Octene hydroformylation by using rhodium complexes tethered onto selectively functionalized mesoporous silica and in situ high pressure IR study

Article abstract of DOI:10.1016/j.cattod.2010.10.065

SBA-15-based heterogeneous catalysts were applied to 1-octene hydroformylation. The turn over frequency over SBA-15/γ- aminopropylmethyldimethoxysilane (AEAPMDMS)/Rh catalyst with triphenylphosphine (TPP) ligand prepared by conventional post grafting method was higher than that of the homogeneous catalyst, (Rh(CH₃COO)₂)₂ with TPP. The SBA-15/AEAPMDMS/Rh catalyst can be easily recycled without rhodium loss. The molar ratio of linear to branched nonyl aldehydes was remarkably enhanced over the heterogeneous catalysts. The selectively functionalized rhodium catalyst (SBA-15/Ph₂Si(OEt)₂/AEAPMDMS/Rh), in which rhodium was selectively tethered intra-pore of SBA-15, was beneficial for improving the selectivity to linear aldehyde. In situ high pressure FT-IR analysis suggested HRh(CO)₂(PPh₃)₂ and HRh(CO)(PPh₃)₃ to be active species over the SBA-15/AEAPMDMS/Rh catalyst with TPP.

Full text of DOI:10.1016/j.cattod.2010.10.065

Catalysis Today 164 (2011) 561–565
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Octene hydroformylation by using rhodium complexes tethered onto selectively
functionalized mesoporous silica and in situ high pressure IR study
Ki-Chang Songa, Ji Yeon Baeka, Jung A Baeb, Jin-Heong Yimb,∗, Young Soo Koa, Do Heui Kimc,
Young-Kwon Parkd, Jong-Ki Jeona,∗∗
a Department of Chemical Engineering, Kongju National University, 275 Budae-dong, Cheonan 331-717, Republic of Korea
b Division of Advanced Materials Engineering, Kongju National University, 275 Budae-dong, Cheonan 331-717, Republic of Korea
c Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352, USA
d School of Environmental Engineering, Graduate School of Energy and Environmental System Engineering, University of Seoul, Dongdaemun-Gu, Seoul 130-743, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 17 November 2010
SBA-15-based heterogeneous catalysts were applied to 1-octene hydroformylation. The turn over
frequency over SBA-15/␥-aminopropylmethyldimethoxysilane (AEAPMDMS)/Rh catalyst with triph-
enylphosphine (TPP) ligand prepared by conventional post grafting method was higher than that of
the homogeneous catalyst, (Rh(CH3COO)2)2 with TPP. The SBA-15/AEAPMDMS/Rh catalyst can be easily
recycled without rhodium loss. The molar ratio of linear to branched nonyl aldehydes was remarkably
enhanced over the heterogeneous catalysts. The selectively functionalized rhodium catalyst (SBA-
15/Ph2Si(OEt)2/AEAPMDMS/Rh), in which rhodium was selectively tethered intra-pore of SBA-15, was
beneficial for improving the selectivity to linear aldehyde. In situ high pressure FT-IR analysis suggested
HRh(CO)2(PPh3)2 and HRh(CO)(PPh3)3 to be active species over the SBA-15/AEAPMDMS/Rh catalyst with
TPP.
Keywords:
Heterogeneous rhodium catalyst
SBA-15
Octene hydroformylation
FT-IR
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Mesoporous silica has an ordered structure with a large surface
area, thereby immobilizing a lot of metal complexes and having
Higher aldehydes and alcohols are very important high-value
added substances in the chemical industry. Recently, there is
growing interest in producing nonyl aldehydes through hydro-
formylation of octene compounds in the presence of hydrogen and
carbon monoxide [1–4]. Homogeneous complex catalysts such as
rhodium complex containing phosphorous ligands have been con-
sidered as an excellent catalyst for the hydrofomylation due to high
activity obtained at mild reaction conditions [5]. In order to facili-
tate separation, recovery and recycling of catalyst, a lot of studies
have been performed about rhodium catalysts supported in porous
organic or inorganic supports such as polymeric resin [6,7], SiO2
[8,9] and hydrotalcite [10]. It is necessary, however, to develop a
heterogeneous catalyst to present more superior activity and sta-
bility in comparison with the homogeneous catalysts. In addition, it
is really important to enhance the ratio of linear to branched alde-
hydes (hereinafter designated L/B), because among isomers of the
aldehydes produced, linear aldehyde is commercially more valu-
able than branched aldehydes.
highly dispersed active sites for catalytic reaction. In addition, its
pore size is larger than microporous supports, thereby leading to
a shape selective reaction in production of aldehydes with high
molecular weight [11]. Immobilization of rhodium complexes on
the mesoporous supports has been widely studied in the last several
decades [12–15]. Also the study on the surface functionalization
of mesoporous materials has grown significantly [16,17]. Among
these useful functional groups, amino groups show fairly good per-
formance for 1-octene hydroformylation catalysts [18].
