4,104 research outputs found
An increased standardised mortality ratio for liver cancer among polyvinyl chloride workers in Taiwan
No full textChronic liver diseases amongst Taiwan vinyl chloride exposed workers - Case-control study
No full textInteraction of vinyl chloride monomer exposure and hepatitis B viral infection on liver cancer
No full textUnveiling the Structure Sensitivity for Direct Conversion of Syngas to C2-Oxygenates with a Multicomponent-Promoted Rh Catalyst
No full textAbstract: Mn and Li promoted Rh catalysts supported on SiO2 with a thin TiO2 layer were synthesized by stepwise incipient wetness impregnation approach. The thin TiO2 layer on the surface of SiO2 was proved to stabilize those small Rh nanoparticles and hinder their agglomeration. The reducibility of Rh on these catalysts depends on Rh particle size as well as the position of manganese oxide, and large Rh nanoparticles with MnO on Rh nanoparticles can be only reduced at an elevated temperature. Catalyst with large Rh particles exhibits a higher CO conversion and higher products selectivity towards long chain hydrocarbons and C2-oxygenates at the expense of decreasing methane formation than a similar catalyst with smaller Rh particles. This was attributed to the synergistic effect of Mn and Li promotion and molar ratio between Rh0 and Rhδ+ sites on the surface of Rh nanoparticles. Moreover, Rh nanoparticles on MnO are proved to be more efficient in promoting hydrogenation of acetaldehyde to ethanol than its counterpart with MnO on Rh nanoparticles. Finally, in order to target high C2-oxygenates selectivity, low reaction temperature together with a low H2/CO ratio in the feed is recommended. Graphic Abstract: [Figure not available: see fulltext.].ChemE/Catalysis EngineeringChemE/O&O groe
Rh-Based Catalysis Chemistry of Aqueous-Phase Nitrogen Treatment Reactions
No full textOver the past century, the increase in human population has driven a need for the increased fixation of atmospheric nitrogen to produce nitrogen-based fertilizers and munitions. These anthropogenic processes have led to significant pollution of freshwater by inorganic nitrogen species (e.g. NO3-, NO2-, NH4+). Nitrate (NO3-) and nitrite (NO2-) consumption is toxic to humans, and ammonia/ammonium (NH3/NH4+) is toxic to aquatic life. Both the oxidized and reduced species contribute towards eutrophication and soil acidification. Catalytic denitrification has emerged as a promising technology for the remediation of nitrogen-contaminated waters. The primary goal of this work is to investigate rhodium (Rh)-based catalysts for the remediation of inorganic nitrogen contaminants in water. This study addresses the effects of pH and salinity on the catalytic mechanism of nitrate/nitrite hydrogenation. A new support material for Rh was developed and a bifunctional reaction mechanism was found for ammonia oxidation. This work provides new insights into nitrogen conversion mechanisms in water over Rh, and insights into the design of active and selective catalysts for a desired treatment application.
The NO2- reduction properties of alumina-supported Rh were investigated using Pd as a benchmark, where the bulk solution pH was varied to probe the effect of reaction conditions on the catalytic chemistry. Pd expectedly showed high reduction activity and high N2 selectivity at low pH, and near inactivity at high pH. Rh, while inactive at low pH, showed moderate activity and high NH4+ selectivity at high pH. Hydrazine (N2H4) was also detected as a reaction intermediate when NH4+ was formed. Density functional theory (DFT) simulations of the reactions performed by collaborators revealed new insights into the reaction mechanism at different pH, which were corroborated by in aqua surface-enhanced Raman spectroscopy (SERS). These results update the common view that only Pd-based catalysts are effective for NO2- reduction and suggest unexplored avenues for nitrogen chemistry.
The effect of chloride on the NO3- hydrogenation activity and selectivity was evaluated for carbon-supported rhodium and palladium catalysts. In the absence of buffer, chloride monotonically increases the overall catalytic activity of In-Rh/C. In-Pd/C showed a volcano-shaped dependence on the nitrate reduction rate showing lower activity in 2M NaCl than DI water. CO-SERS analysis of chemisorption on model substrates suggested that suggests that NaCl has an electronic effect on both metals which decreases the N-O bond strength of the crucial NO* surface intermediate. The In-Rh/C catalyst also demonstrated high activity for nitrate reduction towards ammonia in simulated ion-exchange brines implying it may be an option for nutrient recovery from these streams.
