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.