Preparation and performance of anchored heterogenized rhodium complex catalyst for hydroformylation

Article abstract of DOI:10.1016/j.molcata.2005.07.026

In order to solve the difficult problem in separation of homogeneous catalyst from the reaction mixture, heterogenized rhodium carbonyl complex catalyst for hydroformylation of olefins was prepared by copolymerization of functionalized 3-aminopropyltriethoxysalane with tetraethoxysalane (TEOS) via the sol-gel method. The catalyst was characterized by FT-IR, X-ray photoelectron spectroscopy (XPS), ICP and N₂ absorption. The activity, selectivity and stability of this catalyst for 1-hexene hydroformylation have been examined. It was concluded the activity depended on the surface area of the catalyst matrix, which varied according to the pH in the sol-gel process. The conversion of 1-hexene reached 98.8%, with a selectivity of 99.6% of aldehydes and the n/i ratio of 0.86 under optimized conditions. Furthermore, it showed excellent stability and reusability, the catalyst was used for six times without obvious loss of activity.

Full text of DOI:10.1016/j.molcata.2005.07.026

Journal of Molecular Catalysis A: Chemical 241 (2005) 238–243
Preparation and performance of anchored heterogenized rhodium
complex catalyst for hydroformylation
Jiquan Zhaoa,∗, Yuecheng Zhanga,b, Jianping Hana, Yongjie Jiaoa
a School of Chemical Engineering, Hebei University of Technology, Tianjin 300130, PR China
b School of Pharmaceuticals and Biotechnology, Tianjin University, Tianjin 300072, PR China
Received 29 April 2005; received in revised form 12 July 2005; accepted 19 July 2005
Available online 24 August 2005
Abstract
In order to solve the difficult problem in separation of homogeneous catalyst from the reaction mixture, heterogenized rhodium carbonyl complex
catalyst for hydroformylation of olefins was prepared by copolymerization of functionalized 3-aminopropyltriethoxysalane with tetraethoxysalane
(TEOS) via the sol–gel method. The catalyst was characterized by FT-IR, X-ray photoelectron spectroscopy (XPS), ICP and N2 absorption. The
activity, selectivity and stability of this catalyst for 1-hexene hydroformylation have been examined. It was concluded the activity depended on the
surface area of the catalyst matrix, which varied according to the pH in the sol–gel process. The conversion of 1-hexene reached 98.8%, with a
selectivity of 99.6% of aldehydes and the n/i ratio of 0.86 under optimized conditions. Furthermore, it showed excellent stability and reusability,
the catalyst was used for six times without obvious loss of activity.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Rhodium complex; Hydroformylation; Olefin; Heterogenized catalyst; Sol–gel
1. Introduction
Herein, we present an easy and practical heterogenization
method by forming amide bond to anchor Rh carbonyl com-
plex with a carboxy group to the SiO2 matrix by a sol–gel
technique. The catalyst was characterized by FT-IR, XPS, ICP
and N2 absorption. The immobilized catalyst was applied to the
hydroformylation of 1-hexene.
The fatal problem for hydroformylation of olefins in the
homogeneous catalysis is the difficult separation of catalyst
from the reaction mixture. In the past three decades, many efforts
have been made to resolve this problem [1,2]. Various methods
[3–5] of heterogenization for overcoming it have appeared in
recent years. From the pre-works, we can know that the sol–gel
technique is a promising method for obtaining heterogenized
catalysts, because of its diversity, mildness in the procedure,
matrix stability and prevention of catalyst from leaching [6–8].
Generally, there are two sol–gel methods for heterogenizing
homogeneous catalysts. One is physically encapsulating
complex into solid matrix, the other is by the combination of
anchoring and sol–gel process. For the latter method, the com-
plexes are anchored to the matrix by chemical linkage except
for direct encapsulation in the former. It is expected the catalyst
heterogenized by this way is more stable and leaching-proof.
