XANES studies of zirconia-ceria/Ni during partial/total methane oxidation

Zirconia-ceria solid-solutions are extensively used as promoters for three-way catalysts, in addition, these materials can be used as anodes in solid oxide fuel cells (SOFCs) operated with hydrocarbons. The structural features of ZrO2-CeO2 materials in combination with oxygen storage/release capacity (OSC) are crucial for various catalytic reactions. The direct use of hydrocarbons as fuel for the SOFC (instead of pure H2), without the necessity of reforming and purification reactors can improve global efficiency of the system. The samples preparation method was developed using Zr and Ce chloride precursors, HCl aqueous solution, Pluronic P123, NH4OH and a Teflon autoclave. The samples were dried and calcined, until 540°C. The NiO impregnation was made with an ethanol dispersion of Ni(NO3)×6H2O, calcinated in air until 350°C for 2 hours. In-situ XANES experiments are capable to evaluate the reduction/oxidation potencial of Ni and Ce species in ZrO2-CeO2/Ni samples during partial/total methane oxidation and reduction reactions with H2. The experiments at the Ni K-edge/Ce L3-edge were collected at the LNLS D06A-DXAS beam line in transmission mode, using a Si(111) monochromator and a CCD camera as detector. The data were acquired during a series of temperature programmed reduction steps (TPR), under a 5% H2/He until 600°C, and mixtures of 20%CH4:5%O2/He with 2:1, 1:1 and 1:2 ratios. After each process with CH4 and O2, a TPR procedure was performed in order to evaluate the reduction capacity of the sample after reactions with CH4. The results demonstrated that NiO embedded in the porous ZrO2-CeO2 matrix, reduces at lower temperatures than standard NiO, measured in the same conditions, revealing that the mesoporous support improves the reduction of impregnated NiO. For both edges, there was formation of H2 during partial methane oxidation at 600°C. The total oxidation of methane was observed in lower temperatures (500°C). These results reveal that a high ceria content (90%) could be a great candidate for the SOFC anode.

Structural Characterization of Mg₂CoH₅-based Nanocomposites for Hydrogen Storage

Hydrogen is considered the ideal energy carrier, mainly due to its heating power, the highest among all chemical fuels, and to possibility of using it in fuel cells, therefore with efficiency and producing only water as by-product. However, the development of safe and effective hydrogen storage solutions remains as a challenge of applied research. MgH₂, Mg₂FeH6 and Mg₂CoH₅ complex hydrides are promising materials for hydrogen storage, avoiding the inconvenient of gaseous or liquid storage alternatives. The main attractives of these phases are their volumetric and gravimetric hydrogen capacities, their reversibility during absorption/desorption cycles and the relatively low cost. Recently, we have achieved an important control of the synthesis of Mg-based complex hydrides with nanocrystalline structure, using reactive milling (RM) under hydrogen atmosphere as processing route [1, 2]. In this study, we present new results concerning the synthesis, hydrogen storage properties and structural characterization of MgH₂-Mg₂CoH₅ nanocomposites prepared by RM. The nanocomposites were produced by milling different Mg-Co starting compositions (2:1, 3:1, 5:1, 7:1, 1:0) for 12 h in a planetary mill under 3 MPa of H₂. All samples were fully hydrogenated during milling, generating different MgH₂-Mg₂CoH₅ hydride mixtures. Mg presents the tendency of agglomerate during milling, so the sample that presents more MgH₂ shows larger agglomerates. This behavior causes a slight increase in the temperature of hydrogen desorption and the presence of two peaks, showed by DSC analysis for those samples which presents MgH₂ and Mg₂CoH₅. Using in-situ XRD and XANES during hydrogen desorption revealed that Mg and Co tend to remain coupled forming intermetallics after the complex hydride decomposition, differently from that was observed for Mg₂FeH6. This effect is correlated to the high-reversibility exhibited by the Mg₂CoH₅ phase. Furthermore, the nanocomposites of MgH₂+Mg₂CoH₅ showed better H-absorption/desorption kinetics than the Mg₂CoH₅ or MgH₂ alone, as shown by volumetric measurements. The combination of MgH₂ and Mg₂CoH₅ is therefore a promising strategy to produce hydrogen storage materials, matching the good reversibility and high capacity of magnesium hydride with the lower thermal stability.

Crystallography for teachers

In this work we present and analysis of the influence of workshop activities performed in our city regarding the dissemination of crystallographic science in all educational levels. The organized workshops in honor of the IYCr are aimed to introduce crystallography to elementary and high schools teachers. The main goal is to improve teachers' knowledge in crystal formation and its techniques. This will allow teachers to elaborate laboratory projects that include crystallography principles according to their own students' level and to encourage the participation in the national and international crystal growing competition. Topics: 1. Introduction to crystallography 2. Atomic structure, chemical bonds and periodic table 3. Types of crystalline solids: metallic, ionic and covalent 4. Crystalline systems 5. Introduction to structure determination using X-ray diffraction 6. Crystal growing

