Tianliang Lu et al. / Chinese Journal of Catalysis 35 (2014) 1911–1916
1913
Table 1
Table 2
Dehydrogenation of 3,3‐dimethyl‐1‐butanol to 3,3‐dimethyl‐1‐butanal
over different catalysts.
Dehydrogenation of various alcohols over 6.6Cu‐2Ni/γ‐Al2O3 catalyst.
Conv. Select.
(%) (%)
Entry
1
Substrate
Product
Time
(h)
5
Conv.
(%)
—
Select.
(%)
—
>99
>99
>99
>99
>99
>99
Entry
Catalyst
89 >99
1
2
None
6.6Ni/γ‐Al2O3
5
<1
2
91 >99
91 >99
98 >99
38 >99
O
3
4
5
6
7a
6.6Cu/γ‐Al2O3
5
5
5
24
24
11
14
25
52
3
b
6.6Cu/γ‐Al2O3 + 6.6Ni/γ‐Al2O3
6.6Cu‐2Ni/γ‐Al2O3
6.6Cu‐2Ni/γ‐Al2O3
6.6Cu‐2Ni/γ‐Al2O3
4a
5a,b
6a
93
92 >99
>99 >99
Reaction conditions: 3,3‐dimethyl‐1‐butanol 2 mmol, catalyst 0.20 g,
styrene 4 mmol, mesitylene 2 mL, T = 130 °C, N2 atmosphere.
a Catalyst 0.40 g, styrene 8 mmol, T = 150 °C.
7c
8c
b Mechanical mixture of 6.6Cu/γ‐Al2O3 and 6.6Ni/γ‐Al2O3.
O
O
>99 >99
>99 >99
The Ni particles in 6.6Ni/γ‐Al2O3 were much smaller (< 5 nm)
than the Cu particles in 6.6Cu/γ‐Al2O3. This is consistent with
the XRD results. The diffraction peaks of Ni0 in 6.6Ni/γ‐Al2O3
were very weak because the Ni0 particles were small, whereas
the peaks in 6.6Cu/γ‐Al2O3 were very strong because the Cu0
particles were large and highly crystalline (Fig. 1(2) and (3)).
3,3‐Dimethyl‐1‐butanal is a key intermediate in the prepa‐
ration of neotame, which is a high‐intensity sweetener [16].
The conversion of 3,3‐dimethyl‐1‐butanol to 3,3‐dimethyl‐1‐
butanal was selected as a model reaction (Table 1). Initially, the
transformation was performed in mesitylene under N2, and
styrene was used as the hydrogen acceptor. At 130 °C,
3,3‐dimethyl‐1‐butanol conversion was less than 1% within 5 h
when 6.6Ni/γ‐Al2O3 was used as the catalyst (Table 1, entry 2).
Although 6.6Cu/γ‐Al2O3 exhibited much higher activity than
6.6Ni/γ‐Al2O3 under the same reaction conditions, the
3,3‐dimethyl‐1‐butanol conversion was only 11%, which is
roughly in line with previous reports [6] (Table 1, entry 3). The
activity of 6.6Cu‐2Ni/γ‐Al2O3 was higher than that of
6.6Cu/γ‐Al2O3 and 6.6Ni/γ‐Al2O3. 3,3‐Dimethyl‐1‐butanol con‐
version of 25% was observed, which was about twice that
achieved using 6.6Cu/γ‐Al2O3 (Table 1, entry 5). When a me‐
chanical mixture of 6.6Cu/γ‐Al2O3 and 6.6Ni/γ‐Al2O3 was used
as the catalyst (the Cu/Ni ratio was the same as that in entry 5),
a much lower conversion of 3,3‐dimethyl‐1‐butanol was
achieved than with 6.6Cu‐2Ni/γ‐Al2O3 (Table 1, entry 4). The
Cu‐Ni bimetallic catalyst therefore showed excellent catalytic
activity in 3,3‐dimethyl‐1‐butanol dehydrogenation. After sys‐
tematic optimization of the reaction conditions, 93% conver‐
sion of 3,3‐dimethyl‐1‐butanol with 99% selectivity for
3,3‐dimethyl‐1‐butanal was achieved at 150 °C after 24 h (Ta‐
ble 1, entry 7).
9c
10
11
93 >99
37 >99
Reaction conditions: substrate 2 mmol, 6.6Cu‐2Ni/γ‐Al2O3 0.40 g, sty‐
rene 8 mmol, mesitylene 2 mL, T = 150 °C, t = 24 h, N2 atmosphere.
a t = 40 h. b The catalyst was 6.6Cu/γ‐Al2O3. c T = 130 °C.
achieved for n‐octanol and isooctanol, respectively, when the
reaction time was prolonged to 40 h (Table 2, entries 4 and 6).
Conversely, only 38% of n‐octanol was converted under the
same conditions when 6.6Cu/γ‐Al2O3 was used (Table 2, entry
5); this is roughly in agreement with previous results [6]. As
expected, 6.6Cu‐2Ni/γ‐Al2O3 also showed high catalytic activity
for the dehydrogenation of secondary aliphatic alcohols to the
corresponding ketones. Conversions higher than 99% were
easily obtained when the substrate was 2‐octanol, cyclopenta‐
nol, or cyclohexanol (Table 2, entries 7–9), even when the reac‐
tion temperature was as low as 130 °C. It was previously re‐
ported that when Cu/Al2O3 was used in catalytic dehydrogena‐
tion, primary benzylic alcohols such as benzyl alcohol and
2‐phenylethanol were difficult to convert [6]. In this work, 93%
of benzyl alcohol was converted over 6.6Cu‐2Ni/γ‐Al2O3, and
37% conversion of 2‐phenylethanol was achieved. To the best
of our knowledge, this is the first report of Cu‐Ni/γ‐Al2O3‐cata‐
lyzed dehydrogenation of aliphatic alcohols, and a wide range
of non‐activated primary aliphatic alcohols were successfully
converted to the corresponding aldehydes with high conver‐
sions.
We explored the substrate scope over 6.6Cu‐2Ni/γ‐Al2O3
using alcohols other than 3,3‐dimethyl‐1‐butanol (Table 2). The
dehydrogenation of primary aliphatic alcohols such as isoamyl
alcohol, n‐amyl alcohol, and n‐hexyl alcohol produced the cor‐
responding aldehydes with 89%, 91%, and 91% conversions,
respectively, and selectivity for the corresponding aldehydes of
more than 99% (Table 2, entries 1–3). n‐Octanol and isooc‐
tanol, which have higher carbon numbers, were more difficult
to convert. Nevertheless, 98% and 92% conversions were
We examined the recyclability of the 6.6Cu‐2Ni/γ‐Al2O3 cat‐
alyst in the dehydrogenation of 3,3‐dimethyl‐1‐butanol. After
the first run, the solid catalyst was separated from the reaction
mixture by centrifugation and washed with mesitylene. The
catalyst was then used for the next run. The conversion of
3,3‐dimethyl‐1‐butanol in the second run was 85%. Although