Investigations on the kinetics of hydroformylation of 1-hexene using HRh(CO)(PPh3)3 encapsulated hexagonal mesoporous silica as a heterogeneous catalyst

Article abstract of DOI:10.1016/j.molcata.2009.09.018

Kinetics of HRh(CO)(PPh₃)₃ encapsulated in hexagonal mesoporous silica has been investigated for the heterogeneous catalyzed hydroformylation of 1-hexene. The rates of hydroformylation of C₅-C₁₂ alkenes, determined under identical conditions, indicated a decreasing trend on increasing the chain length of the alkenes. The representative alkene, 1-hexene has been subjected for detail kinetic investigations. The 1-hexene hydroformylation kinetics has been studied as the function of the amount of catalyst, concentration of 1-hexene, partial pressure of CO and H₂, and temperature. All these parameters were found to influence the rate of hydroformylation. The rate was observed to be first order with respect to partial pressure of hydrogen. The rate was observed to increase with the increase in the amount of the catalyst and approached saturation on increasing the catalyst amount. Rates increased on increasing the CO pressure and 1-hexene concentration up to certain values, and on further increasing these parameters, substrate inhibited kinetics was observed for both CO and 1-hexene at higher pressures and concentrations, respectively. A kinetic rate model based on the mechanism of hydroformylation of 1-hexene was found to fit with the experimental rate with ±15% deviation.

Full text of DOI:10.1016/j.molcata.2009.09.018

Journal of Molecular Catalysis A: Chemical 316 (2010) 23–29
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journal homepage: www.elsevier.com/locate/molcata
Investigations on the kinetics of hydroformylation of 1-hexene using
HRh(CO)(PPh3)3 encapsulated hexagonal mesoporous silica as a heterogeneous
catalyst
N. Sudheesh, Sumeet K. Sharma, Ram S. Shukla∗, Raksh V. Jasra∗∗
Discipline of Inorganic Materials and Catalysis, Central Salt and Marine Chemicals Research Institute, Council of Scientific and Industrial Research (CSIR),
G.B. Marg, Bhavnagar 364002, Gujarat, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 May 2009
Received in revised form 8 September 2009
Accepted 28 September 2009
Available online 4 October 2009
Kinetics of HRh(CO)(PPh3)3 encapsulated in hexagonal mesoporous silica has been investigated for the
heterogeneous catalyzed hydroformylation of 1-hexene. The rates of hydroformylation of C5–C12 alkenes,
determined under identical conditions, indicated a decreasing trend on increasing the chain length of the
alkenes. The representative alkene, 1-hexene has been subjected for detail kinetic investigations. The
1-hexene hydroformylation kinetics has been studied as the function of the amount of catalyst, concen-
tration of 1-hexene, partial pressure of CO and H2, and temperature. All these parameters were found
to influence the rate of hydroformylation. The rate was observed to be first order with respect to partial
pressure of hydrogen. The rate was observed to increase with the increase in the amount of the cata-
lyst and approached saturation on increasing the catalyst amount. Rates increased on increasing the CO
pressure and 1-hexene concentration up to certain values, and on further increasing these parameters,
substrate inhibited kinetics was observed for both CO and 1-hexene at higher pressures and concentra-
tions, respectively. A kinetic rate model based on the mechanism of hydroformylation of 1-hexene was
found to fit with the experimental rate with 15% deviation.
Keywords:
Hydroformylation
Hexagonal mesoporous silica
Kinetics
1-Hexene
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
still remained as the reasons for restriction of its commercializa-
tion.
Hydroformylation of alkenes used for the synthesis of a wide
range of aldehydes is commercially carried out employing rhodium
and cobalt based homogeneous catalysts [1,2]. The recovery of the
homogeneous catalysts from the product mixture is tedious and
often leads to the loss of valuable catalyst. Using biphasic catalyst
is one way to overcome this problem. However, biphasic systems
have limitations in terms of lower solubility of higher alkenes in
the aqueous phase [3]. Therefore, the development of a heteroge-
neous catalyst is needed that would eliminate the need of catalyst
recovery from the product mixture and also would enable its use
in fixed bed type reactor. Efforts to heterogenize the homoge-
neous catalysts on to a solid support have been reported [4–6].
