Abstract

A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA(4)PW(11)V(1)O(40) and TBA(5)PW(10)V(2)O(40)) and Mo (TBA(4)PMo(11)V(1)O(40) and TBA(5)PMo(10)V(2)O(40)) 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 N-2 physisorption techniques to assess their physicochemical/textural properties and correlate them with their catalytic performances. According to FT-IR and DRS UV-Vis, (PVXW(Mo)(12-X)O-40)((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 aerobic oxidation of benzyl alcohol to benzaldehyde were studied at 5 bar of O-2 at 170 degrees C. Independently of the addenda atom nature, the catalytic activity increased with the number of V in the Keggin anion structure. For both series of catalysts, TBA salts of polyoxometalates with the highest V-substitution degree (TBA(5)PMo(10)V(2)O(40) and TBA(5)PW(10)V(2)O(40)) showed higher activity. The maximum benzyl alcohol conversions obtained were 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%.