Hydroformylation of vinyl acetate and cyclohexene over TiO2 nanotube supported Rh and Ru nanoparticle catalysts

Article abstract of DOI:10.1039/c8ra01399c

TiO₂ nanotube (TNT) supported Rh and Ru nanoparticle catalysts were prepared via impregnation-photoreducing procedure and characterized with various methods. Their catalytic performances in hydroformylation were evaluated by using vinyl acetate and cyclohexene as substrates. The results indicate that the presence of Ru in the catalysts can enhance the catalytic activity of catalysts for the hydroformylation of vinyl acetate, but do not play the same role in the hydroformylation of cyclohexene; the sequence of loading metal has a significant effect on the catalytic performances of the title catalysts. Additionally, it is found that Ru/TNTs shows catalytic activity for the hydroformylation of vinyl acetate though it does not for the hydroformylation of cyclohexene.

Full text of DOI:10.1039/c8ra01399c

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Hydroformylation of vinyl acetate and cyclohexene
over TiO nanotube supported Rh and Ru
2
Cite this: RSC Adv., 2018, 8, 12053
nanoparticle catalysts†
a
a
a
ab
ab
Hongyuan Chuai,
and Weiping Huang*
Xiaotong Liu, Ya Chen, Baolin Zhu, Shoumin Zhang
abc
2
TiO nanotube (TNT) supported Rh and Ru nanoparticle catalysts were prepared via impregnation-
photoreducing procedure and characterized with various methods. Their catalytic performances in
hydroformylation were evaluated by using vinyl acetate and cyclohexene as substrates. The results
indicate that the presence of Ru in the catalysts can enhance the catalytic activity of catalysts for the
hydroformylation of vinyl acetate, but do not play the same role in the hydroformylation of cyclohexene;
the sequence of loading metal has a significant effect on the catalytic performances of the title catalysts.
Additionally, it is found that Ru/TNTs shows catalytic activity for the hydroformylation of vinyl acetate
though it does not for the hydroformylation of cyclohexene.
Received 13th February 2018
Accepted 21st March 2018
DOI: 10.1039/c8ra01399c
rsc.li/rsc-advances
alkenes, the efficiency of Rh should not be the highest one as
the presence of chelation between Rh and functional group. To
1
. Introduction
Nowadays the hydroformylation discovered by Otto Roelen in increase the efficiency of Rh, very expensive metal, in catalysts
938 is still one of the most important catalytic reactions in the people have made great effort. Li et al. reported that using
1
1–4
chemical industry. As for catalysts, including homogeneous rhodium carbonyl and manganese carbonyl as catalyst simul-
5
,6
7,8
9–11
and heterogeneous, the Co-, Ir- and Rh-based catalysts
are widely reported and used for the hydroformylation, but the hydroformylation. Kunimori et al. reported that Mo-promoted
taneously can signicantly increase aldehyde formation in
16
17
Rh-based catalysts are the dominant ones and have been Rh/SiO
2
shows the good activity for hydroformylation. It
For functionalized alkenes, in should be a good scheme utilizing synergistic effect of two or
which there is at least another functional group besides the more transition metals in catalysts to promote the conversion of
1
2,13
increasingly being used.
18,19
C]C bond, e.g. vinyl acetate, their hydroformylation rate is substrate in hydroformylation,
where the main active site
affected by the nearby group or heteroatom as the group is can catalyze main reaction efficiently and the second active site
adjacent to the C]C bond because the group or heteroatom decreases the inuence of the nearby heteroatoms or groups. In
may coordinate to metal centers, and it is the chelation that our previous work, we used TiO
nanotubes (TNTs)-supported
2
14,15
affects the catalytic performances of catalysts.
It is well Rh catalysts with different surface acidities for the hydro-
20
known that the homogeneous catalyst used for hydro- formylation of CN-containing olen, the results showed that
formylation reactions usually contains a type of single-active the higher the surface acidity is, the weaker the inuence of –CN
site, which may lose activity aer being occupied or coordi- group, and the higher the linear-to-branched aldehyde ratio.
nated by the heteroatoms while catalyzing the hydroformylation
In the present contribution, we report TNTs supported Rh
of functionalized olens. Therefore, it might not be the best and Ru nanoparticles catalysts and make comparison of the
option to use the catalyst with only one type of active site for the effect of Ru on the catalytic performances of catalysts for
catalytic hydroformylation of functionalized olens. When Rh is hydroformylation of vinyl acetate and cyclohexene.
