Figure 6
TEM image and diagram of particle size distribution of nanosilica particles.
The milligrams of CaO to grams of nanosilica and RHA are represented in Table 3 for the comparison of lime reactivity. Lime reactivity of nanosilica is relatively high, indicating that the silica is reactive.
Acidity measurements of catalyst by means of potentiometric titration with n-butylamine were used to estimate its relative acid strength according to the two values: (1) E i as initial potential and (2) number of acid sites (Figure 7). The initial electrode potential (E i) indicates the maximum strength of the acid sites, and the value from which the plateau is reached (millimole amine per gram of solid) indicates the total number of acid sites that are present in the titrated solid [27]. The acidic strength of the solids can be classified according to the following range: E i > 100 mV (very strong sites), 0 < E i < 100 mV (strong sites), −100 < E i < 0 mV (weak sites), and E i < −100 mV (very weak sites). According to the potentiometric titration curve, both the commercial silica (Aerosil 300 silica) and the nanosilica presented strong acidic sites. However, nanosilica has a higher surface area and a higher number of surface acidic sites compared with commercial silica (n = 5.4 and 2.6 mmol amine/g solid, respectively).