Adsorption of CO on nanosize Pd particles was studied theoretically by density functional method and spectroscopically by means of infrared reflection absorption spectroscopy (IRAS) and sum frequency generation (SFG). A density functional approach was applied to three-dimensional crystallites of about 140 atoms. The model clusters were chosen as octahedral fragments of the face centered cubic (fcc) bulk, exhibiting (111) and (001) facets. Bare and adsorbate-decorated cluster models were calculated with O h symmetry constraints. Various types of adsorption sites were inspected:  3-fold hollow, bridge, and on-top positions at (111) facets; 4-fold hollow and on-top sites at (001) facets; bridge positions at cluster edges; on-top positions at cluster corners; and on single Pd atoms deposited at regular (111) facets. Adsorption properties of the relatively small regular cluster facets (111) and (001) are calculated similar to those of corresponding ideal (infinite) Pd surfaces. However, the strongest CO bonding was calculated for the bridge positions at cluster edges. The energy of adsorption on-top of low-coordinated Pd centers (kinks) is also larger than that for on-top sites of (111) and (001) facets. To correlate the theoretical results with spectroscopic data, vibrational spectra of CO adsorbed on supported Pd nanocrystallites of different size and structure (well-faceted and defect-rich) were measured using IRAS and SFG. For CO adsorption under ultrahigh vacuum conditions, a characteristic absorption in the frequency region 1950−1970 cm-1 was observed, which in agreement with the theoretical data was assigned to vibrations of bridge-bonded CO at particle edges and defects. SFG studies carried out at CO pressures up to 200 mbar showed that the edge-related species was still present under catalytic reaction conditions. By decomposition of methanol leading to the formation of carbon species, these sites can be selectively modified. As a result, CO occupies on-top positions at particle edges and defects. On the basis of the computational data, the experimentally observed differences in CO adsorption on alumina-supported Pd nanoparticles of different size and surface quality are interpreted. Differences between adsorption properties of Pd nanoparticles with a large fraction of (111) facets and adsorption properties of an ideal Pd(111) surface are also discussed.

The dual-row transmit array provides whole-brain coverage at 9.4 T, which, in combination with the helmet-shaped receive array, is a valuable radio frequency configuration for ultra-high field magnetic resonance imaging of the human brain.

No abstract

For ionic liquids only few toxicological and/or ecotoxicological data are available until now. A strategy is presented which aims at an environmental risk assessment of chemicals, using a combination of structure-activity relationships (SAR), toxicological and ecotoxicological tests and modelling. The parts "test-kit-concept" and "multidimensional risk analysis" are described in detail by means of selected imidazolium ionic liquids. The iterative process of this strategy offers a tool for sustainable product design.

To identify the nature and the local structure of the surface of supported catalyst nanoparticles, we have performed a detailed comparative study of CO adsorption on two categories of oxide-supported Palladium catalysts:  (1) polycrystalline MgO and γ-Al2O3 supported Pd metal catalysts prepared by impregnation techniques and characterized by different degrees of regularity and perfection and (2) single-crystal based Pd model catalysts prepared under ultrahigh vacuum (UHV) conditions. The assignment of the CO vibrational frequencies to different types of sites on these systems has allowed a detailed structural characterization. For the Pd model catalyst, at low CO coverage, the infrared (IR) reflection absorption spectra closely resemble the expected behavior for terminations by a majority of (111) facets and a minority of (100) facets. The spectral features are indicative of defect sites such as particle steps and edges. Occupation of the defect sites can be affected by surface contaminations such as atomic carbon. Thus the CO spectra at high coverage can be used as both a structural and chemical probe under reaction conditions, provided that complementary information on the particle morphology is available. For the MgO and γ-Al2O3 supported Pd systems, two distinct narrow bands (ν ≅ 2070 and ≅ 1970 cm-1) have been assigned to linearly bonded and bridge-bonded CO species, on Pd (100)/(111) edges or facets, in agreement with the previous results obtained on model catalysts. The broad character of the 2070 cm-1 feature indicates the simultaneous presence of (100) and (111) faces, with edge and corner sites present at their intersection. The high intensity and the small half-width (fwhm) of the band at 1970 cm-1 on a Pd/MgO sample treated at high temperature, assigned to bridge-bonded CO species, suggests that the metal particles expose faces with a high level of regularity. Further spectroscopic features (ν ≅ 1920−1800 cm-1), are ascribed to the presence of different types of 3-fold hollow sites on (111) faces.

No abstract

Ionic liquids are discussed as sustainable green solvents, but toxicity and ecotoxicity data are rare. In this paper we present our results for different ionic liquids with the acetylcholinesterase inhibition assay. The results show that the acetylcholinesterase can be inhibited by ionic liquids containing a cation with a positively charged nitrogen and a certain lipophilicity. We tested imidazolium ionic liquids with different alkyl chains at R 1 and R 2 as well as with different anions and compared these results with our findings for other cation structures such as pyridinium ionic liquids and phosphonium ionic liquids. According to our results imidazolium and pyridinium ionic liquids inhibit the purified enzyme with EC 50 values as low as 13 mM. The bulky phosphonium ionic liquids were less inhibitory. These results can be rationalized by structure-activity relationship considerations.

The development of novel radiofrequency (RF) coils for human ultrahigh-field (≥7 T), non-proton and body applications is an active field of research in many MR groups. Any RF coil must meet the strict requirements for safe application on humans with respect to mechanical and electrical safety, as well as the specific absorption rate (SAR) limits. For this purpose, regulations such as the International Electrotechnical Commission (IEC) standard for medical electrical equipment, vendor-suggested test specifications for third party coils and custom-developed test procedures exist. However, for higher frequencies and shorter wavelengths in ultrahigh-field MR, the RF fields may become extremely inhomogeneous in biological tissue and the risk of localized areas with elevated power deposition increases, which is usually not considered by existing safety testing and operational procedures. In addition, important aspects, such as risk analysis and comprehensive electrical performance and safety tests, are often neglected. In this article, we describe the guidelines used in our institution for electrical and mechanical safety tests, SAR simulation and verification, risk analysis and operational procedures, including coil documentation, user training and regular quality assurance testing, which help to recognize and eliminate safety issues during coil design and operation. Although the procedure is generally applicable to all field strengths, specific requirements with regard to SAR-related safety and electrical performance at ultrahigh-field are considered. The protocol describes an internal procedure and does not reflect consensus among a large number of research groups, but rather aims to stimulate further discussion related to minimum coil safety standards. Furthermore, it may help other research groups to establish their own procedures. Copyright © 2015 John Wiley & Sons, Ltd.