The combined hydrolysis and hydrogenation of inulin catalyzed by bifunctional Ru/C

Article abstract of DOI:10.1016/S0008-6215(00)00297-4

A one-pot process for hydrolysis and hydrogenation of inulin to D-mannitol and D-glucitol over a bifunctional Ru/C catalyst was developed. The hydrolysis is catalyzed by the carbon support, onto which acidity was introduced by pre-oxidation. The effect of different carbon treatments on the hydrolysis of inulin was studied. Oxidation with ammonium peroxydisulfate resulted in a carbon with the highest hydrolysis activity. On this carbon, long chain inulin is hydrolyzed faster than inulin rich in short chains. The application of high pressure (up to 100 bar) increased the hydrolysis rate substantially. The combined process was successfully conducted with a Ru-catalyst supported on this oxidized carbon.

Full text of DOI:10.1016/S0008-6215(00)00297-4

www.elsevier.nl/locate/carres
Carbohydrate Research 330 (2001) 381–390
The combined hydrolysis and hydrogenation of inulin
catalyzed by bifunctional Ru/C
Annemieke W. Heinen, Joop A. Peters,* Herman van Bekkum
Laboratory of Applied Organic Chemistry and Catalysis, Delft Uni6ersity of Technology, Julianalaan 136,
NL-2628 BL Delft, The Netherlands
Received 6 September 2000; accepted 7 November 2000
Abstract
A one-pot process for hydrolysis and hydrogenation of inulin to
D
-mannitol and D-glucitol over a bifunctional
Ru/C catalyst was developed. The hydrolysis is catalyzed by the carbon support, onto which acidity was introduced
by pre-oxidation. The effect of different carbon treatments on the hydrolysis of inulin was studied. Oxidation with
ammonium peroxydisulfate resulted in a carbon with the highest hydrolysis activity. On this carbon, long chain inulin
is hydrolyzed faster than inulin rich in short chains. The application of high pressure (up to 100 bar) increased the
hydrolysis rate substantially. The combined process was successfully conducted with a Ru-catalyst supported on this
oxidized carbon. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Activated carbon; Heterogeneous catalysis; Mannitol; Glucitol; Fructose
For the hydrogenation of carbohydrates,
1
. Introduction
Ru has proved to be the most active metal,
although Cu/SiO yields high
D
-mannitol to
2
D
-Mannitol is a valuable, non-hygroscopic,
low-calorie sweetener. Nowadays, -mannitol
is prepared from mixtures of -glucose and
-fructose, obtained by hydrolysis of sucrose
or by enzymatic isomerization of -glucose,
obtained from starch. -Mannitol can be iso-
D
-glucitol ratios in the hydrogenation of
D
-
1
fructose. A one-pot hydrolysis–hydrogena-
D
tion can be conducted with a homogeneous
D
2
catalyst based on Ru(TPPTS) . However, het-
D
3
erogeneous catalysis would offer the great ad-
vantage of easy recovery and re-use of the
catalyst. The most common solid acidic cata-
D
D
lated from the reaction mixture by crystalliza-
tion. Inulin, a polysaccharide containing one
3
,4
5
lysts are zeolites and ion exchange resins,
either used as the catalyst support material or
in a mixture with a hydrogenation catalyst like
D
-glucose and 10–50
be a more attractive feedstock (see Scheme 1),
because it has a higher -fructose content,
and, therefore, it may give a higher -manni-
D
-fructose units, would
6
Ru/C.
D
The benefits of carbon supports are their
low costs, high surface area and the easy
recovery of the supported precious metal by
burning off the carbon. Furthermore, carbon
is capable of adsorbing 5-(hydroxymethyl)-
furfural (HMF), a possible side product,
D
tol yield. A combined, one-pot process, using
a bifunctional catalyst would be desirable.
*
Corresponding author. Tel.: +31-15-2785892; fax: +31-
which is formed by dehydration of
D
-fructose
1
5-2784289.
7
E-mail address: j.a.peters@tnw.tudelft.nl (J.A. Peters).
in acidic environment.
0008-6215/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(00)00297-4

382
A.W. Heinen et al. / Carbohydrate Research 330 (2001) 381–390
Scheme 1. Simplified scheme of the hydrolysis and hydrogenation of inulin. For the sake of simplicity only pyranose forms of
glucose and fructose are depicted. Hydrogenation of inulin fragments, followed by hydrolysis, is also possible.
