Low pressure CO2 hydrogenation to methanol over gold nanoparticles activated on a CeOx/TiO2 Interface

Capture and recycling of CO2 into valuable chemicals such as alcohols could help mitigate its emissions into the atmosphere. Due to its inert nature, the activation of CO2 is a critical step in improving the overall reaction kinetics during its chemical conversion. Although pure gold is an inert noble metal and cannot catalyze hydrogenation reactions, it can be activated when deposited as nanoparticles on the appropriate oxide support. In this combined experimental and theoretical study, it is shown that an electronic polarization at the metal-oxide interface of Au nanoparticles anchored and stabilized on a CeOx/TiO2 substrate generates active centers for CO2 adsorption and its low pressure hydrogenation, leading to a higher selectivity toward methanol. This study illustrates the importance of localized electronic properties and structure in catalysis for achieving higher alcohol selectivity from CO2 hydrogenation.U.S. Department of Energy DE-AC02- 98CH10886, DE-AC02-05CH11231Brookhaven National Laboratory DE-SC001270

Phenotypic Characterization of Multidrug-resistant Escherichia Coli with Special Reference to Extended-spectrum-beta-lactamases and Metallo-beta-lactamases in a Tertiary Care Center

Introduction: The increasing reports on extended-spectrum-beta-lactamase and metallo-betalactamase producing Escherichia coli have addressed a potential threat to global health since it is found to be highly resistance to most of the currently available antibiotics including carbapenems. The present study was aimed to determine the antibiogram of extended-spectrum-beta-lactamase and metallo-beta-lactamase producing MDR E. coli isolates from various clinical samples. Methods: This was a cross-sectional study conducted over a period of seven months (December 2013 to July 2014) at bacteriology laboratory of Tribhuvan University Teaching Hospital. A total of 250 clinical specimens (urine, pus, sputum, blood, body fluid, bile, tissue and central venous pressure line tip) were processed from inpatients, with multidrug-resistant Escherichia coli infections. Standard microbiological techniques were used for isolation and identification of the isolates. The presence of extended-spectrum-beta-lactamase was detected by phenotypic confirmatory test recommended by Clinical and Laboratory Standards Institute and imipenem (IMP) /EDTA combined disc method was performed to detect metallo-beta-lactamase mediated resistance mechanism. Results: We found high level of beta lactamase mediated resistance mechanism as part of multidrug resistance. Among 250 MDR isolates, 60% isolates were extended-spectrum-beta-lactamase producers and 17.2% isolates were metallo-beta-lactamase producers. Co-existence of extended-spectrum-betalactamase and metallo-beta-lactamase identified in 6.8% isolates. Conclusions: Beta-lactamase mediated resistance mechanisms are accounting very high in the multidrug resistant isolates of E. coli. Therefore, early detection of beta lactamase mediated resistant strains and their current antibiotic susceptibility pattern is necessary to avoid treatment failure and prevent the spread of MDR.  Keywords: e. coli; extended-spectrum-β-lactamase; metallo-β-lactamase; multidrug-resistance

Machine Learning Prediction of Surface Segregation Energies on Low Index Bimetallic Surfaces

Surface chemical composition of bimetallic catalysts can differ from the bulk composition because of the segregation of the alloy components. Thus, it is very useful to know how the different components are arranged on the surface of catalysts to gain a fundamental understanding of the catalysis occurring on bimetallic surfaces. First-principles density functional theory (DFT) calculations can provide deeper insight into the surface segregation behavior and help understand the surface composition on bimetallic surfaces. However, the DFT calculations are computationally demanding and require large computing platforms. In this regard, statistical/machine learning methods provide a quick and alternative approach to study materials properties. Here, we trained previously reported surface segregation energies on low index surfaces of bimetallic catalysts using various linear and non-linear statistical methods to find a correlation between surface segregation energies and elemental properties. The results revealed that the surface segregation energies on low index bimetallic surfaces can be predicted using fundamental elemental properties

A Density Functional Theory Study of Electrochemical Nitrogen Reduction to Ammonia on the (100) Surface of Transition-Metal Oxynitrides

The electrochemical nitrogen (N2) reduction reaction (ENRR) to produce ammonia (NH3) under ambient conditions is attractive compared to the energy- and carbon-intensive industrialized Haber–Bosch process. However, efficient catalysts are needed to break an NN bond in an N2 molecule to convert it to NH3. Transition-metal oxynitrides (TMNOs) have shown promising ENRR activities at low potentials. Here, density functional theory (DFT) calculations are performed to study the ENRR activity of TMNO(100) surfaces for TM = Co, Cr, Cu, Fe, Hf, Mn, Nb, Ni, Sc, Ta, Ti, V, Y, Zn, and Zr. Our DFT calculations and microkinetic modeling results show that the ENRR proceeds at a low applied potential on the (100) surfaces of MnNO, CrNO, FeNO, CuNO, HfNO, and VNO. Furthermore, our calculations reveal a volcano-like relation between the limiting potential and binding energy of ENRR intermediates identifying nitrogen binding energy and N2H binding energy as descriptors for ENRR activity on TMNO(100) surfaces

Reaction Pathway for Oxygen Reduction on FeN₄ Embedded Graphene

The detailed reaction pathways for oxygen reduction on FeN₄ embedded graphene have been investigated using density functional theory transition-state calculations. Our first-principles calculation results show that all of the possible ORR elementary reactions could take place within a small region around the embedded FeN₄ complex. It is predicted that the kinetically most favorable reaction pathway for ORR on the FeN₄ embedded graphene would be a four-electron OOH dissociation pathway, in which the rate-determining step is found to be the OOH dissociation reaction with an activation energy of 0.56 eV. Consequently, our theoretical study suggests that nonprecious FeN₄ embedded graphene could possess catalytic activity for ORR comparable to that of precious Pt catalysts

Stability, Electronic and Magnetic Properties of In-Plane Defects in Graphene: A First-Principles Study

The electronic and magnetic properties of graphene can be modified through combined transition-metal and nitrogen decoration of vacancies. In this study, we used density functional theory to investigate the following defect motifs: nitrogen doping, nitrogen decoration of single and double vacancies (SVs and DVs), TM doping (TM = Co, Fe), TM adsorption on nitrogen-doped graphene, and combined TM–nitrogen chemistries in SV and DV (TM–N_<i>x</i>) configurations. The results show that the highest magnetic moments are supported in TM–N_<i>x</i> defect motifs. Among these defects, Co–N₃, Fe–N₃, and Fe–N₄ defects are predicted to show ferromagnetic spin structures with high magnetic moments and magnetic stabilization energies, as well as enhanced stability as expressed by favorable formation energies, and high TM binding energies