Selective production of 1,3-butadiene in the dehydration of 1,4-butanediol over rare earth oxides

Article abstract of DOI:10.1016/j.apcata.2018.05.029

Vapor-phase dehydration of 1,4-butanediol and 3-buten-1-ol to produce 1,3-butadiene was investigated over rare earth oxides such as Lu₂O₃, Yb₂O₃, Tm₂O₃, Er₂O₃, and Sc_1.0Yb_1.0O₃. In the dehydration of 3-buten-1-ol, heavy rare earth oxides such as Lu₂O₃, Yb₂O₃, and Er₂O₃ showed high catalytic performance for the selective formation of 1,3-butadiene with producing small amount of propylene whereas acidic catalysts such as alumina decomposed 3-buten-1-ol into propylene. In particular, over Yb₂O₃ calcined at 800 °C, 3-buten-1-ol was converted with a yield of 1,3-butadiene higher than 95% at 340 °C. In the dehydration of 1,4-butanediol, furthermore, we developed an efficient catalytic system: 1,3-butadiene was produced via an intermediate, 3-buten-1-ol, over Yb₂O₃ with an excellent yield of 96% at 360 °C and a high contact time of 2.26 h. Yb₂O₃ successfully inhibited the major side reaction such as decomposition of 3-buten-1-ol to propylene and provided the selective production of 1,3-butadiene from 1,4-butanediol.

Full text of DOI:10.1016/j.apcata.2018.05.029

Accepted Manuscript
Title: Selective production of 1,3-butadiene in the dehydration
of 1,4-butanediol over rare earth oxides
Authors: Yuchao Wang, Daolai Sun, Yasuhiro Yamada, Sato
Satoshi
PII:
S0926-860X(18)30259-X
DOI:
Reference:
https://doi.org/10.1016/j.apcata.2018.05.029
APCATA 16678
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
16-3-2018
14-5-2018
24-5-2018
Please cite this article as: Wang Y, Sun D, Yamada Y, Sato S, Selective production
of 1,3-butadiene in the dehydration of 1,4-butanediol over rare earth oxides, Applied
Catalysis A, General (2018), https://doi.org/10.1016/j.apcata.2018.05.029
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AmanuscriptfortheoriginalpapersubmittedtothejournalofAppliedCatalysisA: General
Selective production of 1,3-butadiene in the dehydration of 1,4-butanediol over
rareearthoxides
a
a, b
a
a
YuchaoWang ,DaolaiSun , YasuhiroYamada ,SatoshiSato *
a GraduateSchoolofEngineering,ChibaUniversity,Chiba, 263-8522, Japan
b
School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin, 300130,
China
*
Correspondingauthor. Tel.+81432903376;Fax:+81432903401
E-mailaddress:satoshi@faculty.chiba-u.jp(S. Sato)
Graphicalabstract
Highlights

Vapor-phase dehydration of3-buten-1-ol and 1,4-butanediol was performed over rareearth
oxides.


Heavyrareearthoxideswereeffectiveforthedehydrationof3-buten-1-olto1,3-butadiene.
2-Buten-1-ol via isomerization of 3-buten-1-ol was observed as an intermediate to 1,3-
butadiene.
1


High 1,3-butadiene yield was achieved in the dehydration of 1,4-butanediol over Yb
2 3
O
catalyst.
Abstract
Vapor-phase dehydration of 1,4-butanediol and 3-buten-1-ol to produce 1,3-butadiene was
investigated over rare earth oxides such as Lu , Yb , Tm , Er . In the
dehydration of 3-buten-1-ol, heavy rare earth oxides such as Lu , Yb showed high
2
O
3
2
O
3
2
O
3
2
O
3
, and Sc1.0Yb1.0
O
3
2
O
3
2
O
3
, and Er
2 3
O
catalytic performance for the selective formation of 1,3-butadiene with producing small amount of
propylene whereas acidic catalysts such as alumina decomposed 3-buten-1-ol into propylene. In
particular, over Yb
2
O
3
calcined at 800°C, 3-buten-1-ol was converted with a yield of 1,3-butadiene
o
higher than 95% at 340 C. In the dehydration of 1,4-butanediol, furthermore, we developed an
efficient catalytic system: 1,3-butadiene was produced via an intermediate, 3-buten-1-ol, over Yb
2 3
O
o
with an excellent yield of 96% at 360 C and a high contact time of 2.26 h. Yb
2
O successfully
3
inhibited the major side reaction such as decomposition of 3-buten-1-ol to propylene and provided
theselectiveproductionof1,3-butadienefrom1,4-butanediol.
Keywords:1,4-Butanediol; 3-Buten-1-ol;1, 3-Butadiene;Rareearthoxides;Yb
2
O .
3
1. Introduction
In order to reduce the emission of carbon dioxide and other greenhouse gases resulted from
human activity, biomass resources have been expected as an alternative to conventional fossil ones.
In recent years, there is a growing worldwide interest in 1,3-butadiene (BD) as a platform chemical
forproducingadiversityofsyntheticrubbers, elastomersand resins[1].ThemanufactureofBD,
however, is under pressure of not only the fluctuation of price of fossil oils but also the
development of shale gas. Thus, the research activities are concentrated on finding an alternative
route for producing BD. Syntheses of BD from ethanol have studied intensively from the beginning
2

