Communications
preferentially absorbs and activates H to form an activated H
with a stirring speed of 500 rpm. Upon completion of the reaction,
gas in the autoclave was evacuated. The black solid was obtained
by filtration and was repeatedly washed with deionized water and
2
species. Toluene is easily adsorbed and activated at the
Ni(OH) –Co(OH) sites through electrophilic adsorption interac-
2
2
À
anhydrous ethanol until no Cl ions were detected by aqueous
tions between the p electrons of toluene and the positively
charged holes of the nickel hydroxide–cobalt hydroxide NPs.
The activated H species reacts with activated toluene through
the spillover effect of the Ni and Co sites at the interface be-
AgNO solution. Then, it was dried in a vacuum oven at 608C for
3
6
1
h. The Co loading (total Co element) of Co/Co(OH) /C was
2.4 wt%, as determined by inductively coupled plasma atomic
2
mass spectrometry (ICP-MS) by using an Agilent ICP-MS 4500-300.
[
49–53]
tween Ru and Ni(OH) –Co(OH)2
to form methyl cyclohex-
The Ru/Co/Co(OH) /C catalyst was synthesized by a galvanic re-
2
2
[
44–48]
ane. The synergy among the Ru, Ni, Co, and Ni(OH) –Co(OH)2
placement reaction
by adding Co/Co(OH) /C into a precalcu-
2
2
lated amount of an aqueous solution of RuCl (with a concentra-
sites largely enhances the catalytic performance for the tolu-
ene hydrogenation reaction. The abovementioned accurate
synergistic mechanism will be investigated in detail in our
future work by more advanced in situ techniques.
3
À3
À1
tion of 9.64ꢁ10 molL ). The solid was collected by filtration
after 6 h and was thoroughly washed with deionized water and an-
À
hydrous ethanol until no Cl ions were detected by aqueous
AgNO solution. After that, it was dried in a vacuum oven at 608C
3
In summary, we successfully designed and prepared bimetal-
for 6 h. The Co (total Co element) and Ru loadings in Ru/Co/
lic [Ru/Ni/Ni(OH) /C “Ru islands on Ni/Ni(OH) NPs” and Ru/Co/
2
2
Co(OH) /C were 9.2 and 3.7 wt%, respectively, as analyzed by ICP-
2
Co(OH) /C “Ru islands on Co/Co(OH) NPs”] and trimetallic [Ru/
MS. The Ni/Ni(OH) /C and Ru/Ni/Ni(OH) /C catalysts were obtained
2
2
2
2
NiCo/Ni(OH) –Co(OH) /C “Ru islands on NiCo/Ni(OH) –Co(OH)
2
by the same method used to prepare Co/Co(OH)
2
/C and Ru/Co/
2
2
2
2
+
2+
Co(OH) /C, only substituting Ni
for Co
ions; Ni/Ni(OH) /C:
NPs”] nanocatalysts. The Ru/NiCo/Ni(OH) –Co(OH) /C catalyst
2
2
2
2
1
2.4 wt% Ni loading (total Ni element); Ru/Ni/Ni(OH) /C: 9.3 wt%
exhibited high catalytic performance for the hydrogenation of
toluene to methyl cyclohexane, and this catalyst was much
more active than the Ru/Ni/Ni(OH) /C and Ru/Co/Co(OH) /C
2
Ni loading and 3.7 wt% Ru content. Likewise, NiCo/Ni(OH)2–
Co(OH) /C and Ru/NiCo/Ni(OH) –Co(OH) /C were synthesized by
2
2
2
2
2
2+
2+
2+
the above method, but the amount of Co +Ni ions [n-(Co
catalysts. This was mainly attributed to the unique nanostruc-
ture and the synergistic effect of the multiple catalytic sites of
2+
2+
)
/n(Ni )=1:1] added was equal to the amount of Ni ions during
2+
the preparation of Ni/Ni(OH) /C or the amount of Co ions during
2
Ru, Ni, Co, Ni(OH) , and Co(OH)2 in the Ru/NiCo/Ni(OH)2–
the preparation of Co/Co(OH) /C. NiCo/Ni(OH) –Co(OH) /C:
2
2
2
2
Co(OH) /C catalyst. This study provides a new, simple, and
6.1 wt% Co content, 6.0 wt% Ni content. Ru/NiCo/Ni(OH) –
2
2
Co(OH) /C: 4.6 wt% Co loading, 4.6 wt% Ni loading, 3.7 wt% Ru
loading. Ru/C was prepared by incipient wetness impregnation
promising strategy for the design of trimetallic nanocatalysts
with a low noble-metal content and ultrahigh catalytic activity
for many other heterogeneous hydrogenation reactions.
