcohols [6,7]. But, the nickel
based catalysts were found to have some disadvantage (leaching)
resulting in loss of activity and high metal content in the prod-
uct solution [8,9]. Therefore, in recent years the catalysts based
on ruthenium due their higher activities were evaluated in the
hydrogenation of sugars to sugar alcohols (i.e. d-sorbitol, xylitol,
lactitol, etc.) [10–17]. Off these, a sugar alcohol d-manntiol, similar
to d-sorbitol, is of the industrial important since d-mannitol is also
extensively used in food and pharmaceutical industries [18–22]. It
has excellent properties such as non-toxic, non-hygroscopic and
low caloric sugar. d-mannitol is present in small quantities in most
fruits and vegetables [23–27]. Besides small amount of d-mannitol
can be obtained naturally from their sources, commercial large
scale production of d-mannitol was relied on catalytic hydrogena-
tion of an appropriate starting material either d-fructose/invert
sugar (d-fructose/d-glucose mixture) or d-mannose. Most of the
studies were focused for the production of d-mannitol by cat-
alytic hydrogenation of aqueous solutions either of d-fructose
[28] or invert sugar (d-fructose/d-glucose mixture) [29,30] at high
and hydrogenation experiments to produce d-mannitol is scantly
available in the literature [31]. Since d-mannose is a natural
aldohexose and a building block of vegetable polysaccharides,
therefore d-mannose possesses industrial relevance for the pro-
duction of d-mannitol. It is mainly used as a sugar substitute and
for pharmaceutical purposes. d-mannose is chosen here as a start-
ing material for the production of d-mannitol (as represented in
Scheme 1).
Our aim of the work was to evaluate (NiO-TiO2) supported
ruthenium catalyst Ru/(NiO-TiO2) in direct hydrogenation of
d-mannose to d-mannitol. In kinetic study of d-mannose hydro-
genation, both order of reaction and activation energy were also
determined. A set of four experiments was carried out to test the
deactivation of the catalyst.
2. Experimental
2.1. Materials
Ruthenium chloride (RuCl3·xH2O) was purchased from Strem
Chemicals, Newburyport, MA01950 (USA). The nickel chloride,
d-mannose and d-mannitol were purchased from Sigma–Aldrich
company, Inc, (USA). The support titanium (IV) oxide (rutile type)
(TiO2), purity – 99.9%, shape fine powder ca. 1– 2 micron purchased
from Degussa is used after drying at 110 ◦C. De- ionized water was
used as solvent for making all solutions.
∗
Corresponding author. Tel.: +82 42 860 7382; fax: +82 42 860 7676.
E-mail address: jshwang@krict.re.kr (J.-S. Hwang).
0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2012.11.042

14
D.K. Mishra, J.-S. Hwang / Applied Catalysis A: General 453 (2013) 13–19
Scheme 1. A schematic approach for the preparation of active catalyst (Ru/NiO-TiO2) used in hydrogenation of d-mannose to produce d-mannitol.
2.2. Catalyst Ru/(NiO-TiO2) preparation
used as an eluent for the analysis at a flow rate of 0.4 mL/min
at 70 ◦C. The temperature of RI detector was maintained at 35 ◦C
throughout the analysis.
Before starting the TPR experiments, the samples were dried at
120 ◦C for 1 h under Ar flow and then cooled to room temperature.
The (10%) H2/Ar was used as reducing gas at a continuous flow rate
of 10 mL/min.
The preparation of novel catalyst Ru/(NiO-TiO2) was carried
out by impregnation method using ruthenium chloride and new
class of NiO-modified TiO2 support [11,16]. The proposed sup-
port material (NiO-TiO2) was prepared by the following procedure:
required amount (4.8 g) of TiO2 was immersed into aqueous solu-
tion nickel chloride (0.55 g) under magnetic stirring. Then, the
resulting mixture was dried at 110 ◦C overnight and after com-
plete drying the sample was oxidized in air at 500 ◦C for 10 h to
obtain NiO-modified TiO2 support (NiO-TiO2) (Scheme 1). The cal-
culated amount of (NiO-TiO2) was further re-impregnated with
aqueous solution of ruthenium (III) chloride (0.52 g) and was kept
in an oven at 110 ◦C overnight. The catalyst Ru/(NiO-TiO2) thus
prepared was reduced in a continuous flow of (5.0%) H2/Ar at
200 ◦C (temperature determined from temperature-programmed
reduction experiment) for 3 h and then used immediately for the
hydrogenation of d-mannose.