of the 20th century [1, 2]. With a variety of research upon ethanol-based BD, several possible
mechanisms and great perspective catalytic routes have been prospected [1-4]. However, the BD
synthesis from ethanol depending on multifunctional catalysts seems still difficult and has still low
BD yields.
Next to the ethanol dimerization route, several butanediols (BDOs) are reported to produce
BD through a direct and a stepwise dehydration route as shown in Scheme 1 [2]. The paths from
BDOs, i.e. 1,3-, 2,3-, and 1,4-BDO, to BD have attracted much recent attention because BDOs are
the potential resources derived from renewable and waste feedstocks [2, 5, 6]. BDOs can be
converted into BD in a direct approach over acidic oxides, whereas it has been difficult to obtain a
highyield of BD[7-11]. Forexample, overacidic catalysts suchas Al
of 2,3-BDO and 1,4-BDO are primarily conducted to produce 2-butanone and tetrahydrofuran,
respectively [7, 8]. Strong acidic SiO -Al catalyzes the dehydration of 1,3-BDO to BD with the
selectivity as low as 36% because of the decomposition of 1,3-BDO [9]. The direct conversion of
,3-BDO to BD is developed over H-ZSM-5: a maximum BD yield of 60% is provided at 300 oC
10]. Recently, there are several reports on the production of BD from 2,3-BDO [12-21] while there
is a pioneering repot of Winfield on a selective conversion of 2,3-BDO to BD in 1945 [22]. Among
2
O
3
, thedehydration processes
2
O
2 3
1
[
them, selective formation of BD from 2,3-BDO is realized over weak basic catalysts such as Sc
2
O
3
[12] and alkaline phosphates [13, 14]. In a liquid phase, Sralpaert et al. have investigated the use of
ionic liquid tetrabutylphosphonium bromide as a catalyst for dehydration of 1,4-BDO to produce
BD with a yield of 94% [23]. However, there is no reports on the catalytic production of BD from
1,4-BDOoversolidcatalysts.
In our previous works, we have investigated a series of catalytic reaction of BDOs to BD
including both the first dehydration of BDOs to unsaturated alcohols [24-29] and the second step
dehydration of unsaturated alcohols to BD [30]. CeO
presenting total selectivity to 3-buten-2-ol (3B2OL) and 2-buten-1-ol (2B1OL) over 97% at 325 °C
26]. Vapor-phase dehydration of 1,4-BDO is also investigated over rare earth oxides (REOs) [24,
5]. It has been found that weakly basic REOs, such as CeO , Er , and Yb exhibit high
2
catalyzes the dehydration of 1,3-BDO
[
2
2
2
O
3
O
2 3
3

selectivity to 3-buten-1-ol (3B1OL). Recently, vapor-phase dehydration of C4 unsaturated alcohols
such as 3B2OL, 2B1OL, and 3B1OL to produce BD is studied over several solid catalysts[30]. It
hasbeenfoundthatacidic catalysts areeffectivefortheproductionofBDfrom3B2OLand2B1OL,
and that a SiO
acidic catalysts primarilytransform 3B1OLintopropylenethroughtheC-C bondcleavageviaretro-
Prins reaction. In contrast, REOs suchasCeO , whichprovides acid-baseconcertedsites workingas
2
-Al
2
O
3
shows a high catalytic performance. In the dehydration of 3B1OL, however,
2
an effective catalyst in the formation of BD from 3B1OL, reduces the selectivity to propylene less
o
than10%evenatahightemperatureof400 C.
In this paper, to develop an efficient catalyticsystem forthe productionof BD from 1,4-BDO
(Scheme 1), we conducted vapor-phase catalytic dehydration of 3B1OL over the REO catalysts
under different conditions, and investigated the optimal catalytic conditions over Er and Yb O .
2
O
3
2
3
Furthermore, we studied the direct production of BD from 1,4-BDO over Yb
2
O under the
3
appropriatecatalyticconditionsobtainedfromtheresultsof3B1OLdehydration.
2
. Experimental
.1Samples
Unsaturated alcohols such as 3B1OL and 2B1OL were purchased from Tokyo Chemical
Industries Co., Ltd., Japan. 1,4-BDO, 1-hexanol, which was used as an internal standard for
quantitative analysis, Pr(NO 6H O, and Sc(NO 5H O were purchased from Wako Pure
Chemical Industries, Japan. Pr were prepared by the calcination of Pr(NO
.6H
and Sc(NO O at 800°C for 3 h, respectively. Except Pr , REOs such as Yb
.5H
2
3
)
3
2
3
)
3
2
6
O
11 and Sc
2
O
3
3
)
3
2
O
3
)
3
2
6
O
11 and Sc
2
O
3
2
3
O ,
Er
.0, and 1.5) samples were supplied byDaiichi Kigenso Kagaku Kogyo Co., Ltd., Japan. The REO
samples were calcined at 800°C for 3 h before the catalytic reaction while Er was calcined at a
temperaturebetween600and1000°C for3h.
2
O
3
, and Lu
2
O
3
were purchased from Kanto Kagaku Co. Ltd., Japan. Three Sc2-xYb
x
O
3
(x = 0.5,
1
O
2 3
2.2Catalyticreaction
4

The dehydration of unsaturated alcohols and 1,4-BDO was performed in a fixed-bed down-flow
glass reactor with an inner diameter of 17 mm at an ambient pressure of N . Prior to the catalytic
reaction, thecatalyst (0.25-4.0 g)was placedinthecatalyst bedofthereactorand heatedat thereaction
2
3
-1
temperaturefor1h. Then, aliquidreactantwasfedthroughthereactortopataflowrateof1.75cm h ,
-1
-1
which is 1.47 g h for 3B1OL and 2B1OL; 1.77 g h for 1,4-BDO, together with an N flow of 30
2
3
-1
o
cm min . Aliquideffluentwascollectedinanice-watertrapat0 Ceveryhour.A gaschromatograph
with mass-spectrometry (QP5050A, Shimadzu, Japan) was used for the identification of products in
theliquid effluents. Theproducts werequantitativelyanalyzed bya gas chromatograph equippedwith
a flame ionization detector (GC-2014, Shimadzu) and a capillary column of Inert Cap WAX (30 m,
GL-Science, Japan). The gaseous products were analyzed byan on-line gas chromatography(GC-8A,
Shimadzu) with a packed column of VZ-7 (6 m, GL-Science). The conversion of reactant and the
selectivitytoeachproductwerecalculatedasamolarpercentage(mol.%).
2
.3Characterizationofcatalysts
The specific surface area (SA) of catalyst was calculated by the Brunauer-Emmett-Teller (BET)
method using an N isotherm at -196°C. The X-ray diffraction (XRD) pattern was measured on an
XRD7000(Shimadzu,Japan)usingCuKαradiationtodetectthecrystalstructureofcatalyst.
2
3
. Resultsanddiscussion
.1Dehydrationof3B1OLoverREOs
In the previous study, we have tested CeO
3
2
and Yb
2
O , and propylene is found to be produced
3
o
with some amounts in the dehydration of 3B1OL at 400 C [30]. Thus, in this study, the reaction
o
was performed at a low temperature of 360 C. Table 1 summarizes catalytic activities of various
REOs and mixed oxides of Sc2-xYb
x
O (x= 0.5, 1.0, and 1.5) in the dehydration of 3B1OL at a
3
contacttime, W/F=0.34h, whereWandFarecatalyst weight andfeedrateofreactant, respectively.
o
REOs and Sc2-xYb
x
O
3
samples calcined at 800 C are listed in the sequence of ionic radius along
5

