Oxidation of propene by molecular oxygen over Ti-modified silicalite catalysts

Article abstract of DOI:10.1039/b101857o

Ti-modified high silica zeolite with an Si/Al ratio of 1900 was found to be effective for the oxidation of propene to oxygenates such as propene oxide, in the presence of molecular oxygen at 573 K.

Full text of DOI:10.1039/b101857o

Oxidation of propene by molecular oxygen over Ti-modified silicalite
catalysts
Kazuhisa Murata* and Yoshimichi Kiyozumi
Research Institute for Green Technology, National Institute of Advanced Industrial Science and
Technology (AIST), AIST Tsukuba Central 5, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8565, Japan.
E-mail: kazu-murata@aist.go.jp
Received (in Cambridge, UK) 27th February 2001, Accepted 13th June 2001
First published as an Advance Article on the web 5th July 2001
Ti-modified high silica zeolite with an Si/Al ratio of 1900 was
found to be effective for the oxidation of propene to
oxygenates such as propene oxide, in the presence of
molecular oxygen at 573 K.
High silica zeolite (denoted silicalite) with Si/Al ratio of 3000
was prepared from Si(OEt) and tetraethylammonium hydrox-
4
ide by a hydrothermal method followed by calcination in a air
flow at 823 K for 5 h. The other high silica zeolites (denoted
HSZ) employed were provided by TOSO Co. Ltd. [HSZ(68),†
HSZ(190)† and HSZ(1900)†]. Titanium-modified HSZ sam-
ples containing 7.5 wt% Ti[Ti/HSZ(68)] were prepared by the
impregnation method.‡ All chemicals were purchased from
Wako Pure Chemicals Co.. The amounts of adsorption of
Propylene oxide is an important industrial intermediate which
has traditionally been produced by the epoxidation of propene
with organic hydroperoxides. In this proress, organic alcohols
are stoichiometrically produced as by-products. Recently,
titanium silicate-1 (TS-1) zeolite has been shown to be active
2
ammonia or CO were estimated by using a Thermal Analysis
System 001 instrument (MAC SCIENCE Co.).§
1
for the reaction with H
2
O
2
. This process is still liquid phase
whereas the gas phase is more favorable due to product
The catalytic reaction was performed under atmospheric
pressure at temperatures between 473 and 673 K. A tubular
fixed-bed reactor (OD = 1.25 cm, length = 60 cm) was filled
with 1.0 g of catalyst powder and quartz sand (2.0 g). A
pretreatment was done prior to each reaction at 673 K under air
2
separation. Concerning the gas phase, Haruta and coworkers
3
and Moulijn et al. have published work relating to epoxidation
2 2
with propene/O /H over Au dispersed on TS-1 and other Ti-
containing supports. In these cases, selectivity to propene oxide
is high ( > 90%), but propene conversion is < 5% and a large
2
1
3 6
flow (25 ml min ) for 2 h. The reactant feeds were C H (7.5
2
1
21
amount of H
oxidation by molecular oxygen without H
2
is consumed to form H
2
O. Direct propene
into propene oxide
ml min ) and air (17.5 ml min ). Hydrocarbons and
oxygenated compounds were detected by TCD and FID gas
chromatography, the former with Porapack Q (1 m) at 673 K,
the latter with 20 wt% FFAP on Chromosorb W (3 m) at 373 K.
Products in the gas phase was analyzed by another TCD
equipped with a Porapak Q column (3 m) and molecular sieve
5 Å column (3 m) kept at 343 K. The reaction products were also
confirmed by mass spectrometry. In order to check the initial
activities of catalysts, GC analyses were started 15 min after
reaching the reaction temperature. The products were propene
2
would be of value. The possibility to form propene oxide (PO),
in particular, was shown, using AgNO or KNO supported on
TS-1 and K CO or KCl on the same matrix with a PO yield of
.02%. ARCO Chemical Technology has recently reported
3
3
2
3
4
0
5
improved propene oxide yield in the presence of ethyl chloride.
