Ionic liquids—media for unique phosphorus chemistry

Ionic liquids have been shown to offer hitherto unseen control as both a storage solvent for PCl3 and POCl3 and reaction media for fluorination and mixed anhydride formation under benign conditions.

DFT and in situ EXAFS investigation of gold/ceria-zirconia low-temperature water gas shift catalysts: Identification of the nature of the active form of gold

A combined experimental and theoretical investigation of the nature of the active form of gold in oxide-supported gold catalysts for the water gas shift reaction has been performed. In situ extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) experiments have shown that in the fresh catalysts the gold is in the form of highly dispersed gold ions. However, under water gas shift reaction conditions, even at temperatures as low as 100 degrees C, the evidence from EXAFS and XANES is only 14 consistent with rapid, and essentially complete, reduction of the gold to form metallic clusters containing about 50 atoms. The presence of Au-Ce distances in the EXAFS spectra, and the fact that about 15% of the gold atoms can be reoxidized after exposure to air at 150 degrees C, is indicative of a close interaction between a fraction (ca. 15%) of the gold atoms and the oxide support. Density functional theory (DFT) calculations are entirely consistent with this model and suggest that an important aspect of the active and stable form of gold under water gas shift reaction conditions is the location of a partially oxidized gold (Audelta+) species at a cerium cation vacancy in the surface of the oxide support. It is found that even with a low loading gold catalysts (0.2%) the fraction of ionic gold under water gas shift conditions is below the limit of detection by XANES (<5%). It is concluded that under water gas shift reaction conditions the active form of gold comprises small metallic gold clusters in intimate contact with the oxide support.

Bimetallic effects in the liquid phase hydrogenation of 2-butanone

A series of bimetallic Ru-containing monometallic and bimetallic catalysts were prepared and tested for their activity for the hydrogenation of 2-butanone to 2-butanol at 30 °C and 3 bar H2. RuPt bimetallic catalysts were the most active for the reaction, with a ratio of 5 wt% Ru:1 wt% Pt on activated carbon (AC) found to be optimum. The activity of this bimetallic catalyst was more than double that of the sum of the activities of the monometallic Ru and Pt catalysts, providing evidence of a “bimetallic” effect. Structural analysis of the bimetallic catalysts revealed that they consisted of clusters of particles of the order of 1–2 nm. Extended X-ray absorption fine structure analysis showed that there were two types of particle on the surface of the bimetallic RuPt catalyst, specifically monometallic Ru and bimetallic RuPt particles. For the bimetallic particles, it was possible to fit the data with a model in which a Ru core of 1.1 nm is enclosed by two Pt-rich layers, the outer layer containing only 13 at% Ru. Pretreatment of the monometallic and bimetallic catalysts in hydrogen had a significant effect on the activity. Both the bimetallic and monometallic Ru-based catalysts showed a trend of decreasing activity with increasing temperature of prereduction in hydrogen. This loss of activity was almost fully reversible by exposure of the catalysts to air after reduction. The changing activity with exposure to different gas phase environments could not be attributed to changes in particle size or surface composition. It is proposed that the introduction of hydrogen results in a gradual smoothing of the surface and loss of defect sites; this process being reversible on introduction of air. These defect sites are particularly important for the dissociative adsorption of hydrogen, potentially the rate-determining step in this reaction.

Prograded Holocene beach-ridges with superimposed dunes in north-east Ireland: mechanisms and timescales of fine and coarse beach sediment decoupling and deposition

Two depositional models to account for Holocene gravel-dominated beach ridges covered by dunes, occurring on the northern coast of Ireland, are considered in the light of infrared-stimulated luminescence ages of sand units within beach ridges, and 14C ages from organic horizons in dunes. A new chronostratigraphy obtained from prograded beach ridges with covering dunes at Murlough, north-east Ireland, supports a model of mesoscale alternating sediment decoupling (ASD) on the upper beach, rather than macroscale sequential sediment sourcing to account for prograded beach ridges and covering dunes. The ASD model specifies storm or fair-weather sand beach ridges forming at high-tide positions (on an annual basis at minimum), which acted as deflationary sources for landward foredune development. Only a limited number of such late-Holocene beach ridges survive in the observed prograded series. Beach ridges only survive when capped by storm-generated gravel beaches that are deposited on a mesoscale time spacing of 50–130 years. The morphodynamic shift from a dissipative beach face for dune formation to a reflective beach face for gravel capping appears to be controlled by the beach sand volume falling to a level where reflective conditions can prevail. Sediment volume entering the beach is thought to have fluctuated as a function of a forced regression associated with the falling sea level from the mid-Holocene highstand (ca. 6000 cal. yr BP) identified in north-east Ireland. The prograded beach ridges dated at ca. 3000 to 2000 cal. yr BP indicate that the Holocene highstand’s regressive phase may have lasted longer than previously specified.

On the observation of the fine structure effect in non- relativistic (e, 2e) processes

The spin asymmetry arising in an (e,2e) process using spin- polarized incoming electrons with non-relativistic energies is shown to be dominated by the fine structure effect if a suitable kinematical regime is chosen. Calculations in the distorted wave Born approximation (DWBA) for both the triple differential cross-section and the spin asymmetry are presented for the inner shell ionization of argon. This process would provide an accessible target for existing experimental set-ups.

Strong configuration mixing among the fine-structure levels of Cl+

A large-scale configuration interaction (Cl) calculation using Program CIV3 of Hibbert is performed for the lowest 62 fine- structure levels of the singly charged chlorine ion. Our calculated energy levels agree very well with most of the NIST results and confirm the identification of the lowest P-1(o) as actually 3s(2)3p(3)(D-2(o))3d P-1(o) rather than the generally employed 3s3p(5) P-1(o) in measurements and calculations. Discrepancies in the energy positions of some symmetries are found and discussed. Some large oscillator strengths for allowed and intercombination transitions in both length and velocity gauges are presented. Their close agreement gives credence to the accuracy of our CI wavefunctions.