with their SA data. Among those samples, Lu
2
O
3
, Yb
2
O
3
, Tm
2
O
3
, Er
2
O
3
, and Sc2-xYb
x
O showed
3
the selectivity to BD higher than 55% while the other products were propylene, 2B1OL formed via
isomerization of 3B1OL, and esters of unsaturated alcohols, i.e. liner unsaturated ethers that have a
formula of C
of the REO catalysts, whereas propylene was the major product over acidic oxides such as Al
and SiO -Al [30]. In particular, over Lu , Yb , Tm , Er , and
, the propylene selectivity was lower than 4% even at high conversions. In contrast,
, Tb , Gd , Eu , CeO , Nd , and Pr 11 showed low conversions with
relatively lower selectivity to BD and higher selectivity to propylene than heavy REOs did.
Although the selectivity to BD surpassed 50% over Sc , Dy , Sm , and La , the
conversionwas ratherlow.
8
H14O. It should be noted that the selectivityto propylene was relativelylow over most
O
2 3
2
2
O
3
2
O
3
2
O
3
2
O
3
2
O
3
, Sc0.5Yb1.5
O
3
Sc1.0Yb1.0O
3
Y
2
O
3
, Ho
2
O
3
4
O
7
2
O
3
2
O
3
2
2
O
3
6
O
2
O
3
2
O
3
2
O
3
O
2 3
Fig. 1 shows the relationship of catalytic activity of REOsand ionic radius. The formation rate of
BD per unit surface area, which is treated as an intrinsic activity of REOs, roughly increased with
decreasingionicradiusofrareearthcation from Lato Lu anddecreasedfrom Lu toSc:thehighest BD
formation rate was achieved at Lu
2
O
3
among the REOs and Sc2-xYb
x
O
3
catalysts. Over Lu
2
O
3
, Er
2
O
3
,
-1
-2
o
and Sc1.0Yb1.0
O
3
, the BD formation rate exceeded 0.6 mmol h m at 360 C. This tendencyis similar
to that observed in the dehydration of 1,4-BDO [31] and 5-amino-1-pentanol [32] to produce 3B1OL
and 1-amino-4-pentene, respectively. Ionic radius of rare earth cation is concerned with lattice
parameter of the REO crystal structure, which vitally influenced the efficient adsorption. In the
previous study, we have proposed a three-fold adsorption structure model as an active center in the
dehydration of 3B1OL [30]. Thus, the sufficient combination between adsorption sites and rare earth
cationwithanappropriateionicradiuscoulddeterminethecatalyticactivity.
o
In Table 1, the crystal structures of the samples calcined at 800 C are also summarized from the
previous reports. XRD profiles of the samples are presented for clarity of the structures in the
supplementaryinformation (Figs. S1 and S2) [33, 34]. Heavy REO samples with cubic structure such
as Sc
2
O
3
, Tm
2
O
3
, Yb
2
O
3
, Lu
2
O
3
, and Sc
x
Yb1-x
O
3
had high selectivity to BD. Er
2
O , which has a
3
6

mixtureofcubicandmonoclinicphases, wasalsoselectivetoBD. Incontrast, lightREOsamplessuch
as La and Nd with hexagonal structure, Sm , Eu , Gd , Dy , and Ho with
monoclinic structure, and CeO , Pr 11, and Tb with cubic fluorite structure showed relatively low
2
O
3
2
O
3
2
O
3
2
O
3
2
O
3
2
O
3
O
2 3
2
6
O
O
4 7
selectivity to BD because they produced THF and ethers as by-products. Fig. 2 plots the selectivity to
each product with conversion for the results of Table 1. It is reasonable that high BD selectivity is
attained at high conversions. Apparently, the best catalysts are Sc
ScandLureagentsaremoreexpensivethanthoseofErandYb. Therefore, catalyticpropertyofEr
andYb wasexaminedinthefollowingsection.
x
Yb1-x
O
3
and Lu
2
O (Table 1) while
3
O
2 3
O
2 3
3
.2Dehydrationof3B1OLoverEr
Table 2 shows the conversion of 3B1OL and the selectivity to BD as well as the main by-
products such as2B1OL, propyleneandethersofunsaturatedalcohols inthedehydrationof3B1OL
over Er calcined at different temperatures. From the viewpoint of the conversion and the
2
O
3
andYb
2
O
3
O
2 3
selectivity to BD, the catalytic activity was maximized at a calcination temperature of 600 °C.
However, the formation rate of BD per SA moderately increased with the calcination temperature
heated up to 1000 °C, and the selectivity to propylene decreased with increasing calcination
temperature. The sum of the selectivity to BD and 2B1OL was ca. 90% irrespective of calcination
temperatureofEr
2
O
3
. Inthispointofview, thesumoftheselectivityalsoexceeded90%overLu
2
O ,
3
Yb
increasingcalcinationtemperature(Table2). Becausetheconversionof3B1OLwasalmoststableat
3-63%, theformationrateofBDsteeplyincreasedwiththeincreaseinthecalcinationtemperature.
XRDpatternsofEr andYb calcined atdifferent temperatures arepresentedin Fig. S3
and S4, respectively. The crystal phase was identified by Inorganic Crystal Structure Database
ICSD) was used for the identification of crystal structure. In Fig. S3, the XRD profile of Er
2
O
3
, Tm
2
O
3
, and Sc1.0Yb1.0
O
3
(Table 1). The SA of Er
2
O
3
decreased monotonically with
5
2
O
3
O
2 3
(
O
2 3
o
calcined at 1000 C is consistent with cubic Er
2
O
3
, ICSD-39185. TheXRDprofileofEr
2
O
3
calcined
o
o
at600 Cis consistentwith monoclinicEr
2
O
3
, ICSD-419435. Er
2 3
O
calcinedat 800 Chas amixture
7

