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941.
942.
Vendelbo SB Johansson M Nielsen JH Chorkendorff I 《Physical chemistry chemical physics : PCCP》2011,13(10):4486-4493
The influence of monoatomic steps and defects on the methanation reaction over ruthenium has been investigated. The experiments are performed on a Ru(0 1 54) ruthenium single crystal, which contains one monoatomic step atom for each 27 terrace atoms. The methanation activity is measured at one bar of hydrogen and CO in a high pressure cell, which enables simultaneous measurements of the local reactivity of the well defined single crystal surface and the global reactivity of the entire crystal and its auxiliary support. By adding sulfur we observe that the measured activity from the well defined stepped front-side of the crystal is poisoned faster than the entire crystal containing more defects. We also observe that additional sputtering of the well-defined front-side increases the reactivity measured on the surface. Based on this, we conclude that the methanation reaction takes place on undercoordinated sites, such as steps and kinks, and that