Here we report on a study of the combined
hydrolysis–hydrogenation of inulin, using
Ru/C as the catalyst. The carbon support was
made acidic by treatment with different oxi-
dizing agents.
phase reduction with sodium borohydride, the
amount of acid sites as determined by sodium
hydroxide neutralization, decreased to 1.3
meq/g. For comparison, reduction in H at
2
400 °C decreased the sodium hydroxide neu-
tralization capacity to 0.2 meq/g. Liquid phase
reduction with sodium borohydride, therefore,
is capable of reducing the ruthenium, while
keeping most of the oxygen surface sites
intact.
2
. Results and discussion
Catalyst characterization.—The effect of
the carbon treatment on the acidity and the
type of surface sites formed was described in a
Reaction conditions.—The formation of
fructose and -glucose during the hydrolysis
D
-
D
8
previous paper. It was concluded that mainly
of inulin with a dp of 10 at 100 °C on different
amounts of carbon SX1GN65 is shown in Fig.
carboxylic acid groups are formed during
these treatments. Acid sites with different
strengths can be distinguished by selective
neutralization. Sodium hydroxide neutralizes
practically all acidic sites; sodium bicarbonate
only the strongest. The amount of carboxylic
sites can also be deduced from the infrared
spectra, by relating the intensity of the band
1
(a). The formation of monosaccharides was
taken as a measure of hydrolysis activity.
The rate of formation of monosaccharides
increases with the amount of catalyst. An
Table 1
Titration and IR results of the different carbons
−
1
at 1700 cm
(carboxylic acids) to that at
a
−
1
8,9
Carbon
NaOH
meq/g)
NaHCO3
(meq/g)
I
1700/1580
−
1
580 cm (the carbon skeleton). The titra-
1
(
(cm
)
tion and IR data (see Table 1) lead to the
conclusion that oxidation with ammonium
persulfate creates the largest amount of acidic
surface sites.
SX1G
SX1GOCl 0.4
SX1GN65 1.0
0.1
0.05
0.2
0.7
1.2
0.0
0.19
0.38
0.45
SX1GNS
1.4
The amount of Ru dispersed on carbon
SX1GNS (for codes of activated carbon, see
footnote of Table 1), as determined with X-
ray fluorescence spectroscopy, amounted to
a
SX1G, untreated steam-activated peat-based carbon;
SX1GOCl, SX1G oxidized with calcium hypochlorite;
SX1GN65, SX1G oxidized with 65% HNO ; SX1GNS, SX1G
3
0
.89 wt%. Upon impregnation and liquid
oxidized with ammonium persulfate. See also Section 4.

A.W. Heinen et al. / Carbohydrate Research 330 (2001) 381–390
383
formation of monosaccharides at high
conversions.
It may be concluded that the reaction is first
order in catalyst and zero order in substrate.
This suggests that the reaction occurs at the
carbon surface, since the homogeneous reac-
+
tion is known to be first order both in H and
1
0
in substrate. The pH of all reaction mixtures
was between 4 and 5. Similar experiments with
aqueous HCl solutions of pH 4 (in the absence
of carbon) gave no hydrolysis. This indicates
that the hydrolysis of inulin takes place on the
acid sites of the carbon surface.
Inulin was not hydrolyzed fully to the
monomers
D
-glucose and
D
-fructose (see Fig.
1
). Short chain oligomers, mainly unidentified
C compounds, remained after prolonged re-
1
2
action. Possibly, these products are -fructose
D
dianhydrides, which are known to be formed
as byproducts during acid hydrolysis of in-
1
1
ulin.
However, 5-(hydroxymethyl)furfural
(
HMF), was not detected in the products of
the carbon catalyzed hydrolyses.
Fig. 1. (a) Hydrolysis of 1 g inulin dp 10 using different
amounts of SX1GN65: 0.10 g (ꢀ), 0.25 g (ꢁ), 0.50 g ("). (b)
Hydrolysis of 1 g (") and 2 g (2) of inulin dp 10 using 0.250
g SX1GNS; 50 mL aqueous solution; 100 °C. The lines are a
guide to the eye.
