## 3 Results and Discussion
### Catalytic Tests Results  
#### 3.2.1 Homogeneous Catalytic Reactions  
Homogeneous reactions were conducted to assess the selectivity and activity of the nickel-\(\beta\)-diimine complex so that those parameters could be compared with those of the catalytic tests performed with the heterogenized catalyst probably due to decomposition.  
Table 4 presents the results of the catalytic tests. The ratio of Al/Ni was varied between 25 and 100 (entries 1-4). The highest activity was achieved at an Al/Ni ratio of 50, and the highest selectivity in butenes at an Al/Ni ratio of 25. The increase in activity with the Al/Ni ratio may be explained by an increase in the number of active species in the reaction medium. The maximum reactivity occurs before a decrease in activity, indicating catalyst deactivation, probably due to decomposition.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Support** & **A\({}_{\text{BET}}\) a (m\({}^{2}\) g\({}^{-1}\))** & **Pore Diameter b (Å)** \\ \hline MCM-41 & 1038 & 34 \\ IL-MCM-41 & 403 & 28 \\ Al-MCM-41 & 860 & 29 \\ IL-Al-MCM-41 & 465 & 25 \\ Zeo\(\beta\) & 418 & - \\ IL-Zeo\(\beta\) & 32 & - \\ \hline \hline \end{tabular}  
* A\({}_{\text{BET}}\) = specific area obtained using the BET method (total area). b Dp = average pore diameter calculated by intervals obtained using the BJH desorption method.  
\end{table}
Table 2: Structural properties of the synthesized materials.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Support** & **(mmol Ni/g of Support)** & **(mmol Ni/g of Support)** \\ \cline{2-3}  & **Added** & **by AAS** \\ \hline NiIL-Zeo\(\beta\) & & 0.21 \\ NiIL-MCM-41 & & 0.23 \\ NiIL-Al-MCM-41 & & 0.24 \\ NiIL-Zeo\(\beta\) & & 0.10 a  \\ \hline \hline \end{tabular}  
* A\({}_{\text{BET}}\) = specific area obtained using the BET method (total area). b Dp = average pore diameter calculated by intervals obtained using the BJH desorption method.  
\end{table}
Table 3: The results from the atomic absorption spectroscopy (AAS) analysis of the \(\beta\)-diimine/\(\beta\)-zeolite nickel complex.  
When the amount of catalyst was changed from 5 to 10 \(\upmu\)mol (entries 2 and 6), the activity and selectivity of the system decreased. This may be interpreted as resulting from an increase in the number of moles of catalyst precursor, which promotes an increase in the amount of active species in the reaction. Thus, the relative amount of ethylene reacting with the catalytic species is reduced, resulting in lower activity and selectivity in butenes. The reduction was mainly observed in 1-butene selectivity, due to parallel isomerization reaction. C\({}_{6}\) production is not significantly affected, and C\({}_{8}\) products slightly increase. This is consistent with the results reported by [PERSON] et al. [29].  
By increasing the initial reaction temperature from 10 to 23 \({}^{\circ}\)C (entries 4 and 5), the activity of the system also increases. [PERSON] et al. and [PERSON] et al. [30,31] studied the influences of reaction temperature on oligomerization when using nickel complexes and found that the 1-butene best selectivity is achieved at low temperatures. Therefore, the subsequent reactions were performed at 10 \({}^{\circ}\)C.  
The last parameter to be studied was the pressure (entries 2 and 7). In the determination of the effects of pressure on the activity and selectivity in ethylene oligomerization, it can be observed that there are no meaningful changes in the selectivity of the system, likely because the system is close to ethylene saturation.  
Comparing these results with the industrial Shell High Olefins Process (SHOP), our oligomerization process is more selective to light olefins (C\({}_{4}\)-C\({}_{8}\)), while SHOP results in a larger range (C\({}_{4}\)-C\({}_{40}\)).