of cubic and monoclinic structures. Thus, the monoclinic phase of Er
2
O was transformed into cubic
3
phase at 800 °C, and completely transformed at 1000 °C. In Fig. S4, the XRD profile of Yb
2 3
O
o
calcined at 800 C is consistent with cubic Yb
Yb is not found in the ICSD but the XRD profile of as-obtained Yb
monoclinic from the analogy of monoclinic Er
and monoclinic structures. The monoclinic phase of Yb
2
O
3
, ICSD-62871. The crystal data of monoclinic
is speculated to be
calcined at 600 C has a mixture of cubic
was completely transformed into cubic
withthecalcinationtemperature,
2
O
3
O
2 3
o
2
O
3
. Yb
2 3
O
O
2 3
phaseat800°C. ThetransformationofthecrystalstructureofEr
which the metastable monoclinic phase at 600 °C can be transformed into cubic bixbyite phase at
00 and 1000 °C, would be concerned with the formation rate of BD (Table 2). This could offer a
possible explanation: the increase in the catalytic activity to BD is susceptible to the crystallinity of
Er .Thus,thesurfaceofwell-crystallizedREOcouldprovidecatalyticallyactivesites.
Since the decomposition of 3B1OL to propylene is undesirable, catalyst samples calcined at
00 Cwasusedinthefurtherstudy. TableS1 inthesupplementaryinformationsummarizestheeffect
of contact time, W/F, on the conversion of 3B1OL and the selectivity to BD at 360 °C over Er and
2
O
3
8
O
2 3
o
8
O
2 3
Yb
increasing W/F. Over Er
selectivity of 92.7% at a W/F = 2.04 h. The similar tendency was observed over Yb
2
O
3
calcined at 800°C. Both the conversion of 3B1OL and the selectivity to BD increased with
, the conversion of 3B1OL was 98.0% together with the excellent BD
, and the
O
2 3
O
2 3
highest BD selectivity of 94.3% was obtained at W/F = 1.36 h. Fig. 3 shows the changes in the
o
selectivity with the 3B1OL conversion over Er
2
O
3
and Yb
2
O
3
at 360 C. The selectivity to BD
increased with the conversion of 3B1OL, while the selectivity to 2B1OL decreased. The positive
influenceofcontact timeindicates highercatalyticperformancecouldbeobtainedbyadjustingcontact
time. Therefore, in an additional test, it was found that the higher BD selectivity of 96.7% was
achieved over Yb
2
O at 99.6% conversion, a low temperature of 340°C, and W/F = 2.72 h. It is
3
supposed that 2B1OL would be an immediate in the conversion of 3B1OL to BD, which means that
the mechanism of the dehydration of 3B1OL should be more complex than that supposed in the
previous report [30]. Thus, we propose that the overall reaction routes consist of two main routes, a
direct dehydration of 3B1OLto BD and a two-step dehydration, 3B1OLis isomerized into 2B1OL at
8

first andthen2B1OLisfurtherdehydratedintoBD, whiletheevidenceisnot sufficienttodemonstrate
thehypothesisatthepresentstudy.
Table 3 presents the conversion of 3B1OL and the selectivity to BD over Yb
2
O at different
3
reaction temperatures. The selectivity to BD increased drastically from 39.9% to 73.0% with
increasing reaction temperature, while the conversion monotonically increased when reaction
temperature below 360°C but decreased at 380°C probably due to catalytic deactivation. The color of
o
o
the catalyst recovered after reaction at 360 C for 5 h was white, while it was grey at 380 C. Among
themainby-products, theselectivityto propylene increased with risingreactiontemperature. As it was
mentioned above, propylenewas formed in thedecomposition of3B1OL. Thus, thedecompositionof
3B1OL could be inhibited at a relatively low reaction temperature. The isomerization product such as
2B1OLshowed areversetendencyinselectivityincomparison totheformationofpropylene. Inother
words, high reaction temperature could enable 2B1OL absolutely converted into BD according to the
above proposed mechanism. Besides, the selectivity to the ethers produced by the intermolecular
dehydration of 3B1OL and/or 2B1OL was maintained invariably (Table 3). In addition, THF, which
o
canbeformedinthedehydrationof1,4-BDO, wasinertoverYb
2
O
3
evenat360 C.
Fig. 4 displays the changes in the catalytic activity with time on stream over Er
andW/F =0.34 h. Slight declinein theconversion andtheselectivityto BD was observed intheinitial
h of time on stream, along with the increase in the selectivity to the main by-product, 2B1OL. In
2
O
3
at 360°C
5
contrast, the selectivity to propylene maintained at a stable level with time on stream. The continuous
increase of the selectivity to 2B1OL indicates the prominent reaction route could be replaced at low
catalyticactivity, whilemoreevidenceisneeded tosupportthissuggestion.
To produce BD efficiently over the REOs, the dehydration reaction of 3B1OL was carried at
3
40 °C and a high contact time, W/F = 2.72 h. Table 4 shows the catalytic activity of heavy REOs
such as Yb and Er as well as light REOs such as Sm , Dy , and CeO using 4.0 g of
catalyst. Over Yb , 3B1OL was converted with a promising BD selectivity of 96.7% at 99.6%
conversion. The decline in activity of Er
2
O
3
2
O
3
2
O
3
2
O
3
2
O
2 3
o
2
O
3
at 360 C and W/F = 0.34 h (Fig. 4), compared to the
9

