## 4 Conclusions  
This study demonstrated the efficient oxidation of two natural terpen, \(\beta\)-myrcene and \(\beta\)-caryophyllene, using Keggin-type polyoxometalates primarily based on molybdenum and vanadium surrounded by organic cations. These POMs were successfully grafted onto Merrifield resin (**MR**) functionalized with organic groups analogous to those in the ionic salts, yielding heterogeneous catalysts with excellent catalytic properties. Among the studied catalysts, **MRIMd@PMo\({}_{\text{11}}\)VO\({}_{\text{40}}\)**, featuring imidazolium as the organic cation and a vanadium-substituted POM, exhibited superior performance. This superiority was evident for both terpen, achieving very good conversions with high selectivity toward valuable oxidation products. To the best of our knowledge, this is the first time that V-containing POMs have achieved such transformations with those substrates. The catalytic oxidation utilized the benign oxidants hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) and tert-butyl hydroperoxide (TBHP) under solvent-free and green conditions, aligning with sustainable biomass vaporization principles. The ionic immobilization on **MR** allowed easy catalyst recovery and reuse, with the grafted catalysts maintaining their activity and selectivity over at least three consecutive cycles without detectable leaching. Overall, the results highlight the promising potential of organic-salt-modified and POM-grafted Merrifield resin catalysts for selective terpene oxidation, combining efficient conversion, high selectivity, catalyst recyclability and environmentally friendly process conditions. The comparative analysis of homogeneous versus heterogeneous systems underscores the advantages of the immobilized catalysts in practical applications. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app15147981/s1](https://www.mdpi.com/article/10.3390/app15147981/s1)]([https://www.mdpi.com/article/10.3390/app15147981/s1](https://www.mdpi.com/article/10.3390/app15147981/s1)), Figure S1: IR spectrum of (**BmIm)\({}_{3}\)PMo\({}_{\text{12}}\)O\({}_{\text{40}}\)**. Figure S2: IR spectrum of (**BmIm)\({}_{4}\)PMo\({}_{\text{11}}\)VO\({}_{\text{40}}\)**, Figure S3: IR spectrum of (**BuPy)\({}_  
of **(BuPy)\({}_{3}\)PMo\({}_{12}\)O\({}_{40}\)** in d\(\rm{mso}\)-d\({}_{6}\), Figure S16: \({}^{13}\)C[\({}^{1}\)H] NMR spectrum of **(BuPy)\({}_{4}\)PMo\({}_{11}\)VO\({}_{40}\)** in d\(\rm{mso}\)-d\({}_{6}\), Figure S17: \({}^{31}\)P[\({}^{1}\)H] NMR spectrum of **(BmIm)\({}_{3}\)PMo\({}_{12}\)O\({}_{40}\)** in d\(\rm{mso}\)-d\({}_{6}\), Figure S18: \({}^{31}\)P[\({}^{1}\)H] NMR spectrum of **(BmIm)\({}_{4}\)PMo\({}_{11}\)V\({}_{1}\)O\({}_{40}\)** in d\(\rm{mso}\)-d\({}_{6}\), Figure S19: \({}^{31}\)P[\({}^{1}\)H] NMR spectrum of **(BuPy)\({}_{3}\)PMo\({}_{12}\)O\({}_{40}\)** in d\(\rm{mso}\)-d\({}_{6}\), Figure S20: \({}^{31}\)P[\({}^{1}\)H] NMR spectrum of **(BuPy)\({}_{4}\)PMo\({}_{11}\)V\({}_{1}\)O\({}_{40}\)** in d\(\rm{mso}\)-d\({}_{6}\), Figure S21: \({}^{31}\)P and \({}^{13}\)C MAS NMR spectra of **MRImd@PMo\({}_{11}\)VO\({}_{40}\)** before and after the three catalytic runs. Conceptualization, methodology and validation, D.A., A.A.H.H. and P.G. ; formal analysis and investigation, A.A.H.H. ; resources, D.A. and P.G. ; data curation, D.A. and A.A.H.H. ; writing--original draft preparation, A.A.H.H. ; writing--review and editing, D.A., A.A.H.H. and P.G. ; supervision, project administration and funding acquisition, D.A. and P.G. All authors have read and agreed to the published version of the manuscript. This work was funded by the CNRS, the Region Occitanie [Project GreenCatNat grant number N\({}^{\circ}\) 00138053/22009739], the IUT Toulouse Auch Castres and the IUT Chemistry Department and the Syndicat Mixte de la Communaute d'Agglomeration Castres-Mazamet. The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed to the corresponding author.