Hydroformylation of alkenes using heterogeneous catalyst prepared by intercalation of HRh(CO)(TPPTS)3 complex in hydrotalcite

Article abstract of DOI:10.1016/j.molcata.2009.10.014

Intercalation of HRh(CO)(TPPTS)₃ complex into the interlayer space of hydrotalcite was carried out to prepare an eco-friendly heterogeneous hydroformylation catalyst. Intercalated catalyst was characterized by ³¹P NMR, P-XRD, FT-IR, SEM and surface area measurements. Catalytic activity of intercalated catalyst [HT(3.5)-INT] was evaluated for hydroformylation of linear alkenes of varied carbon number from C₅ to C₁₃ as well as cyclic alkenes. Selectivity of the aldehydes was observed to decrease with increase in the carbon chain length of linear alkenes. Effect of reaction parameters on catalytic activity of intercalated catalyst was studied by varying the catalyst amount, 1-hexene concentration, reaction temperature, partial pressure of carbon monoxide and hydrogen for hydroformylation of 1-hexene. The catalyst was re-cycled up to five times without significant loss in the alkene conversion and selectivity of aldehydes.

Full text of DOI:10.1016/j.molcata.2009.10.014

Journal of Molecular Catalysis A: Chemical 316 (2010) 153–162
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Hydroformylation of alkenes using heterogeneous catalyst prepared by
intercalation of HRh(CO)(TPPTS) complex in hydrotalcite
3
Sumeet K. Sharmaa,b, Parimal A. Parikh , Raksh V. Jasraa,∗
b
a
Discipline of Inorganic Materials & Catalysis, Central Salt and Marine Chemicals Research Institute (CSMCRI), G.B. Marg, Bhavnagar 364 002, Gujarat, India
Department of Chemical Engineering, SV National Institute of Technology, Surat 395 007, Gujarat, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 April 2009
Received in revised form 5 October 2009
Accepted 9 October 2009
Available online 17 October 2009
Intercalation of HRh(CO)(TPPTS) complex into the interlayer space of hydrotalcite was carried out to pre-
3
pare an eco-friendly heterogeneous hydroformylation catalyst. Intercalated catalyst was characterized
31
by P NMR, P-XRD, FT-IR, SEM and surface area measurements. Catalytic activity of intercalated catalyst
[HT(3.5)-INT] was evaluated for hydroformylation of linear alkenes of varied carbon number from C5
to C13 as well as cyclic alkenes. Selectivity of the aldehydes was observed to decrease with increase in
the carbon chain length of linear alkenes. Effect of reaction parameters on catalytic activity of interca-
lated catalyst was studied by varying the catalyst amount, 1-hexene concentration, reaction temperature,
partial pressure of carbon monoxide and hydrogen for hydroformylation of 1-hexene. The catalyst was
re-cycled up to five times without significant loss in the alkene conversion and selectivity of aldehydes.
© 2009 Elsevier B.V. All rights reserved.
Keywords:
Hydroformylation
Hydrotalcite
Intercalation
1
-Hexene
Heterogeneous catalyst
1
. Introduction
Hydroformylation or oxo reaction employed for the synthesis of
Selectivity of aldehyde is low in case of cobalt catalyzed hydro-
formylation of alkenes. Though, homogeneous catalysts give higher
conversion and selectivity for desired product in shorter reac-
tion time as compared to heterogeneous catalyst system, yet have
disadvantage in the separation of catalyst from product mixture.
Thus, research efforts are directed towards the heterogenization
of rhodium complex for hydroformylation of alkenes. Therefore,
numerous supported rhodium complexes have been reported in the
literature for the hydroformylation of alkenes. The support mate-
rials studied include MCM-41, silica, alumina, zeolites, activated
carbons, polymeric organic, inorganic and hybrid supports, sup-
ported aqueous phase catalysis (SAPC) [5–14a]. Main disadvantages
of these supported catalysts are, leaching of rhodium complex dur-
ing the reaction, complicated synthesis procedure, lower catalyst
activity and thermal instability. Application of fluorous solvents for
biphasic hydroformylation of alkenes is also reported in literature
to separate the catalyst from product mixture [14b].
aldehyde and alcohol starting from alkene is an important reaction
from industrial and academic perspective. Approximately, 9 mil-
lion metric tons per year of aldehydes and alcohols are produced
using hydroformylation reaction. These products find applications
in the manufacturing of soaps, fragrances, detergents, adhesives,
plasticizers and solvents [1–3]. Commercially, triphenylphosphine
modified rhodium based complex is used as a catalyst for hydro-
formylation of lower carbon chain alkenes (C –C5) under milder
2
reaction conditions. However, this is not used for higher carbon
chain length alkenes due to the decomposition of rhodium complex
during separation of catalyst from product mixture. This problem is
solved by using water soluble, [HRh(CO)(TPPTS) ] catalyst in bipha-
3
sic system for the hydroformylation [4]. The application of biphasic
catalyst system is limited to hydroformylation of propylene and
butene due to lower solubility of higher carbon chain length
alkenes in aqueous medium. Hydroformylation of higher alkenes
is carried out using cobalt based catalysts under homogeneous
conditions. These catalysts require higher temperature, pressure
and longer reaction time as compared to rhodium based catalysts.
Hydrotalcite or layered double hydroxides (LDHs), are syn-
thetic anionic clays having positively charged brucite-like sheets
x+ n−
with general formula [M(II)1 M(III)x(OH)2]
A
(1 − 3x/2)H O
−x
x/n
2
(0.20 < x ≤ 0.33), where M(II) and M(III) are divalent and triva-
lent cations in the octahedral sites within the hydroxyl layers, x
is the molar ratio of M(III)/[M(II) + M(III)] and A is the exchange-
able interlayer anions [15]. Due to excellent anion exchange
property of hydrotalcite, variety of organic and inorganic anions
can be intercalated into the interlayer space of hydrotalcite
and obtained material can be used for specific application
[16–27]. Intercalation of transition metal complexes such as PtCl6,
∗ Corresponding author. Present address: R&D Centre, VMD, Reliance Industries
Limited, Vadodara, 391 346, Gujarat, India. Tel.: +91 265 6696313;
fax: +91 265 6693934.
