G Model
MOLCAA-8938; No. of Pages8
ARTICLE IN PRESS
T. Deng, H. Liu / Journal of Molecular Catalysis A: Chemical xxx (2013) xxx–xxx
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In this work, we report an efficient conversion of cellulose into
acetol. Acetol (1-hydroxy-2-propanone) is an important interme-
diate in the synthesis of acrolein, heterocyclic compounds and
pharmaceuticals, or directly used as an additive in food industry,
a reducing agent in the textile industry and so on [13–15]. It is
currently produced mainly by oxidation of 1,2-propanediol and
esterification/alcoholysis of bromide acetone [16]. New processes
based on catalytic dehydration of glycerol to acetol have also been
explored [17,18]. Recently, we found that SnOx-modified Pt/Al O
300 kV. Samples were prepared by uniformly dispersing in ethanol
and then placing onto carbon-coated copper grids. The average
sizes of metal particles and their size distributions were determined
by measuring more than 300 particles randomly distributed in the
TEM images. Temperature programmed desorption experiments
using CO2 as the probed molecule (CO -TPD) were performed on
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the ChemBET/TPR/TPD unit (Quantachrome). The samples were
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1
◦
treated in the cell in a 99.9999% CO2 flow (30 mL min ) at 25 C
for 30 min, and then flushed in a He flow for 1 h. Afterwards, the
2
3
◦
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−1
(
Pt-SnOx/Al O ) catalysts with Sn/Pt atomic ratios above 2 favor
temperature was ramped from 25 C to 900 C at 10 C min in
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3
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1
the conversion of cellulose to ethylene glycol and especially acetol
over hexitols, most likely due to their inferior hydrogenation activ-
ity and the reactivity of SnOx domains for isomerization of glucose
to fructose and its subsequent cleavage of the C C bonds by retro-
aldol condensation [19]. We herein extend this preliminary work,
and present a systematic study on the selective conversion of cel-
lulose to acetol on Ni-SnOx/Al O bimetallic catalysts with Sn/Ni
a He flow (30 mL min ). Prior to the measurements, the samples
were hydrothermally treated at 210 C for 1 h, and then dried in a
◦
◦
vacuum oven at 25 C for 12 h.
2.3. Cellulose reaction
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3
Cellulose (microcrystalline, Alfa Aesar) reactions were carried
ratios in the range of 0–2.0. We examine the effect of the hydro-
◦
out in a stainless steel autoclave (100 mL) typically at 210 C and
genation activity of Ni-SnOx/Al O on the product distribution, and
2
3
6
MPa H2 for 30 min with vigorous stirring at a speed of 800 rpm.
the mechanism of the SnOx species active for the selective cleavage
of the C C bonds in glucose and fructose involved in the cellu-
lose conversion on the SnOx species. Finally, we obtain high acetol
yields from cellulose, and also from glucose and fructose, being
approximately 35%, 53% and 73%, respectively.
In a typical run, 1 g cellulose and 0.4 g catalyst were introduced
into the autoclave containing 50 mL H O. Afterwards, the reactor
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was fully purged with H2 (>99.999%, Beijing Longhui Jingcheng),
◦
pressurized with H2 to 6.0 MPa and then heated to 210 C which
was kept constant during the reaction. After cooling to room tem-
perature in water, the reaction mixture was filtrated and the solids
were washed several times with deionized water. The solids includ-
ing the catalyst and remaining cellulose were washed with acetone
2
. Experimental details
◦
2.1. Catalyst preparation
three times and then fully dried in an oven at 60 C for 24 h. Cel-
lulose conversions were determined by the change in the weight
of cellulose loaded before and after the reactions. The products in
the liquid phase (e.g. polyols) were analyzed by high-performance
liquid chromatography (Shimadzu LC-20A) using Bio-Rad Aminex
HPX-87H with a RID detector. The product selectivities were
reported on a carbon basis.
