Hydrogenation of methyl isobutyl ketone over bifunctional Pt-zeolite catalyst

Article abstract of DOI:10.1016/j.jcat.2012.06.013

Methyl isobutyl ketone (MIBK) can be viewed as a key intermediate for the conversion of biomass-derived acetone - the by-product of biobutanol production - to transportation fuel. Zeolite H-ZSM-5 doped with Pt nanoparticles was found to be a highly efficient catalyst for gas-phase hydrogenation of MIBK to methylpentanes with >99% yield at 200 °C. The reaction proceeds via bifunctional metal-acid catalysed pathway involving MIBK hydrogenation to 4-methyl-2-pentanol (MP-ol) on metal sites followed by MP-ol dehydration on acid sites to form olefin and finally olefin hydrogenation to 2-methylpentane (2MP) on metal sites, with all three steps occurring on a single catalyst bed. 2MP thus obtained underwent isomerisation over bifunctional Pt/H-ZSM-5 catalyst to give a mixture of 2- and 3-methylpentanes in a ratio of 83:17. The catalyst did not show any deactivation for at least 16 h on stream.

Full text of DOI:10.1016/j.jcat.2012.06.013

Journal of Catalysis 293 (2012) 141–144
Contents lists available at SciVerse ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Hydrogenation of methyl isobutyl ketone over bifunctional Pt–zeolite catalyst
⇑
Mshari A. Alotaibi, Elena F. Kozhevnikova, Ivan V. Kozhevnikov
Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, United Kingdom
a r t i c l e i n f o
a b s t r a c t
Article history:
Methyl isobutyl ketone (MIBK) can be viewed as a key intermediate for the conversion of biomass-
derived acetone – the by-product of biobutanol production – to transportation fuel. Zeolite H-ZSM-5
doped with Pt nanoparticles was found to be a highly efficient catalyst for gas-phase hydrogenation of
MIBK to methylpentanes with >99% yield at 200 °C. The reaction proceeds via bifunctional metal-acid cat-
alysed pathway involving MIBK hydrogenation to 4-methyl-2-pentanol (MP-ol) on metal sites followed
by MP-ol dehydration on acid sites to form olefin and finally olefin hydrogenation to 2-methylpentane
Received 18 May 2012
Revised 19 June 2012
Accepted 19 June 2012
Available online 23 July 2012
Keywords:
(2MP) on metal sites, with all three steps occurring on a single catalyst bed. 2MP thus obtained under-
Methyl isobutyl ketone
Hydrogenation
Platinum
went isomerisation over bifunctional Pt/H-ZSM-5 catalyst to give a mixture of 2- and 3-methylpentanes
in a ratio of 83:17. The catalyst did not show any deactivation for at least 16 h on stream.
Ó 2012 Elsevier Inc. All rights reserved.
Zeolite
Bifunctional catalysis
1
. Introduction
Efficient utilisation of biomass resources is a major goal for
hydrogenation to 2-methylpentane (2MP) which could be blended
with gasoline and used through the existing fuel infrastructure.
However, to the best of our knowledge, there is little data available
on catalytic hydrogenation of MIBK. Here we report a very efficient
gas-phase hydrogenation (hydrodeoxygenation) of MIBK to 2MP
via heterogeneous bifunctional metal-acid catalysis using Pt-doped
zeolite as the catalyst.