an only active site in the hydroformylation of functionalized
2
. Experimental
a
2.1 Preparation of catalyst
College of Chemistry, Nankai University, Tianjin 300071, China. E-mail: hwp914@
nankai.edu.cn; Tel: +86-138-2009-6974
21
TNTs used were synthesized as the previous report.
b
The Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education),
Rh/TNTs was prepared via impregnation-photoreducing
procedure as follows: 1.0 g of TNTs were dispersed in 20.0 mL
of aqueous Rh (Ac) solutions (0.043 g Rh (Ac) ) and strong
Nankai University, Tianjin 300071, China
c
Collaborative Innovation Center of Chemical Science and Engineering (Tianjin),
Tianjin 300071, China
2
4
2
4
agitated for 24 h. Aer ultrasound for 2 h, the mixture was
centrifuged. The green solid obtained was washed twice with
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c8ra01399c
1
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ethanol, and then transferred into a quartz reactor with 50.0 mL
ethanol–water solution (Vethanol : Vwater ¼ 9 : 1). The mixture was
irradiated with a 300 W high-pressure mercury lamp for 4 h
3
. Results and discussion
3.1 Characterization of the catalysts
under stirring at ambient temperature. Aer irradiation, the The SSA of catalysts and contents of Rh or Ru in the catalysts
mixture was centrifuged, solid was washed with distilled water determined by BET and ICP are listed in Table 1. The SSA of all
ꢀ
and ethanol, and dried at 40 C for 12 h in vacuum. The ob- catalysts are signicantly lower than that of pure TNTs, which
tained catalyst was labelled as Rh/TNTs. The other catalysts may be ascribed to that metal nanoparticles deposited on the
were prepared by the same procedure of preparing Rh/TNTs. outer and inner surface or occupied the interspace between
22
ꢀ
For convenience of distinction, catalysts in this contribution walls of TNTs. The SSA of Rh–Ru/TNTs (200 C) is lower than
were labelled as Rh/TNTs, Ru/TNTs, Rh–Ru/TNTs (Ru/TNTs was that of as-prepared Rh–Ru/TNTs because of calcination.
used as supporter to support Rh nanoparticles), Ru–Rh/TNTs
To reveal the role of Ru, the contents of Rh in catalysts are
(
Rh/TNTs was used as supporter to support Ru nanoparticles), purposefully kept in almost identical. The Rh nominal loading
ꢀ
and Rh–Ru/TNTs (200 C) (the catalyst Rh–Ru/TNTs was is 2% and Ru nominal loading is 0.5% for each case. From the
calcined at 200 C for 2 h under N
ꢀ
2
), Rh–Ru/TNTs-U1 (the used ICP data, we can see that Ru exhibits high loading efficiency
catalyst), Rh–Ru/TNTs-U2 (the Rh–Ru/TNTs-U1 used for while Rh not. The difference might be caused by the starting
recycle).
material that chloride salt tends to be more efficiency than that
of acetate salt. XRD was used to analyse the phase structure of
ꢀ
ꢀ
catalysts. The XRD peaks at 25.24 and 48.1 are the diffractions
of the (101) and (200) crystal planes of anatase TiO (JCPDS21-
2.2 Characterization of catalyst
2
The Rh and Ru contents in samples were measured by induc- 1272), respectively (Fig. 1). The phase does not change aer
ꢀ
tively coupled plasma mass spectrometer (X7, Thermo Electron calcination at 200 C (Fig. 1F). In addition, there is no any
Corporation). The specic surface area (SSA) of samples were diffraction related to Rh or Ru nanoparticles, which implies that
determined at liquid N
BET, JW-K); phase structures of catalysts were characterized by distributed.
