Model kit for bifunctional catalysts: colloidal Cu/Zn-based nanoparticles were synthesized and used as building blocks in syngas to dimethyl ether (STD) catalysts.

Recently, magnetic nanoparticles and nanocomposite microspheres have attracted great interest for biomedical and technical application. Magnetic metal nanoparticles are of special interest due to their beneficial, size‐dependent magnetic properties. Superparamagnetic metal nanoparticles and mesoscale nanocomposite particles (viz. Co nanoparticles, Co@SiO2, and Co@SiO2@TiO2 particles) were obtained by a three‐step synthesis, involving consecutive steps of thermolysis and sol–gel procedures. A high‐resolution Schottky‐type field emission scanning electron microscope (FESEM) equipped with an energy dispersive X‐ray spectrometer was used to characterize intermediate and final products at the successive stages of synthesis. The samples were deposited on carbon‐coated transmission electron microscopy (TEM) grids (thin film technique) which afforded enhanced specimen contrast and reduced X‐ray background contribution in microanalysis. The FESEM was equipped with a special mounting device for these grids with an appropriate detector beneath. By this method, the samples, covering sizes from the nanometer to micron scale, could be characterized and analyzed by several imaging modes, viz. with standard SE and BSE detection mode and supplementary with low‐voltage scanning transmission mode (STEM‐in‐SEM) and fundamental information about particle size, morphology, and elemental distribution was obtained. Copyright © 2012 John Wiley & Sons, Ltd.

Ag catalysts are of outstanding importance in the field of heterogeneous catalysis. Optimum distribution and morphology of the Ag particles must be ensured by controlled, tailored catalyst synthesis. Hence, there is a growing demand for the characterization of Agdispersed fine particle systems requiring high-resolution surface observation of particles down to a few tens of nanometers and elemental analysis by field emission scanning electron microscopy and energy-dispersive X-ray spectrometry (FESEM/EDX). It is beneficial to characterize the particle morphology by comparison of different imaging methods like secondary electron (SE)-, backscattered electron (BSE)and transmitted electron (TE) detection. In scanning electron microscopy surface topography becomes visible due to the dependency of the SE yield on the angle of electron incidence. Together with the large depth of field informative images of irregularly shaped particle structures are obtained. The increased BSE yield of high atomic numbers (Z) such as Ag catalysts and promoters (e.g. Cs) compared to a low-density matrix and the high penetration depth of 20-30 keV electrons also allows imaging and analysis of inclusions that would be obscured at low beam energies. Both SE and BSE detectors, in particular at low beam voltages, can additionally reveal interesting surface features of fine Ag particles. A well-known example for a Ag catalyzed reaction is the α-Al2O3 supported Ag-catalyzed epoxidation of 1,3-butadiene to 3,4-epoxybutene. The electrophilic addition of oxygen across the carbon-carbon double bond of 1,3-butadiene, resulting in a three-member ring structure that can undergo further chemical transformations to oxygenated products, such as ketones, alcohols, and ethers. Supported silver catalysts have been shown to epoxidize olefins with nonallylic hydrogen when an alkali promotor is doped on the surface. Thus, the direct kinetically controlled oxidation to the corresponding epoxide is preferred. The guiding hypothesis for this partially oxidation is that surface oxametallacycles are key intermediates for epoxidation on promoted Ag catalysts. Therefore, the preparative application of Ag and promoters (Cs, Ba) on the catalyst support material is of great importance. Another important aspect is sintering of Ag particles which may reduce the catalytically active surface and decreases the overall reaction performance. For this research, catalysts are produced by sequential impregnation of two mineralogically differing support materials (SC13, SLA2) with an

Subcritical water is a high potential green chemical for the hydrolysis of cellulose. In this study microcrystalline cellulose was treated in subcritical water to study structural changes of the cellulose residues. The alterations in particle size and appearance were studied by scanning electron microscopy (SEM) and those in the degree of polymerization (DP) and molar mass distributions by gel permeation chromatography (GPC). Further, changes in crystallinity and crystallite dimensions were quantified by wide-angle X-ray scattering and (13)C solid-state NMR. The results showed that the crystallinity remained practically unchanged throughout the treatment, whereas the size of the remaining cellulose crystallites increased. Microcrystalline cellulose underwent significant depolymerization in subcritical water. However, depolymerization leveled off at a relatively high degree of polymerization. The molar mass distributions of the residues showed a bimodal form. We infer that cellulose gets dissolved in subcritical water only after extensive depolymerization.

