increase of nickel content in Ni–Ca/D152(NH) and Ni– Ca/D152(CH) except the melting samples of D and E due to the catalyses of loaded nickel and calcium [6]. In proceeding steam activation of Ni–Ca/C, the higher the nickel content in the precursor is, the more carbon was burned off, and the more pores formed in carbonization were opened, and therefore, the higher specific surface area of Ni–Ca/C(CH) or Ni–Ca/C(NH) was determined. According to the International Union of Pure and Applied Chemistry (IUPAC) classification (the pore sizes of porous materials are classified into three categories: micropore
(pore diameter 5–20 A˚ ), mesopore (20–500 A˚ ) and macro-
pore (>500 A˚ )) [13], the pore size of Ni–Ca/C mainly falls
into the micropore range.
Nickel dispersion degree (RNi), specific surface area
(SNi) and average crystallite size (d Ni) in Ni–Ca/C were
determined by means of H2–O2 titration and calculated
according to Hughes equation [14,15]. The well-carbonized
bead-shaped Ni–Ca/C showed a good nickel dispersity with a particle distribution in the range of 9–15 A˚ .
The ion exchange reactions between carboxy groups of resin and nickel cations in 75% C2H5OH solution or NH3–NHþ solution led to evenly entrapped nickel ions in the polymer framework on ionic level and minimized the physical adsorption of nickel. The formed network struc- ture during the preoxidation–multistage carbonization effectively prohibited fast transportation and aggregate of nickel in the resin so that very small particle size of nickel in all bead-shaped Ni–Ca/C was finally obtained, even if the nickel content in Ni–Ca/C was as high as 12%.
Tables 1 and 2 also indicate that exchanging Ca/ D152
with Ni2þ – NH3–NHþ solution has an advantage for pre-
paring bead-shaped Ni–Ca/C having low nickel loadings,
and exchanging Ca/D152 with Ni2+–C2H5OH solution is
advantageous for preparing bead-shaped Ni–Ca/C having
high nickel loadings. Ni2+ ions mostly exist as complex ions
NiðNH3Þx (x = 1–6) in NH3–NH4 solution which are very
stable in water solution. Physical adsorption of nickel in
D152 resin is maximally reduced due to the decreased free
Ni2+ ions and hydrolysates in the solution, which ensures