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L. He et al. / Journal of Molecular Catalysis A: Chemical 392 (2014) 143–149
observed in the selective hydrogenation of ethyl stearate to stearyl
alcohol.
2. Experimental
2.1. Synthesis and characterization of catalysts
All chemicals used in the present work are analytical grade and
used without further purification. The Cu/Fe catalysts were pre-
pared by a simple co-precipitation method. Typically, an aqueous
solution of cupric nitrate (Cu(NO3)3·3H2O, 0.25 M) was mixed with
an aqueous solution of ferric nitrate (Fe(NO3)3·9H2O, 0.25 M) with
a Cu/Fe molar ratio of either 1/4 or 4/1. After the mixture solu-
tion was stirred at 80 ◦C for 30 min, an aqueous solution of sodium
hydroxide (NaOH, 1 M) was added dropwise to the salt solution
under vigorously stirring until the pH reached to ca. 9–10. The mix-
ture obtained was further stirred at 80 ◦C for 4 h and then aged for
another 1 h at room temperature. The precipitate formed was fil-
trated, washed with distilled water for several times to remove the
impurities, and then dried at 110 ◦C. The samples so prepared will
be denoted as Cu/4Fe-pre and 4Cu/Fe-pre in which Cu/Fe ratio is 1/4
and 4/1, respectively. These samples were calcined at 300 ◦C for 4 h
in air; the samples will be denoted as Cu/4Fe-C300 and 4Cu/Fe-
C300, respectively. For comparison, monometallic oxide materials
were also prepared by similar procedures. The samples prepared
before and after the calcination will be denoted as Cu-pre (Fe-pre)
and Cu-C300 (Fe-C300), respectively. The samples were further
reduced in hydrogen atmosphere at different temperatures (150,
200 and 500 ◦C) for 90 min, which will be denoted, for example, as
Cu/4Fe-R150.
The structure and crystal phase composition of the samples
were determined by powder X-ray diffraction patterns with a
˚
Brucker D8 GADDS diffractometer using Co K radiation (1.79 A)
and the crystallite size was calculated with the Scherrer’s equa-
tion. The samples for XRD examination were reduced at a certain
temperature and reserved in ethanol for avoiding exposure to
air before XRD tests. The temperature-programmed reduction
(TPR) analysis was performed under a flow of 5% H2/N2 mix-
ture (30 ml/min), with a heating rate of 10 K/min. Surface acidity
was studied by NH3 temperature-programmed desorption (TPD)
on a TP-5080 Multi-functional Automatic Adsorption Instrument
(Tianjin Xianquan Industry and Trade Development Co. Ltd, China)
equipped with a TCD. Prior to the TPD experiments, 100 mg of
the catalyst sample was pre-reduced in situ at 200 ◦C for 90 min
in a N2/H2 gaseous mixture. The morphology of the samples
was recorded by scanning electron microscope (SEM Hitachi S-
4800). N2 adsorption/desorption isotherms were measured using
a Micromeritics ASAP 2020 Analzer (USA). The surface areas were
calculated using the Brunauer–Emmett–Teller (BET) equation. Pore
volume (Vp) was estimated using the adsorption branch of the N2
isotherm curve. Pore size distribution curves were calculated by the
Barrett–Joyner–Halenda (BJH) method using adsorption branch of
the N2 isotherms.
Fig. 1. XRD patterns of precursor and calcined samples.
autoclave was cooled to room temperature. The products were col-
lected and then analyzed by gas chromatography with FID detector
with a DB-1 capillary column and GC–MS.
3.1. Textual properties and surface acidity
Fig. 1 shows the XRD patterns of the precursor and calcined
Cu/Fe catalysts. The monometallic oxides, iron and copper oxides,
were also analyzed for comparison. The Fe-pre sample gave a rel-
33-0664). Both Cu-pre and Cu-C300 sample presented CuO phase.
thermodynamically easy to transfer into more stable compound of
CuO [19]. In this system, the aging temperature was 80 ◦C so that
the precipitate Cu(OH)2 formed was directly decomposed to CuO
in the hot alkali solution [20]. For Cu/4Fe samples, no any diffrac-
tion peaks could be detected before and after the calcination at
300 ◦C, indicating that both the Cu and Fe existed in an amorphous
state. Zhang et al. reported that a certain amount of Cu could pre-
vent the crystallization of ␣-Fe2O3, and more importantly it could
increase the temperature of phase transformation from Fe(OH)x
2.2. Activity test
Reaction experiments were carried out in a 50 ml stainless steel
autoclave. All the catalysts were pre-reduced in hydrogen at tem-
perature (150, 200, 500 ◦C) for 90 min before the reaction. After
reduction, the catalyst was transferred into the autoclave, in which
5.0 ml hexane was added as solvent, under the protection of hydro-
gen. After that, a certain amount of ethyl stearate was added and
the autoclave was sealed. The reaction was operated under a stir-
ring rate of 1300 rpm (without diffusion limitation) at 230 ◦C and a
H2 pressure of 3.0 MPa H2. After the reaction for several hours, the