Effect of carbon pretreatment.—As shown
in Fig. 2, the activity increases with the carbon
acidity, as determined by titration and IR. It
can been seen that treatment of the carbon
with ammonium persulfate results in the most
active catalyst for hydrolysis. Untreated
SX1G has almost no activity.
No loss of activity was observed upon re-
use of the acidic carbons. IR spectra of the
carbon before and after catalytic experiments
also revealed no loss of carboxylic acid
groups. However, after the experiments, the
IR spectra showed an increased absorption at
−
1
1
100 cm , which was no longer present after
washing with hot water. This adsorption is
most probably due to the CꢀO stretching vi-
bration of adsorbed carbohydrate species.
Region of splitting.—To get more insight
into the hydrolysis process, samples taken
during the experiments were analyzed with
high pressure anion exchange chromatogra-
phy, coupled with a pulsed amperometric de-
tector (HPAEC–PAD), as described by De
Fig. 2. Hydrolysis of inulin dp 10 with different carbons;
SX1GNS ("), SX1GN65 (ꢁ), SX1G (ꢂ), 50 mL aqueous
solution of 1 g inulin and 0.250 g carbon; 100 °C. The lines
are a guide to the eye.
induction period is observed, which may be
ascribed to the large amounts of long chains
still present at this time, leading to hydrolysis
without significant formation of monosaccha-
rides. Upon doubling of the starting concen-
tration of inulin, the induction period and the
initial rate remained the same (see Fig. 1(b)),
indicating pseudo zero order kinetics. Both
Fig. 1(a) and (b) show a decreasing rate of
12
Leenheer. In this way, inulin can be sepa-
rated upon chain length. The eluent is strongly
alkaline, converting the hydroxyl groups
partly into oxyanions. Therefore, the longer
chains exhibit longer elution times.

384
A.W. Heinen et al. / Carbohydrate Research 330 (2001) 381–390
The chromatogram of inulin with an aver-
Hydrolysis rate and chain length.—The hy-
drolysis of inulin with various molecular
weight distributions on SX1GNS is shown in
Fig. 5(a). Besides inulin dp 10, dp 25 (a long
chain fraction of dp 10) and dp 30, a long
chain and a short chain fraction of this ‘dp 30’
were used as substrate. These fractions were
obtained by precipitation of the long chains
out of an aqueous solution of inulin dp 30 at
4 °C. It is striking that these long chain frac-
tions result in a significantly higher rate of
monosaccharide formation than the unfrac-
tionated inulin and the short chain fraction.
As shown in Fig. 5(b), the hydrolysis of a
1:1 mixture (on weight base) of inulin dp 10
and dp 25 results only in a small decrease in
the rate of monosaccharide formation, com-
pared to 100% for dp 25. A similar effect was
observed with a mixture of sucrose (10 wt%)
age dp of 10 is shown in Fig. 3(a). Inulin not
only consists of the so called GF chains, but
n
1
2
also contains small amounts of F chains,
m
which do not contain a
D
-glucose end group.
These chains are visible as the small shoulders
of the GF peaks. The difference in average
n
degree of polymerization between inulin dp 10
and its long chain fraction dp 25, obtained by
selective precipitation, is clearly shown in Fig.
(b).
Fig. 4 presents the chain length distribution
3
of inulin dp 25 at different time intervals
during the hydrolysis. The increasing concen-
tration of F –F chains indicates that hy-
1
8
24
drolysis takes place by random-splitting of the
chains rather than by sequential hydrolysis of
end groups. This is in line with the observed
quasi induction time, which would be absent
in the latter case. It should be noted that no
peaks corresponding to F –F are observed
and inulin dp 25. Addition of 0.1 g
D-glucose
to 0.9 g inulin dp 25 gave the same curve for
the monosaccharide formation as a solution of
1 g of this inulin, despite the lower inulin
10
17
in the chromatograms, probably due to over-
lap with other peaks.
Fig. 3. (a) HPAEC chromatogram of inulin dp 10 and (b) chain length distribution of inulin dp 10 (ꢃ) and its long chain fraction
with dp 25 (ꢁ).