SnOx-modified Ni/Al O3 (denoted as Ni-SnOx/Al O ) catalysts
with five different Sn/Ni molar ratios in the range of 0–2.0, were
2
2
3
prepared by the incipient wetness impregnation of ␥-Al O (Alfa
2
3
2
−1
Aesar, 208 m g ) with aqueous solutions of Ni(NO ) ·6H O (AR,
3
2
2
Beijing Yili Chemical), and of Ni(NO ) ·6H O (AR, Beijing Yili Chem-
3
2
2
ical) and SnCl ·2H O (AR, Shantou Xilong Chemical) with several
2
2
drops of aqueous HCl solution, respectively. The impregnated sam-
3. Results and discussion
ples were dried at room temperature for about 12 h and then at
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1
10 C overnight. Afterwards, they were reduced in a H /N (1/4)
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2
SnOx-modified Ni/Al O (Ni-SnOx/Al O ) catalysts with five dif-
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3
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3
flow at 600 C for 4 h. The Ni-SnOx/Al O samples were denoted
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3
ferent Sn/Ni atomic ratios of 0, 0.2, 0.5, 1.0 and 2.0 were examined
as Ni-SnOx(m)/Al O , where the m in parentheses represents their
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3
◦
in the cellulose reaction in water at 210 C and 6 MPa H . As shown
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nominal Sn/Ni atomic ratio. For example, Ni-SnOx(0.2)/Al O rep-
2
3
in Table 1, the cellulose conversions fell in the range 20–30% after
reaction for 0.5 h, but the selectivities to polyols on these cata-
lysts changed significantly with their Sn/Ni ratios. On Ni/Al O ,
resents the sample with a Sn/Ni atomic ratio of 0.2.
SnOx-modified Pt/Al O , Ru/Al O and Cu/Al O3 catalysts were
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3
2
3
2
2
3
prepared in the same way using H PtCl ·6H O (AR, Beijing Chem-
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6
2
the hexitol selectivity was 63.3%. The other identified products
mainly included pentitols (4.7%), tetritols (2.4%), glycerol (6.1%),
ical), RuCl ·nH O (GR, SinopharmChemical) and Cu(NO ) ·3H O
3
2
3
2
2
(
AR, Beijing Yili Chemical), respectively, followed by reduction in
1
,2-propanediol (5.2%), lactic acid (1.0%) and ethylene glycol (2.8%)
◦
a H /N2 (1:4) flow at 400 C for 4 h. Their nominal metal load-
2
(Table 1 and Table S1). Trace amount of glucose (0.3%) was also
ings were 2 wt% Pt, 1 wt% Ru and 5 wt% Cu, respectively, and
their Sn/Pt, Sn/Ru or Sn/Cu atomic ratios were 0.5. In a similar
way, SnOx/Al O (5 wt% Sn), CeOx/Al O3 (5.9 wt% Ce), ZnOx/Al O3
detected. The total selectivity to the identified products was 85.8%.
The missing carbon balance was most likely due to the formation of
the unidentified products (e.g. humins) derived from the condensa-
tion or degradation of glucose and other sugar intermediates. Upon
2
3
2
2
(
2.7 wt% Zn) and AlOx/Al O3 (1.1 wt% Al) with the same metal
2
molar loading were prepared by the incipient wetness impregna-
addition of a small amount of SnOx to Ni/Al O3 at a Sn/Ni ratio of
2
tion of Al O with aqueous solutions of SnCl ·2H O, CeCl ·2H O
2
3
2
2
3
2
0
.2, the hexitol selectivity decreased slightly from 63.3% to 62.6%,
(
AR, SinopharmChemical), ZnCl ·2H O (AR, Shantou Xilong Chem-
2
2
and the selectivities to the cracking products (e.g. C2 and C3 poly-
ols) remained similar to those on Ni/Al O . The total selectivity to
ical) and AlCl ·2H O (AR, SinopharmChemical) with several drops
3
2
◦
2
3
of HCl solution. They were reduced in a H /N (1/4) flow at 600 C
2
2
the identified products reached 88.0%. After the Sn/Ni ratio was
increased to 0.5, the hexitol selectivity sharply decreased to as low
as 0.2% with the concurrent increase in the acetol selectivity to as
high as 53.9%. The selectivities to glycerol and 1,2-propandiol also
sharply decreased to 1.5% and nearly zero, respectively. However,
further increasing the Sn/Ni ratios to 1.0 and 2.0 led to a slight
decrease in the acetol selectivity to 47.1% and 42.9%, and to the
respectively. Moreover, the selectivity to the glucose intermedi-
ate monotonically increased from 0.5% to 2.8% with increasing the
for 4 h.
2.2. Catalyst characterization
XRD patterns were recorded on a Rigaku D/MAX-2400 diffrac-
tometer using Cu K␣1 radiation (ꢀ = 1.5406 A˚ ) operated at 40 kV and
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1
4
00 mA. The 2ꢁ angle was scanned in the range of 25–50 at a rate of
min . TEM images with Energy dispersive X-ray (EDX) analysis
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−1
were taken on a Philips TEM instrument (Tecnai F30 FEI) operated at