Full text of DOI:10.1002/1099-1581(200005)11:5<258::AID-PAT974>3.0.CO;2-N

POLYMERS FOR ADVANCED TECHNOLOGIES
Polym. Adv. Technol. 11, 258±261 (2000)
Catalytic Behaviors of Silica-supported
Natural Biopolymer±Oxalic Acid±Pt
Complexes in Hydrogenation²
Hong-Wen Liu*, Dong-Yue Li, Mei-Yu Huang and Ying-Yan Jiang
Institute of Chemistry, The Chinese Academy of Sciences, Zhongguancun, Beijing 100080, China
their derivatives such as chitin [2], wool [3] and
carboxymethylcellulose [4] have been found to be
ABSTRACT WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW
useful as effective ligands. It is well known that
enzymes are natural biopolymeric catalysts and
have extremely high activity and selectivity in mild
conditions. In addition, an enzyme consists of
several kinds of polymers of amino acids, and has
a higher-order structure. In order to imitate the
function of enzyme, the useful application of
natural biopolymers may be one of the effective
Three kinds of natural biopolymers, gelatin, alginic acid
and sodium carboxymethylcellulose (NaCMC), were
reacted with oxalic acid in the presence of silica to yield
complexes on the surface of silica, followed by reaction
with H2PtCl6 6H2O to form Pt complexes, SiO2±
gelatin±(COOH)2±Pt, SiO2±alginic acid±(COOH)2±Pt,
and SiO2±NaCMC±(COOH)2±Pt, respectively. These
complexes were able to catalyze the hydrogenation of 1-
courses.
heptene to give n-heptane and that of nitrobenzene to give
Four kinds of natural biopolymers, gelatin,
alginic acid, sodium carboxylmethylcellulose
(NaCMC) and casein were employed to react with
oxalic acid in the presence of silica to yield
aniline at 25°C and under 1 atm H2 in 100% yields.
Experimental data show that the catalysts were very
stable and could be reused without any remarkable
change in catalytic activity. Copyright Ó 2000 John
Wiley & Sons, Ltd.
complexes on the surface of silica, followed by the
reactions with H2PtCl6Á6H2O to produce Pt com-
plexes (Fig. 1). These silica-supported biopolymer±
oxalic acid±Pt complexes, SiO2±gelatin±(COOH)2±
Pt, SiO2±alginic acid±(COOH)2±Pt, SiO2±NaCMC±
KEYWORDS: biopolymer; oxalic acid; Pt complex
catalyst; hydrogenatiorr, nitrobenzene
(COOH)2±Pt,
SiO2±casein±(COOH)2±Pt, were
found to catalyze the hydrogenation of 1-heptene
to give n-heptane and that of nitrobenzene to give
aniline in 100% yields at 25°C and under 1atm H2,
respectively. These catalysts were very stable and
could be reused without obvious loss in catalytic
activities.
INTRODUCTION WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW
Many polymer±metal complexes have been used to
catalyze the hydrogenation of various organic
compounds [1]. In general, synthetic polymers
have been used as the polymer ligands. In the
previous papers, some natural biopolymers and
EXPERIMENTAL WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW
* Correspondence to: H.-W. Liu, Institute of Chemistry, The
Chinese Academy of Sciences, Zhongguancun, Beijing 100080,
China
Preparation of Silica-supported Oxalic Acid
In a typical experiment, 0.45g of oxalic acid
dihydrate was dissolved in 40ml of H2O to prepare
oxalic acid aqueous solution, to which 4g of silica
² This paper was presented at the 2nd International Symposium on
Hi-tech Polymers and Polymeric Complexes (HPPC-II), Zhengzhou
University, China on 13±19 September 1999.
Received 12 September 1999
Revised 1 November 1999
Accepted 10 December 1999
Copyright ã 2000 John Wiley & Sons, Ltd.

Silica-supported Complexes / 259
cylinder, catalyst, SiO2±gelatin±(COOH)2±Pt, SiO2±
alginic acid±(COOH)2±Pt, SiO2±NaCMC±(COOH)2
±Pt or SiO2±casein±(COOH)2±Pt, and the substrate
1-heptene or nitrobenzene, as well as solvent, were
placed. The hydrogenation reaction system was
alternately evacuated and flushed with hydrogen
several times. The hydrogenation was carried out at
room temperature and under atmospheric hydro-
gen pressure. During the hydrogenation, the
volume of hydrogen absorbed was measured. After
the reaction, the reaction mixture was filtered to
separate the catalyst. The recovered catalyst may be
reused. The hydrogenation products were ana-
lyzed by gas chromatography (GC).
FIGURE 1. Structures of silica-supported bio-polymer±
oxalic acid±Pt complexes.
