A Fine Dispersed Cobalt Catalyst with Macro-Pore for Hydroformylation of 1-Hexene

Article abstract of DOI:10.1007/s10562-016-1853-z

Abstract: A highly dispersed cobalt catalyst for hydroformylation of 1-hexene was developed using macroporous silica (pore diameter 83.7?nm) as support. The effects of support pretreatment on the properties and catalytic activities of the obtained catalysts were investigated. The results indicated that slurry impregnation (SI) method could significantly enhance the interaction between support and cobalt precursors, leading to the formation of small cobalt particles. Moreover, this interaction would increase with the pretreating temperature or the number of hydroxyl groups in pretreating solvent. Due to the small cobalt particles and high diffusion rate of reactants and products in the macropore, the highly dispersed Co/Q-100 (PTO, SI-333) catalyst exhibited 11 times higher heptanal yield and much higher n/i ratio than the conventional Co/SiO₂ (EG) catalyst which was prepared on mesoporous silica which contained similar cobalt particle size. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-016-1853-z

Catal Lett
DOI 10.1007/s10562-016-1853-z
A Fine Dispersed Cobalt Catalyst with Macro-Pore
for Hydroformylation of 1-Hexene
Yi Liu1 · Zhenhao Li1,2 · Bin Wang1 · Yi Zhang1
Received: 1 June 2016 / Accepted: 29 August 2016
© Springer Science+Business Media New York 2016
Abstract A highly dispersed cobalt catalyst for hydrofor-
mylation of 1-hexene was developed using macroporous
silica (pore diameter 83.7 nm) as support. The effects of
support pretreatment on the properties and catalytic activi-
ties of the obtained catalysts were investigated. The results
indicated that slurry impregnation (SI) method could sig-
nificantly enhance the interaction between support and
cobalt precursors, leading to the formation of small cobalt
particles. Moreover, this interaction would increase with the
pretreating temperature or the number of hydroxyl groups
in pretreating solvent. Due to the small cobalt particles and
high diffusion rate of reactants and products in the macro-
pore, the highly dispersed Co/Q-100 (PTO, SI-333) catalyst
exhibited 11 times higher heptanal yield and much higher
n/i ratio than the conventional Co/SiO2 (EG) catalyst which
was prepared on mesoporous silica which contained similar
cobalt particle size.
Graphical Abstract
Conv.
Total Sel.
Yield
70
60
50
40
30
20
10
0
n/iso
Keywords Hydroformylation · 1-Hexene · Syngas ·
Cobalt catalyst · Macroporous silica
1 Introduction
The hydroformylation reaction, catalyzed by transition
metal complexes, is the addition of hydrogen and carbon
monoxide to olefins, yielding aldehydes in one-step fash-
ion with 100% atomic economy [1]. Formed aldehydes are
valuable final products and intermediates in the synthesis
of bulk chemicals like alcohols, esters, and amines [2].
The typical catalysts for hydroformylation of olefins are
homogeneous rhodium complexes, which is too expensive
and insufficient for large-scale industry. Hence, the devel-
opment of a heterogeneous catalyst for hydroformylation
could avoid the drawbacks of homogeneous catalyst, such
as very high pressure and the reuse of the catalyst.
ꢀ Yi Zhang
yizhang@mail.buct.edu.cn
1
State Key Laboratory of Organic–Inorganic Composites,
Although previous studies found that the cobalt-based
catalysts exhibit high activity in Fischer–Tropsch synthe-
sis [3, 4], the cobalt catalysts always exhibit low catalytic
activity and selectivity in liquid-phase hydroformylation of
Department of Chemical Engineering, Beijing University of
Chemical Technology, Beijing 100029, China
2
Petrochemical Research Institute, PetroChina,
Beijing 100195, China
1 3