So it is interesting and useful to find new anchoring method for
obtaining stable heterogenized complex catalyst.
2. Experimental
2.1. Materials and methods
Triphenylphosphine, acrylic acid, teraethoxysilane (TEOS),
N-hydroxysuccinimide and 1,3-dicyclohexylcarbodiimide
(DCC) were purchased from Aldrich. THF was distilled from
sodium. Other solvents were dried and distilled prior to use as
usual. Water was distilled under N2 prior to use. The complex
of [Rh(CO)2Cl]2 was prepared by the McCleverty’s method
[9].
2.2. Characterization of the catalysts
∗
The H NMR spectrum was measured on a Bruker AC-P
300 (300 MHz for proton) spectrometer. FT-IR spectra were
Corresponding author. Tel.: +86 22 26564279; fax: +86 22 26564733.
E-mail address: zhaojiquan@jsmail.hebut.edu.cn (J. Zhao).
1381-1169/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2005.07.026

J. Zhao et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 238–243
239
recorded in KBr pellet, using a Bruker Vector 22 spectropho-
tometer, in the range 400–4000 cm−1. To determine the metal
content, the sample was dissolved in concentrate HNO3 and
HF, and then the metal content of these solutions was deter-
mined by a T.J.A ICP-9000(N+M) type ICP-AES instrument.
X-ray photoelectron spectroscopy (XPS) measurements of
the heterogenized catalysts were recorded in a PHI5300
ESCA instrument at 10−7 Pa, the pass energy of 50 eV and
using nonmonochromatized Mg K␣ as the radiation source.
N2 adsorption measurements were performed at 77 K on a
Micromeristics ASAP 2010 sorptometer. Prior to measurement,
all samples were dried under 110 ◦C for 3 h, and then degassed
for 15 h at 110 ◦C. Surface areas were determined from the BET
equation, while pore volumes were determined from the BJH
equation.
3-aminopropyltriethoxysilane. The mixture was stirred for 24 h,
then the solvent was distilled off and a solid product (B) was
obtained. B was dissolved in 50 ml of toluene. To the solu-
tion was slowly added 0.240 g of [Rh(CO)2Cl]2 in 10 ml of
toluene, and the solution obtained was stirred for 4 h, then the
toluene was distilled off to produced C. C was dissolved with
10 ml of ethanol. Fifteen milliliters of TEOS and 7.5 ml of dis-
tilled water were added to the above solution under stirring
to get a homogeneous solution. To the solution, hydrochloric
acid was added to adjust the pH to 3. The stirring was con-
tinued under 60 ◦C until gelation was completed. The gel was
dried under 50 ◦C till a constant weight was obtained and then
washed with boiling water until the pH of the washing water
reached 7. Finally, the heterogenized catalyst (D) was obtained
after the gel was extracted with toluene in a Soxhlet extractor
for 10 h.
2.3. The analysis of the products
2.6. Hydroformylation reaction
Reaction products were analyzed on a Shandong Lunan
Ruihong Gas Chromatograph, SP-6800A, equipped with
an SE 30 capillary column, 30.0 m × 0.25 mm and an FID
detector. Nitrogen was the carrier gas. The products were also
characterized by a Trace-DSQ GC–MS system with a CP Sil
CB-MS capillary column, 30 m × 0.25 mm × 0.25 ␮m (Thermo
Electron Cooperation, USA).
All the hydroformylation reactions were carried out in a
250 ml stainless steel autoclave with a magnetic stirrer supplied
by Weihai Autoclave Cooperation, China. An amount of 0.238 g
of the heterogenized catalyst was introduced into the autoclave
under a nitrogen atmosphere. The resulting solution composed
of 1-hexene (5 ml, 0.04 mol) and toluene (50 ml) was charged
into the reactor by suction. The reaction vessel was purged with
carbon monoxide and hydrogen two times alternatively and then
filled with H2 and CO to the needed pressure (H2:CO = 1:1). The
mixture was heated up to the needed reaction temperature and
stirred magnetically at 800 rpm for 9 or 10 h. After the reaction
completed, the mixture was cooled to ambient temperature and
analyzed by GC.
