Vapor-phase intramolecular aldol condensation of 2,5-hexanedione to 3-methylcyclopent-2-enone over ZrO2-supported Li2O catalyst

Article abstract of DOI:10.1016/j.catcom.2017.01.010

Vapor-phase intramolecular aldol condensation of 2,5-hexanedione to produce 3-methylcyclopent-2-enone was performed over several ZrO₂-supported alkali and alkali earth metal oxides. Among the tested catalysts, ZrO₂-supported Li₂O showed a stable catalytic activity. A high 2,5-hexanedione conversion of 99% with a 3-methylcyclopent-2-enone selectivity of 96% was achieved over a 20?mol% Li₂O-loaded ZrO₂catalyst at 250?°C.

Full text of DOI:10.1016/j.catcom.2017.01.010

Accepted Manuscript
Vapor-phase
,5-hexanedione
ZrO2-supported Li2O catalyst
intramolecular
aldol
condensation
of
over
2
to 3-methylcyclopet-2-enone
Daolai Sun, Shigenori Chiba, Yasuhiro Yamada, Satoshi Sato
PII:
S1566-7367(17)30018-3
doi: 10.1016/j.catcom.2017.01.010
CATCOM 4909
DOI:
Reference:
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
26 September 2016
26 November 2016
12 January 2017
Please cite this article as: Daolai Sun, Shigenori Chiba, Yasuhiro Yamada, Satoshi Sato
,
3
Vapor-phase intramolecular aldol condensation of 2,5-hexanedione to
-methylcyclopet-2-enone over ZrO2-supported Li2O catalyst. The address for the
corresponding author was captured as affiliation for all authors. Please check if
appropriate. Catcom(2017), doi: 10.1016/j.catcom.2017.01.010
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ACCEPTED MANUSCRIPT
A revisedmanuscriptfortheoriginalpapersubmittedtothejournalofCatalysisCommunications
Re.CATCOM-D-16-00909
Vapor-phaseintramolecularaldol condensationof2,5-hexanedioneto
3
-methylcyclopet-2-enoneover ZrO -supported Li Ocatalyst
2
2
DaolaiSun,ShigenoriChiba, YasuhiroYamada,SatoshiSato*
GraduateSchoolofEngineering,ChibaUniversity,Chiba,263-8522,Japan
*
Correspondingauthor. Tel.+81432903376;Fax:+81432903401
E-mailaddress:satoshi@faculty.chiba-u.jp(S. Sato)
1

ACCEPTED MANUSCRIPT
Abstract:
Vapor-phase intramolecular aldol condensation of 2,5-hexanedione to produce 3-methylcyclopet-2-
enone was performed over several ZrO -supported alkali and alkali earth metal oxides. Among the tested
2
catalysts, ZrO -supported Li Oshowedastablecatalyticactivity. A high2,5-hexanedioneconversionof99%
2
2
with a 3-methylcyclopet-2-enone selectivity of 96% was achieved over a 20 mol% Li O-loaded ZrO
2
2
o
catalystat250 C.
Keywords:aldolcondensation,2,5-hexanedione, ZrO -supported Li O, alkalimetaloxides.
2
2
2