2
Y. Liu et al.
olefin [5, 6]. The main drawback of the liquid-phase reac-
tion was the slow diffusion rate of the reactants and prod-
ucts inside the pores [7, 8]. For supported cobalt catalysts,
the support with large pore sizes could improve the inside-
pore mass transfer rate, contributing to high diffusion effi-
ciency [9, 10]. On the other hand, the hydroformylation
activity of cobalt catalyst depended on the particle size and
the number of active sites [11, 12]. Cobalt should be highly
dispersed in order to promote the CO insertion reaction rate
and increase the active sites. Therefore, the most optimum
catalyst for liquid-phase hydroformylation reaction was pro-
posed to contain larger pores to reduce the pore diffusion
resistance and smaller cobalt particles to increase the active
sites. Although the catalyst with macropores is favorable to
increase diffusion efficiency of reactants and products in the
intra-pellet structure, lower BET surface area of macropore
support determined larger metallic size and low metal dis-
persion, resulting in relative low reaction activity [13, 14]. It
was found that the metal particle size of supported catalysts
often increased with the increase of pore size. Consequently,
it is necessary to solve this contradiction for the development
of excellent highly dispersed catalysts with large pores for
hydroformylation reaction.
was dispersed in a certain amount of pretreating solvent
(EG or PTO) and stirred for 0.5 h at different tempera-
tures. After then, the solvent was decanted and the support
was dried in air at 393 K for 12 h. The volume of pre-
treating solvent was approximately 20 times of the total
pore volume of support. As comparison, Q-100 was also
pretreated with EG at room temperature by IWI method,
which denoted as Q-100 (EG). The pretreated Q-100 sup-
ported 10 wt% Co catalysts were prepared as the following
steps: a certain amount of Co(NO3)3·6H2O was dissolved
in water and then the cobalt nitrate aqueous solution was
impregnated on the support. The obtained samples were
dried in air at 393 K for 12 h and calcined at 673 K for 2 h
with a heating rate of 2 K min−1. The prepared catalysts
were denoted as Co/Q-100 (EG), Co/Q-100 (EG, SI-RT),
Co/Q-100 (EG, SI-333) and Co/Q-100 (PTO, SI-333). The
sample, Co/Q-100, which used non-pretreated silica sup-
port, is used as a reference. Before hydroformylation reac-
tion, the catalysts were reduced by hydrogen at 673 K for
10 h and passivated by 1% oxygen diluted with nitrogen
at room temperature.
2.2 Catalyst Characterization
The concentration, distribution, and nature of hydroxyl
groups (silanols) on the silica surface played important roles
in the dispersion of supported metal on the silica [15–18].
Generally, incipient wetness impregnation (IWI) method
was used to pretreat silica support at room temperature and
the volume of solvent used here was equal to total pore vol-
ume of support, resulting in nonuniform modification. How-
ever, slurry impregnation (SI) method using excess amount
of pretreating solvent could guarantee the adsorption of sol-
vent on the support to achieve maximum and could also be
carried out at higher temperature [19, 20].
Herein, highly dispersed silica supported Co catalysts
were prepared using macroporous silica as support. SI
method was used to pretreat the silica support by different
pretreating temperatures and solvents to improve the dis-
persion of supported cobalt particles. All the catalysts were
applied in slurry phase hydroformylation reaction of 1-hex-
ene and investigated using FT-IR, XRD, TEM, H2-TPR, H2
chemsorption, XPS and in-situ DRIFT measurements.
The Fourier transform infrared (FT-IR) spectra of the pre-
treated supports in the region of 2500–4000 cm−1 were
recorded via the KBr pellet technique on a Bruker Vertex
70V FT-IR spectrometer. An X-ray diffractometer (XRD,
Shimadzu XRD-6000) was used to detect crystalline size
of the fresh catalysts. The crystalline average size was cal-
culated by L=Kλ/∆ (2θ) cos θ0, where L is the crystalline
size, K is a constant (K=0.9), λ is the wavelength of X-ray
(Cu Kα=0.154 nm), and ∆ (2θ) is the width of the peak at
half height. The morphologies and sizes of the passivated
products were observed by transmission electron micro-
scope (TEM, JEOL 2100F). The specimen was prepared
by ultrasonically suspending the catalyst powder in etha-
nol. A drop of the suspension was deposited on a carbon-
enhanced copper grid and dried in air. X-ray photoelectron
spectrum (XPS) of the calcined catalyst was performed on
a ThermoFisher Scientific ESCALAB 250 spectrometer to
investigate the chemical state of surface cobalt species. The
spectra were excited by the monochromatized Al Kα source
(1486.6 eV). The analyzer operated in the constant ana-
lyzer energy (CAE) mode. Survey spectra were measured
at 30 eV pass energy. The peak positions were corrected
for sample charging by setting the C 1 s binding energy at
284.8 eV.
