Fig. 5 depicts SEM images of dried eggshell and SBES catalyst.
Before calcination, eggshell shows a generally irregular crystal
structure. Many pores and pits were distributed over the entire
eggshell surface. After calcination at 800 C for 5 h, as shown in
Fig. 5b, the crystal structure has been changed and more developed
pores are observed, indicative of dramatic increasing in the BET
surface area of the SBES catalyst.