## 3 Results and Discussion
### Characterization of the Catalysts
#### 3.2.2 Immobilized POMs on Functionalized MRs  
* _IR Characterization of MR@Org_  
The IR spectra of **MR@Imd** and **MR@Pyr** (Figure 4) exhibit several key peaks that confirm the successful grafting of the imidazolium and pyridinium groups. Broad absorption bands observed in the 3100-3500 cm\({}^{-1}\) range correspond to N-H and C-H stretching vibrations, characteristic of imidazolium and pyridinium rings. The presence of peaks around 1600-1700 cm\({}^{-1}\) likely indicates C=N and C=C stretching. Additionally, multiple peaks in the fingerprint region (500-1500 cm\({}^{-1}\)) suggest vibrations associated with the grafted functional groups [54].  
* _Quantitification of the functional groups on MR@Org_  
The quantification of functional groups (Imd or Pyr) (Table 1) on the modified **MR** was essential before the immobilization of the POMs on the **MR@Org** surfaces. This quantification was possible by the determination of the N content of the **MR@Org** objects by elemental analysis. As described in Table 1, the content of the organic moieties (in mmol per g of **MR@Org**) is 1.5 and 1.6 for Imd and Pyr, respectively. Considering the Cl content of the **MR** (indicated to be 1.4-1.6 mmol/g), the values of Imd and Pyr indicate full substitution.  
* _Quantification of POM loading on MR@POM_ Based on these results, an accurate quantity of POMs was added for their immobilization on **MR@Org**. POM loading could be determined from TGA experiments (Table 1), with the remaining residue after 400 \({}^{\circ}\)C being attributed to the POM content. Compared to our previous work [52], the quaternization procedure significantly improved the accessibility of POMs to the ionically functionalized moieties. This enhancement resulted in POM loadings ranging from 0.40 to 0.44 mmol per gram of Merrifield resin (**MR**), which was substantially higher than the maximum loading of 66.7 mmol/g reported previously.
* _IR Analysis of MR@Org_@POM_ The successful immobilization of POMs on **MR@Org** was clearly demonstrated by IR spectroscopy, as shown in Figure 5. The IR spectra in orange correspond to either H\({}_{3}\)PMo\({}_{12}\)O\({}_{40}\) or H\({}_{4}\)PMo\({}_{11}\)VO\({}_{40}\), and those in blue correspond to the difference between **MROrg@POM** and **MR@Org** IR spectra (see the figure affiliation). Indeed, the characteristic vibrations attributed to POMs clearly indicated their presence at the surface of the materials. In particular, a shoulder at 1055-1100 cm\({}^{-1}\) corresponds to P-O vibrations, a sharp peak at 1000-900 cm\({}^{-1}\) is attributed to Mo-O stretching and metal-oxygen-metal bridging interactions are observed in the 850-700 cm\({}^{-1}\) region. The expected V-O absorption may be masked by overlapping Mo-O vibrations [51]. Also, a small peak observed around 1600 cm\({}^{-1}\) may be attributed to C=N stretching, and may originate from the pyridine and methylimidazole groups grafted onto it, which is further confirmed by elemental analysis (EA).  
\begin{table}
\begin{tabular}{c c c c} \hline  & **Imd or Pyr Content** & & **POM Loading** \\  & **(mmol/g MR) 1** & & **(mmol/g of MR@POM 2** \\ \hline \multirow{2}{*}{**MR@Imd**} & \multirow{2}{*}{1.5} & **MRIM@PMo\({}_{12}\)O\({}_{40}\)** & 0.444 \\  & & **MRIm@PMo\({}_{11}\)VO\({}_{40}\)** & 0.402 \\  & & **MRPy@PMo\({}_{12}\)O\({}_{40}\)** & 0.426 \\  & & **MRPy@PMo\({}_{11}\)VO\({}_{40}\)** & 0.43 \\ \hline \end{tabular} \({}^{\dagger}\) from E.A and 2 from TGA.  
\end{table}
Table 1: Imd and Pyr content on MROrg and POM loading on MR@POM.  
Figure 4: IR spectra of (**a**) **MR@Imd** and (**b**) **MR@Pyr**.