Chiral supported ionic liquid phase (CSILP) catalysts for greener asymmetric hydrogenation processes

Chiral supported ionic liquid phase (CSILP) catalysts were prepared by physical adsorption (within highly porous carbons or mesoporous silica) of Ir, Ru and Rh complexes as IrCl(COD)-(S, S)-BDPP, [IrCl-(S)-BINAP](2), RuCl(p-cymene)[(S, S)-Ts-DPEN], RuOTf(p-cymene)[(S, S)-Ts-DPEN], [Rh(COD)(S, S)-DIPAMP][BF4], and [Rh(COD)(R, R)-Me-DuPHOS][BF4]. For the syntheses of CSILP catalysts [EMIM][NTf2], [BMIM][BF4] and [BMIM][PF6] ionic liquids were used. Comparative homogeneous and heterogeneous experiments were carried out using the asymmetric hydrogenation of double -C N- and -C C- bonds in trimethylindolenine, 2-methylquinoline and dimethylitaconate, respectively. The conversion and enantioselectivity was found to depend on the nature of the complex (metal and ligand), the immobilization method used, nature of the ionic liquid, nature of the support and the experimental conditions. (C) 2012 Elsevier B.V. All rights reserved.

A computational study of the mechanism of CO oxidation by a ceria supported surface rhodium oxide layer

A mechanism of CO oxidation by a thin surface oxide of Rh supported on ceria is proposed: CO is oxidized by the Rh-oxide film, which is subsequently reoxidized by a ceria surface O atom. The proposed mechanism is supported by in situ Raman spectroscopic investigations.

Review of: Tykot, R.H. and Andrews, T.K. 1992. Sardinia: a footprint in the sea: studies in Sardinian Archaeology presented to Miriam Balmuth. Sheffield Academic Press

Proceedings of the Prehistoric Society, 1994. 60: p. 455-6.

Microneedle/nanoencapsulation-mediated transdermal delivery:Mechanistic insights

A systematic study was undertaken to gain more insight into the mechanism of transdermal delivery of nanoencapsulated model dyes across microneedle (MN)-treated skin, a complex process not yet explored. Rhodamine B (Rh B) and fluorescein isothiocyanate (FITC) as model hydrophilic and hydrophobic small/medium-size molecules, respectively, were encapsulated in poly lactic-co-glycolic acid (PLGA) nanoparticles (NPs) and delivered through full thickness porcine skin pretreated with MN array. Permeation through MN-treated skin was affected by physicochemical characteristics of NPs and the encapsulated dyes. Dye flux was enhanced by smaller particle size, hydrophilicity, and negative zeta potential of NPs. Regarding encapsulated dyes, solubility at physiological pH and potential interaction with skin proteins proved to outweigh molecular weight as determinants of skin permeation. Data were verified using confocal laser scanning microscopy imaging. Findings coupled with the literature data are supportive of a mechanism involving influx of NPs, particularly of smaller size, deep into MN-created channels, generating depot dye-rich reservoirs. Molecular diffusion of the released dye across viable skin layers proceeds at a rate determined by its molecular characteristics. Data obtained provide mechanistic information of importance to the development of formulation strategies for more effective intradermal and transdermal MN-mediated delivery of nanoencapsulated therapeutic agents.

Investigation of moisture condition and Autoclam sensitivity on air permeability measurements for both normal concrete and high performance concrete

