Advanced Supported and Non Supported Polyoxometalate Materials for Oxidative Catalytic Reactions

In this work, new heterogeneous catalysts based on mesoporous silica nanoparticles (MSNPs) with different cations of ionic liquids (ILs) covalently bonded to their surface, 1-butyl-3-methylimidazolium ([C4MIM]+), 1-butylpyridinium ([C4Py]+) and tetrabutylammonium ([N4,4,4,4]+), and with the polyoxometalate (POM) derived from phosphomolybdic acid ([H(3-x)PMo12O40]x-) as anions were prepared. Their analogous homogeneous compounds were also prepared for comparison (POM-ILs), [N4,4,4,4]3[PMo12O40], [C4MIM]3[PMo12O40] and [C4Py]3[PMo12O40]. The catalysts were characterized by elemental analysis, in solution (1H and 31P) and solid-state (13C and 31P) NMR spectroscopy, DLS (for the silica nanoparticles), SEM, TEM, EDS, X-ray fluorescence spectroscopy, FTIR spectroscopy and ICP-MS. The homogeneous catalysts were applied in the preliminary oxidation reactions of two lignin model compounds, cinnamyl alcohol and guaiacol, varying the reaction conditions (time, presence of hydrogen peroxide and use of conventional heating or microwave heating). The results obtained were characterized by solution 1H NMR spectroscopy. The oxidation of cinnamyl alcohol seems to be promissory using microwave heating process in comparison to conventional process. All catalysts prepared were also applied in the oxidative desulfurization reactions of a multicomponent model diesel, composed by 1-benzothiophene, dibenzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene in order to study the performance of each catalyst in the removal of sulfur compounds present in fuels. This part of the study was performed in Faculdade de Ciências from Universidade do Porto, and the catalytic performance was evaluated by gas chromatography. The heterogeneous catalysts had the most promising results, in particular MSNPs-[N4,4,4,4]POM achieving 100% of total desulfurization after only 2 hours. Its recycling ability was evaluated for three consecutive cycles and it was observed an increase of the catalytic efficiency for the second and third cycles reaching the complete desulfurization of the model diesel after just 1h instead of the 2h. The catalysts with cation tetrabutylammonium had the best results in both heterogeneous and homogeneous catalysis in comparison to the other two catalysts. In general, all catalysts tested had interesting results