Y. Hu et al. / Catalysis Communications 54 (2014) 45–49
47
Table 2
studies investigated the reduction behavior of CuO/m-ZrO2 catalysts
Catalytic results of C3–C8 primary alcohols with ammonia over 5%Cu/m-ZrO2.
and concluded that the highly dispersed CuO was easily reducible com-
pared with bulk CuO. These results further confirmed the possible exis-
tence of highly dispersed CuO. With the increase and shifting of the Tm
toward higher temperatures, the result may be assigned to the increase
in crystalline CuO particle size as evidenced from XRD results. The larger
β peak area of TPR (Fig. 1b) and the larger signal intensity of CuO peaks
in XRD (Fig. 1a) were observed, which further suggested that the β peak
was ascribed to bulk CuO and the α peak to highly dispersed CuO.
Hence, a substantial amount of Cu species over m-ZrO2 is in highly dis-
persed CuO.
NH3-TPD and CO2-TPD profiles of Cu/m-ZrO2 catalysts are shown in
Fig. 1c and d. The total amounts of acid sites of 0.61 mmol NH3/g and the
total amounts of basic sites of 0.38 mmol CO2/g on the m-ZrO2 were de-
termined, which showed that there were not only acid sites but also
basic sites on m-ZrO2 while acid sites dominated on γ-Al2O3. Moreover
CO2-TPD profiles can provide more information about the surface prop-
erties of m-ZrO2, because CO2 adsorbs specially on three different types
of basic sites over the surface of m-ZrO2 including coodinatively unsat-
urated (cus) O2− centers which play an important role in increasing
CuO dispersion [17–19]. Compared with γ-Al2O3, more amounts of
desorption CO2 indicate the possibility of more cus O2− centers on
m-ZrO2. CuO species are formed on the surface of m-ZrO2, i.e., with
Cu2+ ions incorporation into the available vacant sites and the accom-
pany cus O2− sitting on the top for charge compensation [19]. After
the surface available sites are being occupied, further increasing the
loading of will lead to the formation of the bulk CuO.
Entry Substrate
Conversion wt.% Product
Selectivity wt.%
2b 99.09
1
2
1b
1c
99.58
96.25
2c 87.25
3
4
5
6
1d
99.23
2d 99.31
2e 98.48
2f 97.96
2g 93.22
1e 100.00
1f 100.00
1g
96.89
Reaction conditions: 0.1 MPa, 280 °C, 2.0 g catalyst samples, 0.7 ml/h alcohol, and
NH3/alcohol molar ratio = 7.0.
the reactant from ethanol to C3–C8 fatty primary alcohols to evaluate the
suitability of the reaction. In the presence of 5%Cu/m-ZrO2, C3–C8 fatty
primary alcohols can be converted into the corresponding nitriles with
high yield in one-step synthesis (Table 2). In general, alcohols exhibit
good yield under the same conditions. The conversion of alcohols and
selectivity of nitriles are greater than 96.25 and 87.25 wt.%, respective-
ly; conversion of many reactions can reach or approach 100 wt.%. In
addition, the conversion of alcohols and selectivity of nitriles have not
obvious change varied with the carbon numbers of alcohols. But the se-
lectivity of C2-substituted 2c with the methyl group is lower than that of
2b, and the similar results also appear in comparison of C2-substituted
2g with 2f. It is obvious that the yield of fatty nitriles is obviously influ-
enced by the C2-substitution in the reaction.
