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Abstract: The study of isoprene (2-methyl-1,3-butadiene) gas phase hydrogenation on ThNi2 and UNi2 was undertaken and the effect of the 5f element on nickel catalytic behavior investigated. At nearly steady state, the reaction products were isopentane and isopentenes (2-methyl-2-butene, 2-methyl-1-butene and 3-methyl-1-butene). The total selectivity to isopentenes was higher on ThNi2 (∼80mol%) than on UNi2 (∼50mol%) but, in both cases lower than that on pure Ni (∼96mol%). The sum of 2-methyl-2-butene+2-methyl-1-butene selectivities (valuable products for the tert-amyl methyl ether process) was ∼75mol% on ThNi2, whereas on UNi2 it was significantly lower (∼50mol%). ThNi2 and UNi2 total selectivity to isopentenes is nearly time invariant. The difference of catalytic properties between ThNi2 and UNi2 can be explained by electronic transfer from the 5f element to Ni that generates an electronic density supply on nickel, which is higher on ThNi2. [Copyright &y& Elsevier]

Abstract: Soda-lime glasses doped with Eu3+ were synthesized using a variety of compositions, namely changing the fraction of CaO or Eu2O3. Those glasses were characterized with several techniques, including ellipsometry, UV–vis–NIR absorption spectroscopy, steady-state photoluminescence spectroscopy and time-resolved luminescence. The compositions' effects on optical properties such as refraction indexes, Eu3+ oscillator strengths and luminescence lifetimes were accessed from the analysis of the experimental results. Judd–Ofelt theory was used to analyze all these aspects, which allow the detection of a mismatch of optical properties from absorption and emission spectroscopy. This mismatch was confirmed from the time-resolved data, showing the existence of two different spectroscopic Eu3+ species. From those results it is concluded that there is evidence for lanthanide aggregation, giving rise to self-quenching effects that may be described through resonance energy transfer mechanisms. The difference between luminescence lifetimes for isolated and aggregated Eu(III) is interpreted as due to different interactions with oxygen in the matrix, namely degree of covalency of the Eu–O bond and point group symmetry of the lanthanide. [Copyright &y& Elsevier]