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Utilizing the molecular beam epitaxy technique, a nanoscale thin-film magnet of c-axis-oriented Sm2Co17 and SmCo5 phases is stabilized. While typically in the prototype Sm(Co, Fe, Cu, Zr)7.5-8 pinning-type magnets, an ordered nanocomposite is formed by complex thermal treatments, here, a one-step approach to induce controlled phase separation in a binary Sm-Co system is shown. A detailed analysis of the extended X-ray absorption fine structure confirmed the coexistence of Sm2Co17 and SmCo5 phases with 65% Sm2Co17 and 35% SmCo5. The SmCo5 phase is stabilized directly on an Al2O3 substrate up to a thickness of 4 nm followed by a matrix of Sm2Co17 intermixed with SmCo5. This structural transition takes place through coherent atomic layers, as revealed by scanning transmission electron microscopy. Highly crystalline growth of well-aligned Sm2Co17 and SmCo5 phases with coherent interfaces result in strong exchange interaction, leading to enhanced magnetization and magnetic coupling. The arrangement of Sm2Co17 and SmCo5 phases at the nanoscale is reflected in the observed magnetocrystalline anisotropy and coercivity. As next-generation permanent magnets require designing of materials at an atomic level, this work enhances our understanding of self-assembling and functioning of nanophased magnets and contributes to establishing new concepts to engineer the microstructure for beyond state-of-the-art magnets.

Catalysis science & technology 8(10), 2686 - 2696 (2018). doi:10.1039/C8CY00516H, The effect of the support material and chemical state of Rh in Rh/A$_2$O$_3$ and Rh/SiO$_2$ model catalysts during CO$_2$ hydrogenation were studied by a combined array of in situ characterisation techniques including diffuse reflectance infrared Fourier transform spectroscopy, energy-dispersive X-ray absorption spectroscopy and high-energy X-ray diffraction at 250–350 °C and atmospheric pressure. CO$_2$ methanation proceeds via intermediate formation of adsorbed CO species on metallic Rh, likely followed by their hydrogenation to methane. The linearly-bonded CO species is suggested to be a more active precursor in the hydrogenation compared to the bridge-bonded species, which seems to be related to particle size effects: for larger particles mainly the formation of inactive bridge-bonded CO species takes place. Further, analysis of the chemical state of Rh under the reaction conditions reveal a minor formation of RhOx from dissociation of CO$_2$, which is a consequence of the increased activity observed over the Rh/Al$_2$O$_3$ catalyst., Published by RSC Publ., London

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Pt based catalysts were measured with in situ X ray absorption fine structure spectroscopy (XAFS) to obtain information about the catalyst crystalline structure and electronic properties as a function of catalyst composition, method of preparation, inlet feed conditions and temperature. In these experiments, two type of catalysts were studied: i) nanoparticles of Pt occluded in Al2O3 or CeO2-Al2O3 matrix containing 1.5 % of Pt where two different methods to incorporate the cerium were used and ii) conventional Pt supported catalysts containing 0.3 and 1 % of Pt on Al2O3 or with addition of 6 or 12 % of ceria. For catalysts based on nanoparticles, XAFS spectra were acquired at Pt L3-edge and Ce K and L3-edge under reduction and water gas shift (WGS) reaction conditions. The XAFS results reveal, after the reduction, the presence of Pt nanoparticles with similar coordination numbers (NPt-Pt), about 6, and similar Pt-Pt distances, about 2.75  0.01 Å. The catalyst activity for WGS and the strength of interaction between the metal and the support are related with cerium oxide structure revealed by XAFS analysis at Ce K and L3 edges. In situ infrared spectroscopy under WGS conditions revealed the presence of formates on the catalyst surface and that they are probably spectators for the reaction. It was possible to observe that these catalysts changes according to the atmosphere and temperature. Thus, it was possible to demonstrate, using the pre-formed nanoparticles that several parameters affect the catalyst behavior like: the metallic and the oxide particle size, the contact between them and what is exposed on the surface. For the conventional catalysts, the addition of ceria on 03PtAl sample enhances Pt oxidation, reflecting in a larger Pt-O coordination number for this sample. After reduction, 03PtAl resulted in larger Pt particles compared to the 12Ce03PtAl. For Ce-containing samples, in addition to the Pt-Pt contribution, a Pt-O contribution had to be considered to fit the spectra. This Pt-O increases proportionally to the cerium amount demonstrating that Pt clusters are anchored on support through a Pt-O bond. The Pt structure changes depends on the temperature, support nature and reactants composition, demonstrating that the catalytic properties requires the use of in situ characterization techniques. Catalisadores de Pt foram preparados, informações estruturais e eletrônicas foram obtidas usando espectroscopia da estrutura fina de absorção de raios X (XAFS) em função da composição do catalisador, método de preparação, composição da atmosfera e temperatura. Dois tipos de catalisadores foram estudados: i) catalisadores sintetizados com nanopartículas de Pt (1,5% de Pt) ocluídas em uma matrix de Al2O3 ou CeO2-Al2O3. Neste estudo, dois métodos de preparação para incorporação do cérioforam utilizados e ii) catalisadores de Pt convencionais com 0,3 ou 1% de Pt em Al2O3 e ainda com a adição de céria 6 ou 12%. Para os catalisadores baseados em nanopartículas, os experimentos de XAFS foram realizados na borda L3 da Pt e nas bordas L3 e K do Ce sob atmosfera de redução e condições de reação de deslocamento gás-água (WGS). Os resultados de XAFS, após a redução, revelaram a presença de nanopartículas com número de coordenação (NPt-Pt) similares, em torno de 6, e distância Pt-Pt em torno de 2.75  0.01 Å, para todas as amostras. A atividade catalítica e a intensidade da interação metal-suporte estão relacionadas com a estrutura do óxido de cério revelada através das análise de XAFS nas bordas K e L3 do Ce. Medidas de infravermelho in situ revelaram a presença de formiatos na superfície do catalisador e que esses são provavelmente espectadores da reação. Foi possível observar que estes catalisadores mudam segundo a atmosfera e a temperatura. Assim, foi possível demonstar, usando as nanopartículas de platina, que diversos parâmetros afetam o comportamento do catalisador como: o tamanho do domínio cristalino do óxido, o contato entre o metal e o óxido e os sítios ativos expostos na superfície. Para os catalisadores convencionais, as amostras contendo cério apresentaram-se mais oxidadas do que as amostras de platina-alumina; estas após tratamento em alta temperatura aglomeraram. No ajuste dos espectros de EXAFS, para as amostras contendo Ce, foi necessário incluir a contribuição Pt-O além da contribuição Pt-Pt. Essa contribuição Pt-O aumentou proporcionalmente à concentração de Ce demonstrando o ancoramento da Pt ao suporte através dessa ligação. A estrutura da Pt mudou de acordo com a temperatura, o suporte e composição dos reagentes na atmosfera demonstrando a importante ferramenta que são as técnicas de caracterização in situ para o entendimento das propriedades catalíticas. FAPESP: 2010/52291-0