E-mail address: rakshvir.jasra@ril.com (R.V. Jasra).
1
381-1169/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2009.10.014

1
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S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 153–162
Scheme 1. Intercalation of HRh(CO)(TPPTS)3 complex into the interlayer space of hydrotalcite.
palladium, cobalt(II)-phthalocyanine, ruthenium-, chromium-,
iron(III)-hexacyano, copper(II)- and nickel(II)-nitrilotriacetate in
the layered double hydroxide has been reported in the literature
(0.704 mmol) was dissolved in 1 mL water followed by addition
of 50 mg of Rh(CO) (acac) under inert atmosphere. Mixture was
2
warmed gently till the complete dissolution of Rh(CO) (acac). Syn-
2
[
28–37]. Intercalation of trans-RhCl(CO)(TPPTS)2 complex with
gas (CO + H = 1:1) was charged into solution from top of the flask.
2
and without excess TPPTS [tris(m-sulfonatophenyl)phosphine] into
Zn–Al layered double hydroxides was reported by Duan et al.,
and trans-RhCl(CO)(TPPTS)2 complex intercalated with excess
TPPTS was used as a catalyst for hydroformylation reaction
Color of the solution changed from maroon to yellow on pass-
ing syn-gas. After 6 h, solution was filtered to remove unreacted
rhodium metal under inert atmosphere. Yellow precipitate was
obtained by adding saturated ethanol (8 mL) with syn-gas into the
filtrate. The precipitated material was again filtered, washed with
ethanol and dried under vacuum.
[
38]. In another study, RhCl(TPPTS)3 complex was heteroge-
nized onto Zn–Al layered double hydroxides via ion exchange
method and used as a heterogeneous catalyst for hydrogenation
of bicyclo[2.2.2]octenes [39]. In the present study, intercalation
of HRh(CO)(TPPTS)3 complex was carried out in the inter-
layer space of Mg–Al hydrotalcite of Mg/Al molar ratio of 3.5
2.3. Synthesis of hydrotalcite [HT(3.5)-N]
Hydrotalcite of Mg/Al molar ratio 3.5 [HT(3.5)-N] was syn-
(
Scheme 1) and applicability of intercalated complex as a hetero-
thesized by co-precipitation of metals salt solutions at constant
pH [15]. Typically, for synthesis of hydrotalcite of Mg/Al molar
ratio 3.5, an aqueous solution (A) of Mg(NO ) ·6H O (0.105 mol)
geneous catalyst for hydroformylation of alkenes was studied in
detail.
3
2
2
and Al(NO ) ·9H O (0.03 mol) in 80 mL double distilled deionized
3
3
2
2
. Experimental
water was prepared. The solution A was added drop wise into a
second solution (B) containing NaNO3 (0.10 mol) in 80 mL double
distilled deionized water, for about 1 h under vigorous stirring at
room temperature. pH of the content was maintained to 9.5 by
2.1. Materials
◦
The
(acetylacetonato)dicarbonylrhodium
(Rh(CO) (acac);
adding the ammonia solution. The content was aged at 65 C for
2
9
8%), tris(3-sodium sulfonatophenyl) phosphine (TPPTS; P(m-
14 h under autogenous pressure. The formed precipitate was fil-
tered and washed with hot distilled water until pH of filtrate was
7. Washed precipitate was dried in vacuum at room temperature.
C H SO Na) ), and alkenes were purchased from Sigma–Aldrich,
6
4
3
3
USA. Magnesium nitrate (Mg(NO ) ·6H O, 99.99%), aluminum
3
2
2
nitrate (Al(NO ) ·9H O, 99.99%), sodium nitrate (NaNO , 99.99%),
3
3
2
3
ammonia solution (40%) and toluene (99.9%) were purchased from
s.d. Fine Chemicals, India. CO (99.9%) and H2 (99.99%) gases were
purchased from Alchemie Gases and Chemicals Pvt. Ltd., India.
Double distilled milli-pore deionized water was used during the
synthesis of catalyst.
2.4. Intercalation of HRh(CO)(TPPTS)3 complex into the layers of
hydrotalcite[HT(3.5)-INT]
Intercalation of HRh(CO)(TPPTS) complex into interlayer space
3
of [HT(3.5)-N] was carried out by addition of 3.24 g hydrotalcite in
a solution of 1.04 g HRh(CO)(TPPTS)3 complex in 25 mL deionized
double distilled water. The suspension was stirred at room temper-
ature for 96 h under inert atmosphere of nitrogen gas. After 96 h,
yellow color suspension was filtered and dried in vacuum and the
catalyst thus obtained was termed as [HT(3.5)-INT].
2.2. Synthesis of HRh(CO)(TPPTS)3 complex
Synthesis of HRh(CO)(TPPTS)3 complex was carried out by
reported procedure [40]. In a typical procedure, 400 mg of TPPTS

S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 153–162
155
samples was calculated from N adsorption isotherms measured at
2
7
7.4 K using Brunauer, Emmett, Teller (BET) method. Pore size dis-
tribution was calculated from desorption branch using the Barrett,
Joyner and Halenda method [42].
2.6. Hydroformylation reaction
Hydroformylation reaction was carried out in 100 mL EZE–Seal
stirred reactor supplied by Autoclave Engineers, USA, equipped
with a controlling unit [43,44]. In a typical reaction procedure,
0
.025 moles of 1-hexene and 0.1 g tridecane (as an internal stan-
dard) dissolved in 50 mL of toluene as a solvent with 100 mg
of [HT(3.5)-INT] catalyst were added into the reactor. The reac-
tor was flushed twice with nitrogen after that the synthesis gas
(
CO/H = 1:1) was introduced into the reactor up to 40 atm. The
2
◦
reactor temperature was brought up to 80 C by heating and stir-
rer of the reactor was started at 1000 rpm. Constant pressure was
maintained during the reaction by supplying syn-gas from reser-
voir. After completion of the reaction, reactor was cooled to room
temperature by circulation of cold water in the coil provided inside
the reactor. Product mixture was then analyzed by gas chromatog-
raphy (GC) and GC–mass spectroscopy (GC–MS).