However, loss of activity and leaching of heterogenized catalyst
We have recently reported a heterogeneous catalyst system of
rhodium complex HRh(CO)(PPh3)3 encapsulated into the pores of
hexagonal mesoporous silica (HMS) [7]. The catalyst was found
to be active for hydroformylation of C5–C12 olefins. The het-
erogeneous catalyst system [7] has shown better performance
in the terms of conversion, turn over frequency and percentage
of rhodium loading on the support HMS, in comparison of the
other closely related rhodium silica based heterogeneous cata-
lyst systems [7–9] reported for hydroformylation of 1-hexene.
Kinetic investigations of a catalytic reaction are important to
obtain a systematic analysis of the catalyst system for improve-
ment in its performance as well as optimizing the parameters
to commercial level [10]. The kinetics of hydroformylation using
different homogeneous catalysts of rhodium phosphine ligands
[11–20], arsine ligands [1] and phosphite ligands [21–25] have
been reported. But the kinetic investigations of heterogeneous
hydroformylation are scanty [26–29]. The aim of present work
is to investigate the kinetics of 1-hexene hydroformylation using
HRh(CO)(PPh3)3 encapsulated hexagonal mesoporous silica (Rh-
HMS) as a heterogeneous catalyst to develop a kinetic rate
model.
∗
Corresponding author. Tel.: +91 278 2567760; fax: +91 278 2566970.
Corresponding author. Present address: R&D Center, Vadodara Manufac-
∗∗
turing Division, Reliance Industries Limited, Vadodara 391346, Gujarat, India.
Tel.: +91 278 2567760; fax: +91 278 2566970.
E-mail addresses: rshukla@csmcri.org (R.S. Shukla), rakshvir.jasra@ril.com
(R.V. Jasra).
1381-1169/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2009.09.018

24
N. Sudheesh et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 23–29
2. Experimental
2.1. Materials
Carbon monoxide (CO, 99.8%) and hydrogen (H2, 99.98%)
were procured from Alchemie Gases and Chemicals Private
Limited, India. RhCl3·3H2O, triphenylphosphine (PPh3), sodium
borohydride (NaBH4, 99.98%) and formaldehyde (HCHO, 34%)
were purchased from Sigma–Aldrich, USA. Tetraethylorthosilicate
(TEOS) and 1-hexene were purchased from Sigma–Aldrich, USA.
Hexadecyl amine was procured from Sisco Laboratories, India. All
chemicals were used without further purification. The double dis-
tilled milli-pore de-ionized water was used during the synthesis.
2.2. Synthesis of the catalyst
Fig. 1. Effect of alkene chain length on the rate; alkene = 47.6 × 10−2 M, cata-
lyst = 100 mg, pCO = 20 bar, pH2 = 20 bar, T = 80 ◦C, and toluene = 50 mL.
The catalyst, HRh(CO)(PPh3)3 encapsulated hexagonal meso-
porous silica (Rh-HMS) was synthesized by reported method [7].
HRh(CO)(PPh3)3, Rh-complex was prepared by reported method
[30] followed by encapsulation into the pores of HMS. For encap-
sulation, in a typical synthesis, 0.0027 mol of hexadecyl amine was
dissolved in a mixture of 0.0909 mol of ethanol and 0.296 mol of
de-ionized water by stirring with a magnetic stirrer. To this stirring
solution 0.07 mmol of the Rh-complex was added. To this suspen-
sion 0.01 mol of TEOS was added drop wise. Stirring was continued
for 1 h and a pale yellow precipitate was formed, which was kept for
18 h for aging at room temperature. The yellow precipitate was fil-
tered and washed with 1:1 (v/v) ethanol–water mixture and dried
in vacuum at room temperature. The detail characterization of the
catalyst was performed by FT-IR, PXRD, surface area analyzer, TGA,
31P CP-MAS NMR, SEM and ICP-AES by using the methodologies
and instruments reported in our earlier publication [7].
detailed study on the kinetics of hydroformylation. The parameters
like concentration of 1-hexene, amount of catalyst, partial pres-
sure of hydrogen and carbon monoxide and temperature are found
to affect on the rate of hydroformylation reaction. Hence these
parameters were varied to study the kinetics of the hydroformy-
lation reaction of 1-hexene using Rh-HMS catalyst. n-Heptanal and
2-methyl hexanal were the major products during the employed
reaction conditions.
