Tuning the Integration Rate of Ce(Ln)O2 Nanoclusters into Nanoparticulated ZrO2 Supports: When the Cation Size Matters

Three nanostructured catalysts with low total rare earth elements (REEs) content (i.e., 15 mol.%) were prepared by depositing CeO(2)or Ln(3+)-doped CeO2(Ln(3+)= Y(3+)or La3+; Ln/Ce = 0.15) on the surface of ZrO(2)nanoparticles, as nanometre-thick, fluorite-type clusters. These samples were subjected to successive reduction treatments at increasing temperatures, from 500 to 900 degrees C. A characterisation study by XPS was performed to clarify the diffusion process of cerium into the bulk of ZrO(2)crystallites upon reduction to yield Ce(x)Zr(1-x)O(2-delta)surface phases, and the influence of the incorporation of non-reducible trivalent REE cations, with sizes smaller (Y3+) and larger (La3+) than Ce(4+)and Ce3+. For all nanocatalysts, a reduction treatment at a minimum temperature of 900 degrees C was required to accomplish a significant cerium diffusion. Notwithstanding, the size of the dopant noticeably affected the extent of this diffusion process. As compared to the undoped ZrO2-CeO(2)sample, Y(3+)incorporation slightly hindered the cerium diffusion, while the opposite effect was found for the La3+-doped nanocatalyst. Furthermore, such differences in cerium diffusion led to changes in the surface and nanostructural features of the oxides, which were tentatively correlated with the redox response of the thermally aged samples

Tailoring CO2 adsorption and activation properties of ceria nanocubes by coating with nanometre-thick yttria layers

[EN] Ceria (CeO2) is a ubiquitous component in catalysts for environmental protection processes, especially those devoted to CO2 valorisation. Aimed at preparing ceria-based nanomaterials with enhanced CO2 adsorption and activation properties, both the surface acid-base and redox features of ceria nanocubes were modulated by a novel, simple, wet chemistry synthetic strategy consisting of their coating with yttria (Y2O3) layers of variable thickness in the nanometre scale. The as-synthesised samples were characterised with special attention to their surface basicity and reducibility. Characterisation results revealed that the surface doping with yttria not only improved both the reducibility at low temperature and CO2 adsorption capacity of ceria nanocubes, but also introduced a variety of basic sites with different strength. Finally, the careful control of the yttria layer thickness allowed to modulate these effects and thereby the ability of nanostructured ceria to adsorb and activate the CO2 molecule

Methanation of carbon dioxide over ceria-praseodymia promoted Ni-alumina catalysts. Influence of metal loading, promoter composition and alumina modifier

[EN] Two series of ceria-praseodymia promoted Ni-alumina catalysts were prepared from two different commercial modified alumina supports (3.5 wt% SiO2-Al2O3 and 4.0 wt% La2O3-Al2O3) by the incipient wetness impregnation method in two successive steps. The resulting materials were characterized in terms of their physicochemical properties by means of N2 physical adsorption at −196 °C, powder X-ray diffraction (XRD) and temperature programmed reduction with H2 (H2-TPR). Furthermore, the as-prepared catalysts were tested for the CO2 methanation reaction in a fixed-bed reactor at atmospheric pressure, gas hourly space velocity (GHSV) of 72,000 cm3·(h·gcat)−1 and CO2/H2 molar ratio of 1/4 over the temperature range from 25 up to 850 °C. The influence of the nominal Ni loading (3, 5 and 10 wt%), molar composition of the Ce/Pr mixed oxide promoter (80/20 and 60/40), and alumina modifier (silica and lanthana) on the catalytic performance was carefully analyzed. Among these three composition parameters, the alumina dopant and especially the Ni content appear to have by far a much more pronounced effect on both the CO2 conversion and CH4 selectivity as compared to the Ce/Pr mixed oxide composition. Specifically, from the catalytic tests the sample containing a 10 wt% Ni loading, a Ce/Pr mixed oxide promoter of 80/20 molar composition, and silica as modifier provides the highest catalytic activity in terms of CO2 conversion and CH4 selectivity. Such behaviour has been ascribed to a complex interplay between several factors, mainly the larger fraction of catalytically active β-type NiO specie

The educational e-portfolio: preliminary evidence of its relationship with student\u2019s self-efficacy and engagement

