## 3 Results and Discussion
### Effect of CNT Functionalization  
The CNT-NM hybrids were used as catalysts in the Heck reaction of iodobenzene with styrene. All the reactions were carried out keeping substrate to Pd molar ratio constant at 0.01 mole percent. In all cases, trans-stilbene was the only product detected which was established by the single spot in the TLC analysis and confirmed by GC analysis. This was also confirmed by the melting point of 122.5 \({}^{\circ}\)C and UV max at 296 nm of the isolated product. The mechanism of the reaction in presence of PPh\({}_{3}\) is shown in Figure 5. In general, the Pd from the CNT-NM desorbed to a soluble form to form a loose complex such as Pd(PPh\({}_{3}\))\({}_{4}\). These complexes were more soluble than Pd and facilitated desorption of Pd from the catalyst. This may account for the high yield observed in the presence of PPh\({}_{3}\). At the end of the reaction, the Pd readsorbed on the CNT phase. Table 2 presents isolated yields of all the reactions after the completion of the reaction and recrystallization. The results of reaction at 150 \({}^{\circ}\)C are presented in Table 2 and Figure 6. In general, shorter reaction times and greater yields were obtained with p-MWCNT-Pd and np-MWCNT-Pd compared to Pd/C, demonstrating the superiority of these nanohybrids in the reaction. The time to completion for the reaction for both p-MWCNT-Pd and np-MWCNT-Pd were 60 min in DMF compared to 90 min for Pd/C. Similar results are also seen in Figure 6, where yield enhancement of CNT-NM hybrids with respect to Pd/C is also presented. Figure 5: The role of CNT-Pd in the in the Heck reaction. It is estimated that the ODA group will cause steric hindrance of the reactants. To test this hypothesis, the reactions were carried out under microwave conditions in absence of solvent. The reaction was complete in 17 min. During microwave heating, the CNT catalysts were seen to mix uniformly in the reaction mixture. The isolated yields for the reactions are shown in Table 2. The yield was much higher in the p-MWCNT-Pd than in np-MWCNT-Pd. The difference was attributed to steric effects, where the ODA group provided steric hindrances leading to lower yield. In DMF, the p-MWCNT-Pd showed higher catalytic activity than np-MWCNT-Pd which was better than commercial Pd/C and PdCl\({}_{2}\). The yield for p-MWCNT-Pd reached as high as 99.78% in DMF, \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**S.No.**} & \multirow{2}{*}{**Catalyst**} & **Reaction Completion** & \multirow{2}{*}{**\% Yield**} & **Yield** \\  & & **Time (min)** & & **Enhancement** \\ \hline \multicolumn{5}{c}{Dimethylformamide (DMF) as solvent} \\ \hline
1 & Pd/C & 90 & 55.70 & - \\
2 & np-MWCNT-Pd & 60 & 58.70 & 5\% \\
3 & p-MWCNT-Pd & 60 & 99.78 & 79\% \\
4 & PdCl\({}_{2}\) & 120 & 45.67 & - \\ \hline \multicolumn{5}{c}{Toluene as solvent} \\ \hline
5 & Pd/C & 105 & 10.90 & - \\
6 & p-MWCNT-Pd & 90 & 14.39 & 32\% \\
7 & np-MWCNT-Pd & 90 & 17.44 & 60\% \\ \hline \multicolumn{5}{c}{Microwave (solvent free)} \\ \hline
8 & p-MWCNT-Pd & 17 & 90.01 & - \\
9 & np-MWCNT-Pd & 17 & 66.92 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Isolated yields of all the reactions at completion. Analysis was done after recrystallization. Figure 6: Yields of the CNT-metal nanohybrids and Pd/C catalyzed reactions (**a**) in DMF and (**b**) in toluene from GC analysis (Tri-butyl amine as base, temp 150 \({}^{\circ}\)C); (**c**) yield enhancement with respect to Pd/C in DMF; (**d**) enhancement with respect to Pd/C in toluene. whereas np-MWCNT-Pd, Pd/C, and PdCl\({}_{2}\) showed yields of 58.7%, 55.7%, and 45.7%, respectively. The catalytic activity of p-MWCNT-Pd with larger particle size was higher than np-MWCNT-Pd with smaller particle size (Table 1). The p-MWCNT-Pd was more polar than np-MWCNT-Pd and its interactions with DMF, which is a polar solvent, were better. Also, the long C\({}_{18}\) chain from octadecyl group in np-MWCNT-Pd may have provided some steric hindrance to the reactants.