3.2. Dehydrogenation–amination of ethanol to acetonitrile over Cu/m-ZrO2
3.4. Role of Cu and m-ZrO2 on Cu/m-ZrO2 for ethanol to acetonitrile
For comparison with Cu/γ-Al2O3, dehydrogenation–amination of
ethanol to acetonitrile over Cu/m-ZrO2 is shown in Table 1. The ethanol
conversion and the acetonitrile selectivity during the time-on-stream of
0–5 h are 96.9 and 98.4 wt.%, respectively, over 5%Cu/m-ZrO2. By
contrast, the corresponding values are only 61.0 and 42.6 wt.% over
5%Cu/γ-Al2O3; meantime the direct transformation of ethanol to ethyl-
ene and ethyl ether predominates [12]. The Cu/m-ZrO2 catalyst also ex-
hibited better stability than the Cu/γ-Al2O3 catalyst according to the
decreasing amplitude of the ethanol conversion and the acetonitrile
selectivity during the time on stream of 0–10 h. Based on the results
of characterization and catalytic performance, satisfactory catalytic ac-
tivity is found to be closely related to CuO, and the active Cu site from
CuAl2O4 has weaker activity and stability than Cu from CuO.
To study the catalytic effect of Cu and m-ZrO2, the CuO catalyst was
used alone to catalyze ethanol under the same conditions. However, the
main reaction product on CuO is 1-aminoethanol trimers (IR cm−1
:
3,341, 3,328, 3,243, 1,500, 1,384, 1,376, and 1,306) which have a high
melting point of 97 °C. The outlet line from the reactor can be plugged
by crystals of 1-aminoethanol trimers and the test of catalytic perfor-
mance would have to be terminated. 1-Aminoethanol is the nucleophil-
ic addition product of acetaldehyde and ammonia. The Cu0 active site
reduced from the highly dispersed CuO participates in the conversion
of ethanol into acetaldehyde, but further intermolecular dehydration
of 1-aminoethanol into imine does not occur.
Yinning Zhang et al. [11] and Roger et al. [20,21] mentioned that the
formation of imine is a step for acetonitrile synthesis. Thus, further in-
termolecular dehydration of 1-aminoethanol on Cu/m-ZrO2 is caused
by m-ZrO2, and the following steps for acetonitrile synthesis can be
smoothly completed. Therefore, m-ZrO2 participates as the carrier for
the Cu0 active site and it has the catalytic function for intermolecular de-
hydration because m-ZrO2 possesses acidic and basic sites. It is generally
known that acid sites can catalyze intermolecular dehydration.
Based on the above results, a plausible reaction mechanism using
C2–C8 over Cu/m-ZrO2 is proposed (Scheme 1). First, alcohols are
dehydrogenated to produce corresponding aldehydes over the Cu0
Therefore, m-ZrO2 is favorable to the formation of highly dispersed
CuO even at low Cu loading. In addition, satisfactory catalytic perfor-
mance can be obtained over Cu/m-ZrO2 with low Cu loading of 5%.
3.3. Dehydrogenatiobn–amination of C3–C8 fatty primary alcohols to
nitriles over Cu/m-ZrO2
This transformation is desirable because of its relatively simple,
non-corrosive, high atom efficiency, lack of toxic. Therefore, we expand
Table 1
Dehydrogenation–amination of ethanol to acetonitrile over Cu/m-ZrO2 and Cu/γ-Al2O3.
Catalyst
Ethanol conversion/wt.%
Acetonitrile selectivity/wt.%
0–5 ha
5–10 hb
Decreasing amplitude
0–5 h
5–10 h
Decreasing amplitude
3% Cu/m-ZrO2
5% Cu/m-ZrO2
7% Cu/m-ZrO2
10% Cu/m-ZrO2
5% Cu/γ-Al2O3
10% Cu/γ-Al2O3
98.9
96.9
99.8
98.1
61.0
99.2
94.9
92.7
96.6
97.4
31.0
81.0
4.0
4.2
3.2
0.7
30.0
18.2
75.1
98.4
96.1
99.9
42.6
76.8
74.6
94.7
93.6
94.1
12.6
62.5
0.5
3.7
2.5
5.8
30.0
14.3
Reaction conditions: 0.1 MPa, 280 °C, 2.0 g catalyst samples, 0.7 ml/h ethanol, and NH3/ethanol molar ratio = 7.0.
a
Ethanol conversion in the time on stream of 0–5 h, and so on.
Ethanol conversion in the time on stream of 5–10 h, and so on.
b