2.4. Catalysts characterization
The metal contents (amount of Ru loading) of the catalysts were
determined by using EDX, Quantax 200 Energy Dispersive X- ray
Spectrometer, Bruker. The stability of catalysts (before and after
reactions) was determined with X-ray diffraction (RIGAKU, Mini-
flex Instruments). The amount of metal ions present in the reaction
mixture after hydrogenation was analyzed with an inductively
coupled plasma-atomic emission spectrometry (Thermo Scientific
ICAP 6500 duo). Both, morphology and particle size were deter-
mined by the transmission electron microscopy (Maker FEI, Model
Technai G2). For the electron microscopy examination, the catalyst
samples were dissolved in 2-propanol, dispersed carefully in an
ultrasonic bath, and then deposited on carbon-coated copper grids.
BET surface area was determined by N2 adsorption–desorption at
77 K liquid N2 temperature with a MICROMETRICS, Tristar II ana-
lyzer. For each measurement, the sample was degassed at 250 ◦C
for 3–4 h, then analyzed at 77 K with N2 gas at relative pressures
(P/P0) from 0.005 to 1.0 (adsorption) and 1.0 to 0.1 (desorp-
tion). CO chemisorption was carried out by using an instrument
model ASAP 2020C V1.09 G. Before adsorption of the CO, the cat-
alysts (weighed approximately 0.12 g) were pre-treated in He for
35 min, and in O2 for 15 min, and were then reduced for 30 min
in a (5.0%) H2/Ar gas flow of 50 mL/min, and in He gas flow for
15 min at 400 ◦C in a reaction chamber. After this pre-treatment,
the samples were cooled down to 50 ◦C under He gas flow and
CO pulse measurements were carried out using (5.0%) CO/He gas
flow of 50 mL/min. Finally, the surface concentration and disper-
sion of metallic Ru were obtained from the CO pulse analysis
data.
2.3. Hydrogenation of d-mannose
10 wt% d-mannose solution was prepared by dissolving 20 g of
d-mannose in 180 ml de-ionized water. This solution was mixed
with 1.0 g of catalyst Ru/(NiO-TiO2) to form the reaction slurry and
thereafter the hydrogenation experiments of d-mannose were con-
ducted in a 300 mL. The hydrogen gas was purged into the reactor at
2.0 MPa H2 pressure to deoxygenate the reaction mixture followed
by stirring (400 rpm for 30 min) at room temperature and then
pressure was released. The hydrogenation was initiated by stirring
the reaction mixture at constant impeller speed of 1200 rpm and
was continued for 240 min at temperature of 120 ◦C and hydrogen
(H2) pressure of 40–55 bar. At the end of hydrogenation, the solu-
tion was cooled and the catalyst was allowed to settle at the bottom
of reaction flask. The above mentioned procedure was followed
with other catalyst Ru/TiO2 which was reduced at 320 ◦C [11,16].
The supernatant solution was filtered and then analyzed using a
HPLC (Younglin Instrument, Acme 9000) equipped with refractive
index (RI) detector and Sugar-Pak column. Deionized water was

D.K. Mishra, J.-S. Hwang / Applied Catalysis A: General 453 (2013) 13–19
15
Ru/NiO-TiO2(R)
Ru/NiO-TiO2
NiO-TiO2
TiO2
100
200
300
400
500
10
20
30
40
50
60
70
80
90
Temperature (oC)
2theta/degree
Fig. 4. H2-TPR profile of catalyst Ru (1.0%)/NiO (5.0%)-TiO2.