For the recycle test experiments, the heterogenized cata-
lyst was allowed to settle down and the supernatant liquid was
extruded out. The residual catalyst was washed with toluene and
dried under vacuum. The solvent and reactants were introduced
into the vessel according to the same procedure as above and
the reaction was run under the same reaction conditions as in
the first run. For determining the rhodium leaching, the rhodium
content of the catalyst was analyzed by XPS and ICP before and
after the cycle.
2.4. Synthesis of diphenylphosphine propionic acid
The synthesis was performed under nitrogen using standard
Schlenk techniques. To 4.0 g of triphenylphosphine in 25 ml
of THF was added 0.4 g of metallic lithium. The mixture was
stirred for 6 h, then the lithium left was removed by filtration
[10]. To the filtrate, 1.4 g of t-butyl chloride dissolved in 15 ml
of THF was slowly added at 0 ◦C. The solution obtained was
heated up to reflux for 0.5 h, and then cooled to 20 ◦C. To
the solution was slowly added 1.1 g of acrylic acid in 25 ml
of THF, and the solution obtained was stirred for 2 h. The
THF was distilled off and the residue was dissolved in 15 ml
of water. The aqueous solution obtained was extracted with
diethyl ether to remove impurities. The aqueous layer was
acidified with 2N of hydrochloric acid and some precipitate
took place. The precipitate collected was recrystallized from
ethanol. The pure ligand diphenylphosphine propionic acid
was obtained. IR (KBr): 3070, 3016, 2924, 2854, 1709,
3. Results and discussion
1432, 1256, 736 and 695 cm−1; H NMR (300 MHz, CDCl3)
3.1. Preparation of the catalyst
1
δ: 2.29–2.46 (m, 4H, –CH2–), 7.24–7.43 (m, 10H, Ar–H);
EI–MS m/z: 258 (M+ + 1); mp 126.7–127.3 ◦C (literature [11],
127–128 ◦C).
As shown in Scheme 1, an active ester was synthesized
first via the reaction of diphenylphosphine propionic acid
with N-hydoxysuccinimide and used directly. By employ-
ing the reaction of this active ester with the amino group
of 3-aminopropyltriethoxylsalane, the functionalized lig-
and 3-aminopropyltriethoxylsalane (EtO)3SiCH2CH2CH2
NHCOCH2CH2PPh2 (B) was prepared. The conditions of
the process were mild and easy, and the reaction was almost
quantitative. This ligand reacted with [Rh(CO)2Cl]2 smoothly
to give the corresponding homogeneous complex (C) with group
–Si(OEt)3 [12] which allowed the complex to be copolymerized
2.5. Preparation of the heterogenized catalyst
The preparation of the heterogenized catalyst was per-
formed under nitrogen using standard Schlenk techniques. To
1.000 g of diphenylphosphine propionic acid (A) in 25 ml
of THF were added 0.452 g of N-hydroxysuccinimide and
0.834 g of DCC. The mixture was stirred at 25 ◦C for 24 h
and then it was filtrated. To the filtrate was added 0.858 g of

240
J. Zhao et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 238–243
Scheme 1. Outline of the preparation of the heterogenized catalyst.
1087, 740 and 698 cm−1 in (b) can be apparently identified in
(c).
with TEOS to give the heterogenized catalyst (D) by the sol–gel
technique.