This study aims to immobilize the rhodium complexes to SBA-15
for a catalyst producing nonyl aldehydes through hydroformylation
of 1-octene. We tried to enhance the ratio of linear to branched
aldehydes through the selectively tethered rhodium to surface of
mesoporous material. In addition, active species of the heteroge-
neous catalysts were investigated by using in situ high-pressure
FT-IR measured during the in situ reaction at high pressure and
high temperature.
2. Experimental
∗
Corresponding author at: Kongju National University, 275 Budae-dong, Cheonan
330-717, Republic of Korea. Tel.: +82 41 521 9397.
2.1. Catalyst preparation
∗∗
Corresponding author at: Kongju National University, 275 Budae-dong, Cheonan
SBA-15 was synthesized according to the previous lit-
330-717, Republic of Korea. Tel.: +82 41 521 9363.
E-mail addresses: jhyim@kongju.ac.kr (J.-H. Yim), jkjeon@kongju.ac.kr
(J.-K. Jeon).
erature [19].
A conventional post grafting method and a
selective functionalized method have been applied to mod-
0920-5861/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2010.10.065

562
K.-C. Song et al. / Catalysis Today 164 (2011) 561–565
ify SBA-15. The post grafting method, which included reflux
in a non-polar solvent in the presence of N(␤-aminoethyl) ␥-
aminopropylmethyldimethoxysilane (AEAPMDMS, GE Advanced
Materials), was used. 0.5 g of as-synthesized SBA-15 was dis-
persed in 75 ml of toluene for 0.5 h at 50 ◦C with stirring. After
3.5 mg of p-toluenesulfonic acid and 1.0 mmol of AEAPMDMS
were added, the mixture was heated up to reflux tempera-
ture (nearly 120 ◦C) and kept stirring for 2 h. After refluxing for
2 h the solid product was filtered, washed with ethanol several
times. The resulting solid was dried at 100 ◦C for 12 h. 1 g of
amine functionalized SBA-15 was added to a solution of 0.037 g
Rh4(CO)12 in n-hexane under N2. The mixture was stirred at
room temperature under N2 atmosphere for 5 h. Finally the result-
ing solid was dried under vacuum and henceforth designated as
SBA-15/AEAPMDMS/Rh.
3. Results and discussion
3.1. Textural properties of catalysts
Nitrogen adsorption–desorption isotherms of the catalysts are
shown in Fig. 1(a). All catalysts showed typical type IV isotherms
with type-H1 hysteresis loop at P/P0 of between 0.5 and 0.7. The
steep slope and sharp step are typical of multilayered adsorption
followed by capillary condensation in well-ordered channel-like
mesopores [20]. Despite the decrease in the amount of nitrogen
adsorbed, the shape of hysteresis loop is almost same. It means
that the pore shape may not be significantly changed through silane
functionalization process and additional rhodium immobilization
processes. In addition, the ordered hexagonal structures of the
immobilized rhodium catalysts were confirmed with small-angle
XRD results (Fig. 2).
A
selective functionalized method was applied for selec-
tively tethering rhodium onto the internal surface (in pores).
The as-calcined SBA-15 (3.0 g) was then dispersed in 80 mL of
toluene and stirred at 50 ◦C for 0.5 h. After sufficient immersion,
0.021 g of p-toluenesulfonic acid and 6.0 mmol of Ph2Si(OEt)2
were added sequentially and stirred at 120 ◦C for 2 h. The iso-
lated solid product was washed with ethanol three times and
dried at 100 ◦C for 12 h, resulting in external grafting. For the
internal grafting process, 3.0 g of SBA-15/Ph2Si(OEt)2 was added
to 80 mL of toluene. After stirring at 50 ◦C for 0.5 h, 0.021 g of
p-toluenesulfonic acid and 6.0 mmol of AEAPMDMS were added
and the mixture was refluxed at 120 ◦C for 2 h. The solid prod-
uct was filtered and washed with ethanol three times. Then, the
selective functionalized mesoporous silica SBA-15 was dried at
100 ◦C for 12 h. For the purposes of Rh immobilization, the same
process was performed. The final solid was designated as SBA-
15/Ph2Si(OEt)2/AEAPMDMS/Rh.
