Artículos SCI

The hexagonal and monoclinic phases of CePO4 have been demonstrated to be excellent catalytic supports for Pt-based water-gas shift (WGS) catalysts. Consequently, the elucidation of the WGS reaction mechanism in these materials constitutes a fundamental aspect in order to explain their catalytic behavior. Because the observed WGS reaction path is closely related to the absence or presence of oxygen vacancies in the support, the study of the oxygen mobility in these solids constitutes a key factor for the understanding of the structure of the materials and its influence on the reaction mechanism. In this study, the oxygen mobility in CePO4 supports and the corresponding Pt catalysts has been evaluated by means of isotopic exchange experiments using O-18(2) and (CO2)-O-18 as probe molecules. Results demonstrate that the evaluated solids present a low exchange activity when O-18(2) is used, indicating the absence of oxygen vacancies in these solids, thus suggesting a poor influence of the WGS redox mechanism. On the contrary, a high oxygen exchange activity is observed using (CO2)-O-18, demonstrating that the exchange in these materials takes place through the formation of carbonate-like intermediates, thus suggesting the associative mechanism of the WGS reaction as the preferred path in these solids. Operando diffuse reflectance infrared spectroscopy experiments under WGS reaction conditions confirm these results, proving that the WGS reaction in the studied materials takes place through a formate-mediated associative mechanism.

Vanillin hydrodeoxygenation was investigated using noble metal (Pd, Au, Ru) supported on active carbon prepared from waste derived biochars, which were produced via pyrolysis in CO2 atmosphere. Chemical activation with ZnCl2 and HNO3 was also used in the preparation of active carbon to enhance the specific surface area and demineralize material, respectively. Both fresh and spent catalysts were characterized with X-ray diffraction, DRIFTS, zeta potential measurement and HR-TEM. The highest selectivity to p-creosol, 92 % selectivity at complete vanillin conversion after 3 h was obtained in vanillin hydrodeoxygenation at 100 degrees C under 30 bar in hydrogen in water with Pd/C catalyst prepared via pyrolysis under CO2 from wine waste and using ZnCl2 as a chemical activation agent. Hydrodeoxygenation activity increased with increasing metal dispersion. A kinetic model including adsorption of vanillin described well the experimental data.