While on site measurement of air permeability provides a useful approach for assessing the likely long term durability of concrete structures, no existing test method is capable of effectively determining the relative permeability of high performance concrete (HPC). Lack of instrument sensitivity and the influence of concrete moisture are proposed as two key reasons for this phenomenon. With limited systematic research carried out in this area to date, the aim if this study was to investigate the influence of instrument sensitivity and moisture condition on air permeability measurements for both normal concrete and HPC. To achieve a range of moisture conditions, samples were dried initially for between one and 5 weeks and then sealed in polythene sheeting and stored in an oven at 50 C to internally distribute moisture evenly. Moisture distribution was determined throughout using relative humidity probe and electrical resistance measurements. Concrete air permeability was subsequently measured using standardised air permeability (Autoclam) and water penetration (BS EN: 12390-8) tests to assess differences between the HPCs tested in this study. It was found that for both normal and high performance concrete, the influence of moisture on Autoclam air permeability results could be eliminated by pre-drying (50 ± 1 C, RH 35%) specimens for 3 weeks. While drying for 5 weeks alone was found not to result in uniform internal moisture distributions, this state was achieved by exposing specimens to a further 3 weeks of sealed pre-conditioning at 50 ± 1 C. While the Autoclam test was not able to accurately identify relative HPC quality due to low sensitivity at associated performance levels, an effective preconditioning procedure to obtain reliable air permeability of HPC concretes was identified. © 2013 The Authors

Evaluation of an in situ spatial resolution instrument for fixed beds through the assessment of the invasiveness of probes and a comparison with a micro-kinetic model

This paper reports the detailed description and validation of a fully automated, computer controlled analytical method to spatially probe the gas composition and thermal characteristics in packed bed systems. This method has been designed to limit the invasiveness of the probe, a characteristic assessed using CFD. The thermocouple is aligned with the sampling holes to enable simultaneous recording of the gas composition and temperature profiles. This analysis technique has been validated by studying CO oxidation over a 1% Pt/Al2O3 catalyst. The resultant profiles have been compared with a micro-kinetic model, to further assess the strength of the technique. 

Manipulation of intracellular glycerol and erythritol enhances germination of conidia at low water availability

The insect pathogen Beauveria bassiana, Metarhizium anisopliae and Paecilomyces farinosos can be effective biocontrol agents when relative humidity (RH) is close to 100%. At reduced water availability, germination of propagules, and therefore host infection, cannot occur. Cultures of B. bassiana, M. anisopliae and P. farinosus were grown under different conditions to obtain conidia with a modified polyol and trehalose content. Conidia with higher intracellular concentrations of glycerol and erythritol germinated both more quickly and at lower water activity (a(w)) than those from other treatments. In contrast, conidia containing up to 235.7 mg trehalose g-1 germinated significantly (P < 0 05) more slowly than those with an equivalent polyol content but less trehalose, regardless of water availability. Conidia from control treatments did not germinate below 0.951 - 0.935 a(w) (≡ 95.1 - 93.5% RH). In contrast, conidia containing up to 164.6 mg glycerol plus erythritol g-1 germinated down to 0.887 a(w) (≡ 88.7% RH). These conidia germinated below the water availability at which mycelial growth ceases (0.930 - 0.920 a(w)). Germ tube extension rates reflected the percentage germination of conidia, so the most rapid germ tube growth occurred after treatments which produced conidia containing the most glycerol and erythritol. This study shows for the first time that manipulating polyol content can extend the range of water availability over which fungal propagules can germinate. Physiological manipulation of conidia may improve biological control of insect pests in the field.

Temperature controlled motion of an antiferromagnet- ferromagnet interface within a dopant-graded FeRh epilayer

Chemically ordered B2 FeRh exhibits a remarkable antiferromagnetic-ferromagnetic phase transition that is first order. It thus shows phase coexistence, usually by proceeding though nucleation at random defect sites followed by propagation of phase boundary domain walls. The transition occurs at a temperature that can be varied by doping other metals onto the Rh site. We have taken advantage of this to yield control over the transition process by preparing an epilayer with oppositely directed doping gradients of Pd and Ir throughout its height, yielding a gradual transition that occurs between 350 K and 500 K. As the sample is heated, a horizontal antiferromagnetic-ferromagnetic phase boundary domain wall moves gradually up through the layer, its position controlled by the temperature. This mobile magnetic domain wall affects the magnetisation and resistivity of the layer in a way that can be controlled, and hence exploited, for novel device applications.