ACCEPTED MANUSCRIPT
1. Introduction
Thealdol condensationis apowerfulmethodusedfortheproductionofvariousimportant chemicals,
such as 2-ethylhexanal, isophorone, mesityl oxide and crotonaldehyde [1-3]. The intramolecular aldol
condensation of 2,5-hexanedione (2,5-HD) to 3-methylcyclopent-2-enone (MCP) is an important reaction
(Scheme 1) because of the important use of MCP as an intermediate for producing many natural products,
such as trichothecenes, cortisone and precapnelladiene [4]. In liquid-phase reactions, soluble bases such as
NaOH and KOH are reported to be effective for achieving MCP from 2,5-HD, while the separation of the
products with the soluble bases is difficult [4-8]. On the other hand, to our knowledge, vapor-phase
conversionof2,5-HDtoMCPhasnot beenreported yet.
O
O
-
H O
2
O
2
,5-Hexanedione
3-Methylcyclopent-2-enone
(MCP)
(HD)
Scheme1Intramolecularaldolcondensationof2,5-hexanedioneto3-methylcyclopet-2-enone.
In recent years, in orderto alleviatetheshortageoffossil fuels as well as toreduceCO emission, the
2
conversion of biomass to fuels and useful chemicals has been intensively studied [9-13]. 5-Hydroxy-
methylfurfural (HMF) is an important platform molecule derivable from biomass resources such as glucose
and fructose [14]. HMF can be converted to form 2,5-dimethylfuran (DMF), which has been suggested as a
fuel additive [15]. However, such a use was possibly limited due to the toxicity of DMF [16]. Since DMF
could be quantitatively converted to 2,5-HD via hydrothermal hydrolysis [17], Sacia et al. proposed a route
for the production of biomass-derived fuel of methylcyclopentane with high octane number, in which 2,5-
HD can be converted to MCP via intramolecular aldol condensation followed by a hydrogenation step to
form methylcyclopentane [18]. They performed the reactions in a liquid phase: 98% yield of MCP was
o
obtained from 2,5-HDover abasecatalyst ofMg-Al-O at 180 C and 99% yieldofmethylcyclopentanewas
o
achievedfrom MCPoverPt/NbOPO catalyst at150 Cand3MPaH pressure[18]. However, inthestep of
4
2
3

ACCEPTED MANUSCRIPT
2,5-HD conversion to MCP, the Mg-Al-O catalyst deactivated rapidly: the conversion of 2,5-HD decreased
from99%to25%after5reactioncycles.
In this study, we firstly report a vapor-phase intramolecular aldol condensation of 2,5-HD to MCP
over ZrO -supported alkali and alkali earth metal oxide catalysts using a fixed-bed down flow reactor. The
2
effect of the species loaded on ZrO was studied, and the catalytic activity as well as the stability of the
2
preparedcatalystswascompared.
2
. Experimental
.1Samples
,5-HD was purchased from Tokyo Chemical Industries Co., Ltd., Japan, and it was used for the
catalytic reaction without further purification. Monoclinic ZrO (RSC-HP) with a specific surface area of 39
2
2
2
2
-1
m g was supplied by Daiichi Kigenso Kagaku Kogyo Co. Ltd., Japan. ZrO -supported metal oxide
2
catalysts were prepared by impregnation method using the aqueous solutions of the metal nitrates. LiNO3,
NaNO , KaNO , Mg(NO ) ·6H OandCa(NO ) ·4H Owereusedas astheprecursors ofthecorresponding
3
3
3 2
2
3 2
2
metal oxides, and all the precursors were purchased from Tokyo Chemical Industries Co., Ltd., Japan. After
o
o
theimpregnation,thepreparedcatalystsweredriedat110 Cfor12hfollowedbycalcinationinairat600 C
o
for 3 h. The ZrO without modification was also calcined in air at 600 C for 3 h before the reactions. The
2
ZrO -supported catalysts are denoted as x-XO/ZrO , where x indicates the mol percentage of X, and X
2
2
indicatesthespeciesoftheloadedmetal.
2.2Catalyticreaction
The vapor-phase intramolecular aldol condensation of 2,5-HD was performed in a fixed-bed down-
flow glass reactor with an inner diameter of 17 mm. Prior to the reaction, typically, 0.5 g catalyst was placed
o
in the catalyst bed and heated at 250 C for 1 h to stabilize the temperature of the catalyst bed. After the
-1
3
preheat, pure2,5-HDwasfedtothereactorataliquidfeedrateof1.7g h togetherwithanH flowof30cm
2
-1
o
min . Theliquid effluents collectedin adryice-acetonetrap(-78 C)everyhourwereanalyzedbya FID-GC
(GC-14A, Shimadzu) with a 30-m capillary column of TC-1 (GL-Science, Japan). A GC-MS (QP5050A,
4