For finding out reusability, the catalyst was filtered from reac-
tion mixture, washed with 100 mL toluene and dried in vacuum.
The catalyst obtained after drying was used for hydroformylation of
Fig. 1. P-XRD patterns of HRh(CO)(TPPTS)3 complex, [HT(3.5)-N], [HT(3.5)-INT] and
HT(3.5)-INT-R] catalysts.
[
1
–hexene under reaction conditions similar to that of fresh catalyst.
2.5. Characterization of catalyst
2.7. Reaction product analysis
Powder X-ray diffraction (P-XRD) patterns of HRh(CO)(TPPTS)3
complex, [HT(3.5)-N] and [HT(3.5)-INT] were recorded using
Phillips X’Pert MPD system equipped with XRK 900 reaction cham-
ber, using Ni-filtered Cu K␣ radiation (ꢀ = 1.5405 Å) over a 2ꢁ
range of 2–70 . Percentage crystallinity of [HT(3.5)-N] and [HT(3.5)-
INT] was calculated by the summation of integral intensities of
Analysis of product mixture was carried out by GC–MS (Shi-
madzu, GCMS–QP2010) and GC (Shimadzu 17A, Japan) equipped
with 5% diphenyl and 95% dimethyl siloxane universal capillary col-
umn (60 m length and 0.25 mm diameter) and a flame ionization
detector (FID). GC oven temperature was programmed from 40 to
◦
(
[
0 0 3) and (0 0 6) planes and compared with pristine hydrotalcite
HT(3.5)-N]. Values of unit cell parameters (a and c) of [HT(3.5)-
◦
◦
2
00 C at the rate of 6 C/min. Nitrogen gas was used as a carrier
gas. Temperatures of injection port and FID were kept constant at
N] and [HT(3.5)-INT] were calculated by the formula; a = 2(d110
)
◦
200 C. Retention times of different compounds were determined
and c = 3(d003); where d110 and d003 are the basal spacing values of
by injecting pure compound under identical conditions. To ensure
reproducibility of the reaction, repeated experiments were car-
ried out under identical reaction conditions. The conversion and
selectivity data was found to be reproducible in the range of ± 3%
variation. % conversion of alkenes, % selectivity of aldehydes and
TOF values were calculated by following formula:
(
1 1 0) and (0 0 3) planes, respectively [41].
Fourier transform infrared spectra (FT-IR) of HRh(CO)(TPPTS)3
complex, [HT(3.5)-N] and [HT(3.5)-INT] were recorded using
PerkinElmer spectrum GX FT-IR system in the region of
−
1
4
00–4000 cm using KBr pellets.
31P MAS NMR spectra of TPPTS, HRh(CO)(TPPTS)3 complex
Moles of alkene reacted
Moles of alkene fed
and [HT(3.5)-INT] were recorded on Bruker Avance II-500 (FT-
NMR–500 MHz) spectrometer.
%
Conversion =
× 100
Moles of aldehydes formed
Moles of (aldehydes + isomerized alkene + alkane)
%
Selectivity of aldehydes =
× 100
Moles of aldehydes formed
Moles of Rh present in the catalyst × time)
Thermogravimetric analysis (TGA) of HRh(CO)(TPPTS)3 com-
plex, [HT(3.5)-N] and [HT(3.5)-INT] was carried out using
Mettler TGA/SDTA 851e equipment in flowing nitrogen (flow
TOF = (
◦
rate = 50 mL/min), at a heating rate of 10 C/min.
3. Results and discussion
Surface morphology of the [HT(3.5)-N] and [HT(3.5)-INT]
was determined using scanning electron microscope (Leo Series
VP1430, Germany) having silicon detector. The samples were
coated with gold using sputter coating prior to measurement. Anal-
ysis of samples was carried out at an accelerating voltage of 15 kV.
Chemical analysis of the catalyst was carried out using Induc-
tive Coupled Plasma (ICP) Spectrometer, PerkinElmer, Optima 2000
instrument.
3.1. Characterization of catalyst
P-XRD patterns of HRh(CO)(TPPTS) , [HT(3.5)-N] and [HT(3.5)-
3
INT] are shown in Fig. 1. P-XRD pattern of [HT(3.5)-N] shows sharp
and symmetric peaks at lower diffraction angles (2ꢁ = 10–25) and
broad asymmetric reflections at higher angles (2ꢁ = 30–50), which
are typical characteristics of pure hydrotalcite. The presence of
−
Surface area measurements of [HT(3.5)-N] and [HT(3.5)-INT]
were carried out using ASAP 2010 Micromeritics, USA. Samples
NO3 anions in interlayer space of [HT(3.5)-N] was confirmed
by the d-spacing of (0 0 3) and (0 0 6) planes, 8.79 and 4.48 Å,
respectively. P-XRD pattern of intercalated material [HT(3.5)-INT]
shows all characteristics peaks of pristine hydrotalcite without
◦
−2
were activated at 80 C for 4 h under vacuum (5 × 10 mmHg)
prior to N adsorption measurements. Specific surface area of the
2

1
56
S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 153–162
any additional peak of HRh(CO)(TPPTS)3 complex. This indicates
intercalation of complex into the interlayer space of [HT(3.5)-N].