academia and industry [1,2]. Presently, about 50% of the crude oil
produced worldwide is refined into transportation fuels. The use
of biomass-derived fuel such as ethanol and biodiesel can signifi-
cantly reduce carbon dioxide emission, diversify energy sources
and improve energy security. It is expected that biomass-based
n-butanol (biobutanol) will also play a major role in the next gen-
eration of biofuels. Butanol produces more power than ethanol,
and 85% butanol/gasoline blends can be used in unmodified petrol
engines [3]. Biobutanol can be produced by the acetone–butanol
fermentation of carbohydrates and cellulosic raw materials using
Clostridium acetobutylicum strain that yields butanol together with
acetone and ethanol in a weight ratio of 6:3:1 [4,5]. This, however,
will produce a surplus of acetone. Therefore, finding new outlets
for acetone, preferably in the transportation fuel sector, would im-
prove the economy of biobutanol production. Acetone can be
2
. Experimental
2.1. Chemicals and materials
Zeolites
H-ZSM-5
(Si/Al = 12,
specific
surface
area
-Beta
2
ꢀ1
2
ꢀ1
S
(
BET = 403 m g ), H-Y (Si/Al = 15, SBET = 780 m g ) and NH
Si/Al = 12, SBET = 680 m g ) were from Zeolyst International.
4
2
ꢀ1
2
ꢀ1
Aerosil 300 silica (SBET = 300 m g ) was from Degussa. MIBK
99.0%), copper chromite Cr Cu and other chemicals used for
catalyst preparation were purchased from Aldrich. Pt and Pd sup-
ported on active carbon were from Johnson Matthey. H gas
>99%) was supplied by the British Oxygen Company.
(
2
2 5
O
6
transformed into C and larger organic molecules by aldol conden-
2
sation. This is employed for industrial production of methyl
isobutyl ketone (MIBK), which is used as solvent in paints, coatings
and resins. MIBK synthesis (Scheme 1) can be carried out either in
three separate steps or more efficiently as one-pot process using a
bifunctional metal-acid catalyst, for example, Pd on an acidic
support ([6–8] and references therein). MIBK can be viewed as a
key intermediate for the conversion of biomass-derived
acetone to transportation fuel. MIBK could be deoxygenated by
(
2.2. Techniques
BET surface area and porosity of catalysts were determined
from nitrogen physisorption measured on a Micromeritics ASAP
2010 instrument at ꢀ196 °C. Before the measurement, the samples
were evacuated at 250 °C for 2 h. Powder X-ray diffraction (XRD)
spectra of catalysts were recorded on a PANalytical Xpert diffrac-
⇑
Corresponding author.
E-mail address: I.V.Kozhevnikov@liverpool.ac.uk (I.V. Kozhevnikov).
tometer with a monochromatic Cu K
XRD patterns were attributed using the JCPDS database. ICP-AES
a radiation (k = 0.154 nm).
0
021-9517/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jcat.2012.06.013

1
42
M.A. Alotaibi et al. / Journal of Catalysis 293 (2012) 141–144
O
O
O
O
-
H O
2
+ H2
2
OH
MIBK
Scheme 1. MIBK production from acetone.
elemental analysis was carried out on a Spectro Ciros emission
spectrometer. Thermo Flash EA 1112 series analyser was used to
determine carbon content in spent catalysts. Pt dispersion in cata-
lysts was measured by hydrogen chemisorption on a Micromeritics
TPD/TPR 2900 instrument as described previously [7].
