2,520 research outputs found
One-, two- and three-dimensional Cu(II) complexes built via new oligopyrazinediamine ligands: from antiferromagnetic to ferromagnetic coupling
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
Computational Exploration of Rh-III/Rh-V and Rh-III/Rh-I Catalysis in Rhodium(III)-Catalyzed C-H Activation Reactions of N-Phenoxyacetamides with Alkynes
No full textThe selective rhodium-catalyzed functionalization of arenes is greatly facilitated by oxidizing directing groups that, act both as directing groups and internal oxidants. We report density functional theory (B3LYP and M06) investigations on the mechanism of rhodium(III)-catalyzed redox coupling reaction of N-phenoxyacetamides with alkynes. The results elucidated the role of the internal oxidizing directing group, and the role of Rh-III/Rh-I and Rh-III/Rh-V catalysis of C-H functionalizations. A novel Rh-III/Rh-V-Rh-III cycle successfully rationalizes recent experimental observations by Liu and Lu et al. (Liu, G. Angew. Chem. Int. Ed. 2013, 52, 6033) on the reactions of N-phenoxyacetamides with alkynes in different solvents. Natural Bond Orbital (NBO) analysis confirms the identity of Rhy intermediate in the catalytic cycle.National Natural Science Foundation of China [21133002, 21203004]; Shenzhen Peacock Program [KQTD201103]; National Science Foundation of the USA [CHE-1361104]; National Science Foundation under the CCI Center for Selective C-H Functionalization [CHE-1205646]; National Science Foundation [OCI-1053575]SCI(E)[email protected]; [email protected]
Solvent effects in heterogeneous selective hydrogenation of acetophenone: differences between Rh/C and Rh/Al2O3 catalysts and the superiority of water as a functional solvent
Full text linkSelective hydrogenation of acetophenone (AP) to 1-phenylethanol (PhE) was investigated over Rh/Al2O3 and Rh/C catalysts in 13 solvents including water and conventional organic solvents. Strong solvent effects on the overall rate of AP conversion were observed in different manners depending on the catalysts used. The conversion obtained is correlated with hydrogen-bond-donation (HBD) capability for Rh/C but with hydrogen-bond-acceptance (HBA) capacity for Rh/Al2O3. The solvent effects should result from interactions between the carbonyl group of AP and the solvent molecules through hydrogen bonding for Rh/C and from those between the solvent molecules and the catalyst surface for Rh/Al2O3 having HBD hydroxyl groups on its surface. Water is the most effective functional solvent in the selective hydrogenation of AP for C and Al2O3-supported Rh catalysts due to its high HBD capability (a) and low HBA capability (beta), respectively. For the hydrogenation with Rh/Al2O3 in water, its large polarity/polarizability index (pi*) may contribute to the high selectivity to PhE
Adverse effects of potassium on NO<sub>x</sub> reduction over Di-Air catalyst (Rh/La-Ce-Zr)
No full textThe influence of potassium in Rh on a lanthium promoted zirconia stablised ceria (CZ) catalysts was studied toward NOxreduction reactivity and selectivity. The results are compared with a Rh/CZ catalyst. The samples were characterised by N2 adsorption, XRD, SEM, ICP, and H2-TPR. The study highlighted the importance of stored NOx regeneration over potassium in determining the overall performance of the Rh/K/CZ catalyst. The NOx stored over Rh/K/CZ in the previous NO gas stream cannot be regenerated sufficiently during the C3H6 gas stream, and stored NOxgradually decreased from one cycle to the next, resulting in deteriorating performance of Rh/K/CZ. Besides, problem of NOx slip, the formation of both NH3 and N2O (selectivities up to 30% for each side product) were observed by the addition of potassium into the Rh/CZ catalyst system, depending on the reaction conditions applied and the severity of the catalyst deactivation.</p
Rh promoted In2O3 as a highly active catalyst for CO2 hydrogenation to methanol
Full text linkSynthesis of methanol with high selectivity and productivity through hydrogenation of CO2 is highly attractive. This work uses a Rh doped In2O3 catalyst to achieve a high methanol productivity of 1.0 g(MeOH) h(-1) g(cat)(-1) while maintaining the intrinsic high selectivity of pure In2O3. Rh facilitated the dissociation of H-2 leading to creation of oxygen vacancies over the In2O3 surface. In addition, Rh atoms also participated in the activation of CO2 to produce formate species with a low activation barrier as evidenced by DFT calculation. Rh species were atomically dispersed in the In2O3 matrix and were stable during a long term reaction. Under reaction conditions, the surface Rh atoms were reduced and were stabilized by charge transfer from neighbouring In atoms. Our results show that incorporation of atomic Rh species in In2O3 can lead to high methanol productivity by creation of oxygen vacancies as well as Rh centred active sites for CO2 activation
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
The response of carbohydrate metabolism to the fluctuation of relative humidity (RH) in the desert soil cyanobacterium Phormidium tenue
