under 500 mL/min N2 followed by physical activation using
500 mL/min CO2 at the same temperature for 90 min was
determined to be optimum preparation condition. Under this
condition activated carbon with high surface area of 1052.9 m2/g
was produced. In another study, they incorporated several metals
into the structure of activated carbon by wet impregnation method
[50]. For this screening work, 4 h of calcination at 400 8C under
argon as inert gas was required to obtain the high surface area of
metal impregnated activated carbons. From the screening study,
cerium was found to be the best metal to be impregnated with
activated carbon because it achieved high SO2 and NO removal
with surface area and pore volume of 997 m2/g and 0.362 cm3/g,
respectively. A detailed study on the activity of cerium impregnated
palm shell based activated carbon was subsequently
published [51]. Cerium was found to have a synergistic effect on
simultaneous SO2 and NO removal. It was concluded that cerium
does not take part directly in SO2 removal but acts as an active site
to catalytically promote NO adsorption. Sumathi et al. performed a
study on effect of humidity, which showed that increasing
humidity could enhance SO2 removal; nevertheless, this will also
reduce the removal of NO [56]. Higher temperature (up to 250 8C)
was found to increase NO removal but SO2 removal started to
reduce beyond 150 8C. Adsorption capacity of 121.7 mg/g and
3.7 mg/g was reported for SO2 and NO removal respectively, using
cerium impregnated palm shell based activated carbon.