ACCEPTED MANUSCRIPT
Shimadzu)wasusedforidentificationoftheproductsintheeffluent.
2.3Characterizationofcatalysts
Thethermogravimetry(TG)analysis was performed usingThermoplus 8120E2(Rigaku)underthe
o
-1
conditions: sample weight, ca. 10 mg; the rate of the temperature increase, 5 C min ; heating range, from
o
theroomtemperatureto750 C.
3. ResultsandDiscussion
3
.1. Intramolecular aldol condensation of 2,5-HD to MCP over ZrO -supported alkali and alkali earth
2
metaloxides.
Table 1 shows the reaction results of intramolecular aldol condensation of 2,5-HD to MCP over
o
ZrO -supported alkali and alkali earth metal oxides at 250 C. In our previous studies, H as a carrier gas
2
2
showed a better performance than N in some dehydration processes, such as the self-aldol condensation of
2
butanal to 2-ethyl-2-hexenal [3] and the dehydration of 1,2-propanediol to propanal [19,20]. Thus, H was
2
selected as the carrier gas in the present study. In another previous study of our group, we found that
monoclinic ZrO -supported alkali and alkali earth metal oxide catalysts have different basicity [21]. Since
2
basic catalystsareeffectivefortheformationofMCPfrom2,5-HD[4-8,18], wetestedaseriesofmonoclinic
ZrO -supportedalkaliandalkaliearthmetaloxidesinthepresentstudy.
2
In the reactions over different ZrO -supported catalysts, MCP was produced at selectivities higher
2
than 95% (Table 1). 3-Hexene-2,5-dione (HDO), which is a dehydrogenation product of 2,5-HD, was
detected as a by-product with a selectivityof 0.3% in the reaction over 10-Li O/ZrO . Pure ZrO gave a 2,5-
2
2
2
HD conversion of 4%, while the conversion of 2,5-HD was significantly increased by the modification of
alkali metal oxides, such as K O, Na O, and Li O. Among the alkali metal oxide-modified catalysts, 10-
2
2
2
K O/ZrO showed thehighest averaged 2,5-HD conversion of 29.1%. In contrast, theZrO -supported alkali
2
2
2
earth metal oxides, such as 10-CaO/ZrO and 10-MgO/ZrO , showed relativelylow catalytic activity for the
2
2
conversion of 2,5-HD. ZrO -supported MgO has been reported to be efficient in some liquid-phase
2
5

ACCEPTED MANUSCRIPT
intermolecular aldol condensation reactions [22-24], such as the aldol condensation between benzaldehyde
and cyclohexanone [23] and self-aldol condensation of cyclopentanone [24]. However, 10-MgO/ZrO was
2
noteffectiveinavapor-phaseintramolecularaldolcondensationof2,5-HD inthepresentstudy.
Fig. 1 shows the changes in the catalytic activity of ZrO and ZrO -supported alkali metal oxide
2
2
catalysts. ZrO showed an initial 2,5-HD conversion higher 20%, while the conversion of 2,5-HD
2
significantly decreased at the initial stage of time on stream. Although 10-K O/ZrO and 10-Na O/ZrO
2
2
2
2
showed higher initial 2,5-HD conversions than 10-Li O/ZrO , they deactivated rapidly. In contrast, the
2
2
catalyticactivityof10-Li O/ZrO wasstable.
2
2
In order to study the catalytic deactivation, TG analysis of the catalysts used after the reactions was
conducted. As shown in Fig. 2, serious weight loss can be observed in the TG profiles of all the used
o
o
catalysts between ca. 200 C to 600 C, which is generally considered as a temperature range for the
decompositionofcarbonaceouscomponents[3,25]. Becauseallthecatalystswerepreparedviacalcinationat
o
o
6
00 C, we confirm that the weight loss in TG profiles at temperature rage between 200 and 600 C is
mainly attributed to the decomposition of coke. The used 10-Li O/ZrO shows two steps of weight loss at
2
2
o
o
temperature ranges from 150 to 450 C and from 550 to 600 C, which indicates the accumulated coke
possibly includes different components. In contrast, the used ZrO , 10-K O/ZrO and 10-Na O/ZrO show
2
2
2
2
2
only one step of weight loss. On the other hand, the amount of accumulated coke in the used 10-Li O/ZrO
2
2
islessthanthoseoftheused10-K O/ZrO and10-Na O/ZrO . Thisindicatesthatthecatalyticdeactivationis
2
2
2
2
possibly caused by the formation of coke. In another word, the relatively stable catalytic activity of 10-
Li O/ZrO is possibly attributed to the relatively small amount of accumulated coke. This is probably
2
2
because of the low dehydrogenation ability of Li O with weak basicity. Dehydrogenation ability is directly
2
concernedwithcarbonformation[26].
In FT-IR analysis of 10-Li O/ZrO before and after the reaction (Fig. S1), the accumulation of
2
2
carbonaceouscompounds,whichincludeC=OandC-Hbonds, oncatalystsurfacewasconfirmed. However,
no significantlydifference was observed from the XRD profiles of the used catalyst (Fig. S2), indicating the
monoclinicZrO structureof10-Li O/ZrO wasmaintainedduringthereaction.
2
2
2
6