No full textThe excreting of exopolysaccharides (EPS) is thought as one of the main protection ways for cyanobacteria in desert algal crusts to survive desiccation. But how cyanobacteria adjust their carbohydrate metabolism to survive this stress is not elucidated. In this study, we treated Phormidium tenue, a cyanobacterium isolated from biological soil crusts with the changes of relative humidity (RH) to simulate different levels of desiccation and investigated its carbohydrate metabolism. It was found that photosynthetic activity (Fv/Fm) and cellular total carbohydrates production decreased significantly at low RH. But the production of EPS, reducing sugar, sucrose and the activity of sucrose phosphate synthase (SPS) increased significantly at low RH and reached maximum at 75% RH. Low RH could also cause the enhanced production of reactive oxygen species (ROS) generation, malondialdehyde (MDA) production and DNA strand breaks. However, when pretreated with exogenous 100 mg/L EPS, Fv/Fm and carbohydrate production were improved significantly, while ROS generation, MDA production and DNA strand breaks decreased significantly at various levels of RH in P tenue. These results indicated that P. tenue in arid regions could enhance desiccation tolerance by adjusting the carbohydrate metabolism to eliminate ROS and decrease oxidative damage. (C) 2011 Elsevier Masson SAS. All rights reserved.The excreting of exopolysaccharides (EPS) is thought as one of the main protection ways for cyanobacteria in desert algal crusts to survive desiccation. But how cyanobacteria adjust their carbohydrate metabolism to survive this stress is not elucidated. In this study, we treated Phormidium tenue, a cyanobacterium isolated from biological soil crusts with the changes of relative humidity (RH) to simulate different levels of desiccation and investigated its carbohydrate metabolism. It was found that photosynthetic activity (Fv/Fm) and cellular total carbohydrates production decreased significantly at low RH. But the production of EPS, reducing sugar, sucrose and the activity of sucrose phosphate synthase (SPS) increased significantly at low RH and reached maximum at 75% RH. Low RH could also cause the enhanced production of reactive oxygen species (ROS) generation, malondialdehyde (MDA) production and DNA strand breaks. However, when pretreated with exogenous 100 mg/L EPS, Fv/Fm and carbohydrate production were improved significantly, while ROS generation, MDA production and DNA strand breaks decreased significantly at various levels of RH in P tenue. These results indicated that P. tenue in arid regions could enhance desiccation tolerance by adjusting the carbohydrate metabolism to eliminate ROS and decrease oxidative damage. (C) 2011 Elsevier Masson SAS. All rights reserved
A new dynamic N2O reduction system based on Rh/ceria-zirconia: from mechanistic insight towards a practical application
No full textSimultaneous reduction of N2O in the presence of co-existing oxidants, especially NO, from industrial plants, is a challenging task. This study explores the applications of a hydrocarbon reduced Rh/Zr stabilized La doped ceria (Rh/CLZ) catalyst in N2O abatement from oxidant rich industrial exhaust streams e.g. NO, CO2, and O2. The reaction mechanism was studied by the temporal analysis of products. The obtained results revealed that hydrocarbon pretreatment led to the creation of ceria oxygen vacancies and the formation of carbon deposits on the Rh/CLZ catalyst surface. These ceria oxygen vacancies are the active sites for the selective reduction of N2O into N2, while the dissociated O atoms from N2O fill the ceria oxygen vacancies. The oxidation of the deposited carbon via the lattice ceria oxygen generates new ceria oxygen vacancies, thereby extending the catalytic cycle. The reduction of N2O over C3H6 reduced Rh/CLZ is a process combining oxygen vacancy healing and deposited carbon oxidation. The results obtained from fixed-bed reactor experiments demonstrated that the hydrocarbon reduced Rh/CLZ catalyst provided a unique and extraordinary N2O abatement performance in the presence of co-existing competing oxidants (reactivity order: N2O ∼ NO > O2 > CO2 ∼ H2O).ChemE/Catalysis Engineerin
Barriers to sustaining antiretroviral treatment in Kisesa, Tanzania: a follow-up study to understand attrition from the antiretroviral program.
Full text linkTwo years after the introduction of free antiretroviral therapy (ART) in Tanzania and in spite of the logistical support provided to facilitate clinic attendance, a considerable level of attrition from the program was identified among clients from a semi-rural ward. Qualitative research on ART patients' health-seeking behavior identified factors affecting sustained attendance at treatment clinics. A mix of methods was used for data collection including semi-structured interviews with 42 clients and 11 service providers and 4 participatory group activities conducted with members of a post-test group between October and December 2006. A socio-ecological framework guided data analysis to categorize facilitators and barriers into individual, social, programmatic, and structural level influences, and subsequently explored their interaction and relative significance in shaping ART clients' behavior. Our findings suggest that personal motivation and self-efficacy contribute to program retention, and are affected by other individual-level experiences such as perceived health benefits or disease severity. However, these determinants are influenced by others' opinions and beliefs in the community, and constrained by programmatic and structural barriers. Individuals can develop the requisite willingness to sustain strict treatment requirements in a challenging context, but are more likely to do so within supportive family and community environments. Effectiveness and sustainability of ART roll-out could be strengthened by strategic intervention at different levels, with particular attention to community-level factors such as social networks' influence and support
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