RSC Advances
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conductivity, low price and high oxidation/acid corrosion
resistance behavior.14–16 Control-experiments and characteriza-
tion results indicate that a synergistic effect between the CuPt
alloy and Cu2O contributes to the activity and stability.
Characterization of the catalyst
X-ray diffraction patterns (XRD) of the catalysts were obtained
on a Bruker D8 diffractometer with Cu-Ka radiation. Trans-
mission electron microscopy (TEM) was performed on a JEOL
2100 F instrument operating at 30 kV. Inductively-coupled
plasma atomic emission spectroscopy (ICP-AES) measure-
ments were performed on a Thermo Scientic iCAP 6300
instrument. X-ray photoelectron spectroscopy (XPS) experi-
ments were performed on a PHI-5500 spectrometer with Al Ka
X-ray radiation as the X-ray source for excitation. Thermal
gravimetric analysis (TGA) experiments were performed on
Shimadzu TGA-50 equipment. H2 temperature programmed
reduction (TPR) of the catalysts was performed on a Xianquan
TP-5800 instrument.
Experimental
Materials
SiC powder (200–300 mesh with a surface area of 0.15 m2 gꢀ1),
H2PtCl6$6H2O and Cu(NO3)2$3H2O were purchased from Sino-
pharm Chemical Reagent Co. Ltd without further treatment.
Other substrates, such as 1-phenylethanol and 2-phenylethanol,
were supplied by Aladdin Reagent Co. Ltd.
Results and discussion
Preparation of the catalysts
Characterization of fresh catalysts
All catalysts were prepared using a simple impregnation and
calcination method. If not specically pointed out, the metal
weight is 10%.
The characterization results of the fresh catalysts are illustrated
in Fig. 1. For Cu/SiC fresh and CuPt–Cu2O-7/SiC fresh, the
characteristic peaks of CuO (2q ¼ 38.7ꢁ) are found in the XRD
patterns (Fig. 1A). The Cu 2p spectra show that peaks at 934.4 eV
and 934.5 eV are assigned to CuO species (Fig. 1B).7,10 The Pt 4f
spectrum indicates that the transformation of H2PtCl6 to metal
Pt0 has occurred in the calcination process for CuPt–Cu2O-7/SiC
fresh (Fig. 1C) and the corresponding diffraction peaks of Pt are
not found in the XRD pattern due to its low content (Fig. 1A).17
The XRD results indicate that the characteristic peaks of Pt0
(2q ¼ 39.6ꢁ and 46.4ꢁ) are clearly observed in the Pt/SiC fresh
catalyst (Fig. 1A). TEM indicates that the particle size of Cu/SiC
fresh is 6 nm and the particles are distributed randomly on the
support (Fig. S1A in ESI†).
The CuPt–Cu2O-7/SiC catalyst (metal loading of 10% and
Cu : Pt molar ratio of 7 : 1) was prepared by impregnation of 1 g
SiC powder, 266 mg Cu(NO3)2$3H2O, 80 mg H2PtCl6$6H2O and
10 mL H2O, followed by drying at 100 ꢁC for 10 h and calcination
at 300 ꢁC in air for 1 h, and is denoted as CuPt–Cu2O-7/SiC
fresh. Additionally, other catalysts such as CuPt–Cu2O-x
(x indicates the molecular ratio of Cu : Pt), Cu/SiC and Pt/SiC
were prepared following the same procedure, by simply
tuning the amount of H2PtCl6$6H2O and copper salts in the
corresponding solutions. CuO/SiC was prepared by impregna-
tion of 1 g SiC powder and 400 mg Cu(NO3)2$3H2O, followed by
drying at 100 ꢁC for 10 h and calcination at 500 ꢁC in air for 5 h.
Catalytic activity
Catalytic tests
The catalytic activity of pure SiC powder (200–300 mesh) with
The gas-phase selective oxidation process was carried out on excellent heat conductivity and corrosion resistance is rather
a xed-bed reactor (inner diameter 10 mm) under atmospheric low (Table 1, entry 1), which is similar to a Ti support.7 With an
pressure.7 The amount of catalyst used in each experiment was increase in the Cu loading from 5% to 10%, the conversion of
0.3 g (200–300 mesh). Alcohols were fed continuously by benzyl alcohol increases from 65% to 85% (Table 1, entries 2
a peristaltic pump, in parallel with the addition of O2 (oxidant) and 3). Given the excellent catalytic activity of Cu/SiC with 10%
and N2 (diluted gas) using calibrated mass ow controllers, into metal loading, we further investigated its stability. The
the reactor, which was heated to the desired reaction tempera- conversion of benzyl alcohol decreases aer just 6 hours (Fig. 2),
ture. The WHSV of alcohol was set to 20 hꢀ1 and the molecular which is in accordance with our previous report.7 When the
ratio of alcohol : O2 : N2 was 1 : 0.6 : 2.4. The products were metal loading is 10 wt% with a Cu : Pt molecular ratio of 1 : 1,
analyzed by Gas Chromatography (SP-7820 with TCD detector) the conversion of benzyl alcohol is 7% and the selectivity of
and GC-MS (Agilent 6890 equipped with a HP-5 column). The benzyl aldehyde is 99%. The conversion of benzyl alcohol
content of negligible benzoic acid, toluene and COx was 0.8%, increases to 93% when the molar ratio increases to 7 : 1
0.2% and 0.3% respectively, so the selectivity of benzylaldehyde (Table 1, entries 4–7).
in our reaction conditions was higher than 98% and the carbon
balance in the liquid phase was 99%.
The catalytic activity of CuPt–Cu2O-9/SiC decreases aer just
a 6 h run, though the initial activity is excellent compared with
In order to prevent the oxidation of our catalyst aer the the aforementioned catalysts (Table 1, entry 8), while the cata-
reaction, the used catalysts were collected aer they had totally lytic activity of Pt/SiC is rather low (Table 1, entry 9), so our
cooled down to room temperature under the protection of N2. catalyst CuPt–Cu2O-7/SiC was selected as the optimal catalyst,
Aer running for 60 h and 120 h, the deposited coke was given its ne activity/selectivity, excellent heat conductivity and
ꢁ
removed by calcination of the catalysts in O2 at 400 C for 2 h low noble metal loading. Table 1 shows that our catalyst
(regeneration process).
exhibits higher activity and selectivity than Au/Cu-ber,10
54862 | RSC Adv., 2017, 7, 54861–54865
This journal is © The Royal Society of Chemistry 2017
Liu, Kun