X-ray Diffraction (XRD, Rigaku D/Max-2500 X-ray diffractometer
The surface composition of Rh/TNTs was characterized by
2
temperature with the BET method Rh or Ru nanoparticles might be very small and well
(
with Cu Ka radiation). The morphology and microstructure of EDX and elemental mapping analysis (Fig. 2). In the marked red
samples were observed with Transmission Electron Microscopy square (Fig. 2A), Ti and O display a homogeneous distribution
(
(
TEM, 100 kV, JEM-2100) and scanning electron microscope (Fig. 2B–C), and Rh nanoparticles are uniformly dispersed on
SEM, 25 kV, X-650). The chemical states of Rh and Ru in the surface of TNTs (Fig. 2D), so as on the other catalysts (S. 3†).
catalysts were determined by X-ray photoelectron spectroscopy
The morphology of catalysts were further observed with TEM
(XPS) using an Al X-ray source (Al Ka-150 W, Kratos Axia Ultra (Fig. 3). TNTs take on perfect tubular morphology and have the
DLA), and the binding energy was calibrated by taking C 1s peak multiwall structure (Fig. 3A–D). There are some black spots in
at 284.6 eV as reference. The infrared spectra were recorded on the as-prepared catalysts, which might be Rh or Ru nano-
an FT-IR spectrometer (USA, Bio-rad, FTS6000) in the spectral particles. The size of particles is in the range of 1–2 nm. In the
ꢁ
1
range 0–4000 cm , KBr wafers were used and the weight process of photo-reduction, the Rh or Ru atoms are apt to
percentage of the samples in KBr was about 0.5%. Before assemble on the new formed Rh or Ru nuclei to form Rh or Ru
testing, all samples were placed in a 250 mL stainless steel particles on the surface of TNTs for strong metal–metal inter-
autoclave reactor pressurized with CO (1.5 MPa) for 12 h.
action. The metal nanoparticles may grow up during calcina-
tion, as a result, the black spots in Rh–Ru/TNTs (200 C)
ꢀ
(
Fig. 3E) are much larger than that in Rh–Ru/TNTs (Fig. 3C). The
2.3 Evaluation of catalytic performance
HRTEM image of the selected black spot in Fig. 3E shows that
The hydroformylation reaction was used to evaluate catalytic the lattice structure of the black spot is clearly different from
performance of catalyst, and the activity of catalyst was that of TNTs (Fig. 3F). This further suggests that the black spots
compared by the percent conversion of olen in the reaction. are metallic nanoparticles. We cannot determine the composi-
The hydroformylation reaction was carried out in a 250 mL tion of nuclear particles accurately for the metallic
stainless steel autoclave reactor with magnetic stirrer. In the
process of experiment, the required amount of catalyst, Table 1 The SSA of catalysts and contents of Rh or Ru in the catalysts
substrate and solvent were put into the reactor in turn. The determined by BET and ICP
reactor was sealed, purged three times with CO or H
2
, and
SSA
(m g
Rh content
(wt%)
Ru content
(wt%)
pressurized to a set pressure with syngas (CO and H ) while
2
2
ꢁ1
Entry
Catalyst
)
stirring, and then heated to the reaction temperature. The
heating and stirring were stopped aer the required reaction
time. When the reactor was cooled down to room temperature,
the pressure was released gradually, and the mixture of reaction
was withdrawn, centrifuged and analyzed using GC analysis
1
2
3
4
5
6
TNTs
Rh/TNTs
Ru/TNTs
Rh–Ru/TNTs
Ru–Rh/TNTs
Rh–Ru/TNTs (200 C)
262.61
228.69
188.12
247.61
237.51
234.24
—
0.10
—
0.09
0.10
0.10
—
—
0.46
0.42
0.47
0.51
(Shimadzu GC-2014 gas chromatograph equipped with a 30 m
ꢀ
ꢂ 0.53 mm ꢂ 1.0 mm SE-30 capillary column and a FID).
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Fig. 1 XRD patterns of TNTs (A), Rh/TNTs (B), Ru/TNTs (C), Rh–Ru/
ꢀ
TNTs (D), Ru–Rh/TNTs (E), Rh–Ru/TNTs (200 C) (F).
Fig. 2 EDX elemental mapping analysis of Rh/TNTs. (A) HAADF-STEM
image of Rh/TNTs, the marked area is scanned and analysed. (B–D)
Mapping results for Ti (B), O (C), and Rh (D).
nanoparticles are too small. The catalyst Rh–Ru/TNTs aer
catalysis used for once and twice still keeps nanotubular
structure very well (Fig. 3G–H).
Fig. 3 TEM images of Rh/TNTs (A), Ru/TNTs (B), Rh–Ru/TNTs (C), Ru–
Rh/TNTs (D), Rh–Ru/TNTs (200 C) (E), and HRTEM image of the
selected area of E (F), Rh–Ru/TNTs-U1 (G), Rh–Ru/TNTs-U2 (H).