Stable Isolated Metal Atoms as Active Sites for Photocatalytic Hydrogen Evolution

The process of using solar energy to split water to produce hydrogen assisted by an inorganic semiconductor is crucial for solving our energy crisis and environmental problems in the future. However, most semiconductor photocatalysts would not exhibit excellent photocatalytic activity without loading suitable co-catalysts. Generally, the noble metals have been widely applied as co-catalysts, but always agglomerate during the loading process or photocatalytic reaction. Therefore, the utilization efficiency of the noble co-catalysts is still very low on a per metal atom basis if no obvious size effect exists, because heterogeneous catalytic reactions occur on the surface active atoms. Here, for the first time, we have synthesized isolated metal atoms (Pt, Pd, Rh, or Ru) stably by anchoring on TiO2, a model photocatalystic system, by a facile one-step method. The isolated metal atom based photocatalysts show excellent stability for H-2 evolution and can lead to a 6-13-fold increase in photocatalytic activity over the metal clusters loaded on TiO2 by the traditional method. Furthermore, the configurations of isolated atoms as well as the originality of their unusual stability were analyzed by a collaborative work from both experiments and theoretical calculations.

A DFT study of the transition metal promotion effect on ethylene chemisorption on Co(0001)

Transition metals are often introduced to a catalyst as promoters to improve catalytic performance. In this work, we study the promotion effect of transition metals on Co, the preferred catalytic metal for Fischer-Tropsch synthesis because of its good compromise of activity, selectivity and stability, for ethylene chemisorption using density functional theory (DFT) calculations, aiming to provide some insight into improving the alpha-olefin selectivity. In order to obtain the general trend of influence on ethylene chemisorption, twelve transition metals (Zr, Mn, Re, Ru, Rh, It, Ni, Pd, Pt, Cu, Ag and Au) are calculated. We find that the late transition metals (e.g. Pd and Cu) can decrease ethylene chemisorption energy. These results suggest that the addition of the late transition metals may improve alpha-olefin selectivity. Electronic structure analyses (both charge density distributions and density of states) are also performed and the understanding of calculated results is presented. (C) 2009 Elsevier B.V. All rights reserved.

An understanding and implications of the coverage of surface free sites in heterogeneous catalysis

The crucial roles of the coverage of surface free sites in determining catalytic activity trend are quantitatively addressed with the help of density functional theory and microkinetics. First, by analyzing activity trends of NO oxidation catalyzed by Ru, Rh, Pd, Os, Ir, and Pt surfaces with full kinetic considerations, we identify that the activity trend is in general determined by the competition between the reaction barrier and the coverage of surface free sites. Second, since the dissociation of many important molecules, such as the dissociation of N(2), O(2), and CO, follows the same Bronsted-Evans-Polanyi relationship, the coverage of surface free sites is usually a decisive term that affects the overall activity. Third, an equation is derived for the coverage of surface free sites and it is found that the coverage of surface free sites contains not only all the key thermodynamic parameters but also all the kinetic properties in the catalytic system. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3140202]

An Energy Descriptor To Quantify Methane Selectivity in Fischer-Tropsch Synthesis:A Density Functional Theory Study

Selectivity is a fundamental issue in heterogeneous catalysis. In this study, the CH(4) selectivity in Fischer-Tropsch synthesis is chosen to be investigated: CH4 selectivity on Rh, Co, Ru, Fe, and Re surfaces is computed by first-principles methods. In conjunction with kinetic analyses, we are able to derive the effective barrier difference between methane formation and chain growth (Delta E(eff)) to quantify the CH(4) selectivity. By using this energy descriptor, the ranking of methane selectivity predicted from density functional theory (DFT) calculations is consistent with experimental work. Moreover, a linear correlation between Delta E(eff) and the chemisorption energy of C + 4H (Delta H) is found. This fundamental finding possesses the following significance: (i) it shows that the selectivity, which appears to have kinetic characteristics, is largely determined by thermodynamic properties; and (ii) it suggests that an increase of the binding strength of C + 4H will suppress methane selectivity.