During experiments simulating the destruction of organic waste or the conversion of biomass with water at supercritical water conditions (SCW, T > 374 degrees C, p > 22.1 MPa), severe corrosion phenomena were observed. Depending on the experimental conditions applied, scale formation and precipitation of corrosion products occurred. The harsh conditions and the chemical properties of the feed solutions lead to consecutive chemical reactions with the materials involved. To study such hydrothermal reactions on simplified model systems, tubular reactors made of Ni-based alloys were exposed to feed solutions composed of water, methanol and alkaline salts. After each experiment, the reaction tubes were cut and examined by optical microscopy. Hydrothermally formed corrosion layers were studied by field emission electron microscopy and combined energy dispersive X-ray spectroscopy. Element line scans and mappings were performed which depicted selective dissolution of alloying elements (dealloying of Ni, Fe, Mo). The formation of the corrosion layers was accompanied by a subsequent reduction of the tube wall diameter. Atomic force microscopy gained additional morphological information; a Monte Carlo programme was applied to simulate X-ray line scans. Copyright (C) 2011 John Wiley & Sons, Ltd.

Electronic instruments mimicking the mammalian olfactory system are often referred to as "electronic noses" (E-noses). Thanks to recent nanotechnology breakthroughs the fabrication of mesoscopic and even nanoscopic E-noses is now feasible in the size domain where miniaturization of the microanalytical systems encounters principal limitations. Here we describe probably the simplest and yet fully functioning E-nose made of an individual single-crystal metal oxide quasi-1D nanobelt. The nanobelt was indexed with a number of electrodes in a way that each segment of the nanobelt between two electrodes defines an individual sensing elemental "receptor" of the array. The required diversity of the sensing elements is "encoded" in the nanobelt morphology via longitudinal width variations of the nanobelt realized during its growth and via functionalization of some of the segments with Pd catalyst. The proposed approach represents the combined bottom-up/top-down technologically viable route to develop robust and sensitive analytical systems scalable down to submicrometer dimensions.

Co-factors control the GTP-induced assembly of tubulin protein into a variety of superstructures with defined geometry at the nanometre scale: microtubules, macrotubes, sheets, or spirals/rings. We report the Zn2+ ion-induced assembly of tubulin protein into sheet-like or tubular structures. Free functional groups of amino acids on the surface of the protein biopolymer provide nucleation sites for further deposition of small metal nanoparticles. This study describes the synthesis of metal particle--protein hybrids by a two-step chemical process that directs metal nanoparticle nucleation at specific surface sites by applying these tubulin assemblies as biotemplates. The hybrids are characterized by transmission electron microscopy (TEM) and scanning force microscopy (SFM). The present study demonstrates the potential and general applicability of tubulin assemblies as tools for the nanofabrication of nanoparticle arrays exhibiting various geometries.

We describe gas-sensing characteristics of percolating SnO2 nanowire (NW) mats employed in Electronic nose (E-nose) instrument. The current strategy is based on combining bottom-up technology of NWs growth and top-down fabrication of multisensor microarray according to KAMINA (KArlsruhe Micro NAse) E-nose architecture. Such issues of the NW-based multisensor systems are discussed as gas-sensing stability, gas sensitivity and gas classification using Linear Discriminant Analysis (LDA) pattern recognition technique.

A comparative study of the long-term gas-sensing performance of chemiresistors made of: (i) mats of randomly oriented single crystal SnO2 nanowires and (ii) thin layers of pristine SnO2 nanoparticles, has been carried out. The sensing elements made of percolating nanowires demonstrate excellent sensitivity and long-term stability toward traces of 2-propanol in air. Different from the nanowire network, the superior initial sensitivity of the nanoparticle layer deteriorates during the first month of the operation and approaches to one observed steadily in the nanowire mats. The better stability of the nanowire mats sensors is explained in framework of reduced propensity of the single crystal nanowires to sinter under real world operation conditions with respect to nanoparticle thin film. At the microscopic level, the letter defines the stability of the percolating paths, analyte delivery and transduction mechanism in nanowire network sensing elements.

Magnetic nanoparticles have emerged as an important class of functional nanostructures with applications in various fields of biology and medicine. We have developed a simple synthetic route for functional Co nanoparticles which further allows their direct integration into Co@SiO2 microspheres, a synthesis that could be also applied to Fe nanoparticles. One advantage of the method described herein, compared to other methods for the synthesis of Co nanoparticles and Co@SiO2 nanocomposites, is the direct decomposition of the dicobalt octacarbonyl precursor in the presence of a silane coupling agent, therefore allowing an easy and size-controlled synthesis of siloxane-functionalized nanoparticles and the further preparation of magnetic nanocomposites. As shown by infrared spectroscopy, nanoparticle formation proceeds via an initial homonuclear disproportionation reaction. We could further show that the size of the particles can be controlled by varying the reaction parameters. The size, structure, and magnetic properties of the particles were characterized by transmission electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, Mossbauer spectroscopy, X-ray diffraction, atomic emission spectroscopy, and magnetic measurements.