However, in our earlier work for the synthesis of multi-functional
catalyst system by impregnation of HRh(CO)(PPh3)3 complex
on the surface of hydrotalcite, we have observed the peaks of
HRh(CO)(PPh ) complex in the P-XRD pattern of multi-functional
3
3
catalyst [45,46]. The main diffraction peaks at 2ꢁ values 5.62 (0 0 3),
1.32 (0 0 6) and 61.1 (1 1 0) were observed in P-XRD pattern of
HT(3.5)-INT] sample. The observed shift in P-XRD pattern of inter-
1
[
calated [HT(3.5)-INT] sample towards lower 2ꢁ values of (0 0 3)
and (0 0 6) planes with respect to pristine hydrotalcite confirmed
the intercalation of HRh(CO)(TPPTS)3 complex. The intercalation
of HRh(CO)(TPPTS) complex was further confirmed by the broad-
3
ening in d-spacing value of (0 0 3) plane of [HT(3.5)-INT] from
8
.79 to 16.8 Å. In order to observe the effect of intercalation
of HRhCO(TPPTS)3 complex on the crystallinity of hydrotalcite
HT(3.5)-N], the pristine hydrotalcite was considered as a 100%
crystalline sample. The crystallinity of [HT(3.5)-INT] was observed
Fig. 2. FT-IR spectra of [HT(3.5)-N], HRh(CO)(TPPTS)3 complex, [HT(3.5)-INT] and
HT(3.5)-INT-R] catalysts.
[
[
to decrease up to 43% on intercalation of HRh(CO)(TPPTS) . The
values of unit cell parameters a were calculated as 3.0 Å for both,
3
−
1
was confirmed by the appearance of bands at 2006 cm
for
−
1
−1
[
HT(3.5)-N] and [HT(3.5)-INT]. The value of c was observed to
ꢂRh–H, 1926 cm
for ꢂC=O, 3468 and 1631 cm
for ꢂO–H, 1465
−
1
−1
for ꢂSO3–, 1096 cm−1 for ꢂ
change significantly for intercalated sample [HT(3.5)-INT]. The
value of c was calculated as 26.4 Å for [HT(3.5)-N], which increased
to 59.4 Å for [HT(3.5)-INT]. The increase in the c value for [HT(3.5)-
INT] catalyst is due to the broadening d-spacing of (0 0 3) plane by
and 1396 cm
for ꢂph, 1193 cm
SO
in
−
1
ꢀ
−1
and 623 cm
for ꢂ
[38]. The band appeared at 1381 cm
FT-IR spectrum of [HT(3.5)-N] confirms the presence of nitrate
anions in the interlayer space of hydrotalcite [15]. The bands at
1193 cm (ꢂSO3 ), 1096 cm (ꢂSO) and 623 cm (ꢂ SO) in the spec-
trum of HRh(CO)(TPPTS)3 complex was observed to shift towards
low frequency region in the FT-IR spectrum of [HT(3.5)-INT] cat-
SO
−
1
−
−1
−1
ꢀ
intercalation of HRh(CO)(TPPTS) complex in the [HT(3.5)-N].
3
FT-IR spectra of HRh(CO)(TPPTS) , [HT(3.5)-N] and [HT(3.5)-
3
INT] are shown in Fig. 2. Formation of HRh(CO)(TPPTS)3 complex
Fig. 3. 31P NMR spectra of TPPTS, HRh(CO)(TPPTS)3 complex and [HT(3.5)-INT] catalysts.

S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 153–162
157
glets at −31.48 ppm in solid state 31P NMR spectra of [HT(3.5)-INT]
catalyst are attributed to the intercalated HRh(CO)(TPPTS) (which
2
is an active species for hydroformylation of alkene) and TPPTS
(intercalated), respectively in the interlayer space of hydrotalcite.
During the intercalation process, dissociation of the TPPTS molecule
from HRh(CO)(TPPTS) complex was reported in the literature also
3
[
3
40,47,48]. The peak of OTPPTS (oxide of TPPTS) was observed at
4.65 ppm in the 31P NMR spectrum of TPPTS (Fig. 3), however,
31
no peak was observed at 34.65 ppm in the P solid state NMR
spectrum of [HT(3.5)-INT]. 31P MAS NMR spectra of [HT(3.5)-INT]
showed a peak at 8.37 ppm which could not be identified.
Thermal stability of HRh(CO)(TPPTS) , [HT(3.5)-N] and [HT(3.5)-
3
INT] samples were evaluated by TGA and results are shown in
Fig. 4. TGA of HRh(CO)(TPPTS)3 showed 63% weight loss in the
◦
temperature range of 160–300 C due to thermal decomposition
of complex. However, only 3% weight loss of HRh(CO)(TPPTS) was
3
◦
observed up to 140 C due to the removal of water molecules. TGA
Fig. 4. TGA of HRh(CO)(TPPTS)3 complex, [HT(3.5)-N] and [HT(3.5)-INT] catalysts.
of [HT(3.5)-N] showed weight loss in two stages, which is a typ-
ical characteristic of pure hydrotalcite sample [15]. The weight
loss in first stage (9%) was observed in the temperature range
alyst. Shifting of these bands in the direction of low frequency
region is due to the coordination between oxygen atom of sulfonate
group of HRh(CO)(TPPTS)3 complex with the layers of hydroxide
◦
of 200 C due to loss of physically adsorb water molecules on
−
1
the surface without collapse of the structure. The weight loss
in second stage (30%) is attributed to the removal of hydroxyl
in the hydrotalcite network. Intensity of the band at 1381 cm
was observed to decrease significantly in the FT-IR spectrum of
HT(3.5)-INT] catalyst, which confirmed that the most of nitrate
◦
groups and nitrate anions in the temperature range of 300–550 C.