The XPS spectra gave the corresponding binding energies
and molar fractions of phosphorus, rhodium and silicon atoms
on the surface of the fresh catalyst and the catalyst after the
first and the seventh runs, respectively. The results are shown in
Fig. 2 and Table 1. From Fig. 2, we can know that the binding
energies of the elements in the catalyst agreed well with those
in literature [5], which indicated that rhodium was present in the
1+ oxidation state as in the homogeneous complex. This fully
supports the idea that the complex suffered from no damages in
the preparation procedures and the catalytic reaction. Thus this
method for preparing the heterogenized catalyst is reliable and
the catalyst obtained will have good recyclability in the catalytic
reaction.
3.2. Catalyst characterization
For elucidation of the structure, the oxidation state, the sur-
face area of the matrix and the content of rhodium, the catalyst
was characterized by FT-IR, XPS, N2 adsorption and ICP. Fig. 1
is the FT-IR spectra of diphenylphosphine propionic acid (a),
the homogeneous complex (b) and the heterogenized catalyst
(c). Comparison of the three IR spectra shows that the rhodium
complex is anchored and entrapped into the SiO2 matrix. The
υ(C O) of the acyl that appeared at 1709 cm−1 in the spectrum
of diphenylphosphine propionic acid (a) shifts to 1648 cm−1 in
the homogeneous complex (b), which suggests the formation
of amide. A sharp band centered at 1973 cm−1 in the homoge-
neous complex (b) is attributed to vibration of CO coordinated
to Rh [13]. This vibration shifts to 1981 cm−1 after encapsula-
tion, which indicates the strength of CO coordination with Rh
is enhanced after the complex is anchored and entrapped in the
matrix. Theothercharacteristicbandsat2927, 2860, 1550, 1435,
3.3. The effect of pH in the sol–gel process on the catalysis
of the catalyst
Generally, the catalysis of heterogenized catalyst via the
sol–gel technique depends on the conditions including encapsu-
lating temperature, drying temperature, the molar ratio of water
to TEOS and the pH employed in the sol–gel process. From
experimental results, we found that pH was the most important
factor in determining the catalysis of the heterogenized complex.
Table 2 presents the conversion and selectivity towards aldehyde
in the hydroformylation of 1-hexene in presence of the catalysts
Table 1
Surface atomic concentration of the heterogenized catalyst determined by XPS
Catalyst
Mole fraction of elements (%)
Si
P
Rh
n(Rh)/n(Si)
n(Rh)/n(P)
Fresh
Running 1 time
Running 7 time
39.60
35.86
41.41
1.07
1.01
1.02
0.43
0.19
0.17
0.011
0.0053
0.0041
0.40
0.19
0.17
Fig. 1. FT-IR spectra of: (a) the ligand diphenylphosphine propionic acid, (b)
the homogeneous catalyst and (c) the heterogenized catalyst.

J. Zhao et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 238–243
241
Fig. 2. XPS profile of P and Rh ions in the heterogenized catalyst: (A) fresh heterogenized catalyst; (B) heterogenized catalyst of running 1 time; (C) heterogenized
catalyst of running 7 time.
encapsulated in different pHs. It can be seen that the highest con-
version (91.0%, corresponding 1172 of the TON) of 1-hexene
was obtained when the catalyst prepared at pH 4 (entry 3) was
employed in the hydroformylation of 1-hexene at 100 ◦C under
5 MPa, while the conversion was only 81.2% for the catalyst
prepared at pH 2. It seems that the pH had no remarkable effect
on the selectivity of the catalyst for the hydroformylation of
1-hexene.
pore volume of the catalyst. Large pores facilitate the fast diffu-
sion of substrates to the active center, which also increases the
catalytic activity of the heterogenized catalyst. Here, all aver-
age pore diameters of the catalysts are larger than the diameter
of 1-hexene, which allows 1-hexene to enter into the matrixes
smoothly, so the diameter is not the key factor determining the
catalytic activities of the catalysts.
