## 4 Types of Catalysts Used in Transesterification
### Nano-Catalysts
#### 4.5.2 Plant and Animal Origin Green Nanocatalysts

Table 8: Clay derived heterogeneous catalyst for sustainable biodiesel production. However, sulfonated _Sargassum horneri_ carbon (10 wt. %) used as a phytonanocatalyst (acid solid catalyst) for oleic acid esterification in the presence of 1:15 M oleic acid/methanol ratio, 70 \({}^{\circ}\)C for 3 h resulting in a 96.4% biodiesel yield [119]. Rubber deoiled cake was used as waste derived heterogeneous acid catalyst, synthesized from Sulfuric acid and chlorosulfuric acid, and a 91.2% FAME yield was achieved from mixed non-edible oil [120]. Previous studies show the use of chicken bones to prepare economical solid base catalyst with same method (calcination at 900 \({}^{\circ}\)C for 4 h). A conversion yield of 89.3% FAME was achieved from soybean seed oil via 5% wt. catalyst loading, 1:15 oil to methanol molar ratio, reaction temperature (65 \({}^{\circ}\)C) and 4 h of reaction time in transesterification reaction. This catalyst was used four times for improvement of process efficiency. So, the reported catalyst appeared to be effective and a prospective substitute to homogeneous catalysts [121]. Animal bones modified by [PERSON] et al. (2017 (with potassium hydroxide to check its efficiency on transesterification of Jatropha under optimized conditions. Methanol to oil ratio was 9:1, 6% wt./wt. of oil taken, 3h reaction time at 70 \({}^{\circ}\)C and it resulted in a high conversion yield (96.1%) [122]. [PERSON] et al. (2018) synthesized CaO nanoparticles by using _Bombax cieiba_ seed extract to synthesize biodiesel from _Bombax cieiba_ seed oil and a 96.2% yield was achieved. The green nano-catalyst was reusable for up to 5 cycles [123]. Figure 8 presents the steps involved in synthesis of phytonanocatalyst by utilizing banana peel contains oxides of sodium and potassium. [PERSON] et al. (2018) used goat bone for transesterification of waste cooking oil and catalytically improved the bone by calcination with CaO and at 1:9 Oil: Met ratio at 65 \({}^{\circ}\)C for 5 h and a 84% yield was achieved with 3 reusability cycles [124]. In a study by [PERSON] et al. (2019), eggshell was used as catalyst up to 8 times and it was prepared from CaO under air static conditions for 2 h at 850 \({}^{\circ}\)C. The vegetable oil was converted to biodiesel with 1:9 oil to methanol molar ratio, 60 \({}^{\circ}\)C, 3 h time duration and 3% catalyst loading, and a 96% conversion efficiency was achieved. Thus, environmentally friendly and economical biodiesel was produced [125]. Many studies have been conducted that involved CaO catalyzed transesterification of oil and fat for biodiesel synthesis. Similarly, in addition to chemical basis, a number of experiments have been performed to synthesize alkaline heterogeneous nano catalysts of animal and plant origin that offer high conversion yield, as shown in Table 9.  
Figure 8: Synthesis of Phyto-nanocatalyst for biodiesel synthesis. So, it can be concluded that the nano-size of catalyst affects the biodiesel yield, owing to their large surface area for catalytic reaction to takes place thus enhancing the rate of reaction efficiently.