Anna Carlsson

The rate of ammonia synthesis over a nanoparticle ruthenium catalyst can be calculated directly on the basis of a quantum chemical treatment of the problem using density functional theory. We compared the results to measured rates over a ruthenium catalyst supported on magnesium aluminum spinel. When the size distribution of ruthenium particles measured by transmission electron microscopy was used as the link between the catalyst material and the theoretical treatment, the calculated rate was within a factor of 3 to 20 of the experimental rate. This offers hope for computer-based methods in the search for catalysts.

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTMesoporous Zeolite Single CrystalsClaus J. H. Jacobsen, Claus Madsen, Jindrich Houzvicka, Iver Schmidt, and Anna CarlssonView Author Information Haldor Topsøe Research Laboratories, Nymøllevej 55 DK-2800 Lyngby, Denmark Cite this: J. Am. Chem. Soc. 2000, 122, 29, 7116–7117Publication Date (Web):July 6, 2000Publication History Received1 March 2000Published online6 July 2000Published inissue 26 July 2000https://pubs.acs.org/doi/10.1021/ja000744chttps://doi.org/10.1021/ja000744crapid-communicationACS PublicationsCopyright © 2000 American Chemical SocietyRequest reuse permissionsArticle Views10986Altmetric-Citations835LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Crystal structure,Crystallization,Crystals,Redox reactions,Zeolites Get e-Alerts

Carbon nanotubes are shown to be useful materials for introduction of nanopores with a controlled diameter into zeolite single crystals. The intracrystalline nanopores are created by crystallization of the zeolite around the carbon nanotubes that are subsequently removed by combustion.

Recently, we have developed a new electron crystallography (EC) method for study of three dimensional (3D) structures of silica-mesoporous materials, and the 3D-structural solutions of MCM-48 and SBA-1, -6, and -16 were briefly reported. The method gives a unique structure solution through the Fourier sum of the 3D-structure factors, both amplitudes and phases, which are obtained from Fourier analyses of a set of high-resolution electron microscope (HREM) images. The method was fully described in an application for structure analyses of two MCM-48 crystals with different crystal morphologies. Little structural difference was observed between the two crystals, although small differences in the structure factors were observed. The space group of MCM-48 was determined to be Ia3̄d, and the wall surface of the two crystals followed exactly the periodic minimal surface of gyroid (G). The wall separated two interpenetrating and noninterconnecting channel systems with different chiralities. After structural analysis of MCM-48, the structures of two different carbon networks, CMK-1 and CMK-4, which were synthesized within the channels of MCM-48 from different carbon sources, were studied by electron microscopy (EM). It was observed that in both cases carbon networks were equally formed in the two channels of MCM-48 without changing the space-group symmetry and that the symmetry of Ia3̄d was retained after the dissolution of silica mesoporous MCM-48 for CMK-4 but changed to I41/a for CMK-1. The simplest model for structure change in CMK-1 was proposed on the basis of the observations of extra reflections in ED patterns and domain structures in HREM images as that the carbon networks equally formed in two noninterconnecting channels of MCM-48 were displaced during the dissolution relative to each other without rotation along the [001] axis by keeping each network rigidly. It is stressed that the method must be extended further for structural study of new materials with orders in two different lengths scales, atomic and mesoscopic scales.

Abstract Decades of research has been focused on improving the high-temperature properties of nickel-based superalloys, an essential class of materials used in the hot section of jet turbine engines, allowing increased engine efficiency and reduced CO 2 emissions. Here we introduce a new ‘phase-transformation strengthening’ mechanism that resists high-temperature creep deformation in nickel-based superalloys, where specific alloying elements inhibit the deleterious deformation mode of nanotwinning at temperatures above 700 °C. Ultra-high-resolution structure and composition analysis via scanning transmission electron microscopy, combined with density functional theory calculations, reveals that a superalloy with higher concentrations of the elements titanium, tantalum and niobium encourage a shear-induced solid-state transformation from the γ′ to η phase along stacking faults in γ′ precipitates, which would normally be the precursors of deformation twins. This nanoscale η phase creates a low-energy structure that inhibits thickening of stacking faults into twins, leading to significant improvement in creep properties.