Argentinean crystal growing competition for high school students

To celebrate the International Year of Crystallography 2014, the Argentinian Crystallography Association ("Asociación Argentina de Cristalografía", AACr) [1] has launched the Crystal Growing Competition to be held June-October 2014 among Argentinean high school students. This activity is sponsored by the IUCr, CONICET (Argentinean Science Council) and MinCyT (Argentinean Ministry of Science, Innovation and Technology). Based on IUCr suggestion [2] and successful previous experiences in other countries [3], we planned the program of the activity. Before the contest, a five hours course including the basic concepts of crystal growing and crystallization experiences demonstrations will be offer for the teachers of the interested schools. They will take place at different regions of the country during April. The information of the contest together with the instructions on how to grow crystals and guidelines for the teachers will be provided on the web. After the students sign up, they will growth their crystals and create a slideshow presentation or a video to show their work to the evaluation committee before the end of August 2014. Winners will be announced on September 15th, they will be invited to show their work at the X Annual Meeting of the Argentinean Crystallographic Association, Mar del Plata, Argentine, 28-31 October 2014. A special session will be held as a satellite activity of the meeting on October 27th and the awards ceremony of the Crystal Growing Competition will be during the opening ceremony. Besides this, everyone participating of the Argentinean contest has a chance to compete in the International Crystal Growing Competition. Trough this exciting, funny and hands-on scientific experience, crystallography and other related scientific fields will be promoted along the high school community across the country being also, a way to encourage youth to continue exploring science and developing their scientific skills.

Argentinian Association of Crystallography: IYCr activities and 10th anniversary

"The history of Crystallography in Argentina is very rich, probably starting with the pioneer work of Prof. Ernesto Galloni in the decade of the `40s. Thanks to Prof. Galloni, the National Committee of Crystallography was founded in 1958 and recognized by the IUCr in 1960. This committee organized several scientific meetings and was in good contact with the Ibero American Crystallography Group during about 35 years. After some crisis in the late `90s, some young crystallographers decided to reorganize the activities and form the Argentinian Association of Crystallography (AACr), which was finally founded on October 30th, 2004, on the occasion of the ""National Workshop on Crystallography"" held in Villa Giardino, Province of Córdoba. Therefore, in the International Year of Crystallography, the AACr is also celebrating its tenth anniversary. The regular annual events of the AACr are a scientific meeting, a school on Crystallography and a workshop. This year, they will be held in Mar del Plata (Province of Buenos Aires) in the period of October 27th-Novembre 7th. In addition, many other academic activities such workshops or postgraduate courses are being organized in the whole country. It is worth to remark the School on Fundamental Crystallography to be held in La Plata, followed by an Agilent-UNESCO-IUCr OpenLab in La Plata and Buenos Aires, in April-May. Moreover, taking into account that Crystallography is a field that needs more promotion in our country, the AACr decided to propitiate several educational and dissemination activities. They include a national crystal growing contest, promotion of Crystallography in high and primary schools through the National Fairs of Science of the Ministry of Education, dissemination talks for different audiences, exhibitions, etc. Acknowledgements: The AACr thanks all the crystallographers that are working hard in these activities: G. Echeverría, O. Piro, S. Suárez, M. Saleta, D. Tobía, R. Carbonio, G. Aurelio, J. Pedregosa, F. Doctorovich, S. Conconi, L. Baqué, F. Napolitano, S. Alconchel, C. Alvarez, A. Ares, C. Bernini, S. Brühl, M. Dailoff, M.A. Foi, M. Harvey, M.S. Lassa, S. Montoro, E. Pannunzio Miner, etc."

XAFS study on nanostructured (La;Sr)CoO and (La;Sr)(Co;Fe)O IT-SOFC cathodes

In the last years, extensive research has been devoted to develop novel materials and structures with high electrochemical performance for intermediate-temperatures solid-oxide fuel cells (IT-SOFCs) electrodes. In recent works, we have investigated the structural and electrochemical properties of nanostructured La₀.₆Sr₀.₄CoO₃ (LSCO) and La₀.₆Sr₀.₄(Co;Fe)O₃ (LSCFO) cathodes, finding that they exhibit excellent electrocatalytic properties for the oxygen reduction reaction [1,2]. These materials were prepared by a pore-wetting technique using polycarbonate porous membranes as templates. Two average pore sizes were used: 200 nm and 800 nm. Our scanning electronic microscopy (SEM) study showed that the lower pore size yielded nanorods, while nanotubes were obtained with the bigger pore size. All the samples were calcined at 1000⁰C in order to produce materials with the desired perovskite-type crystal structure. In this work, we analyze the oxidation states of Co and Fe and the local atomic order of LSCO and LSCFO nanotubes and nanowires for various compositions by X-ray absorption spectroscopies. For this purpose we performed XANES and EXAFS studies on both Co and Fe K edges. These measurements were carried out at the D08B-XAFS2 beamline of the Brazilian Synchrotron Light Laboratory (LNLS). XANES spectroscopy showed that Co and Fe only change slightly their oxidation state upon Fe addition. Surprisingly, XANES results indicated that the content of oxygen vacancies is low, even though it is well-known that these materials are mixed ionic-electronic conductors. EXAFS results were consistent with those expected according to the rhombohedral crystal structure determined in previous X-ray powder diffraction investigations.