spheric pressure in a Pyrex fixed-bed down-flow reactor (9 mm
internal diameter) fitted with an on-line gas chromatograph (Var-
ian Star 3400 CX instrument with a 30 m ꢂ 0.25 mm HP INNOWAX
capillary column and a flame ionisation detector). For more accu-
rate analysis of C
1
AC
5
hydrocarbon products, a 60 m ꢂ 0.32 mm
GSGasPro capillary column was used, which allowed for full sepa-
ration of these hydrocarbons. The temperature in the reactor was
controlled by a Eurotherm controller using a thermocouple placed
2.3. Catalysts preparation
2
at the top of the catalyst bed. MIBK was fed by passing H flow con-
NH -Beta was converted to H-Beta by air calcination at 550 °C
4
trolled by a Brooks mass flow controller through a stainless steel
saturator, which held liquid MIBK at an appropriate temperature
to maintain the chosen reactant concentration. Typically, unless
stated otherwise, the saturator temperature was 35 ± 0.3 °C, which
gave the MIBK partial pressure of 3.64 kPa (3.6 vol%) [11]. The gas
for 4 h. Pt-doped zeolites were prepared by the literature proce-
dure [9,10] involving adsorption of Pt(II) on to zeolite from
0
.01 M aqueous solution of Pt(NH
with distilled water, air calcination at 450 °C for 2 h and reduction
by H at 400 °C for 2 h. The Pt loading in zeolite catalysts was
determined by ICP analysis. 0.5%Pd/SiO was prepared by wet
impregnation of Aerosil 300 with 0.02 M benzene solution of
Pd(OAc) , followed by drying in a rotary evaporator at 60 °C and
reduction with H at 250 °C for 2 h. 0.5%Pt/SiO was prepared by
the same procedure using Pt(acac) as a precursor. 5%Cu/SiO
was prepared by wet impregnation using an aqueous solution of
Cu(NO O, followed by drying in a rotary evaporator, air cal-
ꢁ2.5H
cination at 400 °C for 2 h and final reduction with H at 400 °C for
h. Copper chromite prior to use was reduced at 400 °C in an H
3 4 3 2
) (NO ) followed by washing
2
ꢀ1
feed entered the reactor at the top at a flow rate of 20 ml min
.
2
The downstream gas lines and valves were heated to 180 °C to
prevent substrate and product condensation. Unless otherwise
indicated, the catalyst bed contained 0.2 g of powdered catalyst
2
2
2
(
45–180
alyst diluted with silica to 0.2 g was used to reduce conversion.
Prior to reaction, the catalysts were pre-treated in H flow for 1 h
lm particle size). In some cases, a smaller amount of cat-
2
2
3
)
2
2
2
at the reaction temperature. Once reaction started, the down-
stream gas flow was analysed by the on-line GC to obtain MIBK
conversion and product selectivity. The selectivity was defined as
moles of product formed per one mole of MIBK converted and
quoted in mole per cent.
2
2
2
flow for 2 h. After reduction, it exhibited sharp XRD pattern of Cu
metal, with (111) and (200) reflections at 43.4° and 50.5°, respec-
tively, in agreement with the standard values (JCPDS, copper
0
4-0836). The catalysts were sieved into a powder of 45–180
lm
particle size. Catalyst characterisation is shown in Table 1.
3
. Results and discussion
2.4. Catalyst testing
First, we tested a number of conventional supported metal
catalysts comprising Pd, Pt and Cu supported on silica and active
carbon for MIBK hydrogenation in the temperature range of 100–
400 °C. At 100–200 °C, these catalysts were active for the hydroge-
nation of MIBK to 4-methyl-2-pentanol (MP-ol) (Table 2). The
selectivity to MP-ol decreased with increasing temperature due
to formation of 2MP and hydrogenolysis of CAC bonds giving
The hydrogenation of MIBK was carried out in the gas phase in
flowing H . The catalysts were tested at 100–400 °C under atmo-
2
Table 1
Catalyst characterisation.
1 5
C AC hydrocarbons. The highest 2MP selectivities, 87–94%, were
observed for 10%Pt/C and 10%Pd/C catalysts at 52–84% conversion
at a temperature as high as 300 °C (Table 2), which indicates the
difficulty of direct hydrogenation of MP-ol to 2MP.
Catalysta
Si/
Al
S
(m
c
Pore volume
d
Pore
diameter
Df
BET
2
b
ꢀ1
3
ꢀ1
e
g
)
(cm
g
)
(
Å)
0
0
0
0
5
0
0
1
5
1
.30%Pt/H-ZSM-5 12
.06%Pt/H-ZSM-5 12
362
357
491
690
251
255
287
801
924
823
55
0.23
0.22
0.61
0.44
0.74
0.68
0.52
0.58
0.58
0.57
0.13
25
25
50
26
118
106
74
29
25
28
93
0.88
0.87
0.72
0.62
.39%Pt/H-Beta
12
15
Table 2
.45%Pt/H-Y
a
Hydrogenation of MIBK on supported metal catalysts.