3. Results and discussion
3.1. Effect of chain length
The effect of the chain length of alkenes on the rate of hydro-
formylation of 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene
and 1-dodecene, were studied by conducting the kinetic experi-
ments under identical chemical and physical conditions by varying
these alkenes. The plots of time dependent consumption of C5–C10
linear alkenes were made and the concentrations of the alkenes
were found to be continuously decreased. The rates were deter-
mined from the linear portions of the slopes of the plots of the
decreasing concentration of alkenes as given in Eq. (1).
2.3. Hydroformylation reaction and product analysis
All kinetic experiments were carried out in 100 mL stainless
steel autoclave reactor (Autoclave Engineers, USA, model E 01055A)
equipped with a controlling unit. In a typical hydroformylation
experiment, weighed amount of alkene dissolved in 50 mL of
toluene as solvent, with n-tridecane as GC internal standard was
added to the weighed amount of Rh-HMS in the autoclave reac-
tor. The autoclave was flushed twice with N2 prior to successively
introducing CO and H2 at a desired pressure. The reactor was then
brought to desired reaction temperature. At that time, a sample
of the reaction mixture was withdrawn, which was considered as
the zero time reading. The hydroformylation reaction was then ini-
tiated by starting the stirrer. The reaction was then continued at
constant pressure, by supplying CO and H2 (1:1) from the reservoir
vessel. For kinetic studies, liquid samples were withdrawn during
the experiment by a sampling valve at fixed time interval. After the
set reaction time, the autoclave was then brought to room tem-
perature with the help of a cooling system, and the pressure drops
were also noted. The product analysis was carried out using GC (Shi-
madzu 17A, Japan), having 5% diphenyl and 95% dimethyl siloxane
universal capillary column (60 m length and 0.32 mm diameter)
and flame ionization detector (FID). The initial column tempera-
ture was increased from 40 to 200 ◦C at the rate of 10 ◦C/min. N2 gas
(3.4 mL/min) was used as a carrier gas. The temperature of injection
port and FID were kept constant at 200 ◦C during product analysis.
The retention times for different compounds were determined by
injecting pure compounds under identical GC conditions.
d[Alkene]
Rate = −
(1)
dt
It was found that the reaction rate was maximum for the lower
alkene, 1-pentene. The rate decreased on increasing the chain
length as depicted in Fig. 1 with reactivity order of 1-pentene > 1-
hexene > 1-heptene > 1-octene > 1-decene > 1-dodecene. The de-
crease in the rate was observed to be more from 1-pentene to
1-heptene, than those of 1-heptene to 1-dodecene. The rates for
1-decene and 1-dodecene were almost same indicating that on
further increasing the chain length, the rates of hydroformylation
were not influenced. It may be explainable in the terms of facile
diffusion of lower alkenes into the pore which causes an increase
in the rate of reaction. On increasing the chain length the diffusion
into pores become difficult and thereby causes lowering the
reaction rate. 1-Hexene, having the intermediate effect on the rate
of reaction has been taken as representative alkene for the detail
kinetic investigations.
3.2. Kinetic profiles for hydroformylation of 1-hexene
2.4. Kinetic analysis
The kinetic profile for the hydroformylation of 1-hexene is
shown in Fig. 2. A fast consumption of 1-hexene was observed to
linearly decrease up to 6 h and after that the consumption became
very slow. The rate (v) in terms of the consumption of 1-hexene (Eq.
The effect of alkene chain length on the rate of reaction was
studied. 1-Hexene as a representative alkene was taken for the

N. Sudheesh et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 23–29
25
Fig. 3. Effect of catalyst amount on the rate; 1-hexene = 47.6 × 10−2 M, pCO = 20 bar,
pH2 = 20 bar, T = 80 ◦C, and toluene = 50 mL.
Fig. 2. Kinetic profile of the consumption of 1-hexene and formation of the products;
1-hexene = 47.6 × 10−2 M, catalyst = 10 mg, pCO = 20 bar, pH2 = 20 bar, T = 80 ◦C, and
toluene = 50 mL.