Textural properties of catalysts prepared in this study were
displayed in Table 1. The BET surface areas of functionalized SBA-
15 materials decrease with functionalization and the subsequent
immobilization process, because functionalized silanes and immo-
bilized rhodium are attached to the surface of the mesoporous
material. The pore volume of the rhodium-immobilized catalyst
was greatly decreased, confirming that a tethering agent blocked
pores of SBA-15, resulting in the reduction of surface area. The
pore size distribution was shown in Fig. 1(b). The immobilized
2.2. Catalysts characterization
Nitrogen adsorption–desorption isotherms were determined
using a Micromeritics ASAP 2020 at −196 ◦C. The surface area was
calculated according to the BET equation. The pore volume was
obtained from t-plot method. Small-angle powder X-ray diffrac-
tion (XRD) patterns were recorded on a Rigaku D/max-2500 X-ray
diffractometer.
2.3. Catalytic reactions and in situ high-pressure FT-IR analysis
0.165 g of catalysts was added to a stainless steel autoclave reac-
tor (80 mL) containing 50 ml THF and 4.26 g of 1-octene. And then
0.044 g of triphenylphosphine (PPh3, TPP) was added to the mix-
ture as a ligand. In the case of homogeneous catalytic reaction, we
used (Rh(CH3COO)2)2 as a precursor for a homogeneous Rh catalyst
for octene hydroformylation because (Rh(CH3COO)2)2 is not only
stable in air, but also relatively inexpensive in comparison with
those of other rhodium precursors, Rh(CO)4, Rh6(CO)16, Rh4(CO)12
,
or Rh(acac)(CO)2 [3]. Subsequently, the autoclave was sealed and
flushed with nitrogen gas. Syn-gas (CO/H2 = 1) was pressurized up
to 20 bar in the reactor, and then the reactor was heated to 120 ◦C.
The reactor was kept at that temperature, and the syn-gas was filled
up from a reservoir to maintain the pressure of 20 bar. After the
completion of the reaction, the resulting products were analyzed
by gas chromatography (GC-2014, Shimadzu).
A home-made IR cell was used to observe the intermediates of
1-octene hydroformylation occurred in liquid phase. The IR cell
was made of stainless steel and CaF2 windows, operating up to
400 ◦C and 20 bar. Temperature was measured with a thermocou-
ple and controlled by an external temperature controller. Spectrum
GX (Perkinelmer) with an MCT detector was used for IR spectrum.
Fig. 1. (a) Nitrogen adsorption/desorption isotherms of SBA-15 (᭹: adsorp-
tion, ꢀ: desorption), SBA-15/AEAPMDMS/Rh (ꢀ: adsorption, ꢁ: desorption),
SBA-15/Ph2Si(OEt)2/AEAPMDMS/Rh
(ꢁ:adsorption,
ꢂ:
desorption),
(b)
Pore size distribution of SBA-15 (ꢀ), SBA-15/AEAPMDMS/Rh (ꢁ), SBA-
15/Ph2Si(OEt)2/AEAPMDMS/Rh (ꢁ).

K.-C. Song et al. / Catalysis Today 164 (2011) 561–565
563
SBA-15
SBA-15 / AEAPMDMS/Rh
SBA-15 / Ph2Si(OEt)2 / AEAPMDMS/Rh
1
2
3
4
5
2θ
Fig. 2. XRD patterns.
rhodium catalysts had smaller pore size than that of SBA-15. Inter-
nal pores of two catalysts were functionalized using AEPMDMS,
therefore, the degree of reduction in surface area and pore vol-
ume was similar in both nonselectively functionalized catalyst
(SBA-15/AEAPMDMS/Rh) and selectively functionalized catalyst
(SBA-15/Ph2Si(OEt)2/AEAPMDMS/Rh).
3.2. Hydroformylation of 1-octene
Fig. 3. Conversion of 1-octene, yield of nonyl aldehyde, and selectivity over SBA-
15/AEAPMDMS/Rh catalyst (reaction condition: 20 bar and 120 ◦C, TPP/Rh = 20).