A new Rh supported on a semi-crystalline niobium oxide support was developed to activate aqueous ammonium at room temperature and atmospheric pressure, converting into gas-phase nitrogen species (N2, NO, N2O) and trace amounts of NO3- using only O2. Raman spectroscopy correlated the chemical treatment of the support prior to metal addition to the generation of terminal Nb=O species, which are crucial for catalytic activity. Isotopic experiments reveal a bifunctional mechanism, where Nb binds and converts ammonium to ammonia, which decomposes on Rh. While further optimization is needed to drive selectivity towards N2, Rh supported on modified niobium may be the basis of a new generation of catalysts that can oxidize NH4+ under mild conditions.
In addition to nitrogen contaminant degradation for clean water applications, I also investigated Zr-based metal-organic framework (MOF) materials for the adsorptive treatment of perfluorooctane sulfonate (PFOS) contaminated water. In this work, the sorption properties of UiO-66 metal-organic frameworks (MOFs) with varying defect were studied for the removal of PFOS. Large pore defects (~16 and ~20 Å) within the framework were critical to increasing the capacity due to higher internal surface area and an increased number of coordinatively unsaturated Zr sites to bind PFOS head groups. The enhanced PFOS adsorptive properties of UiO-66 highlight the advantage of structurally defective MOFs as a water treatment approach towards environmental sustainability
Discharge patterns of retinal ganglion cells in rodent models of degenerative retinal diseases
No full text
Expression of Plasmodium falciparum genes involved in erythrocyte invasion varies among isolates cultured directly from patients.
No full textPlasmodium falciparum merozoites invade erythrocytes using a range of alternative ligands that includes erythrocyte binding antigenic proteins (EBAs) and reticulocyte binding protein homologues (Rh). Variation in the expression of some of these genes among culture-adapted parasite lines correlates with the use of different erythrocyte receptors. Here, expression profiles of four Rh genes and eba175 are analysed in a sample of 42 isolates cultured from malaria patients in Kenya. The profiles cluster into distinct groups, largely because of very strong negative correlations between the levels of expression of particular gene pairs (Rh1 versus Rh2b, eba175 versus Rh2b, and eba175 versus Rh4), previously associated with alternative invasion pathways in culture-adapted parasite lines. High levels of eba175 are seen in isolates in expression profile group I, and may be associated with sialic acid-dependent invasion. Groups II and III are, respectively, characterized by high levels of Rh2b and Rh4, and are more likely to be associated with sialic acid-independent invasion
A computational study of supported rhodium catalysts
No full textIn this work, density functional theory (DFT) was used to obtain microscopic structures of heterogeneous catalysts based on rhodium supported on a metal oxide (-Al2O3). Two different methodologies were used. The first methodology uses a periodic model and a plane-wave basis set to solve the Schrödinger equation in the framework of Bloch’s theorem. The optimised structures of RhI(CO)2/ -Al2O3 species obtained at this level of theory have bond lengths in agreement with experimental EXAFS determinations. The weighted linear combination of Rh K-edge XANES spectra computed using the three most dominant structures reproduces well the phase and shape of the oscillations of the experimental XANES spectrum, providing support for the computed structures. The second methodology is based on hybrid quantum mechanical (QM)/molecular mechanical (MM) calculations. Within this scheme the support is described at the MM level of theory while the region of interest, the absorption site where the surface RhI(CO)2 complex lies, is described with a suitable QM approach. These hybrid calculations performed at the PBE/ECP/cc-pVDZ level of theory were used to obtainminimum-energy structures and harmonic stretching frequencies of RhI(CO)2/-Al2O3 species. The computed bond lengths and harmonic stretching frequencies were in good agreement with the experimental evidence and with the results obtained using periodic model
- …
