3.1.2. BET

The surface area, pore size, and pore volume of the bare silica and the freshly calcinated sample values have been detailed in Table 1. The analysis results specified that the BET surface area of the calcinated impregnated samples was slightly lower than the bare SiO2. Nie [45] has also reported the same range of surface area for the silica. The surface area and pore volume of the impregnated samples, as expected and documented previously in the literature, decreased by increasing the zinc load on the support surface [46,47]. In a study by Clerk et al., they declared that various loadings of molybdenum and the surface result in a decrease in the BET surface area [48]. Whilst the loading of the active site resulted in an increase in the BET surface area and pore volume of the samples, it caused decreases in the pore sizes of the samples. This expected trend is due to the selective closing of the small pores with the loading of the zinc metal of the surface of the SiO2 [49]. According to the results, all samples offered type IV isotherms, which indicate a mesoporous texture with capillary condensation.

#### 3.1.3. Thermogravimetric Analysis (TGA)

Thermogravimetry analysis was performed to detect the content of the water and organic compounds of all calcinated samples, and their weight loss was recorded as a function of temperature. TGA results of the samples are presented in Figure 2. In all cases, the weight loss occurred up to 100 ◦C, which is mainly due to the humidity. As it can be observed from Figure 2, calcinated bare SiO2 has around a 2% weight loss whilst the calcinated metalized samples have a minor one (less than 1%). This specifies that by loading the support by zinc metal, less humidity can be absorbed, thus having lower weight loss during the HDO experiments. No high-temperature weight loss was monitored in TGA analysis, which indicates that the samples had no organic carbon impurites.

**Figure 2.** Thermogravimetric analysis for the samples as a function of temperature.