Although the heterogenized catalyst showed excellent con-
version, high selectivity towards aldehyde and TON in the
hydroformylation of 1-hexene, the n/i ratio of the aldehyde was
relatively low. The n/i ratio for all the catalysts in the hydro-
formylation of 1-hexene was not higher than 0.90. The low value
of n/i ratio may be derived from the fact that ligand anchored
to the matrix could not move freely to the catalytic center as
that in the homogenous analogues, which caused no steric effect
enhancing the increase in the n/i ratio. Perhaps, this problem can
be solved by lengthening the anchoring linker. The other reason
might be that the heterogenized catalyst has a strong isomeriza-
tion activity derived from the matrix.
For elucidating why this happened, N2 absorption was
employed to analyze the surface area, pore volume and average
pore diameter of the catalysts. The results are given in Table 3.
The catalytic activity obviously relates with the internal struc-
ture of the catalysts. It is noted that the surface area, pore volume
and average pore diameter of the catalyst prepared at pH 4 are
2
3
˚
389 m /g, 0.20 cm /g and 20 A, respectively, larger than those
prepared at other pHs. Large surface area allows more active
center to be exposed to reactants, giving more chances of sub-
strates contacting the catalytic active center of the catalyst and
enhancing the activity of the catalyst. Therefore, the catalyst
obtained at pH 4 is the best in activity among all the catalysts.
The catalytic property is also related with the pore diameter and
Because the heterogenized catalyst prepared at pH 4 showed
the highest activity, it was studied intensively. The reaction
parameters influencing the catalytic activity were investigated
and optimized.
Table 2
Hydroformylation of 1-hexene with the catalysts prepared at different pH values
Table 3
Entry
pH
Conversion (%)
Selectivity
TON
N2 adsorption results of the catalysts
Aldehyde (%)
n/i
Entry
pH
Surface areaa
(m2/g)
Pore volumeb
(cm3/g)
Average pore
c
˚
diameter (A)
1
2
3
4
2
3
4
5
81.2
85.3
91.0
86.8
99.4
99.4
99.3
99.6
0.81
0.86
0.89
0.84
1046
1113
1172
1121
1
2
3
4
2
3
4
5
290.78
312.37
388.58
314.16
0.11
0.14
0.20
0.13
15.14
17.93
20.32
16.55
Reaction conditions: catalyst—0.238 g, Rh-content in catalyst—1.34%,
a
w/w; PCO/H = 5.0 MPa (CO:H2 = 1:1); temperature—373 K; 1-hexene—5 ml
Calculated from the BET equation.
Calculated from the BJH equation.
Average pore diameter = 4 × pore volume/surface area.
2
b
c
(0.04 mol); solvent—toluene, volume—50 ml; reaction time—9 h; TON—mole
of aldehydes formed/mole of Rh.

242
J. Zhao et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 238–243
Table 4
Table 6
Effect of temperature on the reaction
Effect of solvent on the reaction
T (◦C)
Conversion (%)
Selectivity
TON
Solvent
Conversion (%) Selectivity
Aldehyde (%) n/i
TON
Aldehyde (%)
n/i
90
100
110
120
85.2
96.8
91.2
89.0
100.0
99.3
98.0
95.8
0.94
0.87
0.84
0.78
1104
1246
1159
1105
Toluene
Cyclohexane
1,4-Dioxane
98.7
98.9
98.4
99.6
99.2
99.9
0.86 1274
0.71 1272
1.03 1274
N,N-Dimethylformamide 20.5
100.0
2.18
266
Reaction conditions: catalyst—0.238 g; Rh-content in fresh catalyst—1.34%,
Reaction conditions: catalyst—0.238 g, Rh-content in fresh catalyst—1.34%,
w/w; PCO/H = 4.0 MPa (CO:H2 = 1:1); 1-hexene—5 ml (0.04 mol);
w/w, PCO/H = 5.0 MPa (CO:H2 = 1:1); temperature—373 K; 1-hexene—5 ml
2
2
solvent—toluene, volume—50 ml; reaction time—10 h; TON—mole of
aldehydes formed/mole of Rh.
