Analysis of the state and size of silver on alumina in effective removal of NOx from oxygen rich exhaust gas.

Ag/alumina catalysts with different silver contents for octane-SCR were prepared by impregnation and incipient wetness methods. Activity tests revealed that the decisive factor for high activity is not only a high dispersion of silver, but also the ability of the system to redisperse clustered silver. Determination of dispersion by TEM/HAADF and O2-chemisorption experiments resulted in values close to each other even if the results were not directly comparable. This is suggested to be due to not complete silver reduction below 700 degrees C and the samples being very heterogeneous in terms of particle size, e.g., having a bimodal size distribution. Small charged Agsigman+ clusters containing 2-8 silver atoms highly prevailed in the samples containing <2 wt% Ag and exhibiting high octane-SCR activity. In highly loaded Ag/alumina samples or those reduced and reoxidized at high temperature (>400 degrees C), large metallic particles are stabilized, resulting in poor conversion of NOx to N2.

Structure-activity relationship in HC-SCR of NOx by TEM, O2-chemisorption, and EDXS study of Ag/Al2O3.

Ag/alumina catalysts with different silver loading (1.28-6 wt %) for lean NO reduction activity were prepared by impregnation and the incipient wetness method. Complementary HRTEM, HAADF, O2-chemisorption, and EDXS studies were applied to investigate the dependence between silver particle size and catalytic activities of the prepared materials. The catalyst with the lowest silver loading (1.28 wt %) was found to be the most active catalyst in terms of reacted NO molecules per mole of silver. On the basis of the HRTEM, HAADF, and O2-chemisorption studies it could be concluded that the mean particle size or particle size distribution of the samples alone could not explain the big difference in the activities. EDXS analyses showed on the other hand that all of the samples were very heterogeneous in terms of particle size distribution, e.g., including both small and very big particles. Furthermore, both metallic silver and mainly hexagonal silver oxide (Ag2O) were found to be present in the samples. Despite the valuable information provided by ex situ characterization of the prepared samples, it needs to be emphasized that establishing a structure-reactivity relationship for this type of catalyst requires in situ characterization.

Effect of new manganese contrast agent on tissue intensities in human volunteers: comparison of 0.23, 0.6 and 1.5 T MRI, a part of a phase I trial.

To evaluate the effect of a new oral manganese contrast agent (CMC-001) on magnetic resonance imaging (MRI) intensities at different magnetic field strengths. Twelve healthy volunteers underwent abdominal MRI 1 week before and within 2.5-4.5 h after CMC-001 (MnCl(2) and absorption promoters dissolved in water) intake at three different MR scanners of 0.23, 0.6 and 1.5 T. Image contrast and intensity enhancement of liver and pancreas were analysed relatively to muscle and fat intensities. Manganese blood levels were followed for 24 h. Whole-blood manganese concentration levels stayed within the normal range. The liver intensities on T2w images decreased about 10% for the 1/2 contrast dose and about 20% for the full contrast dose independent of the field strength. The liver intensities on T1w images increased more than 30% for 1/2 contrast dose and over 40% for full contrast dose. The maximum T1 enhancement was achieved at the highest field. Pancreas intensities were not affected. Contrast between liver, muscle and fat intensities increased with magnetic field, as well as standard errors of the volunteer-averaged intensities. Oral intake of CMC-001 influences liver intensities and does not affect pancreas intensities at different magnetic field strengths.

TEM-tomography of FAU-zeolite crystals containing Pt-clusters.

A method for preparing ultrathin sections (- 20 nm) of inorganic solids has been developed using ultramicrotomy of resin-embedded crystal fragments. Undamaged crystals, oriented along a crystallographic direction, could be imaged with transmission electron microscopy (TEM) at a resolution better than 0.5 nm. The true internal structure of the crystals could be investigated by imaging the second in a series of at least three consecutive ultrathin sections. Such TEM-tomography proved that Pt-ion exchanged FAU zeolite crystals, after reduction and oxidation, are occupied internally and randomly of large platinum clusters mainly in the {111-twin planes. TEM-tomography could be useful in man made nanostructures like semiconductors, epitaxial thin films, hard metal coatings, ceramics, catalysts, and biomaterials.

Dynamic atomic-level rearrangements in small gold particles.

Small metal particles (<5 nanometers), which are widely used in catalysis, have physical and chemical properties that are markedly different from those of the bulk metal. The differences are related to crystal structure, and it is therefore significant that structral rearrangements in small particles have been observed in real time by using high-resolution electron microscopy. A detailed investigation at the atomic level has been made of the factors affecting the dynamic activity of small gold crystals that are supported on thin films of amorphous carbon, silicon, and germanium. The rate of activity depends mainly on the current density of the incident electron beam and the degree of contact of the particle with the substrate, but this rate decreases rapidly as the particle size is increased. The activity of the particles is very similar on either carbon or silicon, but it is generally less marked on germanium because of increased contact between the particle and the substrate. The electron beam effectively heats the particles, and it appears that their dynamic behavior depends on their thermal contact with the substrate.

Solid Electrolyte Behavior of NaMgF3: Geophysical Implications.

In the solid state, NaMgF(3) transforms smoothly with temperature into a solid electrolyte phase; the conductivity is 130 siemens per meter just below the melting point. The isostructural compound MgSiO(3) should behave similarly under conditions obtaining in the earth's lower mantle, and so it is expected that the electrical conductivity in that region is ionic rather than electronic.