Adriana Urdă

NiO-based catalysts are among the most active and selective catalytic systems for low-temperature oxidative dehydrogenation (ODH) of ethane into ethylene and, therefore, they have been extensively studied in the last twenty-five years. This paper reviews the most relevant works focusing on NiO-based catalysts for ethane ODH, including promoted and unpromoted, bulk and supported NiO. The effects of the nature of the promoter and of the support together with the influence of the method of preparation used on their activity in ethane ODH are discussed in detail as they were shown to be key factors controlling the catalytic performance, including the catalyst stability. The reaction mechanism involved in ethane ODH reaction over NiO-based catalysts is also presented and discussed.

Ceria materials doped by Gd and/or Pr were prepared by a precipitation route and calcined in air at 500 and 900 °C. The effects of doping and thermal treatment on the materials' surfaces were studied by X-ray photoelectron and Raman spectroscopies. The redox properties were investigated using temperature-programmed reduction experiments in H₂ and CH₄ followed by temperature-programmed oxidation in O₂. The catalytic properties of these materials in CH₄/H₂O reaction in the absence/presence of H₂S were evaluated at 750 °C in a large excess of CH₄ with respect to H₂O. The materials were classified by order of reactivity as follows: CPO > CGPO > CeO₂ > CGO, which can be primarily related to the surface area variation. Comparing the activity per m² of various samples indicates that the catalytic activity is correlated with the Ce³⁺ concentration at the surface as measured by XPS. Gd-doped and undoped samples exhibit the highest surface Ce³⁺ concentration as well as the highest activity in SMR per m², while Pr-doped samples are the least active (activity per m²) with the lowest surface Ce³⁺ concentrations. H₂S has a sharp promoting effect on the catalytic behavior of ceria-based materials, improving the production of H₂ by almost one order of magnitude.

The catalytic properties of ZnAlVO mixed oxides derived from decavanadate-exchanged ZnAl–layered double hydroxide (LDH) precursors prepared by a sol–gel method (ZnAlVO–LDH x,y ) were investigated in the oxidative dehydrogenation of propane and compared with those of supported catalysts obtained by conventional impregnation of NH ₄ VO ₃ on ZnO (ZnVO-I, y ) and ZnAlO mixed oxide (ZnAlVO-I, y ) supports. The effects of composition and calcination time on the catalytic behavior were particularly examined. Higher propane conversions were achieved at higher vanadium content and calcination time of the precursors. The LDH-derived catalysts were the most active ones in all the temperature range studied (300–425 °C). The order of activity for propane conversion for the different catalyst families varies as ZnAlVO–LDH x,y > ZnAlVO-I > ZnVO-I and follows the strength of the Lewis and Brønsted acid sites determined by monitoring of pyridine adsorption by Fourier transform infrared spectroscopy, whereas the propene selectivities are close together in agreement with the similar densities of basic sites determined by CO ₂ –temperature-programmed desorption measurements. It was indeed established that the acidity, rather than the nature of the crystalline phases, the reducibility, or the specific surface area of the samples, governs the catalytic activity.

Herein, we report on the pure and almost pure near-infrared (NIR) emission at around 807 nm observed for Tm(Yb) (co)-doped CeO₂ nanoparticles (NPs) under UV, X-ray and NIR up-conversion excitation. The optical responses are attributed to the low-lying charge-transfer of CeO₂ that acts as a selective antenna sensitizer of the Tm ³H₄ emission and Yb doping that lowers the local symmetry at Tm sites and introduces additional phonon modes. Selective antenna sensitization is also observed for Er/Ho (Yb) (co)-doped CeO₂ NPs. To the best of our knowledge, this is a first study which correlates the down- and up-conversion emission properties of lanthanide(s)-(co) dopants with the CeO₂ structure highlighting also the outstanding potential of these NPs in high-penetration tissue imaging and therapy.

Vanadium-molybdenum oxides supported on Al2O3, CeO2 and TiO2 were prepared by a ?wet? impregnation method, characterized using DRX, N2 adsorption, UV-Vis spectroscopy, electrical conductivity measurements and tested in the oxidative dehydrogenation of isobutane. The catalytic performance in the oxidative dehydrogenation of isobutane at 400-550?C depended on the nature of support and on the content of VMoO species on the support. The catalysts supported on alumina were more active and selective than those supported on ceria and titania.