2. Experimental details
2.1. Preparation of Ni–Ca/C and Ni/AC
Spherical calcium-doped D152 resin (Ca/D152) was made in the same manner as that in the previous study [6]. Nickel-doped Ca/D152 resin (Ni–Ca/D152) was prepared by exchanging Ca2+ in Ca/D152 with Ni2+in a nickel nitrate solution containing 75% ethanol (Ni
–C2H5OH) or 0.1 M NH4Cl and 0.1 M NH3 Ni2þ
NH3 –NH4 for 24 h at ambient
temperature. After washing with 75% ethanol and deionized water at
70 C to no Ni2+ washed out detected by diacetyldioxime indicator, the
Ni–Ca/D152 was dried at 110 C for 8 h. Ni–Ca/D152 samples having var-
ious nickel contents were obtained by varying the concentration of nickel in
75% ethanol solution or 0.1 M NH4Cl + 0.1 M NH3 solution. The influ-
ences of the two ion exchange systems on the properties of nickel and cal-
cium-doped carbonized resin (Ni–Ca/C) will be discussed.
The carbonization of Ni–Ca/D152 was executed in a tube electric furnace
according to preoxidation–multistage carbonization procedure [6]. Ni–Ca/
D152 was pretreated in air at 210 C for 3 h and carbonized under N2 protec-
tion at 420 C for 1 h, then heated to 500 C for 2 h. Steam activation was
conducted in the same tube furnace at 500 C for 3 h. The carbonized resin
was cooled down to room temperature in a flow of nitrogen. Subsequently
the carbon beads were taken out from the furnace boiled in water for 0.5 h
to remove ashes, then dried at 110 C in air for 12 h, and finally Ni–Ca/C
spheres (40–70 meshes) were obtained. The pretreated resin beads were
brown. The spherical product was metallic black after carbonization.
Nickel-doped activated carbon (Ni/AC) was prepared using the impreg-
nation method. The pretreatment procedures of activated carbon (30–60
meshes, obtained from China Medicine Co.) included washing with
HNO3 (0.5 M) and distilled water and finally drying at 110 C for 5 h. Its
BET specific surface area was measured as 750 m2/g and the pore volume
was 0.68 ml/g. Five grams of the pretreated activated carbon was added
to 150 ml solution of Ni(NO3)2 (0.05 M). The mixture was kept on an
80 C water bath until it dried, then further dried at 110 C for 5 h, and
finally calcinated in N2 gas at 500 C for 5 h.
NiO of octahedral morphology was prepared according to the proce-
dure mentioned in previous study [6].
2.2. Characterization
The pyrolysis behavior of Ni–Ca/D152 was determined by thermogravi- metric analysis (TGA) and differential thermal analysis (DTA) using a Gen- eral V 2.2A Dupont 9900 analyzer. The heating rate was set at 5 C/min. The weight loss and thermal change were recorded in the range of 25–800 C. The tail gas of pyrolysis from 100 C to 500 C was determined by a gas chro- matograph (GC) (SP-2305) equipped with a thermal conductivity detector and a capillary column (stationary phase GD • 502, length 3 m).
The nickel contents of Ni–Ca/C and Ni–Ca/D152 were measured by a flame atomic absorption spectrometry at the resonance wavelength using a HITACHI 180-80 apparatus. Elemental analysis of carbon, hydrogen and nitrogen in the carbonized resin was carried out using an Elementar Vario EL elemental analyzer. X-ray analysis was made by a RIGAKU2308 apparatus with a CuKa radiation resource. Hydrogen temperature-pro- grammed reduction (TPR) study was performed from room temperature to 500 C in a conventional apparatus equipped with a thermal conductiv- ity detector (TCD). Oxygen temperature-programmed oxidation (TPO) was run in the same instrument as TPR. The TPO operation is just reverse
to that of TPR. Nickel dispersion (RNi, in %) and particle size (d Ni , in A˚ )
were determined by H2–O2 titration using pulse method. Nitrogen adsorp-
tion/desorption isotherms at liquid nitrogen temperature (77 K) were mea-
sured using a ST-03 instrument. The experimental details were described in
our previous paper [6].
2.3. Catalytic activity measurement of Ni–Ca/C
For measuring the catalytic activity of Ni–Ca/C, the hydrogenations of propenal, styrene and ethylmethacrylate were performed in a glass reactor