RESULTS AND DISCUSSION WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW
Silica-supported biopolymer±oxalic acids were
prepared simply by mixing silica, oxalic acid and
biopolymer which are very cheap commercial
materials [5]. Gelatin is a copolymer of various
amino acids with an average molecular weight of
60,000. It can be obtained from skins and bones of
various animals, and is usually used as hemostatic,
food, adhesive, medicine, capsule etc. Alginic acid
is similar to cellulose in chemical structure except
for the presence of ÐCOOH groups in molecules. It
can be obtained from various brown seaweeds, and
is used as the raw material of fiber, emulsifying
agent of medicines and cosmetics, sizing material
for paper, etc. Sodium carboxymethylcellulose is a
derivative of cellulose produced from cellulose in a
large scale, and commonly used as an additive in
soap, synthetic washing agents, papers, foods,
medicines and cosmetics. Casein is a copolymer
of various amino acids containing phosphoric acid
with a molecular weight of 75,000±375,000. It is
produced from milk, and used as the raw material
of cheese, adhesive water paint, emulsifying agent,
entrophic medicine, etc.
These natural biopolymers, gelatin, alginic acid,
NaCMC oxalic acid and casein are all soluble in
water. When gelatin or casein is reacted with oxalic
acid, a complex connected by ionic bonds is
formed. Similarly, when alginic acid or NaCMC is
reacted with oxalic acid, a complex connected by
hydrogen bonds is produced. These complexes are
insoluble in water and any solvents, probably
because of the crosslinking in the reaction of the
preparing polymer ligand.
(specific surface area, 90m2/g) was added. The
mixture was dried, and milled and sieved to
produce silica-supported oxalic acid, SiO2±
(COOH)2 (4.3g, particles > 100 mesh).
Preparation of Silica-supported Biopolymer±
Oxalic Acid
In a beaker, 1g of gelatin was dissolved in 40ml of
water at 60°C, 1g of alginic acid was dissolved in
40ml of water in a beaker at 50°C, 1g of sodium
carboxymethylcellulose (NaCMC) was dissolved in
40ml of water by stirring in a beaker for 3hr, and 1g
of casein was dissolved in 40ml of 1% NaOH
aqueous solution by stirring for 1hr in a beaker.
To these beakers containing gelatin, alginic acid,
sodium carboxymethylcellulose or casein aqueous
solution, SiO2±(COOH)2 was added, and mixed to
form a paste, dried, milled and sieved to obtain
about 5.3g of >100 mesh particles of SiO2±gelatin±
(COOH)2, SiO2±alginic acid±(COOH)2, SiO2±
NaCMC±(COOH)2 and SiO2±casein±(COOH)2, re-
spectively.
Preparation of Silica-supported Biopolymer±
Oxalic Acid±Pt Complexes
Silica-supported biopolymer±oxalic acid was re-
acted with H2PtCl6Á6H2O to produce Pt complexes
of differing Pt content. For instance, 1g of SiO2±
gelatin±(COOH)2, 0.077mmol H2PtCl6Á6H2O dis-
solved in small amounts of ethanol, and 10ml
ethanol were placed in a 25ml flask equipped with
a magnetic stirrer and reflux condenser. The
mixture was stirred and refluxed under nitrogen
atmosphere for 12hr. The reaction mixture was
filtered, washed with ethanol, and dried to obtain
about 1g of gray powder, SiO2±gelatin±(COOH)2±
Pt (Pt content: 0.077mmol/g).
The structures of biopolymer±oxalic acid±Pt
complexes shown in Fig. 1 are probable examples,
in which COOH, NH2, OH and P(O)(OH)2 groups
in biopolymer±(COOH)2 ligands are connected
with Pt ion in H2PtCl6Á6H2O by coordinate bond
or ionic bond. These functional groups can also
connect with each other by ionic bond or hydrogen
bond. Hence, the structures of biopolymer±oxalic
acid±Pt complexes should be very complicated
which may be varified by Pt content in the
complexes.
Hydrogenation
In 25ml flask equipped with a magnetic stirrer and
a hydrogen inlet tube connected to a hydrogen
volume measuring burette and a hydrogen storage
Experimental results of hydrogenation of 1-
heptene catalyzed by the silica-supported bio-
Copyright ã 2000 John Wiley & Sons, Ltd.
Polym. Adv. Technol., 11, 258±261 (2000)

260 / Liu et al.
TABLE 1. Hydrogenation of 1-Heptene Catalyzed by Silica-supported Bio-polymer±Oxalic Acid±Pt Complexes
Catalyst
Initial
hydrogenation
rate (ml/min)
n-Heptane
yield(%)
1-Heptene
(mmol)
Pt content
(mmol/g)
(mmol/0.2g)
SiO2±gelatin±(COOH)2±Pt
SiO2±Alginic acid±(COOH)2±Pt
SiO2±NaCMC±(COOH)2±Pt
SiO2±casein±(COOH)2±Pt
0.145
0.116
0.077
0.048
0.029
0.023
0.015
0.010
4.63
3.68
2.41
1.60
0.3
1.2
1.9
0.8
100
100
100
100
0.145
0.116
0.077
0.048
0.029
0.023
0.015
0.010
4.63
3.68
2.41
1.60
0.6
1.7
2.8
1.4
100
100
100
100
0.145
0.116
0.077
0.048
0.029
0.023
0.015
0.010
4.63
3.68
2.41
1.60
0.5
1.6
3.0
1.2
100
100
100
100
0.145
0.116
0.077
0.048
0.029
0.023
0.015
0.010
4.63
3.68
2.41
1.60
0
0
87
91
0
0.4
0.7
0
Catalyst, 0.2g; 1-heptene/Pt molar ratio, 160/1; solvent, 5ml ethanol; 25°C, 1atm H2, 6hr.