2 Experimental
2.1 Catalyst Preparation
The commercially available silica Q-100 (Fuji Silisya,
pore volume: 1.354 mL/g, pore diameter: 83.7 nm, specific
surface area: 83.4 m2 g−1) was pretreated with ethylene
glycol (EG) or propanetriol (PTO) for 0.5 h at room tem-
perature or 333 K by SI method. Typically, 2.5 g of Q-100
H2-Temperature programmed reduction (H2-TPR)
experiments were carried out in a quartz tube reactor using
0.05 g calcined catalysts. The reducing gas, a mixture of
10% H2 diluted by Ar, was fed via a mass flow control-
ler at 30 mL/min and the temperature was increased from
1 3

A Fine Dispersed Cobalt Catalyst with Macro-Pore for Hydroformylation of 1-Hexene
3
303 K until 1073 K at a rate of 8 K/min. The effluent of
reactor passed through a 5 A molecular sieve trap to remove
produced water, before reaching TCD. The hydrogen con-
sumption was calibrated using the H2-TPR of CuO (Aldrich,
99.99+%) as the standard sample under the same condi-
tions. H2 chemsorption experiments for passivated catalysts
were performed in a static mode at 373 K using a conven-
tional volumetric apparatus (FINESORB-3010, FINETEC).
Research grade gases (H2: 99.9995%) were used without
further purification. Typically, 0.1 g of catalyst was used.
Before adsorption of H2, the catalysts, which were previ-
ously reduced by H2 and passivated, were treated in H2 at
673 K for 1 h, followed by evacuation. H2 adsorption iso-
therms were measured at 373 K.
The 1-hexene conversion (C, %), heptanal selectiv-
ity (S, %) and ratio of normal heptanal and isomeric hep-
tanal (n/iso) was defined as: Conv.=(n1−n2)/n1 ×100%,
Sel.=na/(n1−n2)×100% and n/iso=nnormal/niso. Where n1 is
the mole number of 1-hexene into the reactor; n2 is the mole
number of unreacted 1-hexene after reaction; nnormal and niso
are the mole number of normal heptanal (n-heptanal) and
isomeric heptanal (iso-heptanal) produced during reaction,
respectively.
3 Results and Discussion
3.1 Catalyst Characterization
Diffuse reflectance infrared Fourier transform (DRIFT)
spectra were recorded with a Vertex 70V spectrometer
(Bruker) equipped with a liquid nitrogen-cooled MCT
detector (resolution 2 cm−1), using an in-situ cell with CaF2
windows. About 15 mg of the sample, which was previously
reduced by H2 and passivated, was loaded into the cell. Prior
to CO adsorption, the sample was in-situ treated with a H2
(30 mL/min) gas flow at 673 K for 1 h, followed by purging
with a N2 (30 mL/min) gas flow at the same temperature for
0.5 h, and then was cooled to 303 K. CO (30 mL/min) was
introduced into the cell at room temperature for 0.5 h. After
the catalysts were outgassed by a N2 (30 mL/min) gas flow
for 0.5 h to remove the physical adsorption CO, the spectra
of adsorbed CO were collected.