[
TGA curve of [HT((3.5)-INT] catalyst was observed similar to the
anions present in the interlayer space of hydrotalcite were replaced
HRh(CO)(TPPTS) complex. TGA of intercalated catalyst [HT((3.5)-
by HRh(CO)(TPPTS) complex. Qualitative and quantitative analy-
3
3
INT] catalyst showed 10% weight loss in the temperature range of
ses of the filtrate also confirmed the presence of a water soluble
NaNO3 salt. The other observed vibrations in the FT-IR spectra
of HRh(CO)(TPPTS)3 complex and [HT(3.5)-N] were found to be
present in the FT-IR spectrum of [HT(3.5)-INT] catalyst. Above data
◦
1
40–200 C due to removal of water molecules. The major weight
loss (42%) was observed in second stage due to removal of anions
from the interlayer space of hydrotalcite in the temperature range
◦
of 220–350 C. The higher weight loss in [HT((3.5)-INT] as compared
show that the HRh(CO)(TPPTS) complex is intercalated into inter-
3
to pristine [HT((3.5)-N] is attributed to the decomposition of bulkier
anions (TPPTS) from the interlayer space of [HT((3.5)-INT]. The
observed higher thermal stability of [HT((3.5)-INT] catalyst as com-
layer space of [HT(3.5)-N].
31
P MAS NMR spectra of TPPTS, HRh(CO)(TPPTS) complex and
3
HT(3.5)-INT] catalyst are shown in Fig. 3. The 3 P NMR spectra
1
[
pared to HRh(CO)(TPPTS) complex is due to the strong interaction
of TPPTS shows peaks at–5.4 and 34.65 ppm which is attributed
to the uncoordinated TPPTS and oxides of TPPTS, respectively. The
3
of HRh(CO)(TPPTS)3 complex and interlayer network of hydrotal-
cite structure. Due to the higher thermal stability of [HT((3.5)-INT],
it has potential for catalytic applications in heterogeneous hydro-
formylation and hydrogenation reaction.
The SEM images of [HT(3.5)-N] and [HT(3.5)-INT] are given in
Fig. 5. The micrographs of [HT(3.5)-N] and [HT(3.5)-INT] show a
well developed layered structure and possess platelet structures.
However, due to overlapping of such platelets spongy type struc-
ture is exhibited.
appearance of doublet at 44.32 [J(Rh–P) = 152 Hz] in 31P NMR spec-
tra of HRh(CO)(TPPTS)3 complex shows the trigonal bipyramidal
structure with three phosphorous atoms present in the same envi-
ronment and are in equatorial plane. The hydride (H) and CO are
in axial positions [40]. Doublet at 42.34 ppm was observed in solid
3
1
state P NMR spectra of [HT(3.5)-INT] catalyst, confirming that
the HRh(CO)(TPPTS) complex was intercalated into the interlayer
3
space of the hydrotalcite. The observed doublet at 37.59 and sin-
Fig. 5. SEM images of [HT(3.5)-N] and [HT(3.5)-INT] catalysts.

1
58
S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 153–162
movement is restricted in intercalated catalyst as compared to
that in its biphasic analogues [HRh(CO)(TPPTS)3 catalyzed hydro-
formylation in biphasic medium], as a result, the steric effect of
ligand is less operative to increase the n/iso ratio of aldehydes in
this study. Another reason for lower n/iso ratio of aldehydes is due
to the absence of excess ligand (TPPTS) in the present study. As to
achieve higher n/iso ratio of aldehydes, isomerization of alkenes
is normally suppressed by adding excess amount of ligand which
creates a sterically demanding environment around the rhodium
metal centre. Lower n/iso ratio of aldehydes in the range of 0.5–0.64
was also reported by the Chaudhary et al. for hydroformylation
of alkenes using HRh(CO)(TPPTS)3 supported on carbon surface
[
49].
In case of hydroformylation of cyclic alkenes, 98% con-
version of cyclohexene with 100% selectivity for cyclohexanal
m/z = 112) was observed. The conversion decreased to 42%
(
Fig. 6. Surface area measurements of [HT(3.5)-N] and [HT(3.5)-INT] catalysts.
for cis–cyclooctene hydroformylation with 95% selectivity for
cyclooctanal (m/z = 140). However, for the hydroformylation
of 1-cycloheptene, 98% selectivity for cycloheptanemethanol
Nitrogen adsorption–desorption isotherms of [HT(3.5)-N] and
(m/z = 128) was observed, which was formed via subsequently
[
HT(3.5)-INT] samples measured at liquid nitrogen temperature
hydrogenation of hydroformylation product. The order of cat-
alytic activity for the hydroformylation of cyclic alkenes was
observed as; cyclohexene > cycloheptene > cyclooctene under iden-
tical reaction conditions. For hydroformylation of styrene, 95%
conversion with 92% selectivity of aldehydes (3-phenylpropanal,
␣-phenylpropionaldehyde; m/z = 134) was observed, while the
conversion decreased to 64% with 89% selectivity of aldehy-
des (benzenebutanal, ␣-ethyl-benzeneacetaldehyde; m/z = 148) for
the hydroformylation of allylbenzene. The results described in
Table 2 indicate that the HRhCO(TPPTS)3 complex intercalated in
hydrotalcite [HT(3.5)-INT] is an active heterogeneous catalyst for
hydroformylation of various alkenes starting from n-alkenes (lin-
ear), cyclic as well as functionalized alkenes. In all the reactions,
comparable catalytic activity was observed with its homogeneous
analogues. 1-Hexene was selected as a model reactant to study
the effect of reaction parameters such as, alkene concentration,
amount of catalyst, partial pressure of CO and H2 and reaction
temperature on the catalytic activity of intercalated catalyst. The
reusability of catalyst was also evaluated by performing repeated
experiments under reaction conditions to those used for fresh cat-
alyst.
are shown in Fig. 6. Surface area and pore volume of [HT(3.5)-
N] and [HT(3.5)-INT] samples are given in Table 1. Surface area
2
of [HT(3.5)-N] sample was calculated as 76 m /g that decreased
2
up to 33 m /g after intercalation of HRh(CO)(TPPTS)3 in inter-
layer space of [HT(3.5)-N]. Pore volume of [HT(3.5)-N] sample
3
was also observed to decrease from 0.4 to 0.1 cm /g for interca-
lated [HT(3.5)-INT] catalyst. Surface area measurements data also
support the results observed in P-XRD analysis of [HT(3.5)-INT]
catalyst.
