Haishuang Zhao

Sinter-resistant metal nanoparticle catalysts achieved by immobilization within zeolite crystals via seed-directed growth

AbstractSupported metal nanoparticle catalysts are widely used in industry but suffer from deactivation resulting from metal sintering and coke deposition at high reaction temperatures. Here, we show an efficient and general strategy for the preparation of supported metal nanoparticle catalysts with very high resistance to sintering by fixing the metal nanoparticles (platinum, palladium, rhodium and silver) with diameters in the range of industrial catalysts (0.8–3.6 nm) within zeolite crystals (metal@zeolite) by means of a controllable seed-directed growth technique. The resulting materials are sinter resistant at 600–700 °C, and the uniform zeolite micropores allow for the diffusion of reactants enabling contact with the metal nanoparticles. The metal@zeolite catalysts exhibit long reaction lifetimes, outperforming conventional supported metal catalysts and commercial catalysts consisting of metal nanoparticles on the surfaces of solid supports during the catalytic conversion of C1 molecules, including the water-gas shift reaction, CO oxidation, oxidative reforming of methane and CO2 hydrogenation.Supported metal nanoparticles are indispensable catalysts in industry, yet they are often subjected to severe sintering. Now, a general method based on metal immobilization within zeolite is reported for the preparation of highly sinter-resistant catalysts for a broad range of industrially relevant processes.

A consistent path for phase determination based on transmission electron microscopy techniques and supporting simulations

This work addresses aspects for the analysis of industrial relevant materials via transmission electron microscopy (TEM). The complex phase chemistry and structural diversity of these materials require several characterization techniques to be employed simultaneously; unfortunately, different characterization techniques often lack connection to yield a complete and consistent picture. This paper describes a continuous path, starting with the acquisition of 3D diffraction data - alongside classical high-resolution imaging techniques - and linking the structural characterization of hard metal industrial samples with energy-loss fine-structure simulations, quantitative electron energy-loss (EEL) and energy-dispersive X-ray (EDX) spectroscopy. Thereby, the compositional analysis of a MAX phase indicated an offset of the hydrogenic, theoretical sensitivity factors, originating from poorly-adjusted screening factors. In a next step, these results were matched against quantitative compositions and parameters obtained from X-ray spectroscopy data, carried out synchronously with EELS.

Investigation of layered and porous nanomaterials by electron diffraction tomography

Yasar Krysiak1, Haishuang Zhao1, Bastian Barton1, Jürgen Senker2, Reinhard B. Neder3, Ute Kolb1 1Inst. Of Inorg. Chemistry And Analyt. Chemistry, Johannes Gutenberg University, Mainz, Germany, 2Inorganic Chemistry III, University of Bayreuth, Bayreuth, Germany, 3Chair for Crystallography and Structural Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany E-mail: krysiak@uni-mainz.de

Optimization of automated electron diffraction tomography for challenging applications

Ten years after the development of automated electron diffraction tomography (ADT) [1, 2] the analysis of the sequentially scanned reconstructed reciprocal space and the use of extracted reflection intensities for direkt crystal structure analysis has gained strong attention in many subjects. Especially in combination with precession electron diffraction allowing for reflection integration (ADT/PED) it was possible to extract fine structural details often explicitly important for physical properties of the material. The variety of nanocrystalline materials solved with ADT on the basis of quasi-kinematical electron diffraction intensity data covers alloys, large cell porous minerals, zeolites, beam-sensitive metal-organic frameworks and small organic molecules. Some originating from single nanocrystals down to 30 nm, strongly agglomerated particles or FIB lamellae. In combination with other approaches like HR-TEM imaging, X-ray diffraction methods analysing reflections (XRPD) or total scattering information (PDF) and neutron diffraction (ND) or spectroscopic measurements like solid state nuclear magnetic resonance (SS-NMR) it was possible to describe the crystal structure solutions gained for twinned, pseudo-symmetric or disordered material even more detailed [3]. ADT data can be in principle collected using standard TEMs but in order to collect electron diffraction data in a quality necessary to achieve high-end crystal structure solutions the data collection should be tailored to the material and the problem to be solved. Here we focus on the description of different approaches and the applicability to the various material classes.

Solving Challenging Crystallographic Problems with Automated Electron Diffraction Tomography (ADT)

Many important materials, ranging from minerals or catalysts to framework compounds and pharmaceuticals are not suitable for growing large crystals prohibiting single crystal X-ray analysis. Yet, introduction of nano crystallinity and special crystallographic features like disorder, defects, pseudo symmetry or stress/strain effects creates new or allows optimizing existing physical properties. With increasing complexity of the structures and special structural features as well as with decreasing size of crystalline domains, X-ray powder diffraction becomes more and more difficult for structural characterization, which is fundamental for understanding material properties. High-resolution transmission electron microscopy (HR-(S)TEM) allows visualizing structural features directly at the atomic scale but requires high electron dose of several thousand e/Ås causing beam damage. In contrast, electron diffraction needs only a fraction of this electron dose. For a complete structure solution, delivering atomic positions in sub Ångstrom accuracy, needs three-dimensional experimental data with high completeness. Data collection from oriented nano crystals limits the amount of measurable reflections significant and thus, delivers mostly heavy atom positions but hardly lighter atoms. Dynamical scattering effects strongly enhanced in oriented zones and may be reduced by electron beam precession technique [1]