The supported cobalt particle size of various catalysts was
determined by XRD and TEM. XRD patterns of passivated
catalysts are shown in Fig. 1. All of the obtained catalysts
were composed of metallic Co and CoO. The Co/Q-100
catalyst which prepared by non-pretreated silica support,
exhibits sharp and strong peaks, and the crystalline size
is largest (28.1 nm) as compared in Table 1. The others
catalysts, prepared by pretreated silica supports, exhib-
ited smaller cobalt particle size than Co/Q-100. Moreover,
with the increase of pretreating temperature or the number
of hydroxyl groups in pretreating solvent, the characteris-
tic diffraction peaks of cobalt became much weaker and
broader. These results indicated that smaller cobalt particles
were formed on these pretreated Q-100 supports, which was
due to the stronger interaction between cobalt particles and
support. Figure 2 also shows the TEM images of all pas-
sivated catalysts, and the Co dispersion was calculated by
the average particle size of Co as shown in Table 1. The
2.3 Catalyst Evaluation Tests
Hydroformylation of 1-hexene was carried out in a mechan-
ical stirring semibatch autoclave with the inner volume of
85 mL. The detailed procedure was conducted as follows.
13.5 mmol of 1-hexene was mixed with 20 mL of toluene
in the autoclave and then 0.1 g of the obtained catalyst was
loaded into reactor. The autoclave was then firmly sealed
and purged with feed gas to replace the air inside it by
means of pressuring-depressurizing. Firstly the autoclave
was pressured to 3 MPa with syngas (H2/CO=1) at room
temperature, and then the gas was slowly vented. This step
was repeated for 3 times to ensure that there was no oxy-
gen in the autoclave. After that, the syngas was injected to
5 MPa and the autoclave was heated to 403 K. The reaction
was started and lasted for 1 h; meanwhile the autoclave was
mechanically stirred at 1600 rpm. At the end of the reac-
tion, the reactor was cooled in ice bath to lower than 283 K
rapidly and the pressure was released. The liquid product
was separated from the solid catalyst by natural sedimenta-
tion. The resulting mixture was analyzed quantitatively by a
gas chromatograph (GC-2014C, Shimadzu) equipped with
a KB-1 capillary column (0.32 mm×0.25 μm×30 m) and a
flame ionization detector (FID).
Fig. 1 XRD patterns of supported cobalt catalysts: (a) Co/Q-100,
(b) Co/Q-100 (EG), (c) Co/Q-100 (EG, SI-RT), (d) Co/Q-100 (EG,
SI-333), (e) Co/Q-100 (PTO, SI-333)
1 3

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Y. Liu et al.
Table 1 Various properties of silica supported cobalt catalysts
However, SI method could make the supported cobalt parti-
cles well dispersed and the dispersion could further increase
with the pretreating temperature or the number of hydroxyl
groups in pretreating solvent. When support Q-100 was pre-
treated with PTO at 333 K by SI method, the cobalt dis-
persion of obtained catalyst Co/Q-100 (PTO, SI-333) was
almost 9 times higher than that of Co/Q-100. The above
results indicated that the dispersion of supported cobalt par-
ticles could be significantly improved by tuning pretreating
manners. It is considered that the smaller cobalt particle size
was advantageous to CO adsorbed in linear geometry and
insertion in hydroformylation reaction.
Catalyst
Co particle
size (nm)
Reduc- H2 uptake Dis-
tion
(μmol/g)4 per-
degree
sion
XRD1 TEM2
(%)3
(%)5
Co/Q-100
28.1
24.9
17.8
29.5
26.2
15.3
5.4
69.4
57.9
53.6
32.0
25.7
37.3
39.2
35.1
42.9
56.4
3.3
3.7
Co/Q-100 (EG)
Co/Q-100 (EG, SI-RT)
6.3
Co/Q-100 (EG, SI-333) NA
Co/Q-100 (PTO, SI-333) NA
17.8
30.9
3.1
1From XRD patterns of passivated catalysts
2From TEM images of passivated catalysts
The surface properties of all pretreated supports are char-
acterized by FT-IR spectra, as shown in Fig. 3. The absorp-
tion band in the range of 3800–3600 cm−1 is the O–H in
non-H-bonded Si-OH, and the broad band from 3600 to
3200 cm−1 is attributed to the O–H in H-bonded Si-OH
[21, 22]. After EG pretreatment with IWI method, support
Q-100 (EG) still exhibited strong O–H bands and weak
C–H peaks, indicating that IWI method was not efficient
for modifying the surface properties of support. However,
when Q-100 was pretreated by EG with SI method, the O–H
3Determined by TPR profiles from 323 to 673 K. CuO was used as
reference sample
4Determined by H2 chemsorption at 373 K
5Dispersion was calculated by D=96/d(Co) (%). d(Co) was Co par-
ticle size
dispersion of Co/Q-100 (EG) was almost the same to that of
Co/Q-100, indicating that IWI pretreatment did not effec-
tively improve the dispersion of supported cobalt particles.