Fig. 3 presented conversion, yield and selectivity in hydroformy-
lation of 1-octene using SBA-15/AEAPMDMS/Rh with TPP ligand.
1-octene conversion and yield of nonyl aldehydes increased with
reaction time and reached maximum after 30 min. The selectivity
to nonyl aldehydes and octane isomers, which are desired products
of 1-octene hydroformylation, and by-products through isomeriza-
tion of 1-octene, respectively, were not significantly changed with
reaction time. In addition, the molar ratio of linear to branched
nonyl aldehydes (L/B) was not much varied with reaction time.
Fig. 4 exhibited turn over frequency (TOF), nonyl aldehyde
yield and L/B after 30 min of hydroformylation. The TOF of
SBA-15/AEAPMDMS/Rh with TPP, non-selectively functionalized
catalyst, was higher than that of the homogeneous catalyst
(Rh(CH3COO)2)2 with TPP. It can be attributed to the high dis-
persion of active sites tethered onto mesoporous silica having a
large surface area. The TOF of SBA-15/Ph2Si(OEt)2/AEAPMDMS/Rh
with TPP, selectively functionalized catalyst, was lower than that of
the non-selectively functionalized catalyst. Because rhodium active
sites are tethered onto inner surface of the selectively function-
alized catalyst, it appears to be limited by mass transfer of the
reactant, compared to the non-selectively functionalized catalyst.
The molar ratio of linear to branched nonyl aldehydes (L/B) was
0.8 in hydroformylation reaction over the homogeneous catalyst.
L/B were enhanced over the SBA-15/AEAPMDMS/Rh with TPP and
the SBA-15/Ph2Si(OEt)2/ AEAPMDMS/Rh, 2.5 and 2.8, respectively.
It is remarkable that L/B can be enhanced by the selectively func-
tionalized catalyst. It suggested that the catalyst in which rhodium
was selectively tethered inside pores was beneficial for improv-
ing the selectivity to linear aldehyde, compared to the catalyst
that rhodium was non-selectively immobilized inside and outside
mesopores. It is well known that when bulky phosphine ligands
are used in hydroformylation of higher olefins, it improves produc-
tivity of the linear aldehyde because of steric effects [21]. It may
be interpreted that such steric effects are greater due to rhodium
complex tethered inside the mesopore, thereby increasing the L/B,
which are more clearly observed in the selectively functionalized
catalyst.
In addition to the catalytic activity, it is necessary to reduce
the amount of rhodium loss during recycling of catalysts from
the economic point of view, because the amount of rhodium loss
during this process is very important factor of production cost.
The results of recycling of SBA-15/AEAPMDMS/Rh with TPP were
shown in Table 2. The nonyl aldehydes yield over the catalyst
is not significantly changed upon the catalyst recycle. It is note-
Table 1
Textural properties of the catalysts.
Catalyst
SBET (m2 g−1
)
Vtot (cm3 g−1
)
Pore size (nm)
Rh content (wt.%)a
SBA-15
SBA-15/AEAPMDMS
SBA-15/AEAPMDMS/Rh
SBA-15/Ph2Si(OEt)2
SBA-15/Ph2Si(OEt)2/AEAPMDMS
SBA-15/Ph2Si(OEt)2/AEAPMDMS/Rh
623
343
261
598
468
266
0.94
0.45
0.37
0.81
0.72
0.40
5.36
4.33
4.17
4.80
4.67
4.67
–
–
0.92
–
–
1.35
a
By ICP-AES with hydrofluoric acid treatment.

564
K.-C. Song et al. / Catalysis Today 164 (2011) 561–565
3
2
1
0
a
2004
1945
120 min
60 min
30 min
80
60
40
20
0
20 min
10 min
6
4
2
0
1978
5 min
2200
2100
2000
1900
-1
)
Wavenumber (cm
b
1945
2004
120 oC
D
C
B
A
Catalyst
Fig. 4. Turn over frequency (TOF), yield and L/B molar ratio of nonyl aldehyde
on the 1-octene hydroformylation over the rhodium homogeneous and hetero-
geneous catalyst systems. (A: Homogeneous catalyst, [Rh(Ch3COOH)2]2 + TPP, B:
SBA-15/AEAPMDMS/Rh + TPP, C: SBA-15/Ph2Si(OEt)2/AEAPMDMS/Rh + TPP, D: SBA-
15/AEAPMDMS/Rh, Reaction condition: 20 bar and120 ◦C, reaction time: 30 min,
TPP/Rh = 20).