g
%Cu/SiO
2
g
.5%Pd/SiO
2
0.62
0.27
Catalyst
Conversion (%)
Selectivity (%)
g
.5%Pt/SiO
2
2
MP
MP-ol
Other
h
0%Pt/C
h
%Pd/C
0.5%Pt/SiO
10%Pt/C
2
46
47
52
46
37
84
34
41
47
40
87
0
28
94
0
53
56
9
47
66
5
0
4
4
53
6
1
0%Pd/Ch
i
10%Pt/Cb
Cr
Cu
2 2
O
5
0
1
1
5
2
.5%Pd/SiO
2
a
b
c
d
e
f
Pt loading (wt%) from ICP analysis unless stated otherwise.
Si/Al atomic ratio in zeolites.
BET surface area.
Single point total pore volume.
Average BET pore diameter.
Metal dispersion in fresh catalysts from H
Metal loading from preparation stoichiometry.
Metal loading from supplier.
After reduction at 400 °C in H
0%Pd/C
0%Pd/Cb
%Cu/SiO
CuOꢁCr
2
100
82
0
18
c
2
O
3
0
a
2
chemisorption.
At 200 °C, 0.20 g catalyst pre-treated in H
2
at reaction temperature for 1 h, 3.6%
20 ml min flow rate, 4 h time on stream.
g
h
i
ꢀ1
MIBK in H
2
flow
,
b
At 300 °C.
Pre-reduced in H at 400 °C for 2 h.
2
c
2
for 2 h.

M.A. Alotaibi et al. / Journal of Catalysis 293 (2012) 141–144
143
O
OH
H2
- H O
2
H2
+
Metal
site
Acid
site
Metal
site
MIBK
2MP
MP-ol
Scheme 2. Hydrogenation of MIBK via bifunctional metal-acid catalysis.
Table 3
Hydrogenation of MIBK over bifunctional Pt/zeolite catalysts.
a
Catalyst
Temperature (°C)
Conversion (%)
Selectivity (%)
2MP
3MP
MP-ol
Other
H-ZSM-5
H-ZSM-5
100
200
100
200
100
200
100
200
0
20
94
100
92
44
0
9
0
0
0
17
0
4
0
7
34
0
38
0
49
0
0
84
1
0
4
26
15
43
b
0
0
0
0
0
0
.30%Pt/H-ZSM-5
.30%Pt/H-ZSM-5
.39%Pt/H-Beta
.39%Pt/H-Beta
.45%Pt/H-Y
65
83
58
70
36
55
c
c
98
81
0
2
.45%Pt/H-Y
a
b
c
ꢀ1
0
C
.20 g catalyst pre-treated in H
2 2 ,
at reaction temperature for 1 h, 3.6% MIBK in H flow 20 ml min flow rate, 4 h time on stream.
1
AC cracking products, mainly propene and butenes, together with small amount of C6+ condensation products.
5
Mainly C6+ condensation products.
Next we attempted to explore bifunctional metal-acid catalysed
as the main product with 55–83 selectivity. At 200 °C, 2MP isom-
erised to form 3-methylpentane (3MP) and traces of n-hexane, in
agreement with the literature [16]. As expected, the isomerisation
correlates with zeolite acid strength as indicated by 3MP/2MP
product ratio: 0.20 (Pt/H-ZSM-5) > 0.057 (Pt/H-Beta) > 0.036 (Pt/
H-Y) (Table 3). The mechanism of alkane isomerisation over
bifunctional catalysts has been discussed elsewhere ([16] and ref-
erences therein). It involves alkane dehydrogenation on Pt to form
an alkene followed by alkene skeletal isomerisation on acid sites
and finally alkene hydrogenation on Pt to yield the corresponding
alkane isomer. In our case, 4-methylpentene-1 and 4-methylpen-
tene-2 formed in MP-ol dehydration (Scheme 2) may isomerise
on zeolite acid sites to give eventually 3MP. The total selectivity
to methylpentanes increases in the order: Pt/H-Y (57%) < Pt/H-Beta
(74%) < Pt/H-ZSM-5 (>99%). Therefore, amongst the Pt/zeolite cata-
lysts studied, Pt/H-ZSM-5 clearly stands out giving >99% selectivity
to methylpentanes at 100% MIBK conversion at 200 °C (Table 3).