3.2. Catalytic activity for hydroformylation of alkenes
Catalytic activity of intercalated [HT(3.5)-INT] catalyst was
evaluated for hydroformylation of linear alkenes with varied
carbon number from C5 to C13 and some cyclic alkenes (Table 2).
The mass fragmentation data of the products of hydroformylation
of studied alkenes are given in Fig. 1 as the supporting materials
file. As the carbon chain length of linear alkenes increases, the
selectivity for aldehydes was observed to decrease. For example,
1
00% conversion with 98% selectivity of aldehydes was achieved
◦
for hydroformylation of 1-pentene in 10 h reaction time at 80 C,
which decreased to 99% conversion of 1-decene with 83% selec-
tivity of aldehydes. However, for hydroformylation of 1-tridecene,
conversion was further decreased to 88% with 56% selectivity
of aldehydes. This decrease in the selectivity of aldehydes on
increasing the carbon chain length of alkenes is due to faster
isomerization of alkenes as compared to hydroformylation and
formation of ketone under studied experimental conditions.
Reactivity of the catalyst for hydroformylation of linear alkenes
under identical reaction conditions was found to be in the order
of; 1-pentene > 1-hexene > 1-heptene > 1-octene > 1-nonene > 1-
decene > 1-undecene > 1-dodecene > 1-tridecene. The n/iso ratio
of aldehydes for linear alkenes was observed in the range of
3.3. Effect of 1–hexene concentration and amount of catalyst
Data on the conversion and selectivity for 1-hexene hydro-
formylation depicting the effect of varied concentration of
-hexene and amount of catalyst are given in Table 3. 1-Hexene
1
concentration was varied from 6 to 70 mmol keeping constant
amount of the catalyst (100 mg). Complete conversion of 1-hexene
was observed in the entire studied concentration range of 1-
hexene. The selectivity of aldehydes was observed to increase
up to 25 mmol concentration of 1-hexene. On further increasing
the concentration of 1-hexene, the selectivity of aldehydes was
found to decrease significantly. For example, selectivity of alde-
hydes increased from 74 to 95% on increasing the concentration
of 1-hexene from 6 to 25 mmol and selectivity decreased to 83%
on further increasing the concentration of 1-hexene to 50 mmol.
The n/iso ratio of aldehydes was observed in the range of 0.6–0.8.
The higher catalytic activity for isomerization of 1-hexene to 2/3-
hexene at higher and lower substrate concentration results into
the lower selectivity of aldehydes. Hydrogenation of 1-hexene and
aldehydes was not observed in the present study. The calculated
TOF values were found to increase from 52 to 648 on increasing the
1-hexene concentration from 6 to 70 mmol. The maximum conver-
sion of 1-hexene and selectivity for aldehydes (n to iso ratio = 0.8)
were observed at 25 mmol of 1-hexene concentration. Therefore,
0.6–1.3. The main reason for lower n/iso ratio of aldehydes in the
present study could be due to strong coordination of ligand to the
hydrotalcite matrix in [HT(3.5)-INT] catalyst. Therefore, ligands
Table 1
Characterization of [HT(3.5)-N] and [HT(3.5)-INT] catalysts.
Sample
[HT(3.5)-N]
[HT(3.5)-INT]
Crystallinity, %
Surface area, m /g
Pore volume, cm /g
Unit cell parameter (a), Å
Unit cell parameter (c), Å
100
76
0.4
3.0
26.4
43
33
0.1
3.0
59.4
2
3

S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 153–162
159
Table 2
a
Effect of carbon number (chain length) of alkenes on catalytic activity of [HT(3.5)-INT] .
Entry
Alkene
% Conversion
% Selectivity
Aldehydes
n/iso ratio of aldehydes
Isomerization of alkene
2
Hydrogenation of alkene
–
Ketone
–
1
100
98
96
95
95
88
83
1.3
2
100
100
100
100
99
0.8
0.8
0.7
0.7
0.7
4
5
5
7
–
–
–
–
–
–
–
–
5
6
3
4
5b
6c
11
7d
8e
9f
97
95
88
72
67
56
0.6
0.6
0.6
18
21
29
–
–
–
10
12
15
1
0
98
90
100
–
–
–
–
–
2
–
–
1
1g
–
1
2
42
95
–
–
5
–
1
1
3
4
95
64
92
89
0.5
1.1
–
6
8
5
–
–
a
b
c
d
e
f
◦
Reaction conditions: alkene = 0.2 mmol, catalyst = 100 mg, syn-gas = 40 atm (CO/H2 = 1/1), temperature = 80 C, time = 10 h.
-Decanone (m/z = 156).
Undecanone.
-Dodecanone (m/z = 184).
Tridecanone (m/z = 198).
3
3
2
9
-Tetradecanone (m/z = 212).
8% selectivity for cycloheptanemethanol (m/z = 128).
g
2
5 mmol concentration of 1-hexene was taken to study the effect
3.4. Effect of partial pressure of H2 and CO
of other reaction parameters on the conversion and selectivity for
1
-hexene hydroformylation.
Effect of the amount of catalyst on the conversion and selectivity
Partial pressures of H2 and CO have significant effect on the
selectivity of aldehydes (Table 4). The effect of partial pressure of
H2 was studied by varying the pressure of H2 from 2 to 30 atm at
constant pressure of CO (20 atm). The conversion of 1-hexene was
found to increase from 96 to 100% by increasing the partial pres-
for 1-hexene hydroformylation was studied by varying the amount
of catalyst from 10 to 500 mg at constant 1-hexene concentration
(
25 mmol). The selectivity of aldehydes was observed to increase up
to 200 mg catalyst. On further increase in the amount of catalyst, the
selectivity of aldehydes was observed to decrease significantly due
to the higher selectivity of the 1-hexene isomerization products.