A.W. Heinen et al. / Carbohydrate Research 330 (2001) 381–390
385
Fig. 4. Chain length distribution of inulin dp 25 during hydrolysis over SX1GN65; GF (ꢃ) and F chains (ꢁ); 50 mL aqueous
n
m
solution of 1 g substrate and 0.250 g catalyst, 100 °C. The peaks corresponding to F –F probably overlap with other peaks.
10
17
The y-axis scale (in a.u.) in all figures is equal, so at 69 min some bars* exceed the maximum.
concentration. These experiments prove that
short chains do not inhibit the hydrolysis of
longer chains.
strongly acidic polystyrene resin, functional-
ized with sulfonic acid groups. All inulin
oligomers are assumed to be able to diffuse
into the Amberlyst 15 beads. However, on
zeolite H-beta, probably only the di- and
trisaccharides diffuse into the inner pores with
a reasonable rate. The large outer-surface of
H-beta may be responsible for the hydrolysis
of the longer inulin chains.
On Amberlyst 15, both types of inulin are
hydrolyzed with the same rate of monomer
production; the same result was obtained us-
ing a homogeneous HCl solution of pH 3.0.
On zeolite H-beta, the rate of monosaccharide
production out of inulin dp 10 is higher than
that out of inulin dp 25. Apparently, long
chains do not adsorb stronger on the zeolite
surface than short chains. This results in a
faster monosaccharide production with inulin
dp 10. The high acidity of Amberlyst 15 and
its large amount of acid sites (4.6 meq/g)
probably results in fast hydrolysis of all inulin
chains. To obtain insight in the roles of ad-
sorption and diffusion, a more detailed analy-
sis would be required.
Two effects will influence the rate of
monosaccharide formation. Long chains can
be hydrolyzed faster, due to multiside attack
and the increase in entropy upon splitting of
the chain on one hand and a stronger adsorp-
tion on the carbon surface on the other hand.
If long and short chains would hydrolyze with
equal rates, the rate of production of
monosaccharides would be higher with short
chains. The faster formation of monosaccha-
rides from long chains may therefore be as-
cribed to the increasing adsorption strength
13
on carbon with inulin chain length. This also
explains the decreasing rate of monosaccha-
ride formation at high conversions, where pre-
dominantly short chains remain.
In Fig. 6, the hydrolysis of inulin dp 10 and
inulin dp 25 on Amberlyst 15 and zeolite
H-Beta is presented. Compared to oxidized
carbon SX1GNS (Fig. 5(a)), Amberlyst 15 is
slightly more active, whereas H-Beta is less
active. Amberlyst 15 is a macroporous,

386
A.W. Heinen et al. / Carbohydrate Research 330 (2001) 381–390
Effect of pressure.—As will be shown later,
during the combined hydrolysis–hydrogena-
tion of inulin over Ru/C at 100 bar H , the
2
hydrolysis rate under those conditions is much
higher than during the hydrolysis experiments
presented thus far. The hydrolysis rate in the
combined process is determined by monitor-
ing the total concentration of the monosac-
charides and alditols. As shown in Fig. 7(a),
Fig. 7. Hydrolysis of inulin dp 25 (a) in air (1 bar, 100 °C)
with 0.1 g SX1GNS (ꢀ) and Ru/SX1GNS (ꢂ) and (b) at
1
1
00 °C, 0.1 g Ru/SX1GNS and 1 bar air (ꢂ), 25 bar N (×),
2
00 bar N (ꢁ) and 100 bar H (ꢃ). All experiments were
2
2
carried out in an autoclave, containing 80 mL aqueous solu-
tion of 1 g inulin. The lines are a guide to the eye.
hydrolysis of inulin dp 25 on the Ru catalyst
is somewhat faster than on the bare carbon.
Apparently, Ru introduces extra acidity to the
catalyst.
Fig. 5. Hydrolysis of (a) inulin dp 10 (ꢃ), dp 25 (ꢁ), dp 30
A study on the effect of pressure on the
hydrolysis rate led to intriguing results. At
nitrogen pressures of 25–100 bar, the hydroly-
sis rate is much higher than at 1 bar. A similar
pressure effect was observed with zeolite H-
beta as the catalyst (see Fig. 8(a)). The effect
of pressure increased with temperature (90–
(
2), a long chain fraction of ‘dp 30’ (") and a short chain
fraction of ‘dp 30’ (×) with SX1GNS and (b) sucrose (ꢀ),
inulin dp 10 (ꢃ), dp 25 (ꢁ), dp 10+dp 25 (1:1) (×), dp
2
5+sucrose (9:1) (2) with SX1GN65; 50 mL aqueous solu-
tion of 1 g substrate and 0.250 g catalyst; 100 °C. The lines
are a guide to the eye.