In these cases without gaseous co-reactant such as hydrogen,
acidic compounds such as nitrates and chlorides on the catalyst
surface could be important for propene activation. In the course
of our research program on direct oxidation of propene without
any co-reactant, we have reported that titanium sulfate-modified
1 8
oxide (PO), acetaldehyde (AA), C –C hydrocarbons (HC), CO
and CO (CO ) and small amounts of other oxygenates
2
x
6
amorphous zirconia was effective for this reaction, although
[propanal, acetone, formaldehyde, alcohols (MeOH, EtOH,
i
the propene conversion was below 6% and the PO yield only ca.
Pr OH)] were also detected.
0
.5%. Thus, in order to improve propene oxide yield, we tried
The catalytic performances at 573 K are summarized in Table
1. No product was formed through the reactor in the absence of
the use of zeolite families as catalyst supports. In the present
study, we report titanium-modified high silica zeolites with
different ratios of Si/Al which are effective for the propene
catalyst. Both Ti/SiO
propene conversion and only hydrocarbons (HC) and CO
produced. For the HSZ family we found that the catalyst
2
(run 1) and Ti/TiO
2
(run 2) exhibited low
x
were
2
oxidation by O without any co-reactant.
Table 1 Results of the oxidation of propene by molecular oxygen 573 Ka
Conv.
Selectivity (%)d
propene PO yield
Run
(%)
(%)
PO
PA
AA
HA
AL
AC
Alc
HC
CO
x
Residuee
1
2
3
4
5
6
7
8
9
7.5% Ti/SiO
7.5% Ti/TiO
7.5% Ti/HSZ(68)
7.5% Ti/HSZ(190)
7.5% Ti/HSZ(1900)
2
3.76
2.11
97.8
95.5
47.7
1.89
78.2
9.03
83.2
37.3
0
0
0
0
0
0
0
0
6.25
20.0
29.6
0
23.6
23.5
11.3
16.2
0
0
0
0
2.64
0
2.92
0.12
1.73
0.06
0
0
0
0
0
0
0
0
0
0
0
0
0
5.39
0
2.87
0
72.7 24.7
47.0 52.9
2.6
0.1
2
b
3.11
8.90
17.3
Trace
20.4
3.69
6.60
8.81
3.18 5.85
9.32 9.85
36.3
Trace
26.1
40.9
7.93
23.6
44.5
31.4
27.8
5.12 35.6
1.13
0
b
28.3
0.66
0
0
0
3.43
0
9.85
0.13
0
0.14
0
b
0
0
0
0
0
0
b
7.5% Ti/silicalite(3000)
15% Ti/HSZ(1900)
100
0
b
2.60
0
43.9
35.3
69.1
59.7
0.74
0
0.53
0.44
bc
15% Ti/HSZ(1900)
b
HSZ(1900)
0.30 5.32
0
0
0
be
1
0
7.5% Ti/HSZ(1900)
0
a
Reaction conditions: see text. b Number in parentheses is the Si/Al ratio for the catalyst support employed. c Reaction carried out at 523 K. d Products
i
propene oxide (PO), acetaldehyde (AA), formaldehye (HA), acrolein (AL), acetone (AC), alcohol [Alc, (MeOH + EtOH + Pr OH)], hydrocarbons [HC, (C
+
catalyst carried out at 173 K.