The TOF values were expectedly observed to decrease on increas-
ing the amount of catalyst. TOF value was calculated as 1014 at
sure of H from 2 to 10 atm. At lower partial pressure of H , lower
2
2
selectivity of aldehydes was observed due to the slow hydroformy-
lation of 1-hexene as compared to its isomerization. The selectivity
of aldehydes was observed to increase significantly up to 20 atm,
however, on further increase in partial pressure of H , no signifi-
2
1
0 mg catalyst amount, which decreased to 47 at 500 mg of catalyst
cant effect was observed. The selectivity of aldehydes was found to
amount.
increase from 26 to 95% by increasing the pressure of H from 2 to
2

1
60
S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 153–162
Table 3
a
Effect of 1-hexene and catalyst amount on selectivity of aldehydes .
TOF, h 1
−
Entry
1-Hexene, mmol
Catalyst, mg
% Conversion
% Selectivity
Aldehydes
n/iso ratio of aldehydes
2/3-Hexene
1
2
3
4
5
6
7
8
9
0
1
2
3
4
6
12
18
25
30
40
50
70
25
25
25
25
25
25
100
100
100
100
100
100
100
100
10
20
50
200
300
500
100
100
100
100
100
100
100
100
91
74
89
94
95
92
89
83
77
35
54
79
96
92
78
0.6
0.7
0.7
0.8
0.8
0.7
0.7
0.7
0.9
0.8
0.9
0.8
0.8
0.8
26
11
6
5
8
11
17
23
65
46
21
4
52
125
198
281
323
375
466
648
1014
798
383
142
91
1
1
1
1
1
93
100
100
100
100
8
22
47
a
◦
Reaction conditions: syn-gas = 40 atm (CO/H2 = 1/1), temperature = 80 C, time = 8 h.
2
0 atm. The lower selectivity of aldehyde at lower partial pressure
to increase from 135 to 290 on increasing the partial pressure of
CO from 5 to 30 atm. The reason for lower selectivity of aldehydes
at lower partial pressure of CO is the insufficient concentration of
CO to forward the hydroformylation reaction. As partial pressure of
CO increased, the selectivity of aldehydes was observed to increase
due to the enhancement in the CO concentration.
of hydrogen may be attributed to the insufficient concentration of
hydrogen in the reaction medium. The selectivity of isomerization
products (2/3-hexene) was observed to decrease from 74 to 4% on
increasing the partial pressure of H2 from 2 to 30 atm. The n/iso
ratio of aldehydes was observed in the range of 0.7–0.9 on increas-
ing the partial pressure of hydrogen from 2 to 30 atm. Higher value
of the n/iso ratio of aldehydes at 30 atm hydrogen pressure could
3.5. Effect of reaction temperature
be attributed to the formation of HRh(CO)(TPPTS) species, which
2
◦
favored the formation of linear aldehydes. The TOF was calculated
as 75 at 2 atm and it increased to 287 at 30 atm partial pressure
of hydrogen. Hydrogenation products of 1-hexene and aldehydes
were not obtained under the studied reaction conditions or even
The reaction temperature was varied from 50 to 100 C at 40 atm
pressure of syn-gas (CO/H = 1), 100 mg catalyst and 0.025 mol of
1-hexene concentration (Table 5). The selectivity of aldehydes was
observed to increase from 78 to 95% on increasing the reaction
temperature from 50 to 80 C. On further increase in the reaction
temperature to 100 C, the selectivity for aldehydes decreased to
53%. The observed decrease in the aldehydes selectivity is due to
the increased isomerization of 1-hexene to 2/3-hexene at higher
reaction temperature. At 80 C, 5% isomerization of 1-hexene was
obtained and it increased to 47% at 100 C. The n/iso ratio of alde-
hydes was also found in the range of 1.1–0.8 on increasing the
2
◦
at 30 atm partial pressure of H . Effect of the partial pressure of
2
◦
CO on conversion and selectivity was also studied at constant H2
pressure (20 atm). The selectivity for aldehydes was observed to
increase from 47% at 5 atm to 98% at 30 atm of CO partial pressure.
The selectivity of 2/3-hexene decreased significantly from 53 to 8%
by increasing the partial pressure of CO from 5 to 15 atm and selec-
tivity of 2/3-hexene again decreased to 2% on further increasing
the partial pressure of CO to 30 atm. The TOF values were observed
◦
◦
◦
reaction temperature from 50 to 100 C. At higher temperatures,
Table 4
a
Effect of partial pressure of H2 and CO on selectivity of aldehydes .
−
TOF, h
n/iso ratio of aldehydes
1
Entry
Partial pressure of
H2, atm
% Conversion
CO, atm
% Selectivity
Aldehydes
2/3–Hexene
74
50
11
5
1
2
3
4
5
6
7
8
9
2
10
15
20
30
20
20
20
20
20
20
20
20
20
20
5
10
15
20
30
96
100
100
100
100
97
100
100
100
100
26
50
89
95
96
47
78
92
95
98
0.7
0.7
0.7
0.8
0.9
0.7
0.7
0.7
0.8
0.8
75
148
263
281
287
135
231
272
281
290
4
53
22
8
5
2
1
0
a
◦
Reaction conditions: 1-hexene = 25 mmol, catalyst = 100 mg, temperature = 80 C time = 8 h.
Table 5
a
Effect of temperature on selectivity of aldehydes .
◦
−1
TOF, h
Entry
Temperature
C
% Conversion
% Selectivity
Aldehydes
n/iso ratio of aldehydes
2/3-Hexene
1
2
3
4
5
50
60
70
80
100
100
100
100
100
100
78
89
93
95
53
1.1
0.9
0.9
0.8
0.8
22
11
7
5
47
230
263
275
281
157
a
Reaction conditions: 1-hexene = 25 mmol, catalyst = 100 mg, syn-gas = 40 atm (CO/H2 = 1/1) time = 8 h.