(0.04 mol); solvent—toluene, volume—50 ml; reaction time—10 h;
TON—mole of aldehydes formed/mole of Rh.
3.4. Effect of temperature
ratio for the aldehyde increased from 0.83 to 0.87 as the pressure
increased from 3 to 4 MPa, but it did not greatly change when
the pressure increased from 4 to 5 MPa.
The hydroformylation of 1-hexene catalyzed by the heterog-
enized catalyst prepared at pH 4 was studied at 90–120 ◦C and
the results obtained are shown in Table 4. An increase in the
conversion of 1-hexene was observed with the increase in the
temperature from 90 to 100 ◦C. The highest conversion of 1-
hexene was obtained at 100 ◦C. At this temperature, the conver-
sionwas96.8%andtheTONreached1246. Then, theconversion
decreased with the increase in the temperature mainly because
isomerization of 1-hexene was enhanced at high temperature. It
was observed both the selectivity towards aldehyde and the n/i
ratio for the aldehyde decreased with the increase in the temper-
ature, which was also due to the increase in the isomerization of
1-hexene at elevated temperature.
3.6. Effect of solvent
Solvents also have influence on the hydroformylation of
olefin. In order to study the effect of solvent, several solvents
were employed in the hydroformylation of 1-hexene catalyzed
by the above catalyst. As shown in Table 6, the conversion was
higher than 98% when toluene, cyclohexane and 1,4-dioxane
were used as solvents. However, if N,N-dimethylformamide
was employed, the conversion was only 20.5%. It was also
observed that both the selectivity towards aldehyde and the n/i
ratio increased with the increase in the solvent polarity. The
selectivity towards aldehyde was 99.2% and the n/i ratio was
0.71 when cyclohexane was employed. However, the selectivity
reached 100% and the n/i ratio increased to 2.18 in N,N-
dimethylformamide. These results can be explained by the sol-
vating effect. That is, the polar solvent molecules could surround
the active center of the catalyst to generate a solvent cage which
slowed down the substrate to contact the catalyst and decreased
the reaction rate. Furthermore, the solvent molecules in the
cage enhance the coordination of the substrate to the Rh with
the terminal carbon atom or that with fewer substitutes, which
also pushed the isomerization of hexenes shifted to 1-hexene.
From above results, the optimized conditions for the hydro-
formylation of 1-hexene were obtained. When the reaction was
carried out at the optimized conditions (at 100 ◦C under 5 MPa
in toluene for 9 h), the conversion of 1-hexene was 98.8%, with
a selectivity of 99.6% towards aldehyde and the n/i ratio of 0.86.
3.5. Effect of pressure
The activity of the catalyst for the hydroformylation of 1-
hexene was studied at different pressures at 100 ◦C and the
resultsaregiveninTable5. Itwasfoundtheconversionincreased
with increasing pressure of synthesis gas (CO:H2 = 1:1) when
the pressure was lower than or equal to 5.0 MPa. As the pressure
increased from 3 to 5 MPa, the conversion increased from 80.2
to 98.7%, but the selectivity towards aldehyde kept almost con-
stant. The reason may be higher H2 pressure can stabilize the
rhodium hydride that is the key intermediate in the hydroformy-
lation cycle. Once the pressure was higher than 5.0 MPa, the
conversion began to decrease with the increase in the pressure,
which conformed to the kinetics of hydroformylation. The n/i
Table 5
Effect of pressure on the reaction
3.7. Recycle test of the heterogenized catalyst
Pressure (MPa)
Conversion (%)
Selectivity
TON
The goal of heterogenizing homogeneous catalyst is to find
a catalyst with good catalytic performance and reusability. The
heterogenized catalyst was used in subsequent catalytic runs to
obtain information as to its reusability. The results are presented
in Table 7. The conversion decreased by 2.9% in the second
run but it decreased by only 0.9% in the sixth run compared
to the second run. The drop of conversion during the recycle
runs should come from the leaching of rhodium. The conversion
cannot reflect the actual catalyst deactivation. Table 7 also gives
Aldehyde (%)
n/i
3.0
4.0
5.0
6.0
80.2
96.8
98.7
97.8
99.6
99.3
99.6
99.7
0.83
0.87
0.86
0.89
1059
1246
1274
1264
Reaction conditions: catalyst—0.238 g, Rh-content in fresh catalyst—1.34%,
w/w, CO:H2 = 1:1; temperature—373 K; 1-hexene—5 ml (0.04 mol);
solvent—toluene, volume—50 ml; reaction time—10 h; TON—mole of
aldehydes formed/mole of Rh.