Fig. 1. XRD patterns of TiO2, (NiO-TiO2), Ru/NiO-TiO2 (fresh sample), and Ru/NiO-
TiO2 (R) (after hydrogenation).
hydrogenation) are shown in Fig. 1. It is seen from this figure
that the XRD profiles of TiO2 support and NiO-modified TiO2 sup-
port have obvious differences. The presence of characteristics NiO
peaks appeared at 2ꢀ values of 37◦, 43◦, 62◦, 75◦ and 79◦ indicates
successful modification of TiO2 support with nickel chloride salt
precursor. In addition, the XRD profiles of NiO-TiO2 and its catalyst
Ru (1.0%)/NiO (5.0%)-TiO2 look alike. The metallic Ru in the cata-
lysts (before and after hydrogenation) could not be detected as Ru
loadings less than 5.0% are always covered by NiO-modified TiO2
support making it difficult to determine [32].
TEM view of [Ru (1.0%)/NiO (5.0%)-TiO2] catalyst showed that
the size of ruthenium particles was very small 2.0 nm or less
[11,16]. These ruthenium particles were distributed over NiO parti-
cles (10–12 nm) of (NiO-TiO2) support (Fig. 2). The above statement
is in agreement with the results obtained from CO chemisorption
[11,16]. It has been found that the dispersion of ruthenium over
NiO-TiO2 support is 63.2%. In order to confirm the existence all
three metals Ru, Ni and Ti, EDX analysis was also carried out and the
spectrum is presented in Fig. 3. The spectrum undoubtedly shows
the presence of all three components Ru, Ni and Ti of the catalyst
[Ru (1.0%)/NiO (5.0%)-TiO2].
Fig. 2. TEM image of the catalyst Ru (1.0%)/NiO (5.0%)-TiO2)..
3. Results and discussion
The reducibility of the catalyst prepared was examined by TPR.
Fig. 4 showed that the profile of [Ru (1.0%)/NiO (5.0%)-TiO2] dis-
played a peak at 150 ◦C which is attributed to the reduction of
Ru3+ → Ru0 and the second peak at 378 ◦C is due to the reduction of
3.1. Catalyst characterization
The X-ray diffraction patterns of TiO2, (NiO-TiO2), cat-
alyst Ru/(NiO-TiO2) and catalyst Ru/NiO-TiO2 (R) (R: after
Fig. 3. EDX spectrum of the catalyst Ru (1.0%)/NiO (5.0%)-TiO2.

16
D.K. Mishra, J.-S. Hwang / Applied Catalysis A: General 453 (2013) 13–19
Table 1
Time versus d-mannose concentration data using initial d-mannose concentration Ci = 10 wt% (0.555 mol/L), catalyst ratio = 5.0 wt% g at pressure = 40 bar.
Temp. (◦C)
100 ◦
C
120 ◦
C
140 ◦
C
Time (min)
Cf (mol/L)
LN(Ci/Cf)
1/Cf
Cf (mol/L)
LN(Ci/Cf)
1/Cf
Cf (mol/L)
LN(Ci/Cf)
1/Cf
0
30
60
90
120
0.555
0.536
0.490
0.447
0.403
0.000
0.035
0.125
0.216
0.320
1.802
1.865
2.042
2.236
2.480
0.555
0.491
0.407
0.338
0.272
0.000
0.122
0.310
0.495
0.712
1.802
2.035
2.456
2.955
3.670
0.555
0.475
0.347
0.259
0.192
0.000
0.155
0.471
0.763
1.062
1.802
2.104
2.886
3.865
5.208
0.6
0.5
0.4
0.3
0.3
0.2
0.1
oxidized ruthenium deposited on the surface of NiO-TiO2 support.
There is an additional peak observed at 425 ◦C which is attributed
to delayed reduction of Ni2+ → Ni0 [33]. It is clear from the TPR
data that a temperature of ∼200 ◦C is enough for the reduction of
Ru3+ → Ru0 without affecting the NiO- modified TiO2 support.
3.2. Determination of order of reaction and activation energy
For determination of the order of reaction, equations of zero,
first and second-order reaction are used [34]. These equations can
be written as follows:
Zero-order reaction equation
Cf = Ci − k0t
(1)
where Ci = Initial concentration of d-mannose in reaction solu-
tion (mol/L), Cf = final concentration of d-mannose in reaction
solution (mol/L), k0 = zero order rate constant (mol L−1 min−1),
t = temperature.