TABLE 2. Hydrogenation of Nitrobenzene Catalyzed by Silica-supported Biopolymer±Oxalic Acid±Pt Complexes
Catalyst
Initial
Aniline
yield(%)
Nitrobenzene hydrogenation
Pt content
(mmol)
rate (ml/min)
(mmol/g) (mmol/0.2g)
SiO2±gelatin±(COOH)2±Pt
SiO2±Alginic acid±(COOH)2±Pt
SiO2±NaCMC±(COOH)2±Pt
SiO2±casein±(COOH)2±Pt
0.145
0.116
0.077
0.048
0.029
0.023
0.015
0.01
6.96
5.52
3.60
2.40
0.6
1.5
2.5
1.1
100
100
100
100
0.145
0.116
0.077
0.048
0.029
0.023
0.015
0.010
6.96
5.52
3.60
2.40
0.5
1.4
3.3
1.3
100
100
100
100
0.145
0.116
0.077
0.048
0.029
0.023
0.015
0.010
6.96
5.52
3.60
2.40
0.5
1.8
3.2
1.4
100
100
100
100
0.145
0.116
0.077
0.048
0.029
0.023
0.015
0.010
6.96
5.52
3.60
2.40
0
0
90
92
0
0.5
0.8
0
Catalyst, 0.2g; nitrobenzene/Pt molar ratio, 240/1; solvent, 5ml ethanol 25°C, 1atm H2, 18hr.
polymer±oxalic acid±Pt complexes are shown in
Table 1. It can be seen that the initial hydrogenation
rate is greatly affected by Pt content in the complex
catalyst. At 0.077mmol/g Pt content, the catalysts
are more active. When SiO2±gelatin±(COOH)2±Pt,
SiO2±alginic acid±(COOH)2±Pt or SiO2±NaCMC±
(COOH)2±Pt is used as catalyst for this reaction, n-
heptene can be converted into n-heptane in 100%
Copyright ã 2000 John Wiley & Sons, Ltd.
Polym. Adv. Technol., 11, 258±261 (2000)

Silica-supported Complexes / 261
In order to determine the stability of the
catalysts, SiO2±gelatin±(COOH)2±Pt, SiO2±alginic
acid±(COOH)2±Pt and SiO2±NaCMC±(COOH)2±
Pt, the catalysts were recovered and reused. The
results are shown in Fig 2, in which the catalytic
activities do not change obviously regardless of
reuse.
CONCLUSIONS WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW
Silica-supported biopolymer±oxalic acid±Pt com-
plexes, SiO2±gelatin±(COOH)2±Pt, SiO2±alginic
acid±(COOH)2±Pt and SiO2±NaCMC±(COOH)2±
Pt, have been prepared and employed to catalyze
the hydrogenation of 1-heptene to n-heptane and
nitrobenzene to aniline at 25°C, 1atm H2 in 100%
yields respectively. These catalysts could be reused
without obvious changes in catalytic activity.
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FIGURE 2. Reuse stability of catalyst in the hydrogenation
of nitrobenzene: (B) by SiO2±gelatin±(COOH)2±Pt; (C) by
SiO2±alginic acid±(COOH)2±Pt; (D) by SiO2±NaCMC±
(COOH)2±Pt. Catalyst (Pt content, 0.077mmol/g), 0.05g
(Pt, 0.0037mmol); nitrobenzene, 0.98mmol;
nitrobenzene/Pt molar ratio, 265/1; solvent, 10ml
ethanol; 25°C, 1atm H2, 18hr.
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yield. However, when SiO2±casein±(COOH)2±Pt is
used as catalyst, it has no activity at 0.145 and
0.048mmol/g Pt content, and 90 and 92% yield are
obtained at 0.145 and 0.048mmol/g Pt content. This
example shows that the catalytic activity is greatly
affected by the Pt content in the complex. As shown
above the structure of the polymer±Pt complex may
be changed by changing the Pt content.
Table 2 shows the hydrogenation of nitroben-
zene catalyzed by silica-supported biopolymer±
oxalic acid complexes. The results are similar to the
hydrogenation of 1-heptene shown in Table 1.
Copyright ã 2000 John Wiley & Sons, Ltd.
Polym. Adv. Technol., 11, 258±261 (2000)