Thermosetting epoxy resins, such as the triglycidyl derivative of 4-aminophenol, can be polymerized using molybdenum, palladium, or rhodium complexes as initiators. The resulting metal-doped materials proved to be efficient catalysts for epoxidation, carbon–carbon coupling, hydrogenation, and hydroformylation reactions. Propylene oxide yields of around 50% were obtained in the epoxidation of propylene with tert-butyl hydroperoxide as the oxidant, and biphenyl yields of ⩾98% were observed in the Suzuki coupling of iodobenzene with phenylboronic acid. Almost quantitative conversions were accomplished in the hydrogenation of ethyl crotonate, ethyl cinnamate, and croton aldehyde, whereas aldehyde yields of around 16% were obtained in the hydroformylation of 1-octene. Organic–inorganic hybrid catalysts can be obtained in a convenient one-step procedure by the addition of inorganic components to the liquid resins and subsequent polymerization. Different metal species can be combined in one thermoset matrix, affording multifunctional catalysts that can be us in various catalytic liquid-phase transformations. Quantification of metal traces in the reaction mixtures by metal enrichment and atomic spectroscopy demonstrated very low metal losses of the catalysts. The catalysts can be simply recovered by filtration and reused without reconditioning while maintaining stability, activity, and selectivity.

Extract Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

The activity, selectivity, and methanol tolerance of novel, carbon supported high-metal loading (40 wt.%) Pt/C and Pt3Me/C (Me = Ni, Co) catalysts for the O-2 reduction reaction (ORR) were evaluated in model studies under defined mass transport and diffusion conditions, by rotating (ring) disk and by differential electrochemical mass spectrometry. The catalysts were synthesized by the organometallic route, via deposition of pre-formed Pt and Pt3Me pre-cursors followed by their decomposition into metal nanoparticles. Characteristic properties such as particle sizes, particle composition and phase formation, and active surface area, were determined by transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. For comparison, commercial Pt/C catalysts (20 and 40 wt.%, E-Tek, Somerset, NJ, USA) were investigated as well, allowing to evaluate Pt loading effects and, by comparison with the pre-cursor-based catalyst with their much smaller particle sizes (1.7 nm diameter), also particle size effects. Kinetic parameters for the ORR were evaluated; the ORR activities of the bimetallic catalysts and of the synthesized Pt/C catalyst were comparable and similar to that of the high-loading commercial Pt/C catalyst; at typical cathode operation potentials H2O2 formation is negligible for the synthesized catalysts. Due to their lower methanol oxidation activity the bimetallic catalysts show an improved methanol tolerance compared to the commercial Pt/C catalysts. The results indicate that the use of very small particle sizes is a possible way to achieve reasonably good ORR activities at an improved methanol tolerance at DMFC cathode relevant conditions.

Tubulin, a protein isolated from eukaryotic cells, is able to self-assemble in vitro under well-defined chemical conditions into highly ordered polymorphic suprastructures such as tubules, rings or sheets. Here we report about the imaging and the morphological appearance of such tubulin assemblies utilized as templates for the deposition of metal nanoparticles or continuous metallization. The structural imaging and analyzing tools like field emission scanning electron microscopy (FESEM) with respect to different electron detectors (Inlens-SE, BSE, TE) are addressed. An EDX-unit is applied for the verification of the deposited metals. Atomic force microscopy (AFM) in tapping-mode (TM) is adopted for 3D-rendering and morphological measurements (height). Tip-surface interactions, the influence of fixation and cantilever-types are considered. Transmission electron microscopy (TEM) is applied to visualize deposited nanoparticles.

Monodisperse Co nanoparticles were synthesized by thermal decomposition in the presence of aluminium alkyls yielding air-stable Co nanoparticles after surface passivation. Several procedures for surface modification of these pre-stabilized, metallic Co nanoparticles are presented, including direct anchoring of surface-active functional groups and biocompatible dextran layers as well as silica and polymer coatings. As a result, individually coated nanoparticles as well as microspheres can be obtained.

Epoxy resins were polymerised using molybdenum ethoxide and 2-ethylhexanoate as polymerisation initiators. The thermosets thus obtained are useful epoxidation catalysts for a variety of alkenes, including propene with tert-butyl hydroperoxide as an oxidant. To investigate the long-term performance of these resins, they were used repeatedly in up to 120 reactions without any reconditioning. Compared with other catalyst systems based on organic polymers, they reveal unprecedented long-term activities over periods of months so that catalyst lifetimes of years can be expected. Di-, tri-, tetra- and oligofunctional epoxy resin monomers were used and compared. The catalytic performance of the thermosets strongly depends on the resin type and the polymerisation initiator. Promising results were obtained with monomers bearing 3 or 4 glycidyl groups in combination with Mo(OEt)5 as an initiator. Metal leaching, determined by sensitive atomic spectroscopic techniques, is extremely low. Inorganic–organic hybrid catalysts can be easily prepared by adding inorganic components such as silicagel to the liquid resins, followed by polymerisation.