3.3. Dependence of the rate on the amount of the catalyst
The effect of the amount of the catalyst on the various rates was
studied by varying the amount from 10 to 600 mg and the corre-
sponding results are given in Table 1. The rate of isomerization (v1)
is slightly faster than those of hydroformylations (v2 + v3 + v4) at
lower amount, 10 mg of catalyst (Entry 1). Due to lower amount
of the catalyst (10 mg) hydroformylation is less favored, since the
hydroformylation requires a critical minimum concentration of Rh-
complex [31], where as on the other hand isomerization is favored
by the HMS [7]. The rate of isomerization (v1) was increased on
increasing the amount of catalyst from 10 to 100 mg (Entries 1–3)
and on further increasing the catalyst amount the rate (v1) was
decreased. The individual rates v2, v3, v4 and v as well as total
hydroformylation rates (v2 + v3 + v4) were increased on increas-
ing the amount of the catalyst (Entries 2–6). A representative
plot for the rate (v) vs. the amount of the catalyst given in Fig. 3
passes through origin indicating that the reaction is completely
catalytic under the employed reaction conditions. The increase in
the rate (v) was observed up to 300 mg of the catalyst and on
further increasing in the amount, the rate approached to attain sat-
uration. Similar trends were observed for the rates v2, v3 and v4
also after 300 mg of the catalyst. The rate data indicated a first
order dependence trend in the terms of the catalyst towards
lower amounts. In the line of these observations, an amount of
100 mg of the catalyst was considered for the variation of the
other parameters to study their effects on the rate of the reac-
tion.
(2)), was determined to be 68.0 × 10−3 M/h.
d[1-hexene]
v = −
(2)
dt
The rate of formation of isomers 2/3-hexene (v1, Eq. (3))
was increased linearly up to 6 h and after that the formation
started decreasing. The rate of formation of 2/3-hexene was
37.5 × 10−3 M/h.
d[2/3-hexene]
v1
=
(3)
dt
The formation of n-heptanal (v2, Eq. (4)) and iso-heptanal (v3, Eq.
(5)) was linearly increased and the rates were 16.9 × 10−3 M/h (v2)
and 9.6 × 10−3 M/h (v3), respectively. The rate v2 was ∼1.8 times
higher than v3.
d[n-heptanal]
v2
v3
=
=
(4)
(5)
dt
d[iso-heptanal]
dt
The formation of 2-ethyl 3-methyl butanal (v4, Eq. (6)) from the
hydroformylation of 2/3-hexene was observed with very slow rate,
3.6 × 10−3 M/h (v4).
d[2-ethyl 3-methyl butanal]
v4
=
(6)
dt
3.4. Dependence of the rate on the concentration of 1-hexene
Summation of the formation rates (v1 + v2 + v3 + v4 = 67.6 ×
10−3 M/h) was found to be almost identical with the consumption
rate, v (68.0 × 10−3 M/h) indicating a fine balance between the rates
of formations and consumption.
The effects of the variation of concentration of 1-hexene
on the various rates were studied in
a wide range of
(2.38–95.22) × 10−2 M, at 40 bar pressure of syn gas (CO + H2) and at
Table 1
Dependence of the rates on the catalyst amount.
Entry
Catalyst
amount (mg)
Rate2/3-hexene
Raten-heptanal
Rateiso-heptanal
Rate2-ethyl 3-methyl butanal
Rate = (−d[1-
hexene]/dt)
v × 102 M/h
v1 × 102 M/h
v2 × 102 M/h
v3 × 102 M/h
v4 × 102 M/h
1
2
3
4
5
6
10
20
100
300
400
600
3.66
5.01
12.80
11.51
9.01
1.61
3.00
7.95
15.20
17.85
20.97
1.16
1.90
4.26
8.69
10.30
11.75
–
6.48
10.25
26.85
38.36
40.85
44.35
0.16
0.98
2.80
3.10
3.38
7.29
Reaction conditions: 1-hexene = 47.6 × 10−2 M, pCO = 20 bar, pH2 = 20 bar, T = 80 ◦C, and toluene = 50 mL.

26
N. Sudheesh et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 23–29
Table 2
Dependence of the rates on 1-hexene concentration.