1
e
C
2
+ C
3 4 5 6 7 8 2 x
+ C + C + C + C + C )], CO and CO (CO ). Residue estimated using the equation 100 2 sum of all detectable products. Calcination of the
1356
Chem. Commun., 2001, 1356–1357
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b101857o

3 2
Table 2 Quantitative estimation of acid and base sites on Ti-modified HSZ catalysts by NH - or CO
-TPDa
Base sitesb
Acid sitesb
x Within 673 K
CO (g)/Cat(g)
y Within 440 K
CO (g)/Cat(g)
x Within 673 K
y Within 440 K
NH (g)/Cat(g)
c
c
Sample
2
2
y/x (%)
3
NH (g)/Cat(g)
3
y/x (%)
7
7
7
a
.5% Ti/silicalite(3000)
.5% Ti/HSZ(1900)
.5% Ti/HSZ(68)
0.0104
0.0187
0.0196
0.0080
0.0143
0.0147
76.9
76.6
75.0
0.0129
0.0495
0.0339
0.00956
0.042
0.0233
74.1
85.3
68.7
Thermogravimetric analysis conducted in argon in the range 300–673 K. b The acid or base sites were estimated by the amounts of NH
3 2
or CO desorbed
within each prescribed temperature. c These values, calculated [100 (y/x)] can be regarded as the percentage of weak base or acid sites.
performances were strongly dependent on the Si/Al ratio of the
supports. For 7.5% Ti/HSZ(68) (run 3), propene conversion
was very high (97.8%) and some oxygenates were produced
with CO
was only 3.11%. The 7.5% Ti/HSZ(190) (run 4) also showed
high propene conversion of 95.5% and both CO and the amount
x
and a substantial amount of residue, but the PO yield
x
of residue were decreased, while the selectivities to oxygenates
were increased. In this case the PO yield was 8.90%.
On the other hand, the conversion of propene on 7.5% Ti/
HSZ(1900) was approximately half the propene conversion of
7
.5% Ti/HSZ(190), while selectivities to CO
x
and residue
(0.13%) were dramatically lower than for 7.5% Ti/HSZ(190).
For 7.5% Ti/HSZ(1900) (run 5) the selectivity to PO was found
to be 36.3% and major by-products were acetaldehyde (AA) and
hydrocarbons (HC). As a result, the PO yield (17.3%) on
7
7
.5% Ti/HSZ(1900) was twice that of 7.5% Ti/HSZ(190).
.5% Ti/silicalite (3000) (run 6), on the other hand, showed
3
Fig. 1 NH -TPD data for (a) 7.5% Ti/silicalite(3000), (b) 7.5% Ti/
HSZ(1900) and (c) 7.5% Ti/HSZ(68).
much lower propene conversion (1.89%) than 7.5% Ti/
HSZ(1900). Therefore, it is indicated that titanium-modified
HSZ with an Si/Al ratio of 1900 not only has a moderate ability
to activate propene using molecular oxygen, but also properties
suitable for predominant formation of oxygenates (in particular,
PO) over hydrocarbons (HC).
The 15% Ti/HSZ(1900) catalyst (run 7) exhibited higher
propene conversion (78.2%) than 7.5% Ti/HSZ(1900), al-
though the PO selectivity was slightly decreased, while HC
selectivity was increased. In this case, the PO yield was 20.4%,
7.5% Ti/HSZ(1900) at 1073 K, higher by 100 K than the
standard calcination temperature (973 K), would result in a
decrease in weak acid sites, while strong acid sites might still be
retained. As a result, propene conversion was decreased to
37.3% and selectivity to hydrocarbon formation (HC) was
raised to 59.7% (Table 1, run 10).
In summary, Ti-modified HSZ(1900) was found to catalyse
the oxidation of propene to oxygenates, such as propene oxide,
by molecular oxygen at 573 K. The catalyst performances are
affected by the Si/Al ratio of the HSZ supports as well as the
presence of titanium. Cooperation between moderate acid
properties of HSZ(1900) and titanium favors oxygenate forma-
tion. It is expected that fine control of acid properties of these
supports and titanium content well enhance the catalyst
performances for propene oxide formation.