reaction at 340 °C and W/F = 2.72 h g, indicates that the activity of Er
2
O depends upon reaction
3
temperature rather than contact time. The results of Sm
not inhibit the same ability as heavy REOs (Table 4). Besides, the dehydration of 3B1OL presents an
apparent difference in the selectivity to other by-products which account highly for 38.2% over CeO
2
O
3
and Dy
2
O suggest that light REOs could
3
2
.
2
Thisphenomenon couldbeinterpretedbytheredoxpropertyofCeO . Inthedehydrationof1,4-BDO,
CeO produces several dehydrogenated products such as 2-butenal, butanal, and γ-butyrolactone at
2
o
4
00 C [24].
3
.3Dehydrationof2B1OLoverYb
2
O
3
In order to reveal the reactivity of 2B1OLinthe conversion of 3B1OLto BD over Yb
2
O , the
3
o
dehydration of 2B1OL was carried out under the conditions at 360 C with different W/F (Table 5).
The conversion of 2B1OL increased with the increasing W/F, while the increase in the selectivity to
BD was slower than that in the conversion of 3B1OL. In particular, the selectivity to propylene
maintained unchanged regardless of the variation of W/F. In the dehydration of 2B1OL, the observed
catalytic activity of Yb
2
O was considerably lower than that observed in the dehydration of 3B1OL
3
(
TableS1). Thus, thereactivityof 2B1OLis lowerthanthat of3B1OLoverYb
the reaction route of 3B1OL-2B1OL-BD could not be the only route in the formation of BD from
B1OL, and that the direct dehydration of 3B1OL to BD could also proceed. The isomerization of
B1OLto2B1OLisasidereaction,butfortunatelytheproduct2B1OLcanbeareactantofBD. Thus,
2
O
3
. This suggests that
3
3
two formation routes to BD are probable: one is the direct dehydration of 3B1OLto BD and the other
isthedehydrationof2B1OLtoBDthroughisomerizationof3B1OL.
3
.4Dehydrationof1,4-BDOoverYb
2 3
O
In our previous work of the vapor-phase catalytic dehydration of 1,4-BDO over REOs, the
o
high selectivity of 3B1OL was reported whereas BD was not produced at 350 C and a low contact
1
0

time, W/F, of 0.17 h [25]. To verify whether BD can be formed from 1,4-BDO, the dehydration of
,4-BDO was performed at a high W/F. Table 6 shows the effect of reaction temperature in the
1
o
dehydration of 1,4-BDO over Yb
2
O
3
calcined at 800 C. Both the 1,4-BDO conversion and the
o
selectivity to BD increased with increasing the temperature. At 360 C, a 1,4-BDO conversion of
100% and a BD selectivity of 96.6% were achieved. At higher temperatures, the selectivity to
propylene was increased due to the C-C bond cleavage aggravated. In contrast, the selectivity to
tetrahydrofuran(THF)decreasedwiththeincreaseintemperature. This indicatesthatthecyclizationof
1
,4-BDO to THF could be suppressed thermodynamically at high temperatures. In addition, Yb
2 3
O
o
calcined at 600 C (Table 6), which has crystal structures with a mixture of cubic and monoclinic
o
phases (Fig. S4), was less activethan that calcinedat 800 C. This suggests that surfaceof cubicphase
ofREOhastheactivesitesforthedehydration.
Fig. 5 shows the changes in the conversion of 1,4-BDO and the selectivity to each product
o
over Yb
2
O
3
at 360 C with W/F (data of Table S2). The conversion of 1,4-BDO and the selectivity to
BD increased with increasing W/F. The selectivity to 3B1OL was dramatically decreased along with
monotonical increase in the selectivity to BD. The selectivity to 2B1OL was firstly increased with
increasing the W/F, and then decreased at high W/F. The variation in the formation of 2B1OL
indicates that 2B1OL is an intermediate to produce BD. The consumption of 3B1OL and the
formation of BD infers that the formed 3B1OL was dehydrated into BD at high W/F in the
dehydrationof1,4-BDO. Thehypothesisthat 2B1OListheintermediateinthedehydrationof3B1OL
was confirmed again by the change in the selectivity to 2B1OL. The decline of THF shows that the
cyclization of 1,4-BDO can be suppressed at a high W/F (Table S2) as well as high temperatures
(Table6).
Thedehydrationof1,4-BDOwasfurtherperformedoverY
2
O withalongrunfor10h. Fig. 6
3
depicts the changes in the conversion of 1,4-BDO and the selectivity to typical products with time on
o
stream at 360 C and W/F = 2.26 h. At a time on stream of 10 h, the selectivity to BD was maintained
high value of 95.8% at 100% 1,4-BDO conversion. In contrast to the slight increase of THF, the
1
1

selectivities to 3B1OL, 2B1OL, and propylene were almost unchanged with time on stream. The
increaseintheselectivitytoTHFissupposedtobethesignalthatYb deactivatedmildlybecauseof
O
2 3
the accumulation of carbon on the catalyst surface. The color of the top layer of the catalyst bed was
turnedtograyafterthe10h-runtest. In Fig. 4, theconversionslightlydecreasedwithtimeonstream at
a short contact time of W/F = 0.34 h even in the dehydration of 3B1OL. In the dehydration of 1,4-
BDO, gradual decrease in catalytic activity for long time operation would be inevitable. In this paper,
we developed a direct production of BD from 1,4-BDO using Yb
2
O catalyst, which inhibited the
3
majorsidereactionsuchasdecompositionof3B1OLtopropylene.
3.5MechanisticaspectsoftheformationofBDfrom1,4-BDOoverREOs
In Scheme 1, there is a possibility to form BD from THF. However, THF is not an
intermediateofBDfrom1,4-BDObecauseitcannotproduceanyotherproductsoverYb
at360oC
Table 3). This stronglysuggests that BD is formed from 1,4-BDO via 3B1OL and/or2B1OL not via
O
2 3
(
THF. Fortunately, in view of BD production, the THF formation is suppressed at high temperatures.
Thetotalreactionroutesinthedehydrationof1,4-BDOcanbedescribedinScheme2.
We have previously proposed a probable reaction mechanism for the dehydration of diols
overREOs withtheaid oftheoretical calculations[35, 36]. Inthedehydrationof1,4-BDOoverREOs,
the formation of 3B1OL proceeds via acid–base concerted mechanism [36], as shown in the top of
Scheme3. OvertheREOcatalysts, anoxygenanionprovidesabasicsitewhilearareearthcationsuch
3+
3+
as Yb and Er provides anacidicsite. Theinteractions between areactivemoleculeof1,4-BDOand
REO surface are tridentate coordination including an attractive interaction between a position-2
hydrogen atom of diol and an oxygen anion on REO, and attractive interactions between each OH
group of diol and rare earth cations, together with an intramolecular repulsive interaction between the
position-1 carbon atom and the oxygen atom of OH group. After the adsorption, the position-2
hydrogen atom is firstly abstracted by a basic oxygen anion and that the position-1 hydroxyl group is
subsequently abstracted by an acidic rare earth cation. Another OH group on position 4 plays an
1
2

