The influence of over-stoichiometry in La2Ni0.9V0.1O4.15+δ on selective oxidative dehydrogenation of propane

In this study, the non-stoichiometric redox compound La2Ni0.9V0.1O4.15+δ has been tested as an oxidant in selective oxidation of propane. The extent of over-stoichiometry (δ) was varied via both removing oxygen with propane in pulse experiments, as well as partial re-oxidation with oxygen. The optimal degree of over-stoichiometry (δ) has been quantified; olefins are formed whereas formation of CO2 is prevented provided that δ is below 0.03. Additionally, the structural stability of the material was tested with in situ X-ray diffraction in H2 (H2-XRD), temperature programmed reduction (TPR), thermo-gravimetric analysis (TGA), propane-pulse-experiments and re-oxidation cycles. La2Ni0.9V0.1O4.15+δ has demonstrated structure stability at 550 °C and reversibility during oxidation–reduction cycles at 800 °C. Therefore, La2Ni0.9V0.1O4.15+δ is considered suitable for selective oxidative dehydrogenation of propane, provided that the degree of over-stoichiometry is limited to 0.03

The WEBT BL Lacertae Campaign 2001 and its extension : Optical light curves and colour analysis 1994–2002

BL Lacertae has been the target of four observing campaigns by the Whole Earth Blazar Telescope (WEBT) collaboration. In this paper we present UBVRI light curves obtained by theWEBT from 1994 to 2002, including the last, extended BL Lac 2001 campaign. A total of about 7500 optical observations performed by 31 telescopes from Japan to Mexico have been collected, to be added to the ∼15 600 observations of the BL Lac Campaign 2000. All these data allow one to follow the source optical emission behaviour with unprecedented detail. The analysis of the colour indices reveals that the flux variability can be interpreted in terms of two components: longer-term variations occurring on a fewday time scale appear as mildly-chromatic events, while a strong bluer-when-brighter chromatism characterizes very fast (intraday) flares. By decoupling the two components, we quantify the degree of chromatism inferring that longer-term flux changes imply moving along a ∼0.1 bluerwhen- brighter slope in the B − R versus R plane; a steeper slope of ∼0.4 would distinguish the shorter-term variations. This means that, when considering the long-term trend, the B-band flux level is related to the R-band one according to a power law of index ∼1.1. Doppler factor variations on a “convex” spectrum could be the mechanism accounting for both the long-term variations and their slight chromatism.Reig Torres, Pablo, [email protected]

Effect of V in La2NixV1−xO4+δ on selective oxidative dehydrogenation of propane

In this study, non-stoichiometric redox compounds such as La2NiO4+δ, La2Ni0.95V0.05O4.07+δ and La2Ni0.9V0.1O4.15+δ have been tested as oxidants in selective oxidation of propane, in order to judge the suitability of these materials for a dense membrane reactor for selective propane oxidation. Reducibility of the samples has been investigated using temperature programmed reduction in H2/Ar flow. The catalysts’ activity and selectivity at 550 °C have been investigated employing sequential pulses of diluted propane over the oxides.\ud \ud Pulsing with propane induces step-by-step reduction of the oxide; consequently, the activity of remaining oxygen decreases with the number of pulses, affecting the products distribution. It is observed that at 550 °C on oxidized catalysts CO2 and H2O are the main products and the selectivity towards propylene is very low. At a certain reduction level, obtained after pulse 8 in our experiments, the production of CO2 stopped without changing the amount of C3H6 produced. At this stage, also CH4 and C2H4 are being formed. V-doped catalysts have shown a constant level of C3H6 production within a broad window of oxidation degree, while the performance of La2NiO4+δ, catalyst deteriorated drastically after just a few pulses. CO, CH4 and coke deposits are formed with La2NiO4+δ, caused by the formation of metallic Ni. Vanadium is able to prevent this phenomenon, thus drastically broadening the window of selective oxidation of propane