X. Fan et al. / Catalysis Communications 11 (2010) 960–963
961
2
.2. Characterization
Table 2
2 3 5 2 3
The results of the hydrogenation catalyzed by Cu30/γ-Al O and Cu30Cr /γ-Al O .
The composition of the catalysts was measured with an ICP
Entry Catalyst Conversion (%) Selectivity (%)(TMP) Yield (%)(TMP)
instrument. The XRD patterns of the samples were recorded with a
Rigaka D/max 2500 X-ray diffractometer using Cu-K radiation
40 kV, 100 mA) in the range 10–90°. The mean diameter of Cu crystals
was calculated from XRD patterns using Scherrer equation. XPS
measurements were recorded with a PHI 1600 spectrometer using a
1
2
Cu30/γ-Al
2
O
3
87.8
97.1
89.2
92.4
78.3
89.7
α
Cu30Cr /γ-Al O
5
2 3
(
Reaction conditions: 140 °C, 4.0 MPa hydrogen pressure, flow rate of the TAA in
ethanol=0.5 mL/min (concentration of solution=20%).
α
Mg-K X-ray source for excitation. A Micromeritics 2910 apparatus
equipped with a TCD detector was used for TPR measurements. The
calcined samples were heated from room temperature to 600 °Cata rate
and b could be assigned to the crystals of elementary copper. The
diffraction lines labeled with “+” in the XRD pattern of c demonstrates
of 10 °C/min in a mixture of 10% H
2
/Ar.
5 2 3
that Cu presents as CuO in unreduced Cu30Cr /γ-Al O . It can be found
2
.3. Catalyst activity evaluation
that the doped Cr made Cu crystals smaller and dispersed better. The
mean diameter of Cu crystals calculated from the (1 1 1) diffraction
line (43°) on the XRD patterns using Scherrer equation decreases from
Hydrogenation of TAA over these catalysts mentioned above was
carried out in a tubular, fixed-bed reactor with an inner diameter of
5 mm and a length of 660 mm, which was charged with 15.0 g of
2 3
218± 8 Å in the reduced Cu30/γ-Al O to 182± 7 Å in the reduced
1
Cu30Cr /γ-Al . The introduction of Cr led to higher dispersed active
5
2 3
O
catalyst. A solution of TAA in ethanol (concentration: 20%) was dosed
into the reactor at a speed of 0.5 mL/min by a syringe pump. The
temperature in the reaction zone was measured through a thermo-
couple located in the center of the tube and regulated by a PID cascade
controller. The hydrogen pressure in the reaction system was set by
using a hydrogen regulator. The reaction samples were analyzed by
GC using a 30 m SE-54 capillary column every four hours. The
components of the reaction mixture were determined by GC–MS
using a 30 m SE-54 capillary column, and the optical rotation data
were obtained with a WZZ-3 autorotation analyzer.
species, which can supply more active centers and prevent the
sintering of copper. However, no obvious peaks corresponding to Cr
were picked out from the pattern of reduced Cu30Cr /γ-Al O . We
5 2 3
suggest that Cr present as amorphous Cr phase, or it was not
detectable by XRD as a result of its low content in the catalyst.
3
.1.2. XPS
As shown in the left XPS spectra in Fig. 2, the peak at 932.1 eV, the
binding energy of the Cu 2p3/2 level, indicates that Cu exist in
Cu30Cr /γ-Al mainly as elementary copper. This assumption could
be supported by the typical diffraction lines of the elementary copper
crystals in the XRD pattern of the reduced Cu30Cr /γ-Al . The
binding energy of the Cr 2p3/2 level at 576.3 eV in the right XPS
5
2 3
O
5
2 3
O
3
. Results and discussion
+
3
+3
spectra could be assigned to Cr 2p3/2. Cr
CuCr , which could not be identified by our XRD patterns and XPS
spectroscopy. Additionally, the higher content of Cr in the surface of
the reduced Cu30Cr /γ-Al (Cr:Cu=1:2.6) than that in the bulk
2 3
may exist as Cr O or
3
.1. Catalyst selection and catalyst characterization
2 4
O
The hydrogenation of carbonyl group is usually catalyzed by some
5
2 3
O
metals, such as Pt, Ru, Rh, Ni, Cu and so on. Taking the costs of catalysts
into consideration, the noble metals Pt, Ru, and Rh weren't selected as
the main catalysts for this continuous process. Nickel [9–11] and
copper [12–15] based catalysts were reported to exhibit good catalytic
phase (Cr:Cu=1:6) indicates that part of Cr migrated from the bulk
phase of the catalyst to the surface during dryness or calcination.
activity for the hydrogenation of ketones. Thus, Ni30/γ-Al
Cu30/γ-Al were prepared for the hydrogenation of TAA, and the
results are shown in Table 1. Cu30/γ-Al showed much better
activity and selectivity than Ni30/γ-Al in the hydrogenation of TAA
2
O
3
and
3.1.3. TPR
2
O
3
One main peak at 300 °C in the TPR curve of Cu30Cr /γ-Al O is
5
2 3
2
O
3
related to the reduction of CuO to Cu. But no peak around 150 °C, the
temperature used for activation of the catalyst in our work, appears in
Fig. 3. This result did not accord with the conclusion obtained from the
2 3
O
to TMP. Therefore, copper was chosen as the main catalyst.
In order to improve its activity and selectivity, Cr was introduced
2 3
into Cu30/γ-Al O , and the catalytic results are listed in Table 2. It is
obvious that the presence of Cr in the catalyst gives rise to an increase
in the conversion of TAA, selectivity and yield of TMP, which imply
that Cu30Cr
Cu30/γ-Al
catalysts for further understand of the results previously described.
5
/γ-Al
2 3
O displays better catalytic performance over
2 3
O . XRD, XPS and TPR were used to characterize these
3
.1.1. XRD
2 3 5 2 3
The XRD patterns of reduced Cu30/γ-Al O , reduced Cu30Cr /γ-Al O
and unreduced Cu30Cr /γ-Al O were shown in Fig. 1. The typical
5 2 3
diffraction lines at about 43°, 50°, 74°, and 90° in the XRD patterns of a
Table 1
2 3 2 3
The results of the hydrogenation catalyzed by Cu30/γ-Al O and Ni30/γ-Al O .
Entry Catalyst Conversion (%) Selectivity (%)(TMP) Yield (%)(TMP)
1
2
Ni30/γ-Al
Cu30/γ-Al
2
O
O
2 3
3
55.9
87.8
45.0
89.2
25.2
78.3
Reaction conditions: 140 °C, 4.0 MPa hydrogen pressure, flow rate of the TAA in
2 3 5 2 3
Fig. 1. XRD patterns of (a) reduced Cu30/γ-Al O ,(b) reduced Cu30Cr /γ-Al O and (c)
ethanol=0.5 mL/min (concentration of solution=20%).
unreduced Cu30Cr /γ-Al
5
2 3
O .