Fig. 2 TEM images of the pre-
pared catalysts: (a) Co/Q-100,
(b) Co/Q-100 (EG), (c) Co/Q-
100 (EG, SI-RT), (d) Co/Q-100
(EG, SI-333), (e) Co/Q-100
(PTO, SI-333)
1 3

A Fine Dispersed Cobalt Catalyst with Macro-Pore for Hydroformylation of 1-Hexene
5
Fig. 3 FT-IR spectra of support Q-100 pretreated by different meth-
ods: (a) Q-100, (b) Q-100 (EG), (c) Q-100 (EG, SI-RT), (d) Q-100
(EG, SI-333), (e) Q-100 (PTO, SI-333)
Fig. 4 H2-TPR spectra of various catalysts: (a) Co/Q-100, (b) Co/Q-
100 (EG), (c) Co/Q-100 (EG, SI-RT), (d) Co/Q-100 (EG, SI-333), (e)
Co/Q-100 (PTO, SI-333)
bands, both of non-H-bonded and H-bonded one, on the sur-
face of pretreated silica significantly decreased. Meanwhile,
C–H bands (3000–2800 cm−1) were detected, indicating that
the pretreatment of silica supports by EG with SI method
decreased the coverage of OHs and formed oxyls groups
on surface of pretreated silica supports. Moreover, with
the increase of pretreating temperature or the number of
hydroxyl groups in pretreating solvent, the intensity of O–H
on the surface of support further decreased, meanwhile,
the adsorption peaks of C–H became stronger. Because the
supported metal species interacting with H-bonded SiOH
formed large supported metal particle [15], the lower cover-
age of H-bonded SiOHs of pretreated silica could contribute
to forming smaller supported cobalt particle to realize high
dispersion of supported cobalt. On the other hand, the newly
formed oxyl groups from pretreating solvent should modify
the charge of silica surface to increase negative charge on
the surface of pretreated Q-100, contributing to increase
the interaction between support and cobalt particles [18].
As a result, the Q-100 (PTO, SI-333), which was pretreated
with PTO at 333 K by SI method, exhibited the weakest
O–H bands and the strongest C–H peaks, contributing to the
smallest particle size and the highest dispersion of supported
cobalt. From these findings, it is proved that the improved
pretreating manners, including method, temperature and
solvent, significantly enhanced the interaction between sup-
ported cobalt particles and Q-100 support, contributing to
high dispersion of cobalt particles.
of cobalt silicates, which strongly interacted with sup-
port [23, 24]. After pretreatment, the first reduction peaks
of all pretreated catalysts except Co/Q-100 (EG) located
at slightly lower temperature than that of non-pretreated
catalyst. This result indicated that the interaction between
support and cobalt particles was not enhanced by IWI pre-
treatment. When SI method was used to pretreat Q-100 sup-
port, the obtained catalysts Co/Q-100 (EG, SI-RT) exhibited
the weaker reduction peak of CoO to Co and the stronger
reduction peak of cobalt silicates than Co/Q-100. Moreover,
with further increase of the pretreating temperature or the
number of hydroxyl groups in pretreating solvent, the sec-
ond reduction peak was further weakened and the third one
became very strong. These results indicated that the interac-
tion between support and cobalt particles was significantly
enhanced by tuning the pretreating manners, leading to the
formation of very small cobalt particles which was difficult
to be reduced.As compared in Table 1, the reduction degrees
of the catalysts were calculated according to H2-TPR from
323 to 673 K. The reduction degrees of prepared catalysts
decreased with the decrease of cobalt particle size, which
was due to the stronger interaction between support and
smaller cobalt particle. The Co/Q-100 (PTO, SI-333) exhib-
ited the smallest cobalt particles and thus the reduction
degree was lowest in all the prepared catalysts. However,
small cobalt particles are benefit for the formation of cobalt
atoms that locate on the surface of particles. As shown in
Table 1, The H2 chemsorption results also confirmed that
the Co/Q-100 (PTO, SI-333) catalyst realized the maximum
of H2 uptake as 56.4 μmol g−1, indicating the formation of
more active sites for the catalyst.