30
50
70
90
110
130
Time (min.)
Fig. 5. Test for zero order of reaction; catalyst = 1.0 g, d-mannose = 10 wt%, impeller
speed = 1200 rpm and hydrogen (H2) pressure = 40 bar.
First- order reaction equation
ꢀ
ꢁ
Ci
Cf
LN
= k1t
(2)
(3)
suggest the effectiveness and high activity of NiO-modified TiO2
supported ruthenium novel catalyst in d-mannose hydrogenation.
The catalytic activities calculated in terms of initial rate
(2958.3 m mol h
TiO2 supported ruthenium novel catalyst Ru/NiO-TiO2 are also
higher than those for the catalyst Ru/TiO2 (Table 3). The additive
effect of NiO (NiO loading of 5.0 wt%) in NiO modified TiO2 support
plays an important role to raise the reaction rate and selectivity to
the main product i.e. d-mannitol. In the NiO-modified TiO2 sup-
port, the dispersed NiO particles were formed on TiO2 support,
leading to the formation of large numbers of unsaturated NiO sites.
where k1 = first-order rate constant (min−1).
−1
Second-order reaction equation
g
Ru
−1) and TOF (298.9 h−1) for NiO-modified
ꢂ
ꢃ
1
1
=
+ k2t
(Cf )
(Ci)
where k2 = second-order rate constant (1 mol−1 min−1).
Table 1 shows time versus d-mannose concentration data using
initial d-mannose concentration Ci = 10 wt% (0.555 mol/L) and cat-
alyst amount of 1.0 g, at hydrogen (H2) pressure of 40 bar and
different temperatures of 100, 120 and 140 ◦C. This table shows
that the d-mannose concentration decreased with increasing the
temperature of reaction, due to the increase of d-mannose conver-
sion. An increase in temperature from 100 to 140 ◦C at constant
time of 120 min, leads to a decrease in d-mannose concentration
from 0.403 to 0.192 mol/L. Plot of final d-mannose concentration
(Cf) and (1/(Cf)) versus time for zero and second- order, respec-
tively, are nonlinear as shown in Figs. 5 and 7, while plot of LN(Ci/Cf)
versus time for Eq. (2) is linear as shown in Fig. 6. This proves that
the reaction d-mannose hydrogenation follows the first-order in
nature.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
The activation energy is calculated by using Arrhenius equation
which can be written as follows:
k1 = Ae(−E/RT)
(4)
where A = exponential factor, E = activation energy (KJ mol−1), and
R = gas constant (8.3145 mol−1 K−1
)
10
30
50
70
90
110
130
The first-order reaction rate constants (kinetic constants)
(Table 2) are obtained from the slope of curve, plot of LN(Ci/Cf)
against time (min) at different temperatures. From Arrhenius plot
of LN(k1) versus 1/T, K as shown in Fig. 8, activation energy is cal-
culated as 48.2 kJ mol−1. The low value of activation energy may
Time (min.)
Fig. 6. Test for first order of reaction; catalyst = 1.0 g, d-mannose = 10 wt%, impeller
speed = 1200 rpm and hydrogen (H2) pressure = 40 bar.

D.K. Mishra, J.-S. Hwang / Applied Catalysis A: General 453 (2013) 13–19
17
The thus-formed unsaturated NiO sites act as efficient adsorption
sites on the surface of catalyst where d-mannose reacts with the
activated H.
6.5
5.5
4.5
3.5
2.5
1.5
3.3. Tentative mechanism for reduction of d-mannose to
d-mannitol
The hydrogenation of d-mannose to d-mannitol using the
NiO-TiO2 supported ruthenium catalyst is a gas–liquid–solid three-
phase catalytic reaction. The mechanism of reducing d-mannose
with H2 on the catalyst surface is shown in Scheme 2. Hydrogen
(H2) was spread first from air to the liquid membrane. Then, H2
dissolved in the gas–solution interface and it spread from the liq-
uid membrane to d-mannose in the liquid phase. It is supposed
that H2 did not react with the carbonyl group of d-mannose, but
instead was adsorbed by the active centers of the catalyst, produc-
ing activated H on the catalyst [32]. Finally, d-mannose reacts with
the activated H on the surface of catalyst, which is an irreversible
reaction, and then the product desorbs from the catalyst and dif-
fuses into the liquid phase. Therefore, d-mannose hydrogenation
proceeds through H2 dissolution, H2 diffusion, H2 adsorption on
the active centers of the catalyst, to produce activated H. Finally,
the carbonyl group in d-mannose reacted with the activated H on
the surface of catalyst to produce d-mannitol.