The educational use of portfolios has been increasing in the last few years, especially as technology has also developed electronic versions of portfolios. Although there is abundant information about their benefits and practice description, few studies provide empirical evidence of their implementation. The objective of this study was to provide initial evidence about the use of the portfolio in higher education. Concretely, we aimed 1) to explore the correlation between students’ performance on the portfolio and their performance on more traditional assessment methods 2) to explore whether student’s personal variables predict performance in key elements of the e-portfolio, such as individual reflections, and if these contribute to general academic performance in the course, and 3) to evaluate whether the use of the e-portfolio during a semester changes the students’ self-efficacy and engagement. For this purpose, an initial sample of 73 students were recruited, and an e-portfolio (based on Mahara) was implemented over a semester. The results showed that performance on the portfolio correlated with the score obtained on multiple choice tests. There was an increase in self-efficacy after one semester of e-portfolio implementation, and engagement proved to be an important predictor of the final course grade through the mediation of individual reflections. These results offer preliminary and promising evidence about the relationship of a specific element of e-portfolios, individual reflections with several variables related to academic achievement such as self-efficacy and engagement

Adhesive behaviour of carbon fibre reinforced plastic panels manufactured using woven and unidirectional tape after ultraviolet laser surface treatment

This paper describes the results obtained when ultraviolet laser treatment was performed as a surface treatment prior to adhesive bonding for two aeronautical carbon fibre-reinforced plastics based on an epoxy resin prepreg. Different laser processing parameters were employed, and their effect on the surfaces was analysed through morphological characterisation and wettability studies. X-ray photoelectron spectroscopy measurements were performed to determine the cleaning and activation effects of the treatment. The strength of the bonded joint was studied for laser-treated and manually ground samples. Samples processed under the selected laser conditions exhibited better adhesive behaviour than the manually treated samples, thereby suggesting that ultraviolet laser treatment could be used as an alternative method for surface activation of aeronautical composites based on epoxy resin

Thermocatalytic CO2 Conversion over a Nickel-Loaded Ceria Nanostructured Catalyst: A NAP-XPS Study

Despite the increasing economic incentives and environmental advantages associated to their substitution, carbon-rich fossil fuels are expected to remain as the dominant worldwide source of energy through at least the next two decades and perhaps later. Therefore, both the control and reduction of CO2 emissions have become environmental issues of major concern and big challenges for the international scientific community. Among the proposed strategies to achieve these goals, conversion of CO2 by its reduction into high added value products, such as methane or syngas, has been widely agreed to be the most attractive from the environmental and economic points of view. In the present work, thermocatalytic reduction of CO2 with H-2 was studied over a nanostructured ceria-supported nickel catalyst. Ceria nanocubes were employed as support, while the nickel phase was supported by means a surfactant-free controlled chemical precipitation method. The resulting nanocatalyst was characterized in terms of its physicochemical properties, with special attention paid to both surface basicity and reducibility. The nanocatalyst was studied during CO2 reduction by means of Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS). Two different catalytic behaviors were observed depending on the reaction temperature. At low temperature, with both Ce and Ni in an oxidized state, CH4 formation was observed, whereas at high temperature above 500 degrees C, the reverse water gas shift reaction became dominant, with CO and H2O being the main products. NAP-XPS was revealed as a powerful tool to study the behavior of this nanostructured catalyst under reaction conditions

Influence of CO2-Ar Mixtures as Shielding Gas on Laser Welding of Al-Mg Alloys

In this study, AA5083 samples were butt welded under a conduction regime with high-power diode laser (HPDL). Various mixtures composed of Ar and CO2 were used as a shielding gas. The influence of the shielding gas composition on the microstructure and on the properties of laser welds was analyzed. The weld beads were deeply characterized by metallographic/micro- structural studies, X-ray diffraction (XRD), X-ray energy dispersive spectrometry (X-EDS) chemical analyses, X-ray photoelectron spectra (XPS), microhardness, and tensile strength. The corrosion resistance of laser-remelted surfaces with different CO2/Ar ratios was also estimated by means of electrochemical tests. The addition of CO2 to the shielding gas results in a better weld penetration and oxidizes the weld pool surface. This addition also promotes the migration of Mg toward the surface of weld beads and induces the formation of magnesium aluminates spinel on the welds. The best corrosion resistance result is achieved with 20 pct CO2. The overall results indicate that the addition of small percentage of CO2 to Ar leads to improvements of the mechanical and corrosion properties of the aluminum welds

Band gap engineering of ceria nanostructures by incorporating nitrogen-containing heterocyclic ligands.

[EN]A novel facile method to prepare ceria nanocrystals with well-defined cubic morphology and enhanced optical properties is herein disclosed. Both the decrease in the band gap and the appearance of absorption edges above 400 nm, which redound in a significant absorption of visible light, are accomplished by simply incorporating in situ different amounts of a typical chelating bidentate ligand, 1,10-phenanthroline, during the synthesis of these ceria nanocubes. Such a remarkable effect has been tentatively connected with the ability of this nitrogen-containing heterocyclic compound to coordinate Ce3+ cations from the ceria precursor salt, thus yielding intermediate N 2p states along the band gap of the oxide