C. Hao et al. / Journal of Molecular Catalysis A: Chemical 306 (2009) 130–135
131
yield together with the complicated separation and recovery pro-
cedures makes the process far from satisfaction. In light of these
problems, the gaseous decarbonylation including many examples
of DMC preparation from DMO via decarbonylation with alkali cat-
alysts supported on activated carbon (AC) was brought forward by
Katsumasa [21]. It was reported that both the conversion of DMO
and the selectivity to DMC were up to 75% and the gaseous space
time yield (STY) of DMC was above 1000 g/(L h). But for DEC prepa-
ration via decarbonylation from DEO, there were no detailed reports
about the highly active catalyst and the optimum reaction condi-
tion. Consequently, this work tried to deal with the alkali catalysts
and give some details about its performance in the decarbonylation
of DEO for DEC preparation.
(III) Supersonic impregnation. The beaker with potassium contain-
ing aqueous solution and prepared support mixture was placed
in the supersonic container followed by impregnating for
30 min, then dried at 393 K for 24 h under atmospheric pres-
sure.
2.2. Decarbonylation of DEO to DEC
The decarbonylation of DEO over alkali catalysts was conducted
at atmospheric pressure in a continuous flow fixed-bed reactor.
The reactor (400 mm long, 13 mm inner diameter stainless tube
placed coaxially in a Ø 400 mm thermostated furnace) was loaded
with the catalyst. The reactant was pumped (Lab Alliance Series II
Pump) into a preheater and carried by an inert N2 stream into the
reactor.
2. Experimental
The liquid mixture caught in the condensator was ana-
lyzed by an Agilent 4890D gas chromatograph (GC) equipped
with an HP-5 capillary column (Hewlett–Packard Company,
15 m × 0.53 mm ×1.5 m) and a flame ionization detector (FID). The
analysis of the gaseous products collected at the reactor outlet was
performed by SP3420 GC provided with a thermal conductivity
detector (TCD) and a molecular sieve 5 A column. The qualita-
tive analysis of the products was confirmed on an Agilent HP5971
gas chromatograph-mass spectroscopy (GC–MS) in the DEC prepa-
ration from DEO via decarbonylation. The catalytic activity was
expressed by the conversion of DEO, the selectivity and the STY
of DEC.
2.1. Catalysts preparation
2.1.1. Supports preparation
Zirconium was obtained by the precipitation of zirconium oxy-
chloride solution with the necessary amount of ammonia to reach
a constant pH of 10. The precipitated material was filtrated and
washed with deionized water until it was free from chlorine ions,
as determined by the silver nitrate test. The product was then dried
at 393 K for 4 h and calcined at 923 K for 5 h to get a white zirconia
dioxide powder. Finally, the powder was shaped under 25 MPa and
crashed into 20–40 meshes for further use.
Magnesium oxide was synthesized following the similar proce-
dures proposed by Cosimo and co-workers [22]. 20 g commercial
magnesium oxide was added to 200 mL deionized water at room
temperature in a stirred glass reactor. The slurry was stirred for
4 h after the temperature was raised to 353 K. Then, the sample
was dried at 358 K overnight. The obtained Mg(OH)2 was thermally
decomposed in N2 at 30 mL/min (STP) at 623 K for 2 h and then
at 773 K for another 8 h. Finally, the MgO powder was shaped and
crashed into 20–40 meshes.
The 20–40 meshes AC were treated in 0.1 mol/L KOH solu-
tion followed by 0.1 mol/L HNO3 solution, and finally washed with
deionized water in order to remove the adhering ash on the sur-
face. Then the sample was dried at 393 K for 24 h and stored in a
desiccator.
2.3. Catalysts characterization
Powder X-ray diffraction crystalline phases were recorded at
room temperature by using an X-ray powder diffraction (XRD). A
PANalytical X’ Pert Highscore (Holland) diffractometer, equipped
with Co K␣ radiation anode (k = 1.78901 Å, 40 kV and 40 mA), was
used for these measurements. Intensity data were measured by step
scanning in the 2ꢀ ranges with a scanning rate of 12◦ min−1 from
2ꢀ = 10◦ to 80◦.
The specific surface areas of the catalysts were measured on
an adsorption apparatus (Micromeritics Gemini V) by the N2-BET
method at the liquid nitrogen temperature. The point surface area
was determined at P/P0 = 0.1, 0.2, 0.3.
treated in deionized water for 5 h, followed by desiccation at 393 K
for 24 h.
Commercial HZSM-5 was calcined at 773 K for 12 h to eliminate
the water presented as humidity or bonded to the crystals before
impregnation [23].
The surface composition of catalyst was studied by X-ray pho-
toelectron spectroscopy (XPS) in a PerkinElmer PHI 1600 ESCA
system with Mg K␣ 1253.6 eV radiation as the excitation source.
The samples were mounted on the specimen holder by means
of double-sided adhesive tape. Spectra were recorded in steps of
0.15 eV. The C1s peak (284.5 eV) was used as the internal standard
for binding-energy calibration. An estimated error of 0.1 eV can
be assumed for all the measurements. The scanning of the spectra
was done at pressures less than 10−8 Torr and the temperature was
approximately 293 K.
2.1.2. Supported alkali catalysts preparation
Three impregnation methods were investigated in the sup-
ported alkali catalysts preparation as follows:
Further elemental analysis of catalysts was performed by an
inductively coupled plasma-optical emission spectroscopy (ICP-
OES) (Varian VISTA-MPX) at the frequency emission power of
1.2 kW, plasma air flow of 15.0 L/min and ꢁK = 766.491 nm.
(I) Dipping impregnation. 1.062 g K2CO3 was dissolved in 50 mL
water and 10 g support was added. The mixture was placed
under a reduced pressure of 0.09 MPa to impregnate for 3 h
and then heated from room temperature to 353 K to evaporate
water gradually in a rotary evaporator. Thereafter, the residual
mixture was dried at 393 K for 24 h to prepare a solid catalyst.
The total loading of the catalyst in terms of metallic potassium
was 6 wt%.
3. Results and discussion
3.1. Qualitative analysis of the products in the reaction
(II) Incipient wetness impregnation. The prepared support was
added to the necessary amount of solution to fill the pore
volume of the support for 24 h at room temperature and atmo-
spheric pressure, followed by desiccation in an oven at 393 K
for 24 h.
The qualitative analysis of products in the preparation of DEC
from DEO by decarbonylation over K2CO3/AC was performed by
Agilent HP5971 gas chromatography-mass spectroscopy. DEC, DEO,
ethanol, ethyl formate, and 1,1-diethoxyethane were identified,
respectively [24].