1
00 °C; see Fig. 9). The hydrolysis rate in a
homogeneous reaction in a HCl solution at
pH 3.4 was independent of the pressure.
Bubbling air through the reaction mixture
by means of a sintered glass tube (at 1 bar)
did not increase the rate of hydrolysis. More-
over, lower stirring rates, which would in-
crease agglomeration, did not lower the
hydrolysis rate, neither at 1 bar, nor at 100
bar N . Therefore, it seems unlikely that the
2
Fig. 6. Hydrolysis of inulin dp 10 (open symbols) and dp 25
pressure effect is related to decreased catalyst
agglomeration at higher pressures. Further-
more, it appeared that at 100 bar argon, inulin
(
closed symbols) with Amberlyst 15 (ꢂ/ꢀ) and zeolite H-
beta (ꢃ/ꢁ); 50 mL aqueous solution of 1 g inulin and 0.250
g catalyst; 100 °C. The lines are a guide to the eye.

A.W. Heinen et al. / Carbohydrate Research 330 (2001) 381–390
387
hydrolyzed with the same rate as when using
00 bar nitrogen or hydrogen. Since the solu-
1
bility of argon in water is about three times
higher than the solubility of nitrogen and
1
4
hydrogen, it is, therefore, unlikely that the
increase of the hydrolysis rate at high pressure
is due to the influence of the solvated gas.
Impeding the carbon pores by air, which may
be pressed out by applying pressure, was ruled
out as an explanation by means of hydrolysis
reactions on degassed carbon, both at 1 and at
1
00 bar. Again, no change in activity was
observed, compared to the standard
experiments.
Most likely, the rate enhancement upon in-
crease of the pressure is the result of deeper
penetration of the inulin chains into the pore
system at higher pressures. According to the
Washburn equation (Eq. (1)), a liquid is
pressed into smaller pores (with radius r) by
increasing the pressure P:
r= −2k cos q/P
(1)
Since the surface tension k decreases with
increasing temperature, the pressure effect will
be more pronounced at higher temperatures,
Fig. 9. Hydrolysis of inulin dp 25 on SX1GNS at (a) 90 °C;
(
b) 95 °C and (c) 100 °C and at different N pressures: (") 1
2
bar; (ꢃ) 10 bar and (ꢁ) 100 bar. All experiments were
carried out in an autoclave, containing 80 mL aqueous solu-
tion of 1 g substrate and 0.100 g catalyst. The lines are a
guide to the eye.
which is in line with the results presented in
Fig. 9. However, for the Washburn equation
to be valid, the contact angle q must larger
than 90°. For the system water–graphite q=
1
5
8
6°, so the role of this effect in the present
system will depend on the value of q for the
system inulin solution–activated carbon.
Combined hydrolysis–hydrogenation of in-
ulin.—The formation of
D
-fructose,
D
-glu-
cose, -mannitol and
D
D
-glucitol during the
one-pot hydrolysis and hydrogenation of in-
ulin dp 10 over 1% Ru/SX1GNS at 100°C and
1
D
00 bar hydrogen is shown in Fig. 10(a). The
-fructose and
D-glucose concentrations rise
to a maximum value after about 150 min.
Lower pressures (25 and 50 bar) show com-
parable curves, as is expected from the low
Fig. 8. (a) Hydrolysis of inulin dp 10 on zeolite H-beta at 1
bar (×) and 100 bar N (ꢁ); (b) hydrolysis of sucrose on
2
1
6
SX1GNS at 1 bar (×) and 100 bar N (ꢁ).
order in H reported earlier. The faster hy-
2
2

388
A.W. Heinen et al. / Carbohydrate Research 330 (2001) 381–390
drogenation of
D
-fructose, compared to
D
-glu-
In this one-pot process, there is, similar to
the hydrolysis reaction (see above), a large
cose, is also in line with this study.