The reduction performances of cobalt catalysts were
measured by H2-TPR, as shown in Fig. 4. All of the sup-
ported cobalt catalysts undergo two typical steps during
reduction, which were attributed to the transformation of
Co3O4 to CoO followed by the transformation of CoO to Co.
The peak above 900 K should be ascribed to the reduction
XPS was used to probe the surface chemical composi-
tion and electronic structures of the catalysts. As shown
in Fig. 5, the Co 2p spectrum of all catalysts displays two
1 3

6
Y. Liu et al.
Fig. 5 XPS spectra of Co 2p core level recorded from prepared catalysts: a Co/Q-100, b Co/Q-100 (EG), c Co/Q-100 (EG, SI-RT), d Co/Q-100
(EG, SI-333), e Co/Q-100 (PTO, SI-333)
peaks located near 779.82 and 795.09 eV, which come from
the spin-orbit splitting and can be attributed to Co 2p3/2 and
Co 2p1/2, respectively [25, 26]. Meanwhile, two shake-
up satellite peaks were observed at about 5–7 eV higher
energy side from the Co 2p3/2 and Co 2p1/2 peaks due to
the presence of unpaired electrons, indicating the pres-
ence of Co2+ on the surface of catalyst [27]. In addition,
it was found that the Co 2p3/2 and Co 2p1/2 peaks appeared
at relatively higher binding energy when the support was
pretreated by EG with IWI method, and SI method could
further make Co 2p peaks shift to higher binding energy.
Moreover, the binding energy of Co 2p peaks could further
increase with the pretreating temperature or the number of
hydroxyl groups in pretreating solvent. These results indi-
cated that the interaction between support and cobalt par-
ticles was enhanced and the electrons transfer from cobalt
oxide to support along with the improvement of pretreat-
ing manners. Especially, Co/Q-100 (PTO, SI-333) catalyst
1 3

A Fine Dispersed Cobalt Catalyst with Macro-Pore for Hydroformylation of 1-Hexene
7
exhibited the highest binding energy of Co 2p, leading to
the smallest particle size.
IWI with SI as the pretreating method, it was shown that the
linear-adsorbed CO peak of Co/Q-100 (EG, SI-RT) shifted
to higher position to 2021 cm−1 and became stronger due
to the smaller cobalt particles [29]. When increase the pre-
treating temperature or use PTO instead of EG as pretreat-
ing solvent, the wavenumber and the intensity of adsorption
peak for linear-bonded CO further increase, indicating that
linear-type CO adsorption on the surface of catalyst was
enhanced by the improved pretreating manners remarkably.
The Co/Q-100 (PTO, SI-333) catalyst showed the strongest
adsorption band and the most obvious blue shift for linear-
type CO peak. These linear-type adsorbed CO molecules at
high wavenumber (2040 cm−1) preferred to non-dissocia-
tive CO insertion events, which was advantageous to CO
insertion reaction and would contribute to hydroformylation
reaction [30].
