N-Doped Hybrid Graphene and Boron Nitride Armchair Nanoribbons As Nonmagnetic Semiconductors with Widely Tunable Electronic Properties

Russian Journal of Physical Chemistry A - The electronic and chemical properties of N-doped hybrid graphene and boron nitride armchair nanoribbons (N-doped a-GBNNRs) in comparison with graphene...     

Microkinetic simulations of the oxidation of CO on Pd based nanocatalysis: a model including co-dependent support interactions

The catalysed oxidation of CO using mass-selected Pd(13) clusters supported on thin MgO films was modelled using a microkinetic simulation of the reaction. The model of the system includes reverse spill-over calculations which were intrinsically incorporated into the formulation of the kinetics. The spill-over model is based on a capture-zone approach including a co-dependence on the variables of the kinetic equations. The experimental values were determined using dual pulsed-molecular beam measurements and recorded at a range of temperatures. The experiment allowed the turn-over frequency and reaction probability to be determined as a function of mole fraction. Comparison of the kinetic model with the experimental data gives excellent agreement and strongly highlights the importance of substrate effects. In particular, the origin of the low temperature catalysis of the Pd clusters is elucidated. The model allows the mole fraction and temperature dependent values such as the sticking coefficients for these clusters to be predicted.     

Drag reduction behavior of hydrolyzed polyacrylamide/polysaccharide mixed polymer solutions—effect of solution salinity and polymer concentration

Anionic polyacrylamide is a hydrolyzed form of polyacrylamide (HPAM), which suffers from mechanical degradation at turbulent flow rates. In order to investigate the possibility of improving the shear resistance of HPAM, various polyacrylamide/polysaccharide mixtures as well as single xanthan gum (XG) and guar gum (GG) polymer solutions were prepared and drag reduction (DR) measurements were performed in a closed flow loop. It was found that the DR efficiencies of both XG and GG solutions were directly proportional to polymer concentration and both solutions exhibited excellent mechanical resistance at turbulent conditions. The presence of XG in concentrated HPAM/XG solutions (C > 450 wppm) significantly improved both DR efficiency and shear resistance of the solutions (6–8% decline after shearing for 2 h). GG solutions exhibited smaller DR efficiencies than XG solutions. Due to small molar mass and low flexibility, GG was not as good a friction reducer as XG and HPAM; therefore, the presence of GG did not improve the DR behavior of the binary solutions. Another issue associated with HPAM is sensitivity to the presence of salt ions in the solution. The effect of salt on the DR behavior was verified by addition of 2% KCl to single and binary solutions. Drag reduction efficiencies of HPAM/XG/KCl solutions were 28 and 20% compared to 10% DR of 1000 wppm HPAM/KCl solution. It was found that the presence of XG in binary solutions significantly reduced the negative effect of salt ions on HPAM molecules.     

Oxidation state and symmetry of magnesia-supported Pd13O(x) nanocatalysts influence activation barriers of CO oxidation

Combining temperature-programmed reaction measurements, isotopic labeling experiments, and first-principles spin density functional theory, the dependence of the reaction temperature of catalyzed carbon monoxide oxidation on the oxidation state of Pd(13) clusters deposited on MgO surfaces grown on Mo(100) is explored. It is shown that molecular oxygen dissociates easily on the supported Pd(13) cluster, leading to facile partial oxidation to form Pd(13)O(4) clusters with C(4v) symmetry. Increasing the oxidation temperature to 370 K results in nonsymmetric Pd(13)O(6) clusters. The higher symmetry, partially oxidized cluster is characterized by a relatively high activation energy for catalyzed combustion of the first CO molecule via a reaction of an adsorbed CO molecule with one of the oxygen atoms of the Pd(13)O(4) cluster. Subsequent reactions on the resulting lower-symmetry Pd(13)O(x) (x < 4) clusters entail lower activation energies. The nonsymmetric Pd(13)O(6) clusters show lower temperature-catalyzed CO combustion, already starting at cryogenic temperature.