100 oC
80 oC
worthy, moreover, that rhodium in product was detected less
than 0.5 ng/ml, suggesting that loss of rhodium during recycling
is negligible. Consequently, the SBA-15/AEAPMDMS/Rh catalyst is
believed to be easily recycled in comparison with the homogeneous
catalysts.
50 oC
2100
2200
2000
1900
3.3. High pressure in situ FT-IR analysis
-1
)
Wavenumber (cm
The results of FT-IR analysis upon reaction time using SBA-
15/AEAPMDMS/Rh and TPP under 20 bar and 120 ◦C were exhibited
in Fig. 5(a). The peaks at 1945 cm−1 and 2004 cm−1 increased
with reaction time, which could be assigned to HRh(CO)2(PPh3)2
and HRh(CO)(Ph3P)3, respectively [9,15,22]. According to pre-
vious results by Yan et al. [9], two broad peaks around 1938
and 2005 cm−1 appeared on HRhCO(PPh3)3/SiO2. Also, Yan et al.
[15] observed that two peaks at 1940 and 2000 cm−1 on
HRhCO(PPh3)3/SBA-15. These results were well agreed with our
results in Fig. 5(a). Fig. 5(b) displayed the FT-IR spectra of SBA-
15/AEAPMDMS/Rh with TPP, obtained during the reaction while
ramping temperature at a rate of 5 ◦C/min. The rhodium car-
bonyl complex in 1978 cm−1 observed at low temperature, then
the characteristic peaks of HRh(CO)2(PPh3)2 and HRh(CO)(PPh3)3
became apparent at 120 ◦C. Meanwhile, it was difficult to fig-
Fig. 5. (a) Time-resolved FT-IR spectra obtained during the 1-octene hydroformyla-
tion over SBA-15/AEAPMDMS/Rh with TPP (reaction condition: 20 bar, 120 ◦C), (b)
FT-IR spectra obtained during temperature-programmed hydroformylation reaction
of 1-octene over the SBA-15/AEAPMDMS/Rh with TPP (reaction condition: 20 bar).
ure out any other peaks except rhodium carbonyl complex at
1978 cm−1 in the FT-IR spectra of SBA-15/AEAPMDMS/Rh without
ligand, obtained during the reaction while ramping temperature
at a rate of 5 ◦C/min, as shown in Fig. 6. It is noticeable that the
heterogeneous catalyst without TPP ligand demonstrated very low
activity in 1-octene hydroformylation as shown in Fig. 4. Therefore,
TPP is thought to play an important role in readily forming active
sites such as HRh(CO)2(PPh3)2 and HRh(CO)(PPh3)3 which are only
observed on the SBA-15/AEAPMDMS/Rh catalyst containing TPP.
Table 2
Yield of 1-octene hydroformylation and Rh loss during recovery of catalyst.
Catalysta
Nonyl aldehyde yield (wt%)
L/Bb
Rh concentration in product (ng/ml)c
Fresh
Recycled
Recycled twice
69.1
68.6
66.7
2.5
2.6
2.6
<0.5
<0.5
<0.5
a
Catalyst: SBA-15/AEAPMDMS/Rh, TPP/Rh = 20.
Molar ratio of linear nonyl aldehyde to branched nonyl aldehyde.
Determined by ICP after removal of catalyst.
b
c

K.-C. Song et al. / Catalysis Today 164 (2011) 561–565
565
Acknowledgement
This work was supported by Mid-career Researcher Program
through NRF grant funded by the MEST (No. R01-2007-000-20144-
0).
120 ºC
References
100 ºC
80 ºC
[1] M. Beller, B. Cornils, C.D. Frohning, C.W. Kohlpaintner, J. Mol. Catal. A: Chem.
104 (1995) 17.
[2] D. He, D. Pang, T. Wang, Y. Chen, Y. Liu, Q. Zhu, J. Mol. Catal. A: Chem. 174 (2001)
21.
[3] J.K. Jeon, Y.K. Park, J.M. Kim, Chem. Lett. 33 (2004) 174.
[4] D. He, D. Pang, L. Wei, Y. Chen, T. Wang, Z. Tang, J. Liu, Y. Liu, Q. Zhu, J. Catal.
Commun. 3 (2002) 429.
1978
50 ºC
2100
[5] J.N. Armor, Catal. Today 163 (2011) 3–9.