important role of anchoring the diol to the REO surface. At a high 1,4-BDO conversion, 3B1OL can
be adsorbed on the sites because the concentration of strongly adsorptive 1,4-BDO decreases. In the
analogy of the dehydration of 1,4-BDO, it is speculated that an intermediate 3B1OL at high partial
pressures interacts with acid-base pair sites: an oxygen of OH group of 3B1OL interacts with an acid
site as an anchor and a hydrogen on the position 2 is abstracted by a basic site, as proposed in the
bottom of Scheme 3. If the OH group was to be abstracted by an acidic site to form butenyl cation,
propylenecouldbeformed, ashavebeenreportedoversilica-aluminaandalumina[30].
4
. Conclusions
Vapor-phase dehydration of 3B1OL to produce BD was investigated over REOs. In the
dehydration of 3B1OL, BD was produced along with major by-products such as 2B1OL, propylene,
and ethers. Among REOs, heavy REOs such as Lu , Yb , and Er showed high catalytic
performance with high BD formation rate and high BD selectivity with inhibiting the decomposition
2
O
3
2
O
3
O
2 3
to propylene, which is readily produce over acidic catalysts such as alumina. Especially, Lu
2 3
O
-1
-2
exhibited the highest performance with the BD formation rate of 0.734 mmol h m at 360°C and a
W/F of 0.34 h. Furthermore, an excellent catalytic performance with 99.6% conversion and a BD
selectivityof96.7%wasobtainedoverYb
2
O at340°C andaW/Fof2.72h. 2B1OLwasalsoformed
3
viaisomerizationofC=C doublebondof3B1OL, while2B1OLwas fortunatelydehydratedtoBD. A
hypothesis of two exchangeable reaction routes were proposed as a possible mechanism of the
dehydration of 3B1OL over REOs: one is direct dehydration of 3B1OL to BD and the other is a
combination of isomerization of 3B1OL to 2B1OL followed by the dehydration of 2B1OL to BD.
Because of the higher reactivity of 3B1OL than 2B1OL, the former would be the preferential route to
BDinthedehydrationof3B1OLoverYb
Vapor-phase dehydration of 1,4-BDO to produce BD was also investigated over Yb
successfully developed the direct BD production from 1,4-BDO with a yield of 96.6% over Yb
2
O
3
.
2
O
3
. We
at
, 3B1OL primarily formed as an intermediate was
2 3
O
o
3
60 C and a W/F of 2.26 h. Over Yb
O
2 3
1
3

dehydratedtoBDinhibitingthedecompositionof3B1OLtopropylene.
1
4

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[
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8
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1
6

Table1Dehydrationof3-buten-1-oloversREOsandSc2-xYb
x
O
3
at360°C a.
Selectivity(%)c, d
Conv.
Formation rate of
BD
Ionicradiusb
nm)
S.A. b
c
Catalyst
Sc
2
-1
-1 -2
(
(m g ) (%)
BD
Propylene 2B1OL
Ethers
11.6
3.8
(mmolh m )
2
O
3
0.0745(C)
0.0776(C)e
0.0807(C)e
0.0837(C)e
0.0861(C)
0.0868(C)
0.0880(C)
29.0
53.0
35.9
26.2
27.8
28.8
27.0
41.5
53.2
73.8
55.7
75.9
66.6
56.0
53.8
45.8
21.3
35.9
25.5
41.4
30.7
42.2
55.1
30.4
19.5
53.0
68.0
72.5
62.1
67.5
56.9
56.9
55.7
44.7
30.9
51.0
32.2
49.9
47.5
50.5
34.7
49.4
13.4
53.7
6.0
4.3
3.4
2.5
2.7
2.6
2.8
3.4
5.6
7.0
4.2
6.3
4.7
4.7
4.4
4.1
7.9
18.9
6.2
20.8
18.9
18.1
26.5
24.7
34.1
33.4
34.6
38.2
43.2
32.6
41.9
35.9
34.6
35.0
22.8
27.8
14.7
23.4
0.302
0.272
0.594
0.526
0.734
0.524
0.470
0.608
0.279
0.111
0.381
0.185
0.400
0.294
0.419
0.142
0.328
0.046
0.416
Sc1.5Yb0.5
Sc1.0Yb1.0
Sc0.5Yb1.5
O
3
O
3
2.3
O
3
2.6
Lu
Yb
Tm
Er
2
O
3
2.6
2
O
3
3.1
2
O
3
3.3
2
O
3
0.0890(C+M) 19.7
0.0900(C+M) 29.3
3.1
Y
2
O
3
5.8
Ho
Dy
Tb
Gd
2
O
3
0.0901(M)
0.0912(M)
23.7
19.1
17.7
20.6
19.8
20.3
53.7
18.2
22.7
18.0
11.9
6.8
2 3
O
4
O
7
0.0923(C
F
)
13.7
5.4
2
O
3
0.0938(M)
0.0947(M)
0.0958(M)
Eu
2
O
3
8.6
Sm
2
O
3
5.4
CeO
Nd
Pr
La
2
0.0970(C
0.0983(H)
0.0990(C
0.1032(H)
Calcinationtemperature,800°C;N
F
)
11.2
8.2
2
O
3
6
O
11
F
)
38.3
9.0
2
O
3
35.0
3
a
-1
-1
2
flowrate,30cm min ;catalystweight,0.5g; feedrateof3-buten-1-ol,1.47gh ;W/F=0.34h.
bCitedfromRef.[33],crystalphaseinparenthesis:H,A-typehexagonal;M,B-typemonoclinic;C,C-typecubicbixbyite;C
F
,cubicfluorite.
c
Conversionandselectivityareaveragedattimeofstreambetween1and5h.
BD,1,3-butadiene;2B1OL,2-buten-1olincludescisandtransisomers;Ethersrepresentthelinerunsaturatedetherswithachemicalformula
d
8
ofC H14O.
e
CitedfromRef.[31],
Table2Dehydrationof3-buten-1-oloverEr
2
O
3
atdifferentcalcinationtemperaturea.
Selectivity(%)b
Formation rate of
BD
(mmolh m )
Calcination
SA
Conv.b
2
-1
BDc
57.0
59.9
55.7
51.9
2B1OLd Propylene
Etherse Othersf
-1 -2
Temp.(°C) (m g )
(%)
as-obtained
00
00
000
33.1
31.6
19.7
9.0
52.6
60.2
53.8
53.6
29.9
29.7
34.6
39.6
4.6
3.7
3.4
3.3
4.2
2.9
3.1
3.2
4.3
3.7
3.3
0.362
0.456
0.608
1.235
6
8
1
2.0
a
-1
Reactionconditions:reactiontemperature,360°C;catalystweight,0.5g;feedrateof3-buten-1-ol,1.47gh ;W/F=0.34h.
bConversionandselectivityareaveragedattimeofstreambetween1and5h.
c
d
BD,1,3-butadiene; 2B1OL,2-buten-1ol,includescisandtransisomers.
eEthersrepresentthelinerunsaturatedetherswithachemicalformulaofC
fOthersincludebutanal,methanol,3-buten-2-ol,CO
andunidentifiedchemicals.
8
H14O.
2
1
7