conditions2
2 2
10 times those previously reported under O /H
,3
>
and, at least, > 3 times recently reported for Ag-containing
catalyst4,5 or photocatalyst7 systems. At 523 K, the PO
selectivity on 15% Ti/HSZ(1900) was as high as 40.9%, while
the propene conversion was 9.03% (run 8). HSZ(1900) alone
(run 9) showed higher propene conversion and HC selectivity
than 7.5% Ti/HSZ(1900), while less selectivity to oxygenates
was observed. This indicated that surface properties for
oxygenate formation were improved by Ti modification.¶
The mechanism of oxidation of propene over Ti/HSZ
catalysts is not clear. However, catalyst performances are
dependent on Si/Al ratio of the HSZ supports (Table 1) and,
therefore, it seems likely that surface acid–base properties are
responsible for the catalyst behavior, in particular, propene
conversion and residue yield. In fact, as shown in Table 2,
Notes and references
† These zeolites are of H-ZSM-5 type where the number in parentheses is
the Si/Al ratio.
‡
The calcined HSZ was evacuated at 673 K for 3 h in order to eliminate a
i
small amount of water. Then, the HSZ was impregnated with Ti(OPr )
4
in
i
Pr OH, followed by addition of H
2
O (25 g) leading to precipitation of
titanium oxide. The sample was then dried at 373 K for 10 h and finally
calcined at 973 K for 3 h.
§
The sample was evacuated at 673 K for 2 h then, after cooling to 373 K,
where NH
metric methods, 7.5% Ti/silicalite(3000) catalyst exhibited
weaker adsorption for NH as well as CO than the other two
3 2
- or CO -TPD was conducted by using thermogravi-
ammonia adsorption on to the surface was allowed to occur to saturation.
Evacuation was then applied for 1 h at the same temperature followed by
thermal gravimetric (TG) analysis. CO adsorption was carried out at 300 K.
¶ The TS-1 catalyst contains 1.68 wt% Ti and an Si/Al ratio of 46,1 in
contrast to 7.5% Ti and Si/Al ratio of 1900 for 7.5% Ti/HSZ(1900). TS-1 is
thus less effective for selective PO formation than 7.5% Ti/HSZ(1900)
2
catalyst under propene/O .
3
2
2
catalysts; This is in good accordance with much lower propene
conversion of this catalyst relative to the other catalysts (Table
1
, runs 3, 5 and 6).
NH adsorption on 7.5% Ti/HSZ(1900) catalyst was slightly
larger than that on 7.5% Ti/HSZ(68), while the amount of CO
adsorbed was similar (Table 2). However, as much as 85.3% of
NH adsorbed on 7.5% Ti/HSZ(1900) was found to be
desorbed below 440 K (Table 2, y/x ratio and Fig. 1), whereas
the ratio of NH desorption below 440 K on 7.5% Ti/HSZ(68)
3
2
1 L. Y. Chen, G. K. Chuah and S. Jaenicke, J. Mol. Catal. A: Chemical,
1998, 132, 281; M. G. Clerici, G. Bellussi and U. Romano, J. Catal.,
1991, 129, 159.
3
2
T. Hayashi, K. Tanaka and M. Haruta, Am Chem. Soc., Div. Pet. Chem.,
996, 41, 71.
1
3
3
T. A. Nijhuis, B. J. Huizinga, M. Makkee and J. A. Moulijn, Ind. Eng.
Chem. Res., 1999, 38, 884.
was only 68.7%; These findings indicated that the ratio of
strong to weak acid sites on 7.5% Ti/HSZ(1900) is smaller than
that on 7.5% Ti/HSZ(68). This could be consistent with the fact
that the 7.5% Ti/HSZ(1900) catalyst showed lower propene
conversion and smaller amounts of residue product than those
for 7.5% Ti/HSZ(68) (Table 2, runs 3 and 5). The calcination of
4
5
6
S. Yagi and K. Sugita, Jap. Pat., JP 09-291084 A2, 1997.
A. P. Kahn, US Pat., US 1997-903127, 30 July 1997.
C. Murata, K. E. Bere, T. Hayakawa, S. Hamakawa, K. Suzuki and K.
Matano, React. Kinet. Catal. Lett., 2001, 72, 57.
7 A. Yoshida, C. Murata and T. Hattori, Chem. Commun., 1999, 1551.
Chem. Commun., 2001, 1356–1357
1357