Entry
1-Hexene
Rate2/3-hexene
,
Raten-heptanal
,
Rateiso-heptanal
,
Rate2-ethyl 3-methyl butanal
,
Rate = (−d[1-
hexene]/dt),
v × 102 M/h
concentration, M × 102
v1 × 102 M/h
v2 × 102 M/h
v3 × 102 M/h
v4 × 102 M/h
1
2
3
4
5
6
7
2.38
5.95
11.9
23.8
35.7
47.6
95.23
6.50
11.12
14.29
17.40
15.23
12.80
10.32
2.01
4.52
9.42
11.51
8.73
7.95
6.52
1.46
2.96
5.75
6.16
4.6
–
–
–
0.20
0.56
0.98
1.0
10.08
18.72
29.52
35.39
29.88
26.85
23.76
4.26
4.31
Reaction conditions: catalyst = 100 mg, pCO = 20 bar, pH2 = 20 bar, T = 80 ◦C, and toluene = 50 mL.
Scheme 1. Important reaction steps for heterogeneous hydroformylation of 1-hexene.
80 ◦C with 100 mg catalyst and results are given in Table 2. The rates
(v1, v2, v3 and v) were increased on increasing the concentration
of 1-hexene up to 23.8 × 10−2 M (Entries 1–4) and after that rates
were decreased showing substrate inhibition at higher 1-hexene
concentration. The formation of 2-ethyl 3-methyl butanal (v4) was
observed from the 23.8 × 10−2 M concentration of 1-hexene and
increased on increasing the concentration of 1-hexene. The plot of
rate (v) vs. 1-hexene concentration shown in Fig. 4 is indicative of
first order dependence in terms of the concentration of 1-hexene
towards lower concentration. The trend of increase in rates up to
certain concentration of 1-hexene and decrease in rate towards
higher concentration are in the agreement with the observations
[1,26,31] of substrate inhibition kinetics towards higher concen-
tration of alkene indicating a change in the rate determining step.
Also from the important reaction steps (Scheme 1) it is clear that
the coordination of 1-hexene is an equilibrium step and hence the
increase in concentration can favor the backward reaction thus
causing a decrease in the rate.
3.5. Dependence of the rate on the partial pressure of hydrogen
The effect of the partial pressure of hydrogen on the various
rates, studied in the range of 2–30 bar, with 1-hexene concentra-
tion of 47.6 × 10−2 M, amount of catalyst 100 mg, partial pressure
of CO 20 bar and at 80 ◦C were given in Table 3. All the rates
were increased on increasing the partial pressure of hydrogen. The
plot of rate (v) vs. partial pressure of hydrogen is given in Fig. 5.
Similar plots were obtained for other rates for hydrogen pressure
dependence. The kinetics with respect to the partial pressure of
hydrogen was found to follow first order dependence. The first
order dependence of the partial pressure of the hydrogen indi-
cated that the oxidative addition of hydrogen to the acyl complex
(RCO)RhCO(PPh3)2 (R = alkyl) is the rate determining step. At lower
partial pressure of H2 the formation of possible inactive dimeric
species contributes towards decreasing the rate [31].
Fig. 4. Effect of 1-hexene concentration on the rate; catalyst = 100 mg, pCO = 20 bar,
pH2 = 20 bar, T = 80 ◦C, and toluene = 50 mL.
2HRh(CO)(PPh3)3 ꢀ [Rh(CO)(PPh3)2]2 + H2

N. Sudheesh et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 23–29
27
Table 3
Dependence of the rates on partial pressure of hydrogen.
Entry
H2 pressure
Rate2/3-hexene
,
Raten-heptanal
,
Rateiso-heptanal
,
Rate2-ethyl 3-methyl butanal
,
Rate = (−d[1-
v1 × 102 M/h
v2 × 102 M/h
v3 × 102 M/h
v4 × 102 M/h
hexene]/dt),
v × 102 M/h
1
2
3
4
5
2
5
10
20
30
1.47
4.73
8.12
12.80
13.25
0.71
2.06
5.03
7.95
17.48
0.31
0.83
1.63
4.26
6.86
–
–
–
0.98
1.13
2.5
7.92
14.83
26.85
38.88
Reaction conditions: 1-hexene = 47.6 × 10−2 M, catalyst = 100 mg, pCO = 20 bar, T = 80 ◦C, and toluene = 50 mL.