2 3
Table3Dehydrationof3-buten-1-oloverYb O
atdifferentreactiontemperaturesa.
Reaction
Conv.b
Selectivity(%)b
Temp(°C)
(%)
BD c
39.9
55.2
56.9
0
2B1OLd
Propylene
Etherse
2.5
Othersf
2.2
3
20
40
60
60 g
80
40.0
53.8
66.6
0
55.0
37.9
34.1
0
0.4
1.6
2.6
0
3
2.6
2.7
3
3.1
3.2
3
0
0
3
a
57.1
73.0
12.5
6.3
2.6
3.7
-1
Reactionconditions:calcinationtemperature,800°C; catalystweight,0.5g;feedrateof3-buten-1-ol,1.47gh ;W/F=0.34h.
bConversionandselectivityareaveragedattimeofstreambetween1and5h.
c
d
BD,1,3-butadiene, 2B1OL,2-buten-1-ol,includescisandtransisomers.
eEthersrepresentthelinerunsaturatedetherswithachemicalformulaofC
fOthersincludebutanal,methanol,3-buten-2-ol,CO
andunidentifiedchemicals.
THFwasusedasareactantinsteadof1,4-BDOataW/F=0.28h..
8
H14O.
2
g
Table4Dehydrationof3-buten-1-oloverREOsat340°C a..
Conv.b
Selectivity(%)b
BD c
Catalyst
(%)
2B1OLd
0.7
Propylene
0.8
Ethere
0.1
Othersf
1.7
Yb
Er
Dy
Sm
CeO
2
O
3
99.6
81.2
76.7
60.4
81.0
96.7
2
O
3
73.1
19.9
22.3
31.2
8.9
1.3
1.3
1.7
2
O
3
69.7
1.7
1.5
4.8
2
O
3
59.7
1.7
2.3
5.1
2
43.9
2.1
6.9
38.2
a
-1
Reactionconditions:catalystweight,4.0g;feedrateof3-buten-1-ol,1.47gh ;W/F=2.72h.
bConversionandselectivityareaveragedattimeofstreambetween1and5h.
c
d
BD,1,3-butadiene; 2B1OL,2-buten-1ol,includescisandtransisomers.
eEthersrepresentthelinerunsaturatedetherswithachemicalformulaofC
fOthersincludebutanal,methanol,3-buten-2-ol,CO
andunidentifiedchemicals.
8
H14O.
2
1
8

2 3
Table5Dehydrationof2-buten-1-oloverYb O
at360°C. a
W/F
h)
.34
.68
.36
Conv.b
Selectivity(%)b
(
(%)
BDc
76.4
80.2
83.2
Propylene
0.1
Ethersd
2.7
Otherse
20.8
0
33.5
0
66.5
0.1
2.3
17.4
1
75.9
0.1
1.0
-1
15.7
a
3
-1
Calcinationtemperature,800°C;N
2
flowrate,30cm min ; feedrateof2-buten-1-ol,1.47gh .
bConversionandselectivityareaveragedattimeofstreambetween1and5h.
c
e
d
BD,1,3-butadiene, EthersrepresentthelinerunsaturatedetherswithachemicalformulaofC
8
H14O.
Othersinclude1-butanol,3-buten-2-ol,3-buten-1-ol,CO andunidentifiedchemicals.
2
Table6Thedehydrationof1,4-butanedioloverYb2
O
atdifferentreactiontemperaturea.
3
Reaction
Conv. b
Selectivity(%)b
BDc
3B1OLd
83.1
73.9
27.5
64.3
0
2B1OLe
7.1
13.3
20.8
13.6
0
Propylene
0.1
0.1
THFf
3.0
1.6
0.5
Othersg
Temp.(°C)
(%)
3
00
20
40
40 h
60
80
70.9
92.7
100.0
97.9
100.0
100.0
3.1
8.1
46.5
11.5
96.6
96.5
3.6
2.9
4.4
5.4
2.5
2.2
3
3
0.4
3
0.4
0.7
0.9
4.8
0.1
0.3
3
3
0
0
a
-1
Calcinationtemperature,800°C;catalystweight,4.0g;feedrateof1,4-BDO, 1.77gh ;W/F=2.26h.
bConversionandselectivityareaveragedattimeofstreambetween1and5h.
c
d
e
f
BD,1,3-butadiene, 3B1OL,3-buten-1-ol, 2B1OL,2-buten-1ol,includescisandtransisomers, THF,tetrahydrofuran.
g
h
2
Othersincludeethanol,2-pentanone,1-butanol,CO andunidentifiedchemicals.
o
Samplewascalcinedat600 C.
1
9