ACCEPTED MANUSCRIPT
3
.2.EffectoftheloadingamountofLi OonZrO andthecontacttime.
2 2
Because catalytic stability is highly required in industrial processes, ZrO -suppored Li O catalysts
2
2
with relatively stable activity was selected for further study. Table 1 shows the reaction results of aldol
condensation of 2,5-HD to MCP over ZrO -supported Li O with different loadings. 1-Li O/ZrO gave both
2
2
2
2
a lower conversion of 2,5-HD and a lower selectivity to MCP than those of ZrO without modification.
2
However, the conversion of 2,5-HD and the selectivity to MCP increased with increasing the loading of
Li O. This indicates that large loadings of LiO are effective to prepare efficient basic sites for the formation
2
2
of MCP from 2,5-HD, which is confirmed by CO -TPD analysis (Fig. S3). A high 2,5-HD conversion of
2
2
2.9% with a MCP selectivity of 98.0% was achieved over 20-Li O/ZrO . In XRD profiles of Li O/ZrO
2 2 2 2
with different Li O loadings (Fig. S4), the diffraction peaks were assigned as monoclinic ZrO pahse. The
2
2
otherphases such as Li O werenot observed eveninthesample with a Li O loadingof20 %, indicatingthe
2
2
high dispersion of the Li O particles. Fig. 3 shows the changes in activity of Li O/ZrO catalysts at different
2
2
2
Li O loadings. The stabilized conversion of 2,5-HD increased with increasing the loading of Li O. On the
2
2
otherhand, the conversionof2,5-HDsignificantlydecreased withtimeonstream overLi O/ZrO withLi O
2
2
2
loadingslowerthan5%, whichispossiblycausedbythesmallloadingsofLi O. Incontrast, at Li Oloadings
2
2
higher than 10%, the conversions of 2,5-HD were stabilized. Because the number of basic sites increased
with increasing the loading of Li O (Fig. S3), the increase of Li O loading is consistent with the increase of
2
2
contract time, indicating high contract times are effective for promoting the formation of MCP and
decreasingthedeactivationrate.
In order to study the effect of contract time, the reactions over 20-Li O/ZrO were performed with
2
2
different W/F conditions (Table 2), where W and F are the catalyst weight and the feed rate of 2,5-HD,
respectively. TheW/Fwas increasedfrom 0.29to1.76 h, andthe conversionof2,5-HDincreased from 22.9
to 99.2% with increasing the W/F. No significant decrease in MCP selectivity was observed at high W/F
conditions. Catalytic deactivation was observed over 20-Li O/ZrO at high conversion levels (Fig. S5),
2
2
while the selectivity to each product was stable during the reaction. A 99.2% conversion of 2,5-HD with a
6.0% selectivity to MCP was obtained over 20-Li O/ZrO with a W/F of 1.76 h. This result indicates that
9
2
2
7