30
50
70
90
110
130
Time (min.)
Fig. 7. Test for second order of reaction; catalyst = 1.0 g, d-mannose = 10 wt%,
impeller speed = 1200 rpm and hydrogen (H2) pressure = 40 bar.
Table 2
Effect of temperature on d-mannose hydrogenation at d-mannose concentration
Ci = 10 wt% (0.555 mol/L), catalyst ratio = 5.0 wt% g at pressure = 40 bar.
3.4. Optimization of reaction conditions (d-mannose
hydrogenation)
Temp. (◦C)
k1 (min−1
)
(1/T) × 10−3 (K)
LN (k1)
100 ◦
120 ◦
C
C
0.003
0.007
0.014
2.68
2.54
2.42
−5.80914
−4.99083
−4.30507
d-mannose hydrogenation experiments were carried out at con-
stant stirring speed of 1200 rpm. Since TEM views of ruthenium
catalyst showed that ruthenium particles were very small with
average size around 2.0 nm, the mass transfer effects could be
neglected. Furusava et al. reported that there was no influence of
internal diffusion even in liquid phase hydrogenation of d-glucose
if the Ru-B particles were small (20–50 nm) [13,35].
The effect of reaction times on the hydrogenation of d-mannose
is shown in Fig. 9. The d-mannose conversion increased when the
reaction time was increased up to the 260 min; d-mannose was
completely converted. At the early period of the hydrogenation, d-
mannose was converted into d-mannitol and yield/selectivity to
d-mannitol reached the highest level at 240 min. After 260 min,
the mannitol yield declined as the reaction progressed. Perhaps
the product d-mannitol degrades into other products during this
process. Hence, the optimum reaction time was 240 min.
The relationship between catalyst amount (catalyst ratio, wt%
on initial d-mannose concentration) and d-mannose conversion or
yield/selectivity d-mannitol, is indicated in Fig. 10. Figure shows
that the d-mannitol yield increased with an increase in the amount
of catalyst up to the 5.0 wt%, when further increasing catalyst
amount from 5.0 to 6.25 wt%, the yield did not change signifi-
cantly, and d-mannose had already been converted into d-mannitol
completely. In this experiment, the amount of reactant d-mannose
was constant, when excessive dosage of catalyst was employed, no
high conversion rate could be found. Hence the d-mannitol yield
was relatively stable when the dosage of catalyst was 5.0 wt%. The
140 ◦C
8
7
6
5
4
3
2
2.4
2.5
2.6
2.7
(1/T) x 10-3, K
Fig. 8. Effect of temperature on reaction rate; catalyst = 1.0 g, d-mannose = 10 wt%,
impeller speed = 1200 rpm and hydrogen (H2) pressure = 40 bar.
Table 3
Catalytic activity data obtained during hydrogenation of d-mannose.
−1
a
Catalysts
Catalysts (g)
Conversion (%)
Initial rate/gRu (m mol h−1 gRu
)
TOFb (h−1
)
No Catalyst
–
–
–
26.7
18.4
–
–
–
–
NiO(5.0%)-TiO2
Ru(1.0%)/NiO(5.0%)-TiO2
Ru(1.0%)/TiO2
1.0
1.0
1.0
2958.3
2044.2
298.9
206.6
a
Mannose 10 (wt%), time = 60 min, pressure = 40 bar and temp. = 120 ◦C.