[6] F. Hung-Low, G.C. Uzcátegui, M.C. Ortega, A.B. Rivas, J.E. Yanez, J. Alvarez, A.J.
Pardey, C. Longo, Catal. Today 107/108 (2005) 273–281.
[7] S.I. Fujita, S. Akihara, S. Fujisawa, M. Arai, J. Mol. Catal. A: Chem. 268 (2007)
244.
2200
2000
-1
1900
Wavenumber (cm
)
[8] H.J. Zhu, Y.J. Ding, L. Yan, J.M. Xiong, Y. Lu, L.W. Lin, Catal. Today 93–95 (2004)
389.
[9] L. Yan, Y.J. Ding, H.J. Zhu, J.M. Xiong, T. Wang, Z.D. Pan, L.W. Lin, J. Mol. Catal. A:
Chem. 234 (2005) 1.
Fig. 6. FT-IR spectra obtained during temperature-programmed hydroformylation
reaction of 1-octene over the SBA-15/AEAPMDMS/Rh without TPP (reaction condi-
tion: 20 bar).
[10] S.K. Sharma, P.A. Parikh, R.V. Jasra, J. Mol. Catal. A: Chem. 301 (2009)
31.
[11] L. Huang, Y. He, S. Kawi, Appl. Catal. A: Gen. 265 (2004) 247.
[12] N. Sudheesh, S. Sharma, R.S. Shukla, R.V. Jasra, J. Mol. Catal. A: Chem. 296 (2008)
61.
[13] Q. Peng, Y. Yang, Y. Yuan, J. Mol. Catal. A: Chem. 219 (2004) 175.
[14] K. Mukhopadhyay, A.B. Mandale, R.V. Chaudhari, Chem. Mater. 15 (2003)
1766.
[15] L. Yan, Y.J. Ding, L.W. Lin, H.J. Zhu, H.M. Yin, X.M. Li, Y. Lu, Mol. Catal. A: Chem.
300 (2009) 116.
[16] N. Garcia, E. Benito, J. Guzman, P. Tiemblo, V. Morales, R.A. Garcia, Micropor.
Mesopor. Mater. 106 (2007) 129.
[17] J.A. Bae, S.H. Hwang, K.C. Song, J.K. Jeon, S.K. Young, J.H. Yim, J. Nanosci. Nan-
otechnol. 10 (2010) 290.
[18] Q. Wei, Z.R. Nie, Y.L. Hao, L. Liu, Z.X. Chen, J.X. Zou, J. Sol. Gel. Sci. Technol. 39
(2006) 103.
[19] J.A. Bae, K.C. Song, J.K. Jeon, Y.S. Ko, Y.K. Park, J.H. Yim, Micropor. Mesopor.
Mater. 123 (2009) 289.
4. Conclusions
A
non-selectively functionalized rhodium catalyst (SBA-
15/AEAPMDMS/Rh) and selectively functionalized rhodium cat-
alyst (SBA-15/Ph2Si(OEt)2/AEAPMDMS/Rh) were used as hetero-
geneous catalysts in 1-octene hydroformylation. The TOF of
SBA-15/AEAPMDMS/Rh with TPP was higher than that of the homo-
geneous catalyst, Rh(Ch3COOH)2)2 with TPP. The molar ratio of
linear to branched nonyl aldehydes was remarkably enhanced
over the heterogeneous catalysts. The selectively functionalized
rhodium catalyst was beneficial for improving the selectivity to
linear aldehyde, compared to the non-selectively immobilized
rhodium catalyst, where Rh is rather randomly located inside
and outside mesopores. The SBA-15/AEAPMDMS/Rh catalyst can
be easily recycled without rhodium loss. HRh(CO)2(PPh3)2 and
HRh(CO)(PPh3)3 are found to be active species over the SBA-
15/AEAPMDMS/Rh with TPP based on in situ high-pressure FT-IR
results.
[20] S.A. Bagshaw, N.I. Baxter, D.R.M. Brew, C.F. Hosie, N. Yuntong, S. Jaenicke, C.G.
Khuan, J. Mater. Chem. 16 (2006) 2235.
[21] R.H. Crabtree, The Organometallic Chemistry of the Transition Metals, Wiley,
New York, 1988.
[22] J. Zhao, Y. Zhang, J. Hana, Y. Jiao, J. Mol. Catal. A: Chem. 241 (2005) 238.