2
and was then thermally treated in flowing N +10% H of
2
2
À1
À1
8
0 mLmin at 3808C for 3 h with a heating rate of 28Cmin and
a Ru loading of 3.7 wt%, as quantified by ICP-MS.
Experimental Section
Reactants
Characterization
Carbon black (BLACK PEARLS 2000 LOT-1366221) was supplied by
the Cabot Corporation and was used as a catalyst support.
All other reagents, nickel(II) chloride hexahydrate (NiCl ·6H O), co-
The powder X-ray diffraction patterns of the catalysts were record-
ed with a Rigaku X-ray diffractometer equipped with a high-speed
array detection system by using CuK radiation (40 kV and 30 mA)
a
2
2
balt(II) chloride hexahydrate (CoCl ·6H O), anhydrous ethanol,
as the X-ray source. The surface chemical states and composition
of Ru, Co, or Ni were analyzed by X-ray photoelectron spectrosco-
py (XPS) with a PHI Quantum 2000 Scanning ESCA Microprobe
2
2
sodium hydroxide (NaOH), anhydrous ruthenium chloride (RuCl3),
5 wt% hydrazine hydrate solution, methyl cyclohexane, and tolu-
8
ene in analytical grade were purchased from Sinopharm Chemical
Reagent Co. Ltd. (Shanghai, China). Deionized water was used in
this work. All chemicals were used as received.
with monochromic AlK radiation (1846.6 eV) as the X-ray source.
a
Transmission electron microscopy (TEM) and high-resolution TEM
(HRTEM) images of the catalysts were obtained by using a Tecnai
F30 electron microscope with a field-emission source and an accel-
erating voltage of 300 kV. High-angle annular dark-field scanning
TEM (HAADF-STEM) imaging and energy-dispersive X-ray spectros-
copy (EDS) elemental mapping and line-scan profile analysis were
conducted with a Tecnai G2 F30 electron microscope. High-sensi-
tivity low-energy ion scattering (HS-LEIS) measurements were per-
formed with an IonTOF Qtac100 low-energy ion-scattering ana-
Catalyst synthesis
The Co/Co(OH) /C sample was synthesized at room temperature
2
[39–43]
(
RT) by the hydrazine hydrate reduction method.
Typically, an
appropriate amount of cobalt(II) chloride hexahydrate (CoCl ·6H O)
2
2
was dissolved in a mixture of anhydrous ethanol (12.5 mL) and de-
ionized water (82.5 mL), and the mixture was magnetically stirred
at RT for 30 min. An aqueous solution of NaOH (12.5 mL containing
NaOH, 1.813 g) was added to the above-obtained liquid. After
20
+
lyzer, taken with a Ne beam energy of 5 keV and a sample cur-
rent of 1.6 nA.
1
0 min, 85 wt% hydrazine hydrate solution (25 mL) was added.
Catalytic hydrogenation tests
Subsequently, carbon black (1.250 g) with a specific surface area of
2
À1
approximately 1385.3 m g was suspended in the liquid, which
was then vigorously agitated for 10 min. Then, the mixture was
quickly transferred into a stainless-steel high-pressure autoclave
In a typical reaction procedure, a mixture of toluene (20 mL) and
the catalyst (0.1000 g) was placed into a stainless-steel high-pres-
sure autoclave (Parr 4848), then the reactor was quickly installed.
(
Parr 4848). The reactor was purged with N2 for 2 min to exclude
air inside the reactor, which was followed by pressurizing to
.0 MPa N . The preparation process was maintained at RT for 18 h,
The reactor was flushed with N for 1 min to exclude air and then
H2 for 1 min. Hydrogen was continuously added into the reactor
until the initial pressure reached 4.14 MPa at RT and was then
2
1
2
&
ChemCatChem 2018, 10, 1 – 6
4
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!
Zhu, Lihua
