Artículos SCI

The photochemical conversion of methane into methanol from H2O2 aqueous solution as well as the effect of the addition mode were studied. Direct addition of different amounts H2O2 leads to increasing methanol production at the first stage of the reaction. The excess of H2O2 would lead to the reactive oxygen species scavenging and the subsequent O2 production. It was also corroborated that extra hydroxyl radicals in the aqueous medium do not improve the formation of methanol but a noticeable increase in the formation of HCOOH with respect to methanol was evidenced. In contrast, dosing addition at relatively low rates leads to constant methane consumption towards methanol. Methanol formation would be in this case in equilibrium with further oxidation to HCOOH or CO2. This suggests that only a controlled constant availability of HO’s at low concentration can enhance the performance of methanol generation in the photochemical process.

NiO and metal-promoted NiO catalysts (M-NiO, with a M/(M+Ni) atomic ratio of 0.08, with M = Nb, Sn, or La) have been prepared, tested in the oxidative dehydrogenation (ODH) of ethane, and characterized by means of XRD, TPR, HRTEM, Raman, XPS, and in situ XAS (using H-2/He, air or C2H6/He mixtures). The selectivity to ethylene during the ODH of ethane decreases according to the following trend: Nb NiO Sn NiO > La NiO > NiO, whereas the catalyst reducibility (determined by both TPR and XAS using H-2/He mixtures) shows the opposite trend. However, different reducibility and catalytic behavior in the absence of oxygen (ethane/He mixtures) have been observed, especially when comparing Nb- and Sn-promoted NiO samples. These differences can be ascribed mainly to a different phase distribution of the promoter. The results presented here are discussed in terms of the nature of active and selective sites for ODH of ethane in selective and unselective catalysts, but also the role of promoters and the importance of their phase distribution.