In-situ DRIFT spectra of the adsorbed CO on the reduced
catalysts are compared in Fig. 6. The peak at the range of
2003–2040 cm−1 was assigned to the linearly adsorbed
CO on Co0 sites, and the peak at 1934 cm−1 was due to
the bridge-type CO adsorbed on Co0 sites. For the sup-
ported cobalt catalysts with relatively low reduction degree,
the peak at 2117 cm−1 was observed and assigned to the
CO adsorbed on Con+ (n=2, 3) species [28]. The adsorp-
tion peaks of linear- and bridge-type CO for Co/Q-100
(EG) were similar to that for Co/Q-100, indicating that CO
adsorption on the surface of obtained catalysts was not influ-
enced by the pretreatment with IWI method. When replace
3.2 Reaction Performance of 1-Hexene
Hydroformylation
The prepared catalysts were tested in slurry phase hydrofor-
mylation of 1-hexene at 403 K and 5 MPa. As compared in
Table 2, the 1-hexene conversion and yield of heptanal were
very low for Co/Q-100 and Co/Q-100 (EG) catalysts in the
reaction, due to the large particle size and less active sites.
As expected, SI pretreated catalyst Co/Q-100 (EG, SI-RT)
exhibited higher 1-hexene conversion and heptanal selec-
tivity than IWI pretreated catalyst Co/Q-100 (EG), because
of the smaller cobalt particle size. On the other hand, with
the increase of pretreating temperature and the number of
hydroxyl groups in pretreating solvent, the pretreated cobalt
catalysts exhibited higher selectivity toward heptanal due to
the smaller cobalt particles but almost the same conversion of
Fig. 6 In-situ CO-DRIFT spectra of various catalysts: a Co/Q-100, b
Co/Q-100 (EG), c Co/Q-100 (EG, SI-RT), d Co/Q-100 (EG, SI-333),
e Co/Q-100 (PTO, SI-333)
Table 2 Reaction performances of 1-hexene hydroformylation over various catalysts
Catalyst
Conv.
(%)1
Selectivity (%)
n-Hexane
Yield
(%)3
n/iso4
iso-Hexene
n-Heptanal
iso-Heptanal
Total2
Co/Q-100
26.46
26.81
48.10
48.06
50.87
28.34
3.78
3.67
8.07
5.41
1.88
0.00
87.10
85.58
75.41
65.15
35.35
89.56
6.81
8.08
2.31
2.67
5.90
8.00
18.56
4.38
9.12
10.75
16.52
29.44
62.77
10.44
2.41
2.88
2.94
3.03
1.80
2.68
2.38
1.39
Co/Q-100 (EG)
Co/Q-100(EG, SI-RT)
Co/Q-100(EG, SI-333)
Co/Q-100(PTO, SI-333)
Co/SiO2 (EG)5
10.62
21.45
44.21
6.06
7.95
14.15
31.93
2.96
Reaction conditions: CO:H2 =1:1, 403 K, 5 MPa, 1 h, 20 mL of toluene, 13.5 mmol of 1-hexene, catalyst loading=0.1 g
1Conversion of 1-hexene
2Total selectivity of n-Heptanal and iso-Heptanal
3Yield of n-Heptanal and iso-Heptanal
4n/iso n-Heptanal/iso-Heptanal
5The catalyst was prepared on mesoporous SiO2 support (pore volume: 1.061 mL/g, pore diameter: 6.7 nm, specific surface area: 451 m2 g−1
)
pretreated with EG by IWI method, the Co particle size (3.42 nm) was almost the same to that of Co/Q-100 (PTO, SI-333) catalyst, as reported
in our previous work [32]
1 3

8
Y. Liu et al.
same reaction conditions. As shown in Fig. 7, the catalytic
activity of the used Co/Q-100 (PTO, SI-333) catalyst for
hydroformylation of 1-hexene was almost the same as that
of fresh catalyst. Qiu et al. reported that more than 90% of
active metals existed on heterogeneous cobalt catalyst after
the hydroformylation reaction of 1-hexene, and catalytic
activity for hydroformylation of 1-hexene has no direct rela-
tionship with the dissolved active metal [34]. Hence, it was
considered that the active phase of Co/Q-100 (PTO, SI-333)
catalyst for hydroformylation existed on the heterogeneous
catalyst. This result is also well agreed with other reports
[34, 35].