Fig. 7. Effect of temperature on the rate; 1-hexene = 47.6 × 10−2 M, cata-
lyst = 100 mg, pH2 = pCO = 20 bar, and toluene = 50 mL.
Fig. 5. Effect of partial pressure of hydrogen on the rate; 1-hexene = 47.6 × 10−2 M,
catalyst = 100 mg, pCO = 20 bar, T = 80 ◦C, and toluene = 50 mL.
on increasing CO partial pressure may be due to the formation
of inactive dicarbonyl [HRh(acyl)(CO)2(PPh3)2] and tricarbonyl
[HRh(acyl)(CO)3(PPh3)] acyl species [30,31]. Increase in the CO par-
tial pressure is expected to increase the concentration of these
inactive di- and tri-carbonyl species, which cause decrease in the
rate of reaction.
3.6. Dependence of the rate on the partial pressure of carbon
monoxide
The dependence of the various rates on the partial pressure of CO
has been studied in the range of 2–30 bar at 1-hexene concentration
of 47.6 × 10−2 M, amount of catalyst 100 mg, partial pressure of H2
20 bar and 80 ◦C were given in Table 4. The rates (v1, v2, v3 and v)
were found to be increased with increase in partial pressure of CO
up to 5 bar above which the rate decreased and then became inde-
pendent of CO pressure. The rate (v4) was increased on increasing
the partial pressure of CO. Fig. 6 represented the plot of rate (v)
vs. the partial pressure of CO indicating that positive order [31]
kinetics was followed towards low CO pressure. A rate inhibition
3.7. Dependence of the rate on temperature
Temperature dependence experiments were conducted in the
range of 60–100 ◦C and the various rates are listed in Table 5. The
rates of isomerization (v1) and hydroformylation (v2, v3, and v4)
and consumption of 1-hexene (v) were increased with temperature.
A plot of the dependence of rate (v) on temperature is given in Fig. 7.
The activation energy was calculated by considering the rate of con-
sumption of 1-hexene with temperature using Arrhenius equation.
The value of activation energy was found to be 27.89 kJ/mol.
3.8. Kinetic modeling
The kinetic modeling of heterogeneous hydroformylation of
alkenes has not been studied extensively. To develop a suitable rate
equation, the data analysis should be in kinetic regime with negli-
gible mass transfer effects. For this purpose all the reactions were
performed at a stirring speed of 850 rpm so that the reaction takes
place in the kinetic regime. For the selection of kinetic models for
the rate data fit, it is appropriate to derive a rate equation model
from the actual mechanism rather than to derive a semi-empirical
model. For this, the possible steps based on actual mechanism of
hydroformylation were worked out assuming oxidative addition
of hydrogen as the rate determining step. The possible reaction
scheme is shown in Scheme 1.
Rate of hydroformylation reaction is given as,
Fig. 6. Effect of partial pressure of CO on the rate; 1-hexene = 47.6 × 10−2 M, cata-
lyst = 100 mg, pH2 = 20 bar, T = 80 ◦C, and toluene = 50 mL.
rate = kC3[H2]
(7)

28
N. Sudheesh et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 23–29
Table 4
Dependence of the rates on partial pressure of CO.
Entry
CO pressure
Rate2/3-hexene
,
Raten-heptanal
,
Rateiso-heptanal
,
Rate2-ethyl 3-methyl butanal
,
Rate = (−d[1-
hexene]/dt),
v × 102 M/h
v1 × 102 M/h
v2 × 102 M/h
v3 × 102 M/h
v4 × 102 M/h
1
2
3
4
5
6
2
5
10
20
25
30
51.08
72.63
57.13
12.80
12.16
12.12
8.10
9.80
8.32
7.95
7.62
7.31
5.40
6.31
6.26
4.26
4.41
4.21
0.10
0.50
0.91
0.98
1.32
1.23
65.50
90.00
73.80
26.85
26.35
25.20
Reaction conditions: 1-hexene = 47.6 × 10−2 M, catalyst = 100 mg, pH2 = 20 bar, T = 80 ◦C, and toluene = 50 mL.
Table 5
Dependence of rates on temperature.
