**6. Porous ceria**

Recently, our research group succeeded to fabricate porous ceria with high surface area, almost six times higher than commercial ceria. The interesting thing about the porous ceria is the morphological structure. Commercial ceria has bulky plate-like structure, which is always present in agglomerated form. However, the prepared porous ceria exhibited sponge-like structure with rough surface containing plenty of voids, caves, and channels. This structure was achieved by using citric acid as a fuel in a simple flash combustion method (**Figure 4**) [12].

**Figure 4.** *SEM micrograph of porous ceria.*
