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0.1% 3,5-di-tert-butylcatechol) were provided by Alfa-Aesar. Tri-
ethylene glycol (99%) was provided by Sigma–Aldrich. Iron(III) ace-
tylacetonate (98%), 1,3,5-trimethylbenzene (98%), 4-chlorostyrene
(98%, stabilized with 0.1% 4-tert-butylcatechol), 4- methoxystyrene
(95%, stabilized), 2-vinylnaphthalene (98%), trans-stilbene (98%),
cyclohexene (99%), 4-methylstyrene (98+%, stab. with 0.1% 3,5-
di-tert-butylcatechol), and 1,3,5-trimethylbenzene (98%) were ob-
tained from J&K scientific Co., Ltd. Ammonium hydroxide (25%)
and tetrahydrofuran (A.R.) were provided by Beijing Chemical Re-
agent Company. MWCNTs (d=60–100 nm, L=5–15 mm) were pur-
chased from Shenzhen Nanotech Port Ltd Co, China. All chemicals
were used as received without any further purification. Water used
in all experiments was deionized.
Figure 5. Cycling performance of the PdÀFe@meso-SiO2 tubular nanoreac-
tors (green columns) and commercial Pd/C (red columns) catalyst using sty-
rene hydrogenation as a model reaction.
Characterization
similar to the fresh one (Figure S13). In addition, the TEM
image of the recovered catalyst revealed that the shape of the
tubular nanoreactor was maintained during the recycling pro-
cess (Figure S14).
The morphologies of the catalysts were characterized by high-reso-
lution transmission electron microscopy (HRTEM, JEOL 2100F). X-
ray diffraction (XRD) patterns were obtained on a Rigaku D/max-
2500 diffractometer with Cu Ka radiation (l=1.5418 ꢁ) at 40 kV
and 200 mA. The loading content of noble metals (Pd, Pt and Au)
was determined by ICP-AES (Shimadzu ICPE-9000). EDS mappings
of the materials were conducted using scanning TEM (STEM)
equipped with an EDS detector (JEOL 2100F).
The excellent catalytic activity and reusability can be as-
cribed to the following reasons: (i) the confinement effect of
the tubular nanoreactor will increase the local substrate con-
centration around Pd NPs, which will speed up the catalytic
process; (ii) with protection by the outside SiO2 shell, Pd leach-
ing could be efficiently avoided. During the recycling process,
reaction solutions of each run were analyzed by ICP-AES. The
analysis results are summarized in Table S1. ICP-AES analysis of
the filtrates showed that palladium leaching takes place at the
ppb level. This result implied that Pd leaching during the cy-
cling process was indeed negligible; and (iii) due to the mag-
netism of Fe NPs, PdÀFe@meso-SiO2 could be easily separated
from the reaction solution by using a magnet (Figure S15). This
will simplify the recovery procedure and lower the catalyst loss
during the cycling process.
Synthesis of Fe3O4-MWCNTs
In a typical procedure, 320 mg of Fe(acac)3 and 80 mg MWCNTs
were added to a 100 mL flask containing 48 mL of triethylene
glycol (TREG). After ultrasonication for 30 min, the resulting solu-
tion was rapidly heated to 1908C under argon protection, main-
tained at this temperature for 30 min, and then heated rapidly to
2788C, and held at this temperature for an additional 30 min. After
cooling to room temperature, the obtained mixture was centri-
fuged and washed five times with ethyl acetate and dried in
vacuum at room temperature for 6 h.
Synthesis of Fe3O4-MWCNTs@SiO2 composites
Conclusions
In a typical procedure, the obtained Fe3O4-MWCNTs composites
from the above-mentioned step were added to a 250 mL three-
neck round flask containing 93 mL ethanol, 11 mL water and 3.04 g
hexadecyl trimethyl ammonium bromide (CTAB). The mixture was
then sonicated for 3 min. Then 475 mL TEOS was slowly added to
the above solution and stirred for 5 min. Finally, 1 mL ammonium
hydroxide (25%) was added into the solution dropwise. After stir-
ring for 12 h, the reaction mixture was filtrated through a PTFE
membrane with 0.2 mm pore diameter. The composites were
washed with 50 mL H2O for two times and then washed with
50 mL ethanol. Finally, the obtained solid was dried in vacuo at
room temperature for 8 h.
In summary, an efficient and well-controlled method was de-
veloped to prepare magnetic tubular nanoreactors composed
of mesoporous SiO2 shells inside of which iron-noble metal
nanoparticles reside. Making use of the galvanic replacement
reaction between Fe and noble metal ions, all noble metal
nanoparticles were loaded inside the mesoporous SiO2 shell,
which is very difficult to obtain through the traditional impreg-
nation method. In addition, the loading amount of noble
metal nanoparticles can be easily tuned. Taking Pd-Fe@meso-
SiO2 tubular nanoreactor as an example, it exhibited a high
catalytic activity and excellent reusability for styrene hydroge-
nation under mild conditions. We anticipate that this synthesis
route for a nanoreactor will find promising applications.
Synthesis of Fe@meso-SiO2 composites
Firstly, the above obtained Fe3O4-MWCNTs@SiO2 product was cal-
cined at 5508C with heating rate of 28CminÀ1 for 1 h in a tubular
furnace under argon atmosphere. The argon flow was changed to
air atmosphere for 4.0 h to remove MWCNTs and CTAB template,
then the air flow was changed to argon atmosphere for 0.5 h to
exclude air in the tubular furnace. Finally, pure H2 was introduced
to reduce g-Fe2O3 to metallic Fe at 5508C for 12 h. After cooling to
room temperature, a black powder was obtained. (Attention!
Before changing the atmosphere from air to H2, argon flushing for
Experimental Section
Materials
Styrene (extra pure) was provided by Acros. Pd/C (5 wt%), tetrae-
thoxysilane (TEOS, 99.9%), K2PtCl4 (99.9%, metals basis), HAuCl4
(99.999%, metals basis) and 4-methylstyrene (98+%, stab. with
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