J. Zhao et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 238–243
243
Table 7
anchoring and encapsulation. From these results, we also con-
clude besides the rhodium leaching, the impurities deposited on
the surface of the matrix, which blocked the substrates entering
to contact the catalyst, might be another reason to decrease the
conversion.
Recycle test results of the heterogenized catalyst for hydroformylation of 1-
hexene
Recycle runs
Conversion
(%)
Selectivity
TON
TOF
Aldehyde (%)
n/i
1
2
3
4
5
6
7
98.2
95.3
87.8
96.7
93.3
94.4
88.1
99.6
99.8
100.0
99.7
99.8
99.5
99.7
0.86
0.83
0.80
0.85
0.82
0.87
0.86
1268
1406
1297
1425
1376
1389
1298
126.8
140.6
129.7
142.5
137.6
138.9
129.8
4. Conclusions
A novel heterogenized rhodium carbonyl complex catalyst
for hydroformylation was prepared by the combination of chem-
ically anchoring and the sol–gel encapsulation methods. The
catalyst has high activity, selectivity and stability but low n/i
ratios in the hydroformylation of 1-hexene. It can be separated
easilyfromtheproductandreusableinnumerouscatalyticcycles
without much deterioration of the catalytic activity.
Reaction conditions: catalyst—0.238 g, Rh-content in fresh catalyst—1.34%,
w/w, in the catalyst of running 1 time—1.17%, w/w; PCO/H = 5.0 MPa
2
(CO:H2 = 1:1);
temperature—373 K;
1-hexene—5 ml
(0.04 mol);
solvent—toluene, volume—50 ml; reaction time—10 h; TON—mole of
aldehydes formed/mole of Rh; TOF—mole of aldehydes formed/((mole of
Rh) h).
Acknowledgement
We are very grateful for the financial support (no. 200008) of
this work by Science Foundation of Hebei Province of China.
the TOF. It can be seen that the TOF had not reduced markedly
during the recycle test. Compared with that in the second run, the
TOF in the sixth run decreased by 1.2%. The selectivity towards
aldehydes and the n/i ratio almost kept constant.
References
XPS and ICP were used to determine the leaching of rhodium
in the recycle runs. As shown in Table 1, 50% of rhodium atom
in the outer surface was lost after the first run. The heavy losses
of rhodium can be attributed to that the rhodium on the surface of
the matrix was not encapsulated by the matrix but only anchored
by phosphino ligand, while CO in the system could replace the
phosphino ligand from rhodium in the hydroformylation condi-
tions.
The XPS results cannot give the real leaching situation of
the catalyst because it cannot detect the atoms entrapped in the
matrix. For obtaining the accurate rhodium leaching of the het-
erogenized catalyst, the rhodium contents of the fresh catalyst,
the catalysts after the first and seventh runs were analyzed by
ICP, which were 1.34, 1.17 and 1.18%, respectively. From these
results, we can know 12.7% of the rhodium atom was leached
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subsequent runs. From the ICP and XPS results, we concluded
that the rhodium leaching (12.7%) mainly came from the outer
surface of the matrix, while the complex entrapped in the matrix
did not leach enormously with the combination of protection by
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