Figurecaptions
Fig. 1 Changes in the formation rate of BD at 360 °C with different ionic radius of rare earth cations of REO
catalysts.
3
-1
REOswerecalcinedat800 °C.Reactionconditions:N flowrate,30cm min ; W/F=0.34h.
2
Fig.2Selectivity-conversionprofileswiththeresultsofTable1.
REOs were calcined at 800 °C. Reaction conditions: temperature, 360 C; N
.34h.
o
3
-1
2
flow rate, 30 cm min ; W/F,
0
Fig.3Changesinselectivitywith3B1OLconversioninthedehydrationof3B1OLoverEr
andYb (opensymbol)underdifferentW/Fconditionsat 360 °C.
Samples were calcined at 800 °C. Reaction conditions: N flow rate, 30 cm min ; W/F varies from 0.17 to
.04h.
2
O (closedsymbol)
3
O
2 3
3
-1
2
2
Fig.4ChangesincatalyticactivityofEr
Er was calcined at 800 °C. Reaction conditions: catalyst weight, 0.5 g; feed rate of 3B1OL, 1.47 gh ; W/F
0.34h.
2
O
3
withtimeonstreaminthedehydrationof3B1OLat360°C.
-1
O
2 3
=
Fig. 5 Changes in conversion of 1,4-BDO and selectivity to BD and typical by-products with W/F in the
o
dehydrationof1,4-BDOoverYb
2
O
3
at360 C.
3
-1
-1
Yb
2
O
3
wascalcinedat800°C.Reactionconditions:N flowrate,30cm min ; feedrateof1,4-BDO, 1.77gh .
2
Fig. 6 Changes in conversion of 1,4-BDO and selectivity to each product with time on stream in the
o
dehydrationof1,4-BDOoverYb
Yb
W/F=2.26h.
2
O
3
at360 C.
-1
2
O was calcined at 800 °C. Reaction conditions: catalyst weight, 4.0 g; feed rate of 1,4-BDO, 1.77 g h ;
3
2
0

1
.8
.6
.4
.2
0
0
0
0
Lu
Sc Yb
x
2-x
Er
Yb
x=1
Sm
x=1.5
La
Gd
Dy
Tm
Y
Nd
Sc
Eu
Tb
x=0.5
Ce
Ho
Pr
0.07
0.08
0.09
0.1
0.11
Ionic radium / nm
Fig. 1 Changes in the formation rate of BD at 360 °C with different ionic radius of rare earth cations
ofREOcatalysts.
3
-1
REOswerecalcinedat800 °C.Reactionconditions:N flowrate,30cm min ; W/F=0.34h.
2
2
1

1
00
8
6
4
2
0
0
0
0
0
BD
2
B1OL
Propylene
80 100
0
20
40
60
Conversion /%
Fig. 2Selectivity-conversionprofileswiththeresultsofTable1.
Samples were calcined at 800 °C. Reaction conditions: temperature, 360 C; N
o
flow rate, 30 cm3
2
-1
min ;W/F, 0.34h.
2
2

1
00
8
6
4
2
0
0
0
0
BD
2
B1OL
Propylene
20
0
40
60
80
100
Conversion of 3B1OL / %
Fig. 3 Changes in selectivity with 3B1OL conversion in the dehydration of 3B1OL over Er
2 3
O
(
closedsymbol)andYb (opensymbol)underdifferentW/Fconditionsat360°C.
2 3
O
3
-1
Samples were calcined at 800 °C. Reaction conditions: N
2
flow rate, 30 cm min ; W/F varies from
0.17to2.04h.
2
3

100
80
60
40
20
Conv. of 3B1OL
BD
2B1OL
Propylene
0
1
2
3
4
5
Time on stream/ h
Fig. 4 Changes in catalytic activity of Er
60°C.
Er was calcined at 800 °C. Reaction conditions: catalyst weight, 0.5 g; feed rate of 3B1OL, 1.47
2
O
3
with time on stream in the dehydration of 3B1OL at
3
O
2 3
-1
gh ; W/F=0.34h.
2
4

1
00
Conv. of 1,4-BDO
8
6
4
2
0
0
0
0
BD
3
B1OL
2
2
B1OL
1
0
3
W/F / h
Fig. 5Changesinconversionof1,4-BDOandselectivitytoBDandtypicalby-productswithW/Fin
o
thedehydrationof1,4-BDOoverYb
2
O
3
at360 C.
3
-1
Yb
2
O
3
was calcined at 800 °C. Reaction conditions: N flow rate, 30 cm min ; feed rate of 1,4-
2
-1
BDO, 1.77gh .
2
5

1
00
8
6
4
2
0
0
0
0
0
2
.0
Conv. of 1,4-BDO
BD
THF
1.0
0
Propylene
3
2
B1OL
B1OL
0
2
4
6
8
10
Time on stream / h
Fig. 6 Changes in conversion of 1,4-BDO and selectivity to each product with time on stream in the
o
dehydrationof1,4-BDOoverYb
2
O
3
at360 C.
Yb
2
O was calcined at 800 °C. Reaction conditions: catalyst weight, 4.0 g; feed rate of 1,4-BDO,
3
-1
1
.77gh ;W/F=2.26h.
2
6

Scheme1Productionof1,3-butadienefrombutanediolsviaunsaturatedalcohols.
Anareasurroundedbyreddottedlinesindicatesthetargetreactionsstudiedinthiswork.
2
7

O
OH
HO
-
H O
2
-
H O
2
HO
-
H O
2
-
H O
2
HO
-
H O
2
-
H O
2
O
O
+
H
H
Scheme2Probableformationroutesof1,3-butadienefrom1,4-butanediol.
H
H
+
H O
2
OH
OH
OH
OH
A
H
OH
OH
+
H
H
A
A
A
OH
B
B
B
B
A
A
A
A
Adsorption
Dissociation
Desorption
Regeneration
H O
H
2
H
H
OH
OH
+
+
H
H
A
A
A
A
OH
B
B
B
B
A
A
A
A
Adsorption
Dissociation
Desorption
Regeneration
Scheme3Proposedreactionmechanisminthedehydrationof1,4-butanediolto1,3-butadiene.
3+
2-
AandBrepresentanacidicsitesuchasYb andabasicsitesuchasO , respectively.
2
8