3.1.5. FESEM

Micrographs of the bare silica and the selected impregnated catalysts are presented in Figure 4 (1% Zn/SiO2 and 3% Zn/SiO2). The image of the silica represents a big slab formed surface with clusters of silica nanoparticles. From the micrographs of the impregnated samples, it can be perceived that the bright spots, which are the zinc metal, become more densely colonized as the Zn loading was elevated from 1% to 3%. However, no agglomeration of the zinc metal particles has been detected in the sample with the highest loading of the active site (3% Zn/SiO2). Previous studies have mentioned that by overloading the catalyst surface by an active site, some of the particles might cause agglomeration and might, therefore, result in a reduction in the catalyst performances [44].

**Figure 4.** Field-emission scanning electron microscopy (FESEM) micrographs of the selected samples.
