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reactor. It was reported that when Cu/SiO2 catalyst was used in
the gas phase hydrogenation of MA, SA was dominantly formed at
temperatures of 170–220 ◦C [4]. Unfortunately, after reacting for
240 min, the catalytic activity decreased from 100% to ca. 50% at
220 ◦C [4]. When Ni/HY-Al2O3 catalyst was used as the catalyst
in a fixed bed reactor at 190 ◦C and 1 MPa of H2, MA was effec-
tively converted to SA and the yield of SA reached 95% at complete
conversion of MA. But, after reacting for more than 20 h, the SA
yield and MA conversion decreased from 95% to 76% and 100% to
83%, respectively [16]. Although the catalytic activity of the cata-
lyst was almost recovered by oxidation and subsequent reduction
[4], frequent catalyst regeneration unavoidably causes impractical
in commercialization using fixed bed reaction system. The catalyst
and reaction system for selective conversion of MA to SA still need
further investigation.
are widely used in liquid phase hydrogenation reactions. Specifi-
cally, Ni nanoparticles show high catalytic activity and selectivity
in hydrogenation reaction, such as hydrogenation of nitrophenol
to aminophenol [17–20]. Although metallic Ni catalysts have many
advantages in catalytic hydrogenation reactions, metallic Ni cata-
lysts are seldom investigated in the hydrogenation of MA to SA.
In our present work, selective hydrogenation of MA to SA cat-
alyzed by Raney Ni and Ni nanoparticles was investigated in batch
type reactor under mild reaction conditions. Solvent with higher
polarity favored the liquid hydrogenation of MA to SA as compared
to that with lower polarity. Without using solvent, ␥-butyrolatone,
as a byproduct, was formed through hydrogenation of the resultant
SA. Ni nanoparticles showed higher catalytic activity than Raney
Ni catalyst in the liquid phase hydrogenation of MA to SA at low
reaction temperature. The nanoparticle size and crystal structure
played important roles in the hydrogenation reaction. The reaction
route was also briefly discussed.
2.3. Preparation of Raney Ni catalyst
Raney Ni catalyst was prepared by the following procedure: 1.0 g
of Ni–Al alloy with a weight ratio of 47:53 and an average particle
size of 13 m was added to an aqueous solution of NaOH (5.0 M,
10 mL) under gentle stirring at 50 ◦C. After that, the reaction solu-
tion was heated to 80 ◦C and stirred for 1 h. The black precipitate
was washed with distilled water to neutrality and then washed
with acetone to replace the water. The as-prepared Raney Ni cata-
lyst was kept in acetone.
2.4. Characterization
The XRD data of ethanol-washed Ni nanoparticles were
recorded on a diffractometer (D8 super speed Bruke-AEX Company,
Germany) using Cu K␣ radiation (ꢀ = 1.54056 A) with Ni filter, scan-
˚
ning from 20◦ to 80◦ (2ꢁ). The crystallite sizes of metallic nickel,
(1 1 1) plane, in Ni nanoparticles were calculated by using Scherrer’s
equation: D = Kꢀ/(B cos ꢁ), where K was taken as 0.89 and B was the
full width of the diffraction line at half of the maximum intensity.
The crystallite sizes of metallic Ni (1 1 1) of the Ni nanoparticles are
listed in Table 1.
Scanning electron microscopy (SEM) was performed on a scan-
ning electron microscope (JSM 7001F) operated at an acceleration
voltage of 10 kV to characterize the morphology of Raney Ni cat-
alyst. High resolution transmission electron microscopy (HRTEM)
images were obtained on a microscope (JEM-2100) operated at an
acceleration voltage of 200 kV to characterize the morphologies and
the crystal structures of the Ni nanoparticles. The TEM specimens
were prepared by placing a drop of Ni nanoparticle ethanol suspen-
sion onto a copper grid coated with a layer of amorphous carbon.
The average particle sizes of the Ni nanoparticles were measured
from the TEM images by counting at least 150 individual particles.
The average particle sizes of the Ni nanoparticles were calculated
by a weighted-average method according to the individual particle
sizes of the all counted particles.
2. Experimental
2.1. Materials
2.5. Catalytic test
The chemicals, maleic anhydride, succinic anhydride,
␥-butyrolacetone, anhydrous ethanol, acetone, acetic anhy-
dride, nickel acetate (Ni(CH3COO)2·4H2O), hydrazine hydrate
(N2H4·H2O), sodium hydroxide (NaOH), citric acid (CA), sodium
dodecylbenzene sulfonate (SDBS), polyvinylpyrrolidone (MW
40000, PVP), and D-sorbitol (DS), were of reagent grade and were
purchased from Sinopharm Chemical Reagent Co., Ltd. China. All
chemicals were used as received without further purification.
The hydrogenation of MA was carried out in a 1000 mL capacity
stainless steel autoclave fitted with a magnetically driven impeller.
The autoclave was charged with the appointed MA, solvent, and
catalyst. First, the autoclave was purged with nitrogen for 10 min.
Then hydrogen from a cylinder was introduced, and the pressure
was raised to the desired value. Under stirring at 400 rpm, the reac-
tion was carried out at given temperature for a certain time. At
the end of reaction, the autoclave was cooled to ambient tempera-
ture and slowly depressurized. The reaction mixture was analyzed
by GC equipped with FID and a SE-54 packed capillary column
(0.25 mm × 30 m). The reactant and product were identified on the
basis of the retention times of authentic compounds.
2.2. Preparation of Ni nanoparticles
Ni nanoparticles were prepared by reducing nickel acetate with
hydrazine hydrate in the presence of organic modifiers with dif-
ferent functional groups, such as CA, DS, PVP, and SDBS. Typically,
organic modifier (0.37 g) and nickel acetate (2.49 g) were dissolved
in anhydrous ethanol (70 mL) by ultrasonic treatment for 30 min.
While the mixture was heated to 60 ◦C, an ethanol solution of NaOH
(1.0 M, 20 mL) was added dropwise to adjust the pH value of the
reaction solution to 12. After that, a hydrazine hydrate ethanol
solution (8.0 mL in 100 mL anhydrous ethanol) was added drop-
wise to the mixture and heated to 80 ◦C for 4 h under mild stirring.
After reduction, the color of the reaction solution changed to black,
indicating that Ni2+ was reduced to metallic Ni0. The as-prepared
Ni nanoparticles were cooled to room temperature and kept in an
anhydrous ethanol solution. Ni nanoparticles were centrifugated
and washed with anhydrous ethanol before they were character-
ized and used as catalysts in hydrogenation of MA.
3. Results and discussion
The XRD patterns of the Ni nanoparticle samples prepared by
using organic modifiers with different functional groups are shown
in Fig. 1. The XRD diffraction peaks appearing at 2ꢁ = 44.5, 51.9,
and 76.4◦ were indexed as the (1 1 1), (2 0 0), and (2 2 0) planes of
detected, indicating that phase-pure metallic Ni nanoparticles were
prepared under the present experimental conditions. The crystal-
lite sizes (1 1 1) of the Ni nanoparticles were estimated by Scherrer’s
equation (Table 1). As shown in Table 1, the crystallite sizes of the