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M.S. Khayoon, B.H. Hameed / Applied Catalysis A: General 464–465 (2013) 191–199
Scheme 1. Glycerol acetalization with acetone.
2. Materials and methods
scanning electron microscope (Zeiss, Jena, Germany) coupled with
FEI as a source of electrons and accelerated at 300 kV.
2.1. Materials
The identification of the surface functional groups was per-
formed by Fourier transform infrared spectroscopy (FTIR). The IR
spectra for the as-synthesized catalysts were collected on Perkin-
Elmer System 2000 spectrometer using the KBr disk method. The
Anhydrous glycerol of high purity (>99%) and sodium hydroxide
(98%) were obtained from Sigma, Germany. Acetone (HPLC grade,
≥99.8%) and chromatography grade ethanol and methanol (99.7%)
were supplied by Merck, Malaysia. Nickel(II) nitrate hexahydrate
Ni(NO3)2·6H2O and zirconium(III) chloride ZrCl3 were obtained
from Fluka, Germany. Activated carbon (particle size: 10–900 m)
was purchased from Galcon Carbon Corporation, USA. Hydrochlo-
ric acid (HCl 37%) from Mallinckrodt, USA was used. All reagents
were used without further treatments.
spectra were recorded in the range of 2000–400 cm−1
.
Temperature-programmed reduction (TPR) was performed to
determine the reduction behavior of catalysts. The experiments
were performed on the Micromeritics AutoChem 2920II instru-
ment, using 50 mg of catalyst and the temperature was increased
from 35 ◦C to 1000 ◦C at a heating rate of 10 ◦C/min. 5%H2 in Ar gas
mixture was allowed to flow through the reactor at 15 cm3/min.
This analysis is important to elucidate the metal–support interac-
tion in the prepared catalysts.
2.2. Synthesis of the composite catalysts
The verification of different surface oxidation states of Ni and
Zr was based on XPS analyses. XPS spectra were acquired with a
Rigaku XPS7000 spectrometer equipped with AlK␣ X-ray source
(1486.6 eV) and a hemispherical electron analyzer. Prior to the anal-
ysis, the sample was heated to 100 ◦C under a flow of He gas. To
investigate the influence of oxidation of the catalyst surface, the
samples were, in some cases, exposed to air at 100 ◦C.
The Ni–Zr/AC catalysts were synthesized by incipient wetness
impregnation (WI) of activated carbon with an aqueous solution
containing Ni(II) nitrate and/or Zr(III) chloride. Prior to metals load-
ing, virgin AC was pretreated by 2 M HCl and 2 M NaOH solutions at
50 ◦C to remove the mineral matters and to eliminate their effects
on the acetalization reaction. Then AC was thoroughly washed with
hot distilled water until neutrality of the rinse water. For the Ni–Zr
catalyst, the order of impregnation is given by the sequence of
elements, i.e., Ni followed by Zr. Briefly, 5 g of AC were first impreg-
nated with solution containing Ni (1–5 wt.%) and the resulting
suspension was then left at room temperature for 24 h. Liquid was
then removed by evaporation and the solid was dried in an oven
at 110 ◦C for 6 h. Thereafter, the resultant solid was impregnated
with solution of Zr(III) chloride containing the preferred amount
of Zr (1–5 wt.%) and the same procedure was repeated. The as-
composition is given as the calculated amount of NiO (5%) and ZrO2
(1%) and it was denoted as Ni–Zr/AC composite catalyst. The find-
ings of Fidalgo et al. were interestingly noted during the catalyst
preparation [20].
The structures of the synthesized materials have been investi-
gated by wide angle XRD (10◦ ≤ 2Â ≤ 50◦) with a step size of 0.03◦
over a Bruker X-ray diffractometer (Bruker D2 Phaser Germany,
˚
2011). The Cu K␣ radiation electrons (ꢀ = 1.5406 A) were acceler-
ated at 30 kV and 10 mA in an evacuated X-ray tube with Ni filter,
and the data were interpreted using EVA and EXPERT software.
2.4. Catalytic reaction
All the catalytic acetalization experiments were carried out
under nitrogen flow conditions and constant stirring (530 rpm). In
a typical experiment, 5.0 g of anhydrous glycerol, 23.88–39.8 mL
of acetone at variant molar ratios of glycerol to acetone were fed
to the reaction vessel. To that, 0.20 g of the catalyst was added.
The reaction media was heated to the desired reaction temperature
(25–65 ◦C) for reaction duration of 0.5–4 h. After completion of the
reaction, the catalyst was separated by centrifugation and regen-
erated by washing it with methanol at 45 ◦C and then air dried at
80 ◦C for 4 h to recuperate its catalytic activity.
The progress of the reaction was monitored by periodical with-
drawing samples using 1 mL glass sampling syringe with 6 in.
length stainless steel needle fitted to quick-fit with rubber septum.
Reaction samples were quantitatively analyzed by gas chromato-
graph (GC; Shimadzu 2010 plus, Japan) equipped with a flame
ionization detector (FID) and using a ZB5-HT capillary column
(30 m × 0.25 mm × 0.25 m). Samples for analysis were prepared
by adding 10 L of cyclohexanone as internal standard to 0.50 mL
2.3. Catalyst characterization
The textural characteristics which include the Brunauer–
Emmet–Teller (BET) surface area, pore volume and average pore
diameter of the developed catalysts were characterized by nitrogen
adsorption–desorption isotherms at −197 ◦C using Micromeri-
tics ASAP 2020 surface area and porosity analyzer (Micromeritics
Instruments Corporation, USA).
The mean metallic amounts of nickel and zirconia presented
within the structure of the catalyst before and after the acetaliza-
tion reaction were determined by EDX using Zeiss Supra TM 35 VP