4 Conclusions
Fig. 7 Hydroformylation of 1-hexene over fresh or used Co/Q-100
(PTO, SI-333) catalyst. Reaction conditions: CO:H2 =1:1, 403 K,
5 MPa, 1 h, 20 mL of toluene, 13.5 mmol of 1-hexene, catalyst
loading=0.1 g
A highly dispersed cobalt-based catalyst supported on mac-
roporous silica Q-100 was successfully obtained by pre-
treating Q-100 with SI method. The promotional effects of
pretreating manners on the catalytic performances of the
obtained catalysts were investigated by several characteriza-
tion methods. The results indicated that pretreatment of sup-
port with SI method significantly enhanced the interaction
between cobalt precursor and support, resulting in high dis-
persion of cobalt particles. Moreover, this interaction would
increase with the pretreating temperature and the number of
hydroxyl groups in pretreating solvent. High dispersion of
Co/Q-100 (PTO, SI-333) contributed to forming the large
number of active sites and more linear-adsorbed CO mol-
ecules with strong C–O bond, which were benefit for the
catalytic activity in 1-hexene hydroformylation. Therefore,
the heptanal yield of Co/Q-100 (PTO, SI-333) was 13 times
higher than that of Co/Q-100. On the other hand, the large
pores of catalyst improved the diffusion efficiency of reac-
tants and products, therefore the Co/Q-100 (PTO, SI-333)
catalyst supported on macroporous silica exhibited 11 times
higher heptanal yield than Co/SiO2 (EG) catalyst, which
was prepared by mesoporous silica and contained the almost
same cobalt particle size.
1-hexene because of the relatively low reduction degree. The
catalyst Co/Q-100 (PTO, SI-333) realized 13 times higher
heptanal yield as 31.93% than non-pretreated catalyst Co/Q-
100. It is reported that the atoms at the corners and edges of
metal particles are advantageous to CO adsorption in linear
geometry, which benefit the CO insertion during the hydro-
formylation reaction [30, 31]. Hence, the Co/Q-100 (PTO,
SI-333) catalyst modified by PTO, which exhibited the large
percentage of atoms at the corners and edges of metal par-
ticles due to the significantly higher dispersion of supported
cobalt and smaller particles, was beneficial to enhance the
catalytic activity of hydroformylation of 1-hexene.
In addition, as shown in Table 2, the highly dispersed
macroporous Co/Q-100 (PTO, SI-333) catalyst exhibited
much higher activity in 1-hexene hydroformylation than
Co/SiO2 (EG), which was prepared by mesoporous support
with 6.7 nm pore diameter, and the total heptanal yield of
Co/Q-100 (PTO, SI-333) was 11 times higher than that of
Co/SiO2 (EG), although the cobalt particles size was similar
for two catalysts. Meanwhile, the n/i (n-Heptanal/iso-Hep-
tanal) ratio of Co/Q-100 (PTO, SI-333) was much higher
than that of Co/SiO2 (EG). These results could be explained
by that macroporous Q-100 could reduce the pore diffusion
resistance and thus improve the diffusion rate of reactants
and products, contributing to higher activity and selectiv-
ity of hydroformylation reaction. Therefore, due to the syn-
ergetic effects of small particles and macroporous support,
Co/Q-100 (PTO, SI-333) realized the best catalytic activity
and selectivity in this study.
Acknowledgments This work was supported by National Natural
Science Foundation of P. R. China (No. 91334206, 21606011), Min-
istry of Education of P. R. China (NCET-13-0653), National “863”
program of P. R. China (No. 2013AA031702), Innovation and Pro-
motion Project of Beijing University of Chemical Technology (No.
JC1505), BUCT Fund for Disciplines Construction and Develop-
ment (No. XK1505), and China Postdoctoral Science Foundation
(2016M591051).
However, the active metal has been reported to leach
from the supports under typical hydroformylation condi-
tions even for the supported catalyst [33]. Based on this, the
used Co/Q-100 (PTO, SI-333) catalyst, after removal of sol-
vent, was tested in hydroformylation of 1-hexene under the
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