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RSC Advances
materials and mesoporous molecular sieves.19–21 Mesoporous dried under vacuum at 50 C for 4 h, giving 7.5%MF@MN (M
materials are the ideal carrier materials due to the advantages of stands for tetramethoxy-silane (TMOS), F stands for TFPS and N
uniform and adjustable pore structure, large specic surface stands for APTS). Mesoporous silica with different content of
area and an amount of silicon hydroxyl on the surface of mes- uorine were synthesized according to the above procedures and
oporous materials. Qiu et al. reported that Ni nanoparticles denoted as 0%MF@MN, 2.5%MF@MN and 12.5%MF@MN,
supported on MCM-41 were used to catalyze the hydrogenation respectively. Moreover, the mesoporous silica without modica-
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of guaiacol at 150 C and the conversion was 97.9%.22 Cobalt tion (SiO2) and that only modied with hydrophobic TFPS
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carbonyl cluster anchored on functionalized SBA-15 showed (MF@M) were prepared, respectively.
promising catalytic activity on hydroformylation of 1-octene
(97.0% conversion) with excellent selectivity towards hydro-
formylated product (90.0%).23 However, these mesoporous
materials could not disperse into the organic-aqueous biphase
system due to their inherent hydrophilicity in the process of
hydrogenation, which made the reaction conditions very harsh.
Micelles are characteristic of the core–shell structure owing
to the coexistence of the polar headgroup and the hydrophobic
tail. Hydrophilic shell makes micelles evenly dispersed in water
while hydrophobic core can solubilize organic substrate.
Inspired by the structure of micelles, Yang et al. synthesized
amphiphilic mesoporous silica with “micelle-like” structure
through the introduction of hydrophilic and hydrophobic
functional groups into mesoporous silica. 99.0% phenol
conversion was achieved and the selectivity for cyclohexanone
was close to 99.0%.24–26 For our work, Ru nanocatalysts loaded
on amphiphilic mesoporous silica were successfully synthe-
sized, and applied in the hydrogenation of a-pinene in aqueous
medium, exhibiting superior activity and selectivity.
2.3 Preparation of nanocatalyst
Ruthenium nanoparticles were embedded in the amphiphilic
mesoporous silica by impregnation method. 0.03 g RuCl3$3H2O
as metal precursor and 0.20 g 7.5%MF@MN were added into
4 mL ethylacetate and dispersed for 30 minutes under ultra-
sonic. The mixture was dipped for 12 h under magnetic stirring
at 40 ꢀC. Ethylacetate was removed by centrifugation and
another 4 mL fresh ethylacetate was added. Then, 0.04 g NaBH4
was slowly added into the above mixture under vigorous stir-
ring. Aer 2 h, the excessive NaBH4 was removed by ethanol and
the black precipitate was collected and dried under vacuum at
50 ꢀC for 4 h, giving Ru/MF@MN. Catalysts denoted as Ru/MN,
Ru/SiO2, Ru/MF@M were synthesized when the carrier was
correspondingly replaced by 0%MF@MN, SiO2 and MF@M
(mentioned in Section 2.2), respectively.
2.4 Selective hydrogenation of a-pinene in water medium
0.30 g a-pinene, 5 mg Ru/MF@MN and 1 mL H2O were added
into a 75 mL autoclave equipped with a Teon liner. The
autoclave pressurized with 2 MPa H2 was placed into a 35 C
water bath under stirring for 1 h. Aer centrifugation, the upper
product phase was collected with a pipette for gas chromatog-
raphy (GC) analysis.
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2. Experimental section
2.1 Materials
Hexadecyltrimethylammonium chloride (CTAC), TMOS, TFPS,
APTS, methanol and sodium hydroxide (NaOH) were used in the
synthesis of amphiphilic mesoporous silica, and purchased from
the Aladdin Industrial Corporation. The metal precursor RuCl3-
$3H2O were obtained from the Aladdin Industrial Corporation.
Sodium borohydride (NaBH4, 98%), ethanol and ethylacetate were
supplied by Sinopharm Chemical Reagent Co., Ltd. Hydrogen
(99.99 wt%) was obtained from Qingdao Airichem Specialty Gases
& Chemicals Co., Ltd. a-Pinene (98%) was purchased from Jiangxi
Hessence Chemicals Co., Ltd. All chemicals were not puried and
used directly. Water was double deionized for use.
2.5 Characterizations
The morphology of amphiphilic mesoporous silica was deter-
mined with a JEOL JSM-6010LV scanning electron microscope and
a JEOL JEM-2100 transmission electron microscope. FT-IR spectra
were obtained using a Nicolet 510P FT-IR spectrometer with the
KBr method (frequency range from 4000 to 400 cmꢁ1). XRD
measurements were performed on a Rigaku D/max-2400 diffrac-
tometer when Cu-Ka anode radiation was used as the X-ray source
at 40 kV and 100 mA in the 2q range of 0–80ꢀ with a scan speed of
2ꢀ per minute. The porous structure of the catalysts was measured
by a Micromeritics ASAP 2020 N2 adsorption–desorption isotherm
at 77 K. The content of Ru was determined by using ICP-AES
method which was running at 1200 W. Before the analysis, Ru/
MF@MN catalyst was dissolved in a mixture of hydrouoric acid
and aqua regia. The XPS data were recorded by using mono Al Ka
as X-ray source and the hydrocarbon peak of C 1s at 284.60 eV was
used to calibrate binding energies.
2.2 Preparation of functionalized core–shell mesoporous
silica
Amphiphilic mesoporous silica was prepared by one-step
synthesis. Typically, 0.88 g CTAC, 125 mL methanol and 625 mL
NaOH (1 mol Lꢁ1) were mixed with 100 mL water and vigorously
stirred at room temperature for 2 h. 0.17 g TMOS and 0.05 g TFPS
were added into the above mixture drop by drop and stirred for
2 h. Then 0.19 g TMOS and 0.02 g APTS were dropwise added into
the above solution. Aer that, the solution was further stirred for
12 h and crystallized for 12 h. The white solid was obtained by
ltration and washed to be neutral with water. Then it was dried
3. Results and discussion
3.1 Synthesis and characterization of mesoporous silica
under vacuum at 50 ꢀC for 4 h. The solid powder was washed with The water contact angles of four kinds of mesoporous silica
ethanol 3 cycles (12 h per cycle) to remove excessive CTAC, and were shown in Fig. 1. Interestingly, water contact angles
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RSC Adv., 2017, 7, 51452–51459 | 51453