TOF for the given conversion.
b

18
D.K. Mishra, J.-S. Hwang / Applied Catalysis A: General 453 (2013) 13–19
H+
HO
OHHO
H2
Ru-H
Ru
+
O
HO
D-mannose
OH
HO
H
OHHO
Hydrogen transfer
Ru
O
HO
OH
H2
Ru-H
HO
OHHO
HO
OHHO
Ru
O
HO
HO
OH
HO
OH
D-mannitol
Scheme 2. Tentative mechanism for reduction of d-mannose to d-mannitol.
d-mannitol selectivity decreased continuously on increasing the
catalyst ratio from 5.0 to 6.25 wt%. For highest yield d-mannitol,
the catalyst ratio on initial d-mannose is found to be sufficient in
between 5.0 wt%.
Conversion
Yield
Selec.
110
102
94
110
100
90
3.5. Deactivation of catalysts
The reusability of the catalyst is of great importance for com-
mercial feasibility; therefore, a set of four successive experiments
were carried out for the possibility of reusing it. At the end of the
first experiment the separated catalyst was fed into the reaction
flask and the procedure was repeated for three times. Each filtrate
from these experiments was analyzed directly for d-mannitol con-
tent. The results of these experiments are tabulated in Table 4. The
results of this table show that the deactivation of the catalyst is
slow due to leaching of less content of Ni as well as Ru metals and
80
86
70
78
60
70
50
4
4.5
5
5.5
6
6.5
Catalyst ratio, wt %
Fig. 10. Effect of catalyst ratio on d-mannose hydrogenation; d-mannose = 10 wt%,
temp. = 120 ◦C, time = 240 min, impeller speed = 1200 rpm, hydrogen (H2) pres-
sure = 55 bar.
%Yield
%conv.
%Selec.
100
80
60
40
20
0
120
100
80
60
40
20
0
can be used several times with only marginal effect on d-mannose
conversion, yield and selectivity to d-mannitol. This is because d-
mannitol like d-sorbitol has a little effect on the activity of the
catalyst as explained by Pijnenburg et al. [36]. They found that both
d-sorbitol and d-mannitol had a little effect on the activity of the
catalyst.
Table 4
Deactivation of NiO-TiO2 supported ruthenium catalyst and leaching (mg/L) of
metals.
Experiment Mannose
d-mannitol
d-mannitol
Ru Ti
Ni
30
90
150
Time (min.)
210
270
no.
(%conversion)
(%selectivity) (%yield)
1
2
3
4
97.4
96.4
95.3
92.3
93.6
92.3
92.3
92.0
91.2
89.0
88.0
84.9
0.0 N.D 11.1
0.0 N.D. 12.0
0.1 N.D. 13.5
0.3 N.D. 14.5
Fig. 9. Effect of time on d-mannose hydrogenation; catalyst = 1.0 g, d-
mannose = 10 wt%, temp. = 120 ◦C, impeller speed = 1200 rpm, hydrogen (H2)
pressure = 55 bar.

D.K. Mishra, J.-S. Hwang / Applied Catalysis A: General 453 (2013) 13–19
19
4. Conclusions
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NiO-modified TiO2 support ruthenium catalyst is successfully
prepared by impregnation method. In the Ru (1.0%)/NiO (5.0%)-
TiO2 catalyst, ruthenium is highly dispersed over a new class of
NiO-modified TiO2 (NiO-TiO2) support. The hydrogenation of d-
mannose to mannitol using Ru (1.0%)/NiO (5.0%)-TiO2 catalyst is
of first order with respect to d-mannose concentration. The acti-
vation energy for hydrogenation of d-mannose is low indicating
catalyst Ru (1.0%)/NiO (5.0%)-TiO2 is active for d-mannose hydro-
genation. The catalyst Ru (1.0%)/NiO (5.0%)-TiO2 is very stable and
can be used several times with only a small decrease of d-mannitol
yield. Optimized reaction conditions allowing maximum conver-
sion of d-mannose as well as maximum yield and selectivity to
d-mannitol were as follows; 1.0 g of catalyst Ru (1.0%)/NiO (5.0%)-
TiO2, at impeller speed of 1200 rpm, at temperature of 120 ◦C and at
hydrogen H2 pressure of 55 bar for 240 min. Overall, it is concluded
that the novel catalyst Ru (1.0%)/NiO (5.0%)-TiO2 can be used for all
industrial applications in hydrogenation of carbohydrate sugar to
sugar alcohols.
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