Two routes may be faced for this combi-
process: (i) hydrolysis followed by hydrogena-
tion of the monosaccharides; and (ii)
simultaneous hydrogenation and hydrolysis of
inulin fragments. Upon non end-on hydroly-
sis, F and GF chains are formed (Scheme 2).
influence of the chain length on the
tol and -glucitol formation (Fig. 10(b)). The
initial rates of total -mannitol– -glucitol
production are 0.112 and 0.013 mol/L h for
D-manni-
D
D
D
/
inulin dp 25 and dp 10, respectively. With
inulin dp 25, the reaction essentially reaches
completion in 150 min.
m
n
The GF chains do not contain a reducible
n
group. However, the fructose end-group of the
With inulin dp 10, the selectivity to
nitol, defined as the concentration of this com-
pound relative to the concentrations
mannitol and -glucitol, amounted to 37%.
With inulin dp 25, this value was slightly
higher (40%), due to the higher -fructose to
-glucose ratio resulting from long chain in-
ulins. These values are comparable with the
hydrogenation of -fructose over Ru/C
D
-man-
F fragments are reducible and can be hydro-
m
genated, releasing
D
-mannitol and
D-glucitol
D
-
D
after hydrolysis. Hydrogenolysis of inulin
fragments is not likely, because both sucrose
and inulin do not react in the presence of a
non-acidic Ru/C catalyst.
D
D
D
1
6
catalysts.
3
. Conclusions
Our results show that Ru on activated car-
bon oxidized with ammonium persulfate is a
good catalyst for a one-pot process for
D
-
mannitol production from inulin. No
byproduct like HMF is formed, however some
short chain oligomers remain after completion
of the reaction. The hydrolysis of long chains
is faster than the hydrolysis of short chains,
due to multiside attack and a stronger adsorp-
tion of long chains on the carbon surface. The
hydrolysis rate can be increased dramatically
by applying pressure (25–100 bar).
4
. Experimental
Fig. 10. Concentrations of
-mannitol (ꢀ) and -glucitol (ꢁ) formed in the hydrogena-
tion of (a) inulin dp 10 and (b) inulin dp 25; 80 mL aqueous
D-glucose (ꢄ), D-fructose ("),
D
D
Materials.—The activated carbon used in
solution of 1 g inulin and 0.100 g 1% Ru/SX1GNS, 100 °C,
this study (Norit SX1G) was donated by
Norit NV (Amersfoort, The Netherlands). In-
ulin, with an average dp of 10 was a gift from
Sensus (Co o¨ peratie Cosun U.A., Roosendaal,
The Netherlands). From this inulin, a fraction
with an average dp of 25 was obtained by
selective precipitation. Ammonium persulfate,
1
00 bar H . The lines are a guide to the eye.
2
(
NH ) S O , and inulin dp 30 were obtained
4
2
2
8
from E. Merck KGaA (Darmstadt, Ger-
many). RuCl ·x H O (40 wt% Ru) was a gift
Scheme 2. Hydrogenation of inulin GF chains is not possi-
ble; the fructose end-group of Fm chains can possibly be
hydrogenated, before hydrolysis to smaller fragments.
n
3
2
from Johnson Matthey (Hertfordshire, UK),

A.W. Heinen et al. / Carbohydrate Research 330 (2001) 381–390
389
NaBH was obtained from Fluka Chemie AG
An indication of the amount of carboxylic
acid sites was obtained by infrared spec-
troscopy. Infrared spectra were recorded with
a Perkin–Elmer spectrum 1000 FT-IR spec-
trometer. KBr tablets were used, containing 2
mg of carbon in 250 mg KBr. The spectra
were obtained by co-adding 20 spectra with a
4
(
Buchs, Switzerland), Ca(ClO) form Acros
2
Chimica NV (Geel, Belgium) and sucrose
from J.T. Baker Chemicals BV (Deventer, The
Netherlands). Amberlyst 15 was obtained
from Sigma–Aldrich Chemie BV (Zwijn-
drecht, The Netherlands), zeolite H-Beta (Si/
Al=50) from S u¨ d-Chemie AG (M u¨ nchen,
Germany).
−
1
resolution of 4 cm . The original spectra
were corrected for a curved baseline.