ꢀ
XPS proles of all Rh 3d in catalysts show broad doublets
(Fig. 4(1A–1D)), the major Rh 3d 5/2 peaks appear at approximately
307.0 eV and 309.0 eV. These values indicate that the Rh in cata- supporter in the catalyst. These results may be understood by
lysts exists as two chemical states: BE at around 307.0 eV is asso- considering that the binding energy is affected not only by the
0
ciated with metallic Rh , and 309.0 eV is originated from the metal itself, but also by the electronic interaction between the
3
+
15,23
0
oxidized Rh species.
Rh is the dominant component in as- metal and other components in catalyst.
It is well known that the XPS peaks of C 1s and Ru 3d suffer
prepared samples based on the peak area ratio. A small amount
of Rh species in catalysts might be due to the oxidation of surface linear superposition. The broad peaks of samples can be tted
layer in the process of characterization under air. However, the into several Gau ssian peaks (Fig. 4(2A–2D)). Peaks at 284.6 eV
content of Rh in catalyst Rh–Ru/TNTs (200 C) (Fig. 4(1D)) is lower can be attributed to C 1s; peaks at around 280–281 and 285–
than those in other samples based on the peak area ratio of Rh to 286 eV are attributed to Ru 3d 5/2 and Ru 3d 3/2, respectively,
3+
24
0
ꢀ
0
0
0
3+
0
23,25
Rh . In addition, we can nd the variations in BE of Rh 3d, which which are consistent with the literature data of Ru .
means that there are interactions between metals or metal- peaks are attributed to component of RuO . By contrast of XPS
The other
2
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ꢀ
Fig. 4 High-resolution XPS spectra of Rh 3d in Rh/TNTs (1A), Rh–Ru/TNTs (1B), Ru–Rh/TNTs (1C), Rh–Ru/TNTs (200 C) (1D), and Ru 3d in Ru/
ꢀ
TNTs (2A), Rh–Ru/TNTs (2B), Ru–Rh/TNTs (2C), Rh–Ru/TNTs (200 C) (2D).
spectra of Rh 3d and Ru 3d of four samples, it can be concluded
FT-IR was used to explore the CO species adsorbed on cata-
that there must be strong metal–metal interaction between Ru lysts (Fig. 5). All FT-IR spectra of Ru-containing catalysts
and Rh in the Rh–Ru/TNTs because the binding energies of Rh 3d absorbed CO display absorption peaks at 2066.22 and
ꢁ1
and Ru 3d in the Rh–Ru/TNTs changed obviously.
1997.17 cm
(Fig. 5D–G), respectively, which are typical
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Table
2
Hydroformylation of vinyl acetate over catalysts under
a
different reaction time
Conversion of
vinyl acetate (%) aldehyde (%) b : 1
Selectivity for
b
Entry Catalyst
1
2
3
4
5
6
7
8
9
Rh/TNTs (1 h)
Rh/TNTs (2 h)
Rh/TNTs (8 h)
Rh–Ru/TNTs (1 h) 45
Rh–Ru/TNTs (2 h) 71
Rh–Ru/TNTs (8 h) 100
39
68
100
82
60
57
57
57
55
16
45
70
100 : 0
100 : 0
100 : 0
100 : 0
100 : 0
100 : 0
100 : 0
100 : 0
100 : 0
Ru/TNTs (8 h)
Ru–Rh/TNTs (8 h) 83
25
Rh–Ru/TNTs
85
37
ꢀ
(
200 C, 8 h)
Fig. 5 FT-IR spectra of TNTs without CO gas (A); samples with CO 10
gas: TNTs (B), Rh/TNTs (C), Ru/TNTs (D), Rh–Ru/TNTs (E), Ru–Rh/
Rh–Ru/TNTs-U1
51
100 : 0
(8 h)
ꢀ
TNTs (F), Rh–Ru/TNTs (200 C) (G).
a
Reaction conditions: vinyl acetate ¼ 5 mL, solvent (toluene) ¼ 65 mL,
ꢀ
b
catalyst ¼ 0.40 g, syngas pressure 6 MPa (CO/H
is 2-acetoxy propanal : 3-acetoxy propanal.
