Q. Zhao, et al.
AppliedCatalysisA,General594(2020)117470
AIL onto various supports is the foremost strategy to solve these pro-
blems [27], for example, metal oxide [28], activated carbon [29], silica
gel [30] and molecular sieve [31] et al. The mesoporous molecular
sieves (MCM-41, SBA-15) are the best choice as the carrier due to their
advantages like single pore size distribution, highly ordered pore
channels, and large specific surface area et al. Among the mesoporous
molecular sieves, SBA-15 was applied widely as carrier, because its
specific surface areas (600−1000 m2 g−1) and tunable pore diameters
(5−30 nm) are significantly larger than other mesoporous matrials.
Besides, it has better hydrothermal stability than MCM-41 owing to its
thicker walls (3−6 nm) [32,33]. However, pure siliceous SBA-15 ma-
terials have low catalytic activities, thus, active sites are usually pro-
vided by introducing metals (Fe, Sn, Zn, Cu) or other active component
like heteropoly acid, IL, and so on. into the mesoporous SBA-15
[34–36]. So, the composite of modified SBA-15 with BLAIL is easily
separated from reaction system, in the other hand, it can exhibit higher
[MIMPS]+HSO4 with zinc oxide in different proportions to produce
the novel BLAILs [40]. The synthesis of [MIMPS]+HSO4- were carried
out by a known procedure outlined in the literature [14], and the de-
tailed procedure is as follows: 1,3-propane sultone (0.1 mol) was dis-
persed in toluene uniformly at room temperature, then equimolar
amounts of N-methyl imidazole was added drop wise and reflux for 3 h
at 50℃, a white precipitate was obtained after the reaction mixture was
filtered. After that, the obtained white powdery solid was washed with
diethyl ether three times and dried under vacuum at 80℃for 6 h, the
yielded zwitterion donated as [MIMPS]. Next, equimolar concentrated
sulfuric acid was mixed with the obtained precursor [MIMPS], the
mixture was refluxed for 2 h under stirring at 90 ℃, then washed with
diethyl ether, dried in vacuum at 60 ℃ to give Brӧnsted ionic liquid
[MIMPS]+HSO4-.
−
Varied amounts of ZnO was added to the solution of 0.1 mol
[MIMPS]+HSO4 under stirring continuously, the mixture reacts for
−
catalytic activity [37,38].
some time to ensure the solid was completely dissolved. Then the col-
orless and transparent BLAIL with different L/B ratios were produced
after dried under vacuum (100℃) for 12 h, namely [MIMPS]+(1/
−
In this paper, we combined Brønsted acidic IL [PSMIM][HSO4
]
and ZnO in different molar ratios, obtained a series of novel halogen-
free BLAIL. At the same time, the SBA-15 modified by titanium was also
prepared and used as carrier. Immobilized these BLAIL onto the Ti-SBA-
15 to obtained the catalysts. The catalytic performances of catalysts
were investigated in the esterification of acetic acid with BnOH.
Moreover, the effects of reaction time, reaction temperature, catalyst
dosage, recycle of catalyst were further studied. The results showed the
resulting catalysts exhibited excellent performance.
2H+·1/4Zn2+)SO4
,
[MIMPS]+(1/2Zn2+)SO4
,
[(1/2H+·1/4Zn2+
)
re-
2-
2-
MIMPS]+(1/2Zn2+)SO4
,
[(1/2Zn2+)MIMPS]+(1/2Zn2+)SO4
,
2-
2-
spectively, denoted as ILa, ILb, ILc, ILd, as shown in Table 1. The
synthesis process of ILb was displayed in Scheme 1.
2.4. Synthesis of X-[MIMPS]+(1/2Zn2+)SO42−/Ti-SBA-15catalyst
Supported ionic liquid catalysts were prepared by physical adsorp-
2. Experimental
2−
tion of ionic liquid [MIMPS]+(1/2Zn2+)SO4
onto the surface of Ti-
SBA-15, as shown in Scheme 2. In a typical process, Firstly, different
2.1. Materials
2−
amounts of [MIMPS]+(1/2Zn2+)SO4
(1.2 g, 1.5 g, 1.8 g) were dis-
solved in 30 ml methanol and stirring at room temperature to be a
uniform solution. Then, 1.0 g of Ti-SBA-15 support was added to the
solution, and the resulting mixture was refluxed for 24 h at 50 ℃.The
solid catalysts were collected by filtered and washed several times with
diethyl ether, and vacuum-dried at 60 ℃ for 12 h, denoted as 1.2-ILb/Ti-
SBA-15, 1.5-ILb/ Ti-SBA-15 and 1.8-ILb/Ti-SBA-15.
