3.5. Temperature programme desorption carbon dioxide (TPD-CO2)
The basicity characteristic of all samples was investigated
by using TPD-CO2 analysis. All the clamshell derived catalysts
showed considerably high basic strength at CO2 desorption
temperature >500 C (Fig. 4 and Table 4) [9,10,55,56]. In summary,
the catalyst basicity trend was increased in the order of
CS-Ca(OH)2-EG-400 > STD nano-Ca(OH)2 > CS-Ca(OH)2-CTAB-400 >
CS-Ca(OH)2-DE-400 > CS-Ca(OH)2-EG > CS-Ca(OH)2-CTAB > CS-Ca(OH)2-
H2O-400 > CS-Ca(OH)2-DE > CS-CaO. The results significantly
showed that surfactant-hydration treated nano-Ca(OH)2 rendered
higher amount of basicity than untreated combusted clamshell
(CS-CaO). Furthermore, clamshell derived nano-Ca(OH)2 showed
remarkable increased amount of basicity after underwent thermal
activation at 400 C. The TPD-profile of EG surfactant treated nanoCa(OH)2
rendered highest basicity amongst the samples. Furthermore,
basicity characteristic for CS-Ca(OH)2-EG sample activated
at temperature of 100–800 C was studied by using TPD-CO2. It
was found that CS-Ca(OH)2-EG-400 rendered the highest amount
of basicity compared to other samples. This indicated that partial
dehydration of water molecules that physically adsorbed on nano-Ca(OH)2 surface at 400 C resulted in exposure of active
phase on Ca(OH)2 catalysts (Supplementary Result 2).