2
¼ 1), T ¼ 100 C. b : l
2
terminal (M–CO) and bridged (M CO) CO adsorbed on the
26
metals. However, the aforesaid peaks do not appear in the FT-
IR spectra of Rh/TNTs (Fig. 5C), which means that the amount
of CO adsorbed by Rh is quite small or the CO weakly bonded to
the Rh/TNTs escapes away easily during characterization. It can
be inferred that Ru is more favorable for absorbing CO than Rh.
acetate to further evaluate the catalytic performances of cata-
lysts. In the hydroformylation process of cyclohexene, the main
product is aldehyde (S. 2†), and a small quantity of aldehyde will
be reduced to alcohol (Scheme 2). The results of cyclohexene
hydroformylation over different catalysts are presented in
Table 3. It is easily found that the difference in conversion of
1
3.2 Catalytic performances of the catalysts
Usually, the hydroformylation of vinyl acetate will provide two cyclohexene over Rh/TNTs and Rh–Ru/TNTs is obvious at 1 h
functional products: 2-acetoxy propanal and 3-acetoxy propanal and 2 h (entry 1–4). When the reaction lasted for 2 h, the
(Scheme 1), however, in our experiment, the reaction has high conversion of cyclohexene over Rh/TNTs reaches up to 99.28%,
regioselectivity for 2-acetoxy propanal (S. 1†). Table 2 shows the while that over Rh–Ru/TNTs is much lower. These results
catalytic performance of as-prepared catalysts in the hydro- indicate clearly that the presence of Ru in the catalysts does not
formylation of vinyl acetate under different reaction time. It can enhance the hydroformylation reaction rate of cyclohexene
be found that when the reaction time lasted for 1 h and 2 h though Ru has good ability to adsorb CO. This means that the
(entry 1, 2, 4 and 5), the conversion of vinyl acetate over Rh–Ru/ function of Ru in Rh–Ru/TNTs for hydroformylation of vinyl
TNTs is higher than that over Rh/TNTs though the contents of acetate should be related to the coordination between Ru and
Rh in two catalysts are almost identical and, on the contrary, the carboxyl group, by which not only the vinyl acetate is attracted
selectivity for aldehyde is lower, where 2-acetoxy propanal is the to catalyst, but also the effect of carboxyl group on Rh species is
only product besides hydrogenation product. The result indi- decreased, and then the catalytic activity of catalyst is enhanced.
cates that the addition of Ru does promote the activity of cata- Kargbo et al. reported that the nearby heteroatoms of func-
lyst and accelerate the hydrogenation rate of the formed tionalized olens are benecial for catalytic reaction for coor-
17
27
aldehyde, which results in the lower selectivity for aldehyde. dination to metal centers. Because there is no carboxyl group
Two possible factors may be responsible for the results. One is in cyclohexene, Ru cannot play the same role and enhance the
that the introduction of Ru enhances the adsorption capacity of reaction rate in the hydroformylation of cyclohexene. Further-
catalyst for CO, as shown in FT-IR discussion; the other is that more, by contrast, the negative effect of Ru on the hydro-
the Ru active center in the catalyst may act as Lewis acid formylation of cyclohexene is obvious because Ru is not a better
attracting vinyl acetate through the carboxyl (Lewis base) and catalyst than Rh for the hydroformylation.
reducing the inuence of the carboxyl on Rh active center,
which should be advantageous to Rh catalysing the hydro- mance of the catalysts was also examined by hydroformylation
formylation reaction and enhancing the reaction rate.
of vinyl acetate and cyclohexene. The data of vinyl acetate
When the reaction time lasted for 8 h, the catalytic perfor-
To conrm the inference, we made contrast experiments by hydroformylation are shown in Table 2, the catalytic activity of
substituting cyclohexene which has no carboxyl group for vinyl
Scheme 1 Hydroformylation of vinyl acetate.
Scheme 2 Hydroformylation of cyclohexene.
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Table
Paper
ꢀ
Hydroformylation of cyclohexene over catalysts under almost no catalytic activity at 100 C even when the reaction
3
different reaction time
lasted for 8 h (entry 7). However, Ru–Rh/TNTs shows good
catalytic activity at 120 C (entry 8). The results of entry 5 and 7
imply the sequence of loading metal has a great inuence on
ꢀ
Selectivity (%)
Conversion of
Entry Catalyst
cyclohexene (%) Aldehyde Alcohols the activity of the title catalyst and this is accord with the result
of vinyl acetate hydroformylation.
