## 3 Results and Discussion
### Catalytic Tests Results
#### 3.2.2 Catalytic Tests in Heterogeneous Reactions  
The catalytic properties of the \(\beta\)-zeolite-supported nickel-\(\beta\)-diimine complex were tested under different reaction conditions, as shown in Table 5. These experiments were performed to find the conditions under which the reaction showed the best activity and selectivity. We used the same amount of heterogenized catalyst precursor as was determined in the optimization of the homogeneous catalysis (i.e., 5 \(\upmu\)mol). The first parameter studied was the Al/Ni molar ratio. Entries 8, 9 and 10 present the results of catalytic tests with different molar ratios of aluminum from the cocatalyst and nickel. These results show that as we increase the Al/Ni molar ratio, the activity of the catalyst also increases due to the increase in the concentration of active species present in the reaction mixture. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Entry**} & \multirow{2}{*}{**Catalyst (\(\upmu\)mol)**} & \multirow{2}{*}{**Al/Ni**} & \multirow{2}{*}{**T (\({}^{\circ}\)C)**} & \multirow{2}{*}{**Pressure (\(\upmu\)m)**} & \multirow{2}{*}{**TOF (s\({}^{-1}\))**} & \multicolumn{3}{c}{**Selectivity (\%)**} \\ \cline{5-8}  & & & & & & **C\({}_{4}\) (1-C\({}_{4}\))** & \(\mathbf{C_{6}}\) & \(\mathbf{C_{\geq 8}}\) \\ \hline
1 & 5 & 25 & 10 & 5 & 4.7 \(\pm\) 0.1 & 85 (77) & 10 & 5 \\
2 & 5 & 50 & 10 & 5 & 19.3 \(\pm\) 0.2 & 78 (45) & 20 & 2 \\
3 & 5 & 75 & 10 & 5 & 15.9 \(\pm\) 0.2 & 77 (31) & 17 & 6 \\
4 & 5 & 100 & 10 & 5 & 14.4 \(\pm\) 0.2 & 85 (48) & 13 & 2 \\
5 & 5 & 100 & 23 & 5 & 73.1 \(\pm\) 0.2 & 79 (26) & 19 & 2 \\
6 & 10 & 50 & 10 & 5 & 15.7 \(\pm\) 0.2 & 76 (31) & 19 & 5 \\
7 & 5 & 50 & 10 & 10 & 18.0 \(\pm\) 0.2 & 80 (40) & 17 & 3 \\ \hline \hline \end{tabular} Reaction conditions: solvent = toluene, cocatalyst = ethylaluminum sesquichloride (EASC).  
\end{table} 
Table 4: Activity and selectivity in homogeneous catalytic reactions. After assessing the effect of the Al/Ni molar ratio, we set out to determine the optimal temperature for the reaction to obtain the best activity and selectivity in the production of butenes. As shown in entry 10, when the reaction was conducted at 10 \({}^{\circ}\)C, the selectivity was approximately 74% for 1-butene. Based on entry 11, when the reaction was performed at 23 \({}^{\circ}\)C, there was a decrease in the selectivity for 1-butene (approximately 43%) compared to entry 10. Using the conditions described above, this system shows higher selectivity than the homogeneous system (entries 4 and 5, Table 4), so the other reactions were performed at 10 \({}^{\circ}\)C.  
The following studies were performed with pressures between 2.5, 5 and 10 atm to determine the effect of pressure on the activity of the oligomerization of ethylene. It can be observed from entries 9, 12 and 13 that the role of pressure in the system is very important. When comparing the results of reactions run at 2.5 and 5 atm, a slight difference in activity values can be observed, which can be explained by the difficulty of ethylene insertion into the cavities of zeolite due to the presence of the ionic liquid used as catalyst support. On the other hand, increasing the pressure from 5 to 10 atm increases the solubility of ethylene and, as a result, the ethylene enters the cavities, making it closer to the active species, which may explain the increased activity. When comparing the homogeneous (entry 7, Table 4) and heterogeneous (entry 13, Table 5) reactions at 10 atm, it was observed that the heterogeneous reaction was more selective than the homogeneous reaction for 1-butene, which shows that the catalyst lies within the cavities of the \(\beta\)-zeolite and that the increase in selectivity is due to the confinement effect of the catalyst. However, based on the selectivities observed in hexenes and octenes, the reaction may also be occurring with the homogeneous catalyst, as demonstrated by atomic absorption analysis after the reaction of the nickel complex immobilized on \(\beta\)-zeolite.