*2.1. X-ray Diffraction*

Figure 1 depicts changes in the crystal structure of various catalysts (Figure 1A–C). A carbonaceous structure peak at angle 23 can be observed in the XRD pattern of activated carbon derived from "*Lantana Camara*" in Figure 1A [16]. Three processes are involved in the chemical activation using H3PO4: dehydration, degradation, and coagulation. Research revealed that the phosphoric acid forms pores with raw precursor during the carbonization phase [17,18].

**Figure 1.** XRD pattern: (**A**) activated carbon; (**B**) Fe-C catalyst, Fe-C LT-FTS, and Fe-C HT-FTS; (**C**) Fe-C-K catalyst, Fe-C-K LT-FTS, and Fe-C-K HT-FTS.

Figure 1B shows the XRD patterns of the carbon-supported iron catalyst, Fe-C. Because activated carbon was utilized as a support, the large peak at 23◦ can be attributed to the amorphous structure of the carbon. The reflection at a value of 26.5◦ becomes more discernible during FTS reactions, and is attributed to the graphite carbon [19]. The peak at angles of 24◦ and 32◦ in both low- and high-temperature catalysts (Fe-C (LT-FTS) and Fe-C (HT-FTS)) demonstrates the creation of Fe2O3 [7].

Figure 1C shows the XRD patterns of the carbon-supported iron catalyst with potassium promoter (Fe-C-K). Iron carbide (Fe3C) synthesis in the Fe-C-K catalyst at an angle of 37◦ at low and high temperatures is responsible for the formation of gasoline [20]. During the activation procedure, Fe2O3 were converted to Fe3O4and Fe5C2 [21]. Researchers suggested that the creation of Fe5C2 at all times boosts diesel formation [22,23]. The Fe5C2 is considered as an active phase, and is critical for obtaining simultaneous improved selectivity and activity in iron-based Fisher–Tropsch synthesis. Thermal reduction and carburization methods have been frequently used for this purpose. The creation of Fe5C2 occurs during the FTS reaction, as shown by the post Fe-C catalyst, and this is observed at an angle of 44◦ [24]. It was thought that iron carbide (Fe3C) to Fe5C2, which has a better ability to pick out C5+, was the most active iron phase for making the FTs [25]. The results show that changing the catalyst qualities by changing the chemical and physical properties of carbon improves metal oxide reduction [7].

## *2.2. Scanning Electron Microscopy*

Scanning electron microscopy (SEM) images of activated carbon are shown in Figure 2a,b, demonstrating that its interior surface is riddled with voids. These chambers are upright to allow for the development and provision of iron particles, resulting in long-lasting contact between carbon and iron particles.

Figure 3a shows the precise development of iron particles on the surface of activated carbon. On the surface of activated carbon, the production of needle formations is uniformly distributed. The Fe-C (Figure 3b) iron particles are absorbed and agglomerated during the low-temperature (LT-FTS) reaction due to an increase in the Fe crystallite size. The Fe-C (Figure 3c) marginally alters the activation of iron oxides in a high-temperature (HT-FTS) reaction. This demonstrates that temperature has a significant impact on the structure and properties of the catalyst.

**Figure 2.** Scanning electron microscopy of prepared activated carbon (**a,b**) *Lantana Camara*.

**Figure 3.** Scanningelectron microscopy of Fe-C catalyst (**a**), Fe-C LT-FTS (**b**), and Fe-C HT-FTS (**c**).

In Figure 4a, the potassium particles are dispersed into the carbon surface to create the circular structure. This is because only 3% of the promoter was used. The needle and spherical Fe-C-K particles (Figure 4b) react inside the FT reactor to generate carbide particles when a low-temperature (LT-HTS) reaction is carried out. Figure 4c shows that Fe-C-K particles bonded each other to form active carbide phase at high temperatures (HT-FTS).

**Figure 4.** Scanning electron microscopy of Fe-C-K catalyst (**a**), Fe-C-K LT-FTS (**b**), and Fe-C-K HT-FTS (**c**).

#### *2.3. Energy-Dispersive X-ray Analysis*

The EDS results of the catalyst show that the increase in the carbon percentage in the catalysts are responsible for the development of the active carbide phase. Additionally, the presence of oxygen is responsible for the development of Fe2O3 and Fe3O4[26]. Table 1 shows the EDS analysis of the prepared catalysts.


**Table 1.** EDS elemental composition of FTS catalyst and activated carbon.
