Hydrogenation of 2-Ethylhexenal Using Supported-Metal Catalysts for Production of…
989
dropwise into the obtained mixture under vigorous stirring
until the pH of the reaction mixture was 10. The resulting
solution was aged at 30°C for 3 h. The obtained precipitate
was separated, washed 3 times with the distilled water, and
+ H
2
O
OH
Scheme 1 Hydrogenation of 2-ethylhexenal
dried at 105°C, then calcined at 400°C in air, achieving the
Cu/Zn catalyst. The Cu/Cr was prepared in the similar way.
The powder X-ray diffraction (XRD) patterns were
measured in the range from 5° to 75° using a Rigaku
D/max-RA powder diffractometer (Rigaku, Tokyo,
Japan) with Cu K radiation (λ=0.15418 nm). The
Brunauer–Emmer–Teller (BET) surface areas of the sam-
ples were determined using the nitrogen adsorption method
on a Micromeritics ASAP 2020 (Micromeritics Instrument
Co., Norcross, GA) at −196°C. The sample was degassed
under vacuum at 200°C for 4 h prior to adsorption analy-
sis. The high resolution transmission electron microscopy
(HR–TEM) measurements were performed using a high
resolution TEM JEOL 2100F at 200 keV. Temperature-
programmed reduction (H2-TPR) experiments were carried
out in a conventional system equipped with a thermal con-
ductivity detector (TCD). All the samples (100 mg) were
pretreated in a quartz U-tube in a flow of pure N2 at 400°C
for 45 min, then cooled. The reduction reaction was carried
out in a flow of 5% H2 in N2 from 50 to 900°C with a lin-
ear heating rate of 8°C/min. The metal contents in the sam-
ples were analyzed using a PerkinElmer Optima 5300 DV
(PerkinElmer, USA) inductively coupled plasma atomic
emission spectrometer (ICP-AES) system with a radio fre-
quency power of 1300 W.
Table 1 Effect of catalysts on the hydrogenation
Entry
Catalysts
C/%
SOL/%
SAL/%
1
2
3
4
5
6
7
8
Cu/Cr(1:1)
Cu/Zn(1:1)
PdCl2(0.02 g)
Pd/C
90.4
88.9
80.3
82.5
100
93.9
93.1
100
96.5
95.5
/
92.6
90.1
88.6
84.8
99.1
89.2
95.8
95.6
95.1
91.3
/
7.4
9.9
11.4
15.2
0.9
10.8
4.2
4.4
4.9
8.7
/
Pd/ZrO2
Pd/Al2O3
Pd/CeO2
Pd/MAS-7
Pd/MCM-41
Pd/SBA-15
ZrO2
Rh/ZrO2
Ni/ZrO2
Co/ZrO2
Ru/ZrO2
9
10
11
12
13
14
15
97.6
95.8
96.0
97.5
94.7
89.8
90.7
94.9
5.3
10.2
9.3
5.1
2-Ethylhexenal 2.0 g, catalysts 0.10 g, T=240°C, t=7 h, hydrogen
pressure (P) 6 MPa. SOL The selectivity of 2-ethylhexanol, SAL The
selectivity of 2-ethylhexanal
selectivity was calculated by: SOL%= WOL/WALL × 100,
and the 2-ethylhexanal (SAL%) selectivity was calculated
by: SAL%= WAL/WALL × 100, where WOL and WAL are the
amount of 2-ethylhexanol and 2-ethylhexanal, and WALL is
the total amount of the products, including 2-ethylhexanol,
2-ethylhexanal and isooctane, the selectivity of isooctane is
lower than 0.1% in all experiments. All experiments were
repeated four times in order to determine the reproduc-
2.3 Hydrogenation of 2–ethylhexenal
2.0 g 2-Ethylhexenal and 0.1 g Pd/ZrO2 were reacted in a
75 mL stainless-steel autoclave with 6 MPa H2 at 240°C for
7 h with stirring agitation (500 r/min), and then the reacted
mixture was cooled to room temperature and depressur-
ized. The gas phase material was collected in the air bag,
and the upper product was separated by decantation from
the catalyst layer. The catalyst layer was reused directly in
the recycle experiments. The gas phase material and the
liquid phase products were characterized qualitatively with
HP6890/5973 GC/MS equipped with an HP5–MS column,
30 m×0.25 mm×0.25 μm. No small molecule crack-
ing products were found in the gas phase. The products of
2-ethylhexanol, 2-ethylhexanal and isooctane were detected
in the liquid phase. The quantitative analysis of prod-
ucts were determined by GC using HP6890 GC equipped
with an HP5–MS column, 30 m×0.25 mm×0.25 μm,
the contents of the reactants and products were showed
by the system of GC chemstation according to the area
of each chromatograph peak. The 2-ethylhexenal conver-
sion was defined as C%, which is the wt% of 2-ethylhex-
enal consumed in the reaction. The 2-ethylhexanol (SOL%)
3 Results and Discussion
3.1 Effects of the Different Catalysts
on the Hydrogenation
As can be seen from Table 1, compared with traditional cat-
alysts (Entry 1, 2), the supported-metal catalysts exhibited
better catalytic performances. When Cu/Zn or Cu/Cr was
used as the catalyst, the utilization rate of 2-ethylhexenal
was generally low and 2-ethylhexanal was easily generated,
which means that the hydrogenation was not completely
carried out. Otherwise, the hydrogenation results were poor
1 3