Paper Title
Tetrabutyl Ammonium Salts of Keggin-Type Polyoxometalate Catalysts for Selective Oxidation of Benzyl Alcohol towards Lignin Valorization

Abstract
A series of Mo tetrabutyl ammonium (TBA) salts with V-included Keggin-type polyoxoanions (TBA4PMo11V1O40 and TBA5PMo10V2O40) as addenda atoms were prepared using a hydrothermal method. These synthesized materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance (DRS UV-Vis), thermogravimetric analysis (TGA), CHN elemental analysis (EA), inductively coupled plasma spectrometry (ICP-MS) and N2 physisorption techniques to assess their physicochemical/textural properties and correlate them with their catalytic performances. According to FT-IR and DRS UV-Vis, (PVxMo12-xO40)(3+x)- anions are the main species present in the TBA salts. Additionally,CHN-EA and ICP-MS revealed that the desired stoichiometry was obtained. Their catalytic activities in the liquid-phase and aerobic oxidation of benzyl alcohol to benzaldehyde were studied at 5 bar of O2 and 170°C. Independently of the addenda atom nature the catalytic activity increased with the number of V in Keggin anion structure. For both series of catalysts, TBA salts of polyoxometalates with the highest V-substitution degree (TBA5PMo10V2O40 and TBA5PW10V2O40) showed the higher activity. The maximum benzyl alcohol conversion obtained was 93% and 97% using (TBA)5 PMo10V2O40 and (TBA)5 PW10V2O40 as catalysts, respectively. In all the cases, the selectivity toward benzaldehyde was higher than 99%. Finally, the catalysts were used in a operational conditions optimization by an RSM study by using phenethoxybenzene molecule, which is representative of the lignin B-O-4 bond.. This study offers the opportunity to investigate the effect of V-inclusion polyoxotugsto- and polyoxomolybdovanadates with Keggin structures in the catalytic oxidation of benzyl alcohol will help to a better understanding of the mechanisms involved in this reaction. This information will be useful for a next study in the catalytic oxidation of lignin. Keywords - Kegginphosphomolybdovanadate; Kegginphosphotungstovanadate; Lignin model compounds; Selective oxidation; Catalyst; Green oxidant.