Unusual performance for the selective oxidation of ethane to acrolein over mesoporous SBA-15-supported potassium catalysts

Article abstract of DOI:10.1246/cl.2005.1080

SBA-15 silica-supported potassium catalysts were first reported for the selective oxidation of ethane to aldehydes by using oxygen as oxidant. It was found that SBA-15-supported potassium catalysts exhibited very high yield of aldehydes, especially surprisingly high yield of acrolein in the selective oxidation of ethane. The SBA-15-supported catalyst with 2% loading of potassium showed the best performance for the partial oxidation of ethane to aldehydes. The highest yields of acrolein and total aldehydes (formaldehyde, acetaldehyde, and acrolein) were 2.5% and 5.2%, respectively, when the ethane conversion was 14.8% at the reaction temperature of 748 K. Copyright

Full text of DOI:10.1246/cl.2005.1080

1080
Chemistry Letters Vol.34, No.8 (2005)
Unusual Performance for the Selective Oxidation of Ethane to Acrolein
over Mesoporous SBA-15-supported Potassium Catalysts
Zhe Zhang, Zhen Zhao,ꢀ Chunming Xu, Aijun Duan, Shuang Sha, Ying Zhang, and Tao Dou
State Key Laboratory of Heavy Oil Processing, University of Petroleum, Beijing, 102249, P. R. China
(Received April 25, 2005; CL-050557)
SBA-15 silica-supported potassium catalysts were first re-
ported for the selective oxidation of ethane to aldehydes by using
oxygen as oxidant. It was found that SBA-15-supported potassi-
um catalysts exhibited very high yield of aldehydes, especially
surprisingly high yield of acrolein in the selective oxidation
of ethane. The SBA-15-supported catalyst with 2% loading of
potassium showed the best performance for the partial oxidation
of ethane to aldehydes. The highest yields of acrolein and total
aldehydes (formaldehyde, acetaldehyde, and acrolein) were
2.5% and 5.2%, respectively, when the ethane conversion was
14.8% at the reaction temperature of 748 K.
This is the first report on the performance of K/SBA-15 cat-
alysts, which are transition-metal-free and SBA-15-supported
catalyst system, for selective oxidation of ethane to aldehydes,
especially to acrolein.
In this study, the pure siliceous mesoporous SBA-15 was
prepared according to a literature procedure using Pluronic
P123 triblock polymer as template under acidic conditions.10
A solution of P123:2 M of HCl:TEOS:H2O = 2:60:4.25:15
was prepared, stirred for 20 h at 313 K, and then hydrothermally
treated at 373 K for 48 h. The solid products were recovered by
filtering off, then dried overnight at 373 K. SBA-15 formed after
calcinations at 873 K for 5 h in air.
K/SBA-15 samples with different potassium loading (0.5–
10 mol %) were prepared by impregnation of SBA-15 with
aqueous solution of potassium nitrate, followed by drying at
353 K in oven for 14 h and calcining at 873 in air for 6 h.
Activity tests were carried out in a fixed bed flow reactor
(quartz tube, 6 mm i.d.) under atmospheric pressure. The reac-
tant gas mixture consisting of ethane and oxygen (C2H6:O2 =
3:1, mol %) was passed through the catalyst of 0.3 g at a flow rate
of 15 mL/min. Products were analyzed by gas chromatograph.
Double FIDs were used to analyze mixed gas flowing from
reactor: (a) 50 m PONA capillary column for separate of
ethylene, ethane, acetaldehyde, and acrolein; (b) 1 m TDX-01
column to separate carbon monoxide, carbon dioxide, methane,
formaldehyde, ethylene, and ethane. The later was equipped
with a Ni-catalyzed methanizer.
The XRD patterns of bare SBA-15 and K/SBA-15 samples
with different K loadings, the peaks (100), (110), and (200) in-
dexed to hexagonal regularity of SBA-1510 were sustained for
the samples with the potassium loading up to 5 mol %, because
of the collapse of mesoprous channels for the sample with
10% of potassium loading.
Table 1 showed the results of ethane selective oxidation
over the K/SBA-15 catalysts at 723 K. No acrolein was detected
over bare SBA-15. The selectivity to acrolein increased with the
increasing of the K loading from 0.5 mol % to 3 mol %, and then
it decreased with the further increasing of the K loading from
3 mol % to 10 mol %. The selectivity to acrolein increased
remarkably when potassium loading was up to 2–3 mol % and
the main products of aldehydes were acrolein and acetaldehyde,
while the main products of aldehydes were formaldehyde and
acetaldehyde over the low loading K/SBA-15 samples (K ¼
0:5{1:5 mol %). Acrolein was reported to be produced via the
aldol-type condensation between formaldehyde and acetalde-