Other catalysts, Pt/H-Beta and Pt/H-Y, gave significant amounts
of unidentified C6+ condensation by-products. These can be
attributed to aldol condensation of MIBK. The amount of bulky
pathway to achieve MIBK-to-2MP hydrogenation in one step on a
single catalyst bed using platinum metals supported on zeolites
as the bifunctional catalysts. This pathway would involve MIBK
hydrogenation to MP-ol on metal sites followed by MP-ol dehydra-
tion on acid sites to form olefin and finally olefin hydrogenation to
2
MP on metal sites (Scheme 2). Since dehydration of secondary
alcohols on acid catalysts is fast [12,13] and so is hydrogenation
of C@C bond on platinum metals, the bifunctional pathway was ex-
pected to be more efficient that the hydrogenation only pathway.
Our study proved that this was indeed the case for Pt/zeolite
catalysts.
Representative results are shown in Table 3, with zeolite cata-
lysts placed in the order of increasing their pore size. The zeolites
used, H-ZSM-5, H-Beta and H-Y, had close Si/Al atomic ratios (Si/
Al = 12–15) and hence comparable proton site densities. Their acid
strength decreases in the order H-ZSM-5 > H-Beta > H-Y [14,15].
The Pt/zeolite catalysts had high crystallinity and exhibited stan-
dard XRD patterns of the corresponding zeolites. No Pt reflections
were observed in XRD spectra of these catalysts, indicating fine
dispersion of Pt metal, as also confirmed by H
). Despite Pt doping was carried out similarly for all zeolites, using
the same 0.01 M aqueous solution of Pt(NH (NO , the final Pt
2
adsorption (Table
C
6+ by-products formed increased with the pore size of zeolites:
1
3
)
4
3
)
2
100
loading varied between 0.30 and 0.45 wt%, increasing with the
pore diameter of zeolite. This indicates that Pt loading was con-
trolled by the zeolite pore size.
8
6
4
0
0
0
In a blank run, H-ZSM-5 itself was not active at all at 100 °C. At
2
00 °C, it converted 20% of MIBK to give mainly C
1
AC
5
cracking
Conversion
products, mostly propene and butenes, together with small
amounts of 2MP and MP-ol. Doping of zeolites with Pt greatly in-
creased catalyst activity already at 100 °C, giving 92–98% MIBK
conversion to a mixture of 2MP and MP-ol in a molar ratio of
2-Methylpentene
3-Methylpentene
n-Hexane
20
0
1
:(0.5–1.4). At this temperature, the dehydration of MP-ol was
not complete, and the MP-ol/2MP ratio decreased with increasing
zeolite acid strength: 1.36 (H-Y) > 0.66 (H-Beta) > 0.52 (H-ZSM-
0
4
8
12
16
5
), which can be explained by acceleration of alcohol dehydration
with increasing catalyst acid strength. It should be noted that no
MP isomerisation was observed at 100 °C. Increasing the temper-
ature to 200 °C led to complete dehydration of MP-ol, giving 2MP
Time (h)
2
Fig. 1. Time course for MIBK hydrogenation over 0.3%Pt/H-ZSM-5 (0.05 g) diluted
ꢀ
1
with 0.15 g SiO
2
at 200 °C, 3.6% MIBK, 20 ml min
2
H flow rate.