S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 153–162
161
Table 6
Catalytic activity of [HT(3.5)-INT] with its counterpart HRh(CO)(TPPTS)3 in biphasic system and other supported catalysts for hydroformylation of 1-hexene.
Catalyst
% Conversion
% Selectivity of aldehyde
74–95
n/iso ratio
TOF (h−1)
Ref.
HRh(CO)(TPPTS)3 intercalated in HT
HRh(CO)(TPPTS)3
100
100
0.6–0.9
1.5
52–1014
810
Present study
[52]
100
RhCl(CO)(TPPTS)2 intercalated in Zn2-Al LDH with excess TPPTS
RhCl(CO)(TPPTS)2 intercalated in Zn3-Al LDH with excess TPPTS
Rh/SiO2
TPPTS-Rh/SiO2
RhH(CO)(TPPTS)3 supported on SiO2-FA
75.94
60–95
93.6
23.8
72.9
84.34
70–80
5.82
92.4
75
2.19
2.6–3.0
1.7
6.1
3.2
266.97
80–150
11.7
51.7
454.2
[53]
[38]
[48]
[48]
[54]
it is expected that the thermal motion of intermediate catalytic
species increases due to significant decrease in steric factors of
the catalyst which results into increase in polarity of M–H bond
favoringMarkovnikov additionthat results intohigherselectivity of
iso-aldehyde. Another reason for the lower n/iso ratio of aldehydes
at higher temperature could be attributed to the higher concen-
tration of the intercalated HRh(CO) (TPPTS)2 species, which are
2
responsible for the formation of branched aldehydes. Calculated
◦
TOF values were observed to increase up to 80 C and decreased on
further increase in the reaction temperature.
3.6. Kinetics measurements and reusability of the catalyst
The reaction profile with respect to time for hydroformylation
◦
of 1-hexene using [HT(3.5)-INT] catalyst at 80 C and 40 atm syn-
gas pressure is shown in Fig. 7. Rapid consumption of 1-hexene
was observed for hydroformylation and isomerization reactions.
Initially, most of 1-hexene isomerized to 2/3-hexene in the stud-
ied experimental conditions. About 95% conversion of 1-hexene
into 2/3-hexene was observed within 60 min reaction time. How-
ever, after complete consumption of 1-hexene, 2/3-hexene was
converted into aldehydes (mostly for 2-methylhexanal and 2-
ethylpentanal) via hydroformylation reaction which results into
lower n/iso ratio of aldehydes. Higher rate of reaction was obtained
for isomerization of 1-hexene to 2/3-hexene as compared to the
hydroformylation reaction. The higher rate of isomerization reac-
tion is due to the well known property of the Rh-complex and
hydrotalcite for double bond isomerization [50,51]. Hydrogenation
products were not observed during the course of kinetics experi-
ment.
Fig. 8. Reusability of [HT(3.5)-INT] catalyst for hydroformylation of 1-hexene.
hydes could be ascribed to handling losses of the catalyst (since
catalyst is air sensitive) and leaching of rhodium (1.5% (by wt)
leached out after seventh cycle as compared to initial amount) dur-
ing reusability experiments. However, leaching of rhodium from
[
HT(3.5)-INT] catalyst is lower in the present study as compared
to other reported heterogeneous catalyst [38]. The P-XRD and FT-
IR spectrum of used [HT(3.5)-INT] catalyst shown in Figs. 1 and 2
also supported that the structure of [HT(3.5)-INT] catalyst was not
disturbed significantly after repeated experiments with the same
catalyst.
The catalytic activity of [HT(3.5)-INT] was compared with its
counterpart HRh(CO)(TPPTS)3 in biphasic system and other sup-
ported catalysts for hydroformylation of 1-hexene (Table 6). The
HRh(CO)(TPPTS)3 catalyst in biphasic system gave 100% conver-
sion with 100% selectivity of aldehyde, however, the catalyst is
re-cycled up to three cycles [52]. After third cycle significant drop
in the conversion of 1-hexene is reported. The catalyst reported
in the present study showed higher conversion of 1-hexene and
higher selectivity of aldehydes with lower n/iso ratio as compared
to other HRh(CO)(TPPTS)3 supported catalysts reported in the lit-
erature [38,52–54].
The catalyst was re-cycled up to seven times for hydroformyla-
tion of 1-hexene (Fig. 8). Complete conversion of 1-hexene (100%)
was observed in seventh cycle, however, selectivity of the aldehy-
des (n and iso) was observed to decrease after fifth cycle. The 93%
selectivity of aldehydes was obtained at fifth cycle that decreased to
8
7% at the end of seventh cycle. The decrease in selectivity of alde-
4. Conclusions
Intercalation of HRh(CO)(TPPTS)3 complex into interlayer
space of hydrotalcite was confirmed by 31P NMR, P-XRD and
FT-IR spectra of intercalated [HT(3.5)-INT] catalyst. Catalytic
activity of intercalated catalyst was evaluated for hydroformy-
lation of linear alkenes with varied carbon number (C5–C13
)
and cyclic alkenes. As carbon chain length of linear alkenes
increases, the selectivity of aldehydes was observed to decrease.
Activity of the catalyst for hydroformylation of linear alkenes
under identical reaction conditions was found to be in the order
of; 1-pentene > 1-hexene > 1-heptene > 1-octene > 1-nonene > 1-
decene > 1-undecene > 1-dodecene > 1-tridecene. Order of the
catalytic activity for hydroformylation of cyclic alkenes was
observed as; cyclohexene > cycloheptene > cyclooctene under
Fig. 7. Kinetic profile for hydroformylation of 1-hexene using [HT(3.5)-INT] as a
catalyst.

1
62
S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 153–162
identical reaction conditions. The catalyst was re-cycled up to five
times without significant loss in conversion and selectivity for
hydroformylation of 1-hexene.
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