The carrier Ti-SBA-15 material were synthesized using poly (ethy-
lene glycol)-block-poly (propylene glycol)-block-poly (ethylene glycol)
(Pluronic P123) as the structure-directing agent and tetraethyl ortho-
silicate (TEOS 98 %, Aldrich) as silicon source, titanium tetrabutoxide
(TBT 97 %, Aldrich) was used as a titanium precursor, all these reagents
were purchased from Shanghai Chemical Reagent Co., Ltd. Zinc oxide
were purchased from Sigma-Aldrich. Acetylacetone (98 %), hydro-
chloric acid (37 %), 1-methylimidazole (> 99 %), methyl alcohol
(> 99 %), 1,3-propane sulfone, sulfuric acid (98 %), anhydrous ether
(98 %), acetic acid (98 %) and benzyl alcohol (98 %), used in the ex-
periment were of analytical grade and obtained from Kermel Reagent
Co., Ltd.
2.5. Characterization
Catalyst total surface area (SBET) and pore structure was calculated
based on a multipoint BET method and BJH method, respectively. The
catalyst samples were degassed at 200 ℃ and 10−3 Torr for 3 h before
SBET analysis. Adsorption-desorption data were acquired using UHP N2
at -196 ℃ in a Micromeritics ASAP 2020 device. Catalyst thermal sta-
bility were determined by thermogravimetric analysis (TG) using a
Rigaku TG Plus 8102 instrument at a heating rate of 10 ℃· min-1 under
a nitrogen flow. The functional groups of samples were recorded on a
Nexus FT-IR 470 spectrometer over the 4000−400 cm-1 region using
KBr as the reference. Power X-ray diffraction (XRD) patterns were re-
corded with a Rigaku D/MAX 2500PC instrument using Cu Kα radiation
(50 kV, 200 mA) with 0.02° step size and 2 s time over the range 0.5°-5°
(2θ). Transmission electron microscopy (TEM) micrographs were taken
using a Philips Tecnai G2F20 microscope operating at 200.0 kV.
Samples were suspended in ethanol and deposited straight away on a
copper grid prior to analysis. The 1H NMR spectrum of IL was carried
2.2. Synthesis of Ti-SBA-15
The carrier Ti-SBA-15 were prepared by co-condensation method
following previously reported procedures in which Pluronic P123 was
used as a template, the TEOS and TBT were used as silicon and titanium
sources, respectively [39]. The typical synthetic procedure of Ti-SBA-15
was as follows: 2.0 g of P123 was dissolved in a mixture of 15 ml of
distilled water and 60 ml of 2 mol/L HCl aqueous solution. Then, 4.2 g
of TEOS was added in above solution dropwise, meanwhile, premixed
solution of titanium tetrabutoxide (TBT) and acetylacetone was rapidly
added to initial homogeneous solution in a certain proportion(nTBT
/
n
acetylacetone = 5:3), the resulting mixture was stirred for 24 h at 40℃
and white precipitate was generated. Subsequently hydrothermally
treated at 100℃for another 24 h in a static condition to ensure further
framework condensation. The yielded white solid products were re-
covered by filtration and washed with distilled water, dried at 70℃ for
whole night. Finally, the mesoporous Ti-SBA-15 were obtained after the
sample was calcined at 550℃ for 6 h in air (heating rate 2℃·min−1).
Table 1
Various acidic ionic liquid with different L/Ba.
Name
Formula
2−
ILa
ILb
ILc
ILd
[MIMPS]+(1/2H+·1/4Zn2+)SO4
1:3
2:2
3:1
4:0
2−
[MIMPS]+(1/2Zn2+)SO4
[(1/2H+·1/4Zn2+)MIMPS]+(1/2Zn2+)SO4
2−
2.3. Synthesis of Brӧnsted -Lewis acid ionic liquid
[(1/2Zn2+)MIMPS]+(1/2Zn2+)SO4
2−
a
By combining sulfonic acid-functionalized acidic ionic liquid
Molar ratio of Lewis to Brӧnsted acid sites.
2