1
44
M.A. Alotaibi et al. / Journal of Catalysis 293 (2012) 141–144
Table 4
under the conditions applied for MIBK hydrogenation (Table 3),
except for using N (20 ml min ) instead of H . As expected, the
2 2
Effect of MIBK concentration.a
ꢀ1
[
MIBK] (vol.%)
3.6
0.0038
4.9
0.0037
6.4
0.0036
reaction was very fast, yielding two olefins, 4-methylpentene-1
and 4-methylpentene-2, at 100% conversion (Eq. (1)). The same
ꢀ
1
ꢀ1
Rate (mol h
g
)
a
ꢀ1
2 2
reaction under H instead of N gave an 85:15 mixture of 2- and
0
.06%Pt/H-ZSM-5 (0.05 g) diluted with 0.15 g SiO
2
, 200 °C, 20 ml min
2
H flow
rate, 5 h time on stream. The rates were measured at 6–10% MIBK conversion.
3-methylpentanes in a 100% yield (Eq. (2)). These results, therefore,
support the bifunctional mechanism for MIBK hydrogenation over
Pt/H-ZSM-5 catalyst.
Table 5
OH
Effect of Pt loading.a
- H O
2
ð1Þ
ð2Þ
+
Catalyst
Pt
Conversion
Selectivity (%)
MP 3MP n-
Hexane
dispersion (%)
2
Other
OH
H2
+
0
0
.06%Pt/H-ZSM-5 0.87
.3%Pt/H-ZSM-5 0.88
11
67
75
86
15
14
2
<1
8
<1
- H O
2
a
ꢀ1
0
.05 g catalyst diluted with 0.15 g SiO
2
, 200 °C, 3.6% MIBK, 20 ml min
2
H flow
4
. Conclusions
MIBK may be viewed as a key intermediate for the conversion of
rate, 6 h time on stream.
biomass-derived acetone to transportation fuel. Produced by one-
step (one-pot) hydrocondensation of acetone [6–8], MIBK can be
further efficiently hydrogenated via metal-acid bifunctional
pathway on a single bed containing Pt/H-ZSM-5 catalyst to give
methylpentanes with >99% yield. The methylpentenes thus
obtained could be blended with gasoline and used through the
existing fuel infrastructure.
H-ZSM-5 (5.5 Å) < H-Beta (7.6 ꢂ 6.4 Å) < H-Y (7.5 Å), which is an
indication of ‘‘shape-selective’’ catalysis. The amount of coke
(
C wt%) found in spent catalysts after reaction (200 °C, 6 h) also in-
creased in this order: 5.9 (H-ZSM-5) < 10.5 (H-Beta) < 11.9 (H-Y).
This is probably the reason for the drop in conversion at 200 °C
for the larger pore zeolites H-Beta and H-Y (Table 3).
The Pt/H-ZSM-5 catalyst showed excellent performance stabil-
ity. It reached steady state in about 2 h and operated without deac-
tivation for at least 16 h (Fig. 1). It should be noted that in this run
to set the conversion at about 70%, the amount of catalyst had to be
reduced 4-fold compared to that in Table 3.
The rate of reaction over Pt/H-ZSM-5 catalyst practically did not
change with MIBK concentration in the gas feed (Table 4), indicat-
ing that the order in MIBK is close to zero. Therefore, in this system,
MIBK conversion is directly proportional to the reaction rate. The
reaction had a rather low activation energy of 18 kJ/mol, as deter-
mined for 0.06%Pt/H-ZSM-5 catalyst in the temperature range of
Acknowledgment
Support from Salman Bin Abdulaziz University, Saudi Arabia
(
PhD scholarship for M. Alotaibi), is gratefully acknowledged.
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4
3
[
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4
in Table 3 with entry 2 in Table 5). This suggests that hydrogena-
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subsequent dehydration and hydrogenation steps appear to be fast
under the chosen conditions at 200 °C.
[
[
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[