ACCEPTED MANUSCRIPT
high yields of MCP could be achieved by increasing the contact time in such a vapor-phase intramolecular
aldolcondensationof2,5-HD.
4
. Conclusions
Vapor-phase intramolecular aldol condensation of 2,5-hexanedione to 3-methylcyclopet-2-enone
was performed over ZrO -supported alkali and alkali earth metal oxides. ZrO -supported alkali metal oxide
2
2
catalysts showed higher catalytic activities than ZrO -supported alkali earth metal oxide catalysts. Among
2
the ZrO -supported alkali metal oxides, 10-K O/ZrO and10-Na O/ZrO significantlydeactivatedwithtime
2
2
2
2
2
onstream, while10-Li O/ZrO showedarelativelystablecatalyticactivity. Highyieldsof3-methylcyclopet-
2
2
2-enone could be achieved byincreasing the contact time. A 3-methylcyclopet-2-enone selectivity of 96.0%
o
with a2,5-hexanedione conversion of 99.2% was achieved over 20-Li O/ZrO catalyst at 250 C anda W/F
2
2
of1.76h.
Supplementarydata
Supplementarymaterial
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a
Table1. Aldolcondensationof2,5-HDtoMCPoverZrO -supportedcatalysts
2
b
b
Selectivity/mol%
Conversion
Catalyst
ZrO2
c
d
/
mol%
MCP
HDO
Others
4.0
8.9
99.1
98.7
>99.9
96.9
97.1
97.9
90.9
96.8
97.9
98.0
0.0
0.0
0.0
0.0
0.0
0.3
5.4
2.5
0.2
0.2
0.9
1.3
0.0
3.1
2.9
1.8
3.7
0.7
1.9
1.8
1
0-CaO/ZrO2
0-MgO/ZrO2
0-K O/ZrO2
1
1.2
1
29.1
19.1
18.7
1.4
2
1
0-Na O/ZrO2
2
1
0-Li O/ZrO2
2
1
-Li O/ZrO2
2
3
-Li O/ZrO2
4.0
2
5
-Li O/ZrO2
11.1
22.9
2
2
0-Li O/ZrO2
2
a
o
3
-1
b
Reactionconditions:reactiontemperature,250 C; H gasflowrate,30cm min ; W/F, 0.29h;
2
c
d
Averagedactivitybetween2-5h; MCP, 3-methylcyclopet-2-enone; HDO,3-hexene-2,5-dione.
1
0

ACCEPTED MANUSCRIPT
a
Table2. Aldolcondensationof2,5-HDtoMCPover20-Li O/ZrO at differentW/Fconditions.
2
2
b
b
Selectivity/mol%
W/F
Conversion
/mol%
c
d
/
h
MCP
HDO
Others
0
.29
.59
.18
.76
22.9
48.8
87.0
99.2
98.0
97.9
96.5
96.0
0.2
0.0
0.0
0.0
1.8
2.1
3.5
4.0
0
1
1
a
o
3
-1 b
Reactionconditions:reactiontemperature,250 C; H gasflowrate,30cm min ; Averagedactivity
2
c
d
between2-5h; MCP,3-methylcyclopet-2-enone; HDO,3-hexene-2,5-dione.
1
1

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Figure1ChangesincatalyticactivityofZrO andZrO -supportedalkalimetaloxides.
2
2
o
3
-1
Reactionconditions:reactiontemperature, 250 C; H gasflowrate, 30cm min ; W/F,0.29h.
2
1
2

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0
-5
ZrO2
-10
1
0-Li O/ZrO2
2
-15
1
0-Na O/ZrO2
2
1
0-K O/ZrO2
2
-20
1
00 200 300 400 500 600 700
o
Temperature/ C
Figure2TGprofilesofvariouscatalystsusedafterthereactions.
o
3
-1
Reactionconditionsfortheusedcatalysts: reactiontemperature, 250 C; H gasflowrate,30cm min ; W/F,
2
0.29h.
1
3

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40
30
20
10
2
1
5
3
1
0 mol%
0 mol%
mol%
mol%
mol%
0
1
2
3
4
5
Time on stream / h
Figure3ChangesincatalyticactivityofLi O/ZrO catalystswithdifferentLi Oloadings.
2
2
2
o
3
-1
Reactionconditions:reactiontemperature, 250 C; H gasflowrate, 30cm min ; W/F,0.29h.
2
1
4

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Graphicabstract
1
5

ACCEPTED MANUSCRIPT
Highlights




Vapor-phaseintramolecularaldolcondensationof2,5-hexanedionewasinvestigated.
ZrO -supportedalkalimetaloxidesweremoreactivethanZrO -supportedalkaliearthmetaloxides.
2
2
ZrO -supportedLiO showedrelativelystableactivityin theZrO -supportedalkalimetaloxides.
2
2
2
o
A95%yieldof3-methylcyclopet-2-enonewasachievedover20mol.%Li O/ZrO at250 C.
2
2
1
6