Carbon treatments.—The activated carbon
SX1G is a steam-activated peat-based carbon.
This carbon was treated in several ways: (i)
oxidation with nitric acid. Carbon (10 g) was
Catalyst preparation.—A 1% Ru/C catalyst
was prepared by incipient wetness impregna-
tion (i.e. filling of the support with the precur-
sor solution in an amount equal to its pore
volume) of SX1GNS (1 g) with a solution of
RuCl ·2.5 H O (28 mg) in 2.0 mL acetone.
refluxed in conc HNO (65%, 200 mL) for 3 h.
3
Then, the carbon was filtered off, washed with
water until the pH of the filtrate reached a
value of 5.5, dried overnight at ambient condi-
tions, and finally dried for 3 h at 80 °C. The
carbon treated in this way is denoted as
SX1GN65. (ii) Oxidation with calcium
hypochlorite. The oxidation with Ca(ClO)2
was performed at a constant pH of 4.2, at rt.
3
2
The catalyst was dried overnight under ambi-
ent conditions and for 3 h at 80 °C. Reduction
with hydrogen at 400 °C resulted in a major
loss of carboxylic acid sites, essential for the
inulin hydrolysis. Therefore, the precursor was
reduced with NaBH . To this end, aq 1.5 M
4
NaBH (20 mL) was slowly added to a sus-
4
1
7
Vinke et al. showed this to be the optimal
pH for oxidizing physically activated carbon.
SX1G (10 g) was added to 250 mL of aqueous
pension of the catalyst in water (20 mL). After
2 h, the unreduced NaBH was destroyed by
4
addition of HCl (15 mL, 2.5 M). The suspen-
sion was centrifuged and washed twice with
MeOH. The MeOH was evaporated under
reduced pressure and the catalyst support was
protonated with aq HCl (0.1 M).
0
.25 M Ca(ClO) . During the reaction, the pH
2
was adjusted to 4.2 with HCl (0.1 M) and the
suspension was maintained at this pH using
KOH (2 M). After 3 h of reaction, the carbon
was washed and dried as described above.
X-ray fluorescence spectroscopy, XRF
The metal loadings on the support were
measured using X-ray fluorescence spec-
troscopy, XRF (Philips PW1480).
(
Philips PW1480), showed that calcium and
potassium were completely removed from the
carbon. The carbon treated in this way is
coded as SX1GOCl. (iii) Oxidation with
Hydrolysis experiments.—The carbon was
suspended in water (40 mL) and heated to the
desired temperature. The experiment was
started by introducing an aq solution of the
substrate (10 mL). After reaction, the carbon
was centrifuged and washed four times with
water before re-use. Unless otherwise stated,
the experiments were performed at 100 °C,
using 50 mL solutions containing 1 g of sub-
strate and 0.25 g of carbon.
(
NH ) S O . Carbon (10 g) was added to a
4
2
2
8
satd solution of (NH ) S O in 1 M H SO
4
2
2
8
2
4
(
175 mL). After 22 h of reaction at rt, the
carbon was filtered off, washed and dried as
described above. The filtrates were checked
for sulfate with BaCl . The carbon treated in
2
this way is denoted as SX1GNS.
Carbon characterization.—The amount of
acid sites on the carbon surface was deter-
mined by selective neutralization with NaOH,
Hydrogenation experiments.—The hydro-
genation experiments were performed in a
Parr 4842 autoclave, made of Hastelloy C276.
A suspension of the catalyst (100 mg) in water
(50 mL) was introduced into the autoclave.
The system was flushed with N and H and
18
according to the method of Boehm. To 100
mg of carbon, 0.05 M NaOH (10 mL) was
added. After shaking the suspension for 4
days, the carbon was centrifuged, washed and
filtered over a 0.45 mm filter (Chromofil) and
titrated with 0.05 M HCl.
2
2
heated to the desired temperature under 10
bar H (strirring rate 1000 rpm). After that, 30
2
mL of an aq solution of the substrate (1 g) in

390
A.W. Heinen et al. / Carbohydrate Research 330 (2001) 381–390
water was introduced in the system and the H2
pressure was adjusted to the desired value.
Unless stated otherwise, the temperature and
the inulin, and Norit NV, for the activated
carbon. E. Wurtz and L. K o¨ nemann are ac-
knowledged for assisting in the autoclave ex-
periments and A.J. van Wissen for his
experimental contribution.