1
2
3
4
5
6
7
8
Rh/TNTs (1 h)
Rh/TNTs (2 h)
Rh–Ru/TNTs (1 h)
Rh–Ru/TNTs (2 h)
Rh–Ru/TNTs (8 h)
6
94
93
0
6
7
0
0
0
0
0
6
Based on the experiment results and discussion above, we
can draw a conclusion that Rh–Ru catalysis system has its
limitation that it has inuence on functionalized terminal
olens while not on the normal olens. Besides, the ne
structure of Rh–Ru catalysis system need to be further studied.
However, it provides a new view to make functional catalyst.
99
0
1
100
0
0
0
100
0
0
94
a,b
Ru/TNTs (8 h)
Ru–Rh/TNTs (8 h)b
Ru–Rh/TNTs (8 h)
100
There are many researchers focus on multi-active centre catalyst
a
Reaction conditions: cyclohexene ¼ 5 mL, solvent (toluene) ¼ 65 mL,
30–34
system, especially Rh–Ru system.
In current report, their
ꢀ
catalyst ¼ 0.40 g, syngas pressure 6 MPa (CO/H
2
¼ 1), T ¼ 100 C.
b
ꢀ
research hotspot is the tandem reaction of Rh/Ru
hydroformylation/hydrogenation which combines Rh-
T ¼ 120 C.
catalyzed hydroformylation and Ru-catalyzed hydrogenation in
order to get higher efficiency. As for catalysis hydroformylation
of vinyl acetate, most of the catalysts reported are rhodium
complex modied with ligand while Rh–Ru system is rarely
Rh/TNTs is far higher than that of Ru/TNTs. Compared with
over Rh/TNTs, over Rh–Ru/TNTs the conversions of vinyl acetate
are higher at 1 and 2 h, on the other hand, the catalyst Rh–Ru/
TNTs is more active than Ru–Rh/TNTs and Rh–Ru/TNTs (200
35–37
reported.
ꢀ
C). It means that the sequence of impregnation and calcination
have a great inuence on the catalytic activity of Rh–Ru catalysis
4
. Conclusions
system. It is worth noting that the selectivity of reaction for
ꢀ
aldehyde over Rh–Ru/TNTs (200 C) is much higher than that The TiO nanotubes supported Rh and Ru nanoparticles cata-
2
over other catalysts, which might come from the stronger lysts show different catalytic performances in the hydro-
interactions between Rh and Ru caused by calcination. For formylation of vinyl acetate and cyclohexene. Ru itself is not
catalyst Ru–Rh/TNTs, (Rh/TNTs) is used as support to load Ru a good catalyst for the hydroformylation of vinyl acetate and
nanoparticles. It would take place certainly that the Rh nano- cyclohexene, but it can enhance the hydroformylation rate of
particles are partly covered by Ru nanoparticles in the prepa- vinyl acetate by reacting with carboxyl group in Rh–Ru catalysis
ration process of Ru–Rh/TNTs, which may lead to the decrease system. This opens a new way to prepare effective functional
in main active species and the catalytic activity. The larger size catalysts for hydroformylation.
0
of Rh nanoparticles and the lower content of Rh in Rh–Ru/
ꢀ
TNTs (200 C) are responsible for that the Rh–Ru/TNTs (200
C) shows much poor catalytic activity in comparison with Rh–
ꢀ
Conflicts of interest
Ru/TNTs. In order to examine the catalytic performance of the
used catalyst Rh–Ru/TNTs, we collect the mixture by centrifuge
aer reaction. The obtained solid was washed with ethanol for
There are no conicts to declare.
several times and dried in vacuum. Aer treated, we carried Acknowledgements
experiment for recycle test. As shown in Table 2, the conversion
This work is supported by the National Natural Science Foun-
dation of China (21373120, 21301098, 21406120 and 21071086).
of vinyl acetate decreased greatly while the selectivity of alde-
hyde decreased slightly (entry 10). The decrease in the catalytic
activity in recycling might be due to the loss of Rh and Ru
nanoparticles during the recovery and reuse.
Notes and references
The experiment results of cyclohexene hydroformylation
over different catalysts lasted for 8 h are shown in Table 3. One
can see from the data that Ru/TNTs does not shows any catalytic
activity though Ru-complexes-catalyzed hydroformylation was
1
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28,29
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2
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worse when Ru nanoparticles is outside. Ru–Rh/TNTs has
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