hyde.6,11
Direct conversion of ethane to aldehydes by partial oxida-
tion using oxygen is a big challenge in catalyst research on the
effective utilization of light alkanes. The stability of ethane
molecule is only inferior to that of methane molecule, and it is
not easy to obtain aldehydes with yields higher than 2%1 in
the selective oxidation of ethane.
Researches on the conversion of ethane over transition metal
mixed oxides were increasingly more and more since the oxida-
tive dehydrogenation of ethane over Mo and V mixed metal ox-
ides was reported firstly by Throsteinson2 in 1978. In the most
cases, the products of aldehydes were formaldehyde and acetal-
dehyde for the selective oxidation of ethane.3,4
At the end of the 1990s, Zhao and Kobayashi et al.1,5 inves-
tigated the selective oxidation of ethane over the silica-support-
ed low loading metal oxide catalysts modified by alkali metal
(alkali/M/SiO2, alkali:M:Si = 10:1:1000, molar ratio). Com-
pared with the result of the direct selective oxidation of ethane
over high loading catalysts (V:Si > 1 wt %), a higher selectivity
to aldehydes was obtained over the catalysts with highly disper-
sived and isolated active sites, and the acrolein was detected in
the products. The highest yield acrolein of 1.2% was obtained
over K-Fe/SiO2 catalyst in the selective oxidation of ethane.
The ethane conversion was very low over K/SiO2 catalyst
(ꢁ0:1%),6 and the alkali metal, acted as a promoter rather than
the active components, was introduced to the M/SiO2 catalysts.
Since mesoporous molecular sieves possess well-ordered
mesoporous channels and large surface areas, the active compo-
nent may thus be tailored in their nano-order spaces. Very re-
cently, SBA-15, a new type of ordered mesoporous material,
has attracted much attention in the field of catalysis.7–9 SBA-
15 possesses a high surface area (600–1000 m2/g) and is formed
by a hexagonal array of uniform tubular channels with tunable
pore diameters in the range of 5–30 nm. Given its thicker walls
ꢀ
(31–64 A), SBA-15 provides a thermal stability and hydrother-
The apparent performances of the increasing of potassium
loading over SBA-15 are summarized as follows: (a) To shift
in carbon number of aldehydes from lower to higher in the dis-
tribution of the products; (b) To reduce of the COx selectivity
mal stability that exceed those of the thinner walled MCM-41
materials. SBA-15 may be used as a promising catalyst support,
particular for the reactions occurring at high temperatures.
Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.8 (2005)
Table 1. Partial oxidation of ethane over the K/SBA-15 (K:Si = x:100, mol) catalysts at 723 K
1081
Selectivity/%
K loading
/mol %
Conv.
Aldehydes
CH2CHCHO
/%C2H6
COx
C2H4
HCHO
CH3CHO
Total
Empty tube
0.00 (SBA-15)
0.50
0.01
14.3
5.3
6.7
6.9
8.4
8.5
9.2
4.4
100.0
85.5
69.0
64.3
62.3
58.5
56.8
44.5
43.0
49.0
50.5
0.0
4.7
9.0
9.7
7.6
7.0
7.0
6.2
3.4
3.3
3.7
0.0
8.4
14.5
11.0
8.5
9.0
11.2
6.8
0.0
1.40
4.60
11.1
16.4
18.9
16.6
19.4
21.5
17.2
16.1
0.0
0.0
2.9
3.9
5.2
6.7
8.4
23.2
27.5
26.9
24.2
0.0
9.8
22.0
26.00
30.1
34.5
36.2
49.3
53.6
47.7
45.8
0.75
1.00
1.25
1.50
2.00
3.00
5.00
10.00
4.6
3.6
5.5
4.9
3.5
In summary, the catalyst with appropriate potassium loading
on the SBA-15 was a novel type of catalyst system for the selec-
tive oxidation of ethane to aldehydes, especially to acrolein.
2.5
2.0
1.5
1.0
0.5
0.0
This work was supported by the National Natural Science
Foundation of China (Grant No. 20373043), the National Basic
Research Program of China (grant No. 2004CB 217806), and the
Scientific Research Key Foundation for the Returned Overseas
Chinese Scholars of State Education Ministry.
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Figure 1. Effect of K loading amount on the acrolein yield over
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The influence of potassium-loading amounts on the catalytic
performance of K-SBA-15 for ethane oxidation to acrolein was
shown in Figure 1. There was a range of better acrolein yield at
potassium loading of 2–5 mol %. The highest acrolein yield and
the highest total aldehyde yield obtained were 2.5% and 5.2%,
respectively, at the ethane conversion of 14.8%, over the sample
with K/Si ratio of 2/100 at the reaction temperature of 748 K.
The performance of K-SBA-15 for ethane oxidation to acrolein
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Published on the web (Advance View) August 5, 2005; DOI 10.1246/cl.2005.1080