H pressure amounted to 100 °C and 100 bar,
2
respectively.
Product analysis.—Samples were taken
during the hydrolysis and hydrolysis–hydro-
genation experiments. To measure the
D
-fruc-
References
tose, -mannitol and -glucitol concen-
D
D
trations, the samples were filtered and ana-
lyzed by HPLC, using a Millipore-Waters 590
pump and a 300×7.8 mm cation exchange
column in the Pb form (Phenomenex), con-
nected to a refractive index detector (Shodex
RI SE-51). The samples were eluted with de-
gassed water at a flow rate of 0.6 mL/min and
a column temperature of 60 °C.
The different chain lengths of inulin were
separated with high pressure anion exchange
chromatography, coupled with a pulsed am-
perometric detector (HPAEC–PAD). A Wa-
ters 625 LC pump was connected to a Dionex
CarboPac column and a Dionex PAD detec-
tor. The samples were eluted (1 mL/min) with
a degassed and carbonate-free solution of 0.1
M NaOH, with a gradually increasing concen-
tration of NaOAc, up to 0.5 M.
1
2
. Makkee, M.; Kieboom, A. P. G.; van Bekkum, H. Car-
bohydr. Res. 1985, 138, 225–236.
. Heinen, A. W.; Papadogianakis, G.; Sheldon, R. A.;
Peters, J. A.; van Bekkum, H. J. Mol. Catal. A 1999, 142,
2
+
17–26.
3
4
5
6
7
. Jacobs, P. A.; Hinnekens, H. (Synfina-Oleofina S.A.), EP
0 329 923 (1989); Chem. Abstr. 1990, 111, 233477m.
. Ruddlesden, J. F.; Stewart, A. J. Chem. Res. 1981, S,
378.
. Masroua, A.; Revillon, A.; Martin, J.-P.; Guyot, A.;
Descotes, G. Bull. Soc. Chim. Fr. 1988, 3, 561–566.
. Sabadie, J.; Barthomeuf, D.; Charcosset, H.; Descotes,
G. Bull. Soc. Chim. Fr. 1981, 7–8, II288–292.
. Vinke, P.; van Bekkum, H. Starch 1992, 44, 90–96.
8. Heinen, A. W.; Peters, J. A.; van Bekkum, H. Appl.
Catal. 2000, 194–195, 193–202.
9. Vinke, P.; van der Eijk, M.; Verbree, M.; Voskamp, A.
F.; van Bekkum, H. Carbon 1994, 32, 675.
1
1
1
0. Cohen, E.; de Boer, R. B. Z. Phys. Chem. 1913, 84,
41–82.
1. Defaye, J.; Gadelle, A.; Pedersen, C. Carbohydr. Res.
1985, 136, 53–65.
2. de Leenheer, L. In Carbohydrates as Organic Raw Mate-
rials III; van Bekkum, H.; R o¨ per, H.; Voragen, A. L. J.,
Eds.; VCH: Weinheim, 1996; pp. 67–92.
1
1
3. Verraest, D. L.; Peters, J. A.; van Bekkum, H. Carbo-
hydr. Res. 1998, 306, 197–203.
4. Linke, W. F.; Seidell, A. Solubilities. Inorganic and
Metal-Organic Compounds, fourth ed.; ACS: Washing-
ton, 1965;.
Acknowledgements
The Innovation Oriented Program on
Catalysis (IOP-katalyse) is acknowledged for
the financial support. Dr J.J. Derksen of the
Kramers Laboratory, Delft University of
Technology, is acknowledged for the helpful
discussion concerning the pressure effects.
Thanks are also due to Sensus, for providing
15. Boyd, G. E.; Livingston, H. K. J. Am. Chem. Soc. 1942,
64, 2383–2388.
16. Heinen, A. W.; Peters, J. A.; van Bekkum, H. Carbohydr.
Res. 2000, 328, 55–63.
17. Vinke, P.; van der Eijk, M.; Verbree, M.; Voskamp, A.
F.; van Bekkum, H. Carbon 1994, 32, 675–686.
18. Boehm, H. P. Ad6. Catal. 1966, 16, 179–274.
.