Entry
Temperature
(◦C)
Rate2/3-hexene
,
Raten-heptanal
,
Rateiso-heptanal
,
Rate2-ethyl 3-methyl butanal
,
Rate = (−d[1-
hexene]/dt),
v × 102 M/h
v1 × 102 M/h
v2 × 102 M/h
v3 × 102 M/h
v4 × 102 M/h
1
2
3
4
5
60
70
80
90
100
6.19
9.82
12.80
17.19
19.61
5.61
6.48
7.95
10.52
13.15
2.77
3.13
4.26
6.56
7.90
0.41
0.62
0.98
1.32
1.71
15.04
20.10
26.85
36.72
42.84
Reaction conditions: 1-hexene = 47.6 × 10−2 M, catalyst = 100 mg, pCO = 20 bar, pH2 = 20 bar, and toluene = 50 mL.
and the total concentration of catalyst species is,
centration in Eq. (9), but deviations were shown at higher catalytic
amounts. The equation fitted well towards lower amount of the
catalyst. Eliminating the higher catalyst amounts the model fits
within the 15% error which is with in the experimental error for
a heterogeneous hydroformylation reaction (Fig. 8).
C = C1 + C2 + C3 + C4 + C5
(8)
Applying equilibrium approximation and deriving the rate
equation, then Eq. (7) becomes,
kK1K2[C][1-hexene][H2][CO]
rate =
(9)
1 + K1[CO] + K1K2[CO][1-hexene] + K1K2K3[CO]2[1-hexene] + K1K2K3K4[CO]3[1-hexene]
where K1, K2, K3 and K4 are constants from the steady state equi-
It is of interest to have a comparative insight in to the kinetic
librium.
It is easy to calculate the model with homogeneous hydroformy-
performance of the present Rh-HMS heterogeneous catalyst sys-
tem with the homogeneous system for the hydroformylation
of 1-hexene. Isomerization of 1-hexene is not reported in the
homogeneous conditions. The kinetics of hydroformylation of 1-
hexene catalyzed by heterogeneous Rh-HMS and reported [31]
homogeneous HRh(CO)(PPh3)3 system were compared. The kinetic
performance of Rh-HMS for the various parameters like catalyst
amount, 1-hexene concentration, partial pressures of CO and H2
and temperature were found to have almost comparable trend.
Similar to the present heterogeneous catalyst system, in homo-
geneous conditions [31], the rates were increased on increasing
the concentration of the catalyst, partial pressure of hydrogen and
temperature where as the CO pressure and 1-hexene concentration
dependence showed substrate inhibition kinetics. In the line of het-
erogeneous conditions, the kinetics was first order with respect to
partial pressure of hydrogen, catalyst concentration and towards
lower concentration of 1-hexene, and positive order for lower par-
tial pressure of CO in homogeneous conditions [31].
lation reaction as all the species involved are in homogeneous phase
during the reaction so that the concentration of all species can be
calculated. But in the case of heterogeneous reactions the catalyst
is in another phase with respect to all other species. Therefore it
is difficult to calculate the concentration of active species associ-
ated with it. Hence here we are proposing a method to calculate the
rates using the theoretical model as g/L/h rather than mol/L/h. Cal-
culated rates were compared with the experimental rates in g/L/h.
The evaluation of rate parameters were done by putting anticipated
values for constants by iteration method to get best fit. The exper-
imental data were fitted properly for the parameters 1-hexene
concentration, carbon monoxide concentration and hydrogen con-
4. Conclusions
HRh(CO)(PPh3)3 complex encapsulated in the pores of HMS was
synthesized and used to perform the detail kinetic analysis for
the hydroformylation of 1-hexene. The rate of hydroformylation
increased with the increase in catalyst amount and gets saturated
at higher catalyst amount. The rate was first order with partial pres-
sure of hydrogen. But it was inhibited by high concentration of
carbon monoxide and 1-hexene. Kinetic model was derived from
the known mechanism of hydroformylation and tested for compar-
ison of experimental rates with that of model rates. The rates were
calculated in the form of g/L/h and found to be best fit within the
range of experimental error of 15%.
Fig. 8. Comparison of experimental rates with calculated rates from model.

N. Sudheesh et al. / Journal of Molecular Catalysis A: Chemical 316 (2010) 23–29
29
Acknowledgment
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Authors thank Council of Scientific and Industrial Research
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for the Development of Specialty Inorganic Materials for Diverse
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