Etherification of n-Butanol to Di-n-Butyl Ether Over Keggin-, Wells-Dawson-, and Preyssler-Type HPA Catalysts
Kim et al.
In this work, Keggin- (H3PW12O40), Wells-Dawson-
(H6P2W18O62), and Preyssler-type (H14[NaP5W30O110])
HPA catalysts with various structures were examined. Acid
properties of HPA catalysts were determined by NH3-
TPD (temperature-programmed desorption) measurements
in order to elucidate the effect of structural sensitivity on
the acid properties. Etherification of n-butanol to di-n-
butyl ether was carried out over various structural classes
of HPA catalysts. Correlations between acid strength and
catalytic performance were then established.
(10 ml/min). The desorbed ammonia was detected using a
gas chromatograph-mass (GC-MS) spectrometer (Agilent,
MSD-6890 N GC).
2.3. Etherification of n-Butanol to Di-n-Butyl Ether
Etherification of n-butanol to di-n-butyl ether was carried
out over various structural classes of HPA catalysts in a
stainless steel autoclave reactor (200 ml). 1 g of each HPA
catalyst and a mixture of n-butanol (80 ml) and toluene
(20 ml, reaction medium) were charged into the reactor
at room temperature. The reactor was purged with nitro-
gen several times inꢀorder to remove air. The reactor was
then heated to 200 C. The reaction was carried out for
3 h at nitrogen pressure of 30 bar. After the reaction, the
reaction products were sampled and analyzed using a gas
chromatograph (Younglin, YL6100 GC) equipped with a
capillary column (Agilent, DB-5MS, 60 m × 0ꢁ32 mm).
Conversion of n-butanol and selectivity for di-n-butyl
ether were calculated according to the following equations.
Yield for di-n-butyl ether was calculated by multiplying
conversion of n-butanol and selectivity for di-n-butyl ether.
2. EXPERIMENTAL DETAILS
2.1. Catalyst Preparation
Commercially available H3PW12O40 catalyst was obtained
from Sigma-Aldrich. H6P2W18O62 and H14[NaP5W30O110
]
catalysts were prepared according to the methods in the
literatures20ꢀ21 using Na2WO4 ·2H2O (Junsei Chem.), KCl
(Junsei Chem.), hydrochloric acid (Sigma-Aldrich), acetic
acid (Junsei Chem.), sulfuric acid (Samchun Chem.), and
diethyl ether (Samchun Chem.). In order to convert as-
prepared potassium salt into acid form, K6P2W18O62 and
K14[NaP5W30O110] were treated with sulfuric acid, and
subsequently, they were extracted with diethyl ether (ether-
ate method). H6P2W18O62 and H14[NaP5W30O110] were
finally obtained after drying and recrystallization.
Conversion of n-butanol (%)
mole of n-butanol reacted
=
×100 (1)
×100 (2)
mole of n-butanol in the feed
Delivered by Publishing Technology to: York University Libraries
Selectivity for di-n-butyl ether (%)
IP: 69.168.47.28 On: Sun, 29 Nov 2015 03:02:47
2×mole of di-n-butyl ether formed
2.2. Catalyst Characterization
Copyright: American Scientific Publishers
=
mole of n-butanol reacted
Successful formation of heteropolyanion framework was
confirmed by fourier transform-infrared spectroscopy
(FT-IR) measurements using a Nicolet 6700 spectrometer.
Chemical compositions of constituent elements in the HPA
catalysts were determined by inductively coupled plasma-
atomic emission spectrometry (ICP-AES) analyses using
an ICP-1000IV instrument (Shimadzu). 31P nucler mag-
netic resonance (NMR) measurements (Bruker, AVANCE
600 spectrometer) were conducted using D2O and H3PO4
as a solvent and as an external reference, respectively. All
3. RESULTS AND DISCUSSION
3.1. Characterization of HPA Catalysts
Figure 1 shows the molecular structures of Keggin-
([PW12O40]3−), Wells-Dawson- ([P2W18O62]6−), and
Preyssler-type ([NaP5W30O110]
14−) heteropolyanions. The
[PW12O40]3− heteropolyanion (Fig. 1(a)) consists of a cen-
tral PO4 tetrahedron sharing corners with twelve WO6 octa-
hedra, resulting in a soccer ball-shaped [PW12O40]3− 20ꢀ22
.
ꢀ
the HPA catalysts were thermally treated at 200 C in a
stream of nitrogen prior to characterization and catalytic
reaction.
The [P2W18O62]6− heteropolyanion (Fig. 1(b)) consists of
two defected Keggin fragments ([PW9O34]9−) which are
linked by six nearly linear W
O
.
W bonds, resulting in a
Acid properties of HPA catalysts were determined by
ammonia temperature-programmed desorption (NH3-TPD)
measurements. Each catalyst (200 mg) was charged into
a tubular quartz reactor of the conventional TPD appara-
14−
The [NaP5W30O110]
rugby ball-shaped [P2W18O62]6− 20
heteropolyanion (Fig. 1(c)) comprises five PW6O322− units.
Each PW6O32−2 unit is structurally related to Keggin anion
formed by the removal of two sets of three corner-shard
WO6 octahedra from [PW12O40]3−. Five PW6O232− units
are joined together in a pie-wedge fashion by corner-
ꢀ
tus. The HPA catalyst was preheated at 200 C for 1 h
under flow of He (20 ml/min) to remove any physisorbed
organic molecules. Ammonia (20 ml/min) was then pulsed
into the reactor every minute at room temperature under a
flow of He (5 ml/min), until the acid sites were saturated
with ammonia. The physisorbed ammoniꢀa was removed
by evacuating the catalyst sample at 100 C for 1 h. The
furnace temperature was increased from room temperature
to 800 ꢀC at a heating rate of 5 ꢀC/min under a flow of He
sharing of WO6 octahedra, resulting in an oblate spheroid
14− 21
[NaP5W30O110
]
.
Successful formation of HPA catalysts was confirmed
by FT-IR analyses. Figure 2 shows the FT-IR spectra
of HPA catalysts. Formation of heteropolyanions can be
identified by four characteristic IR bands in the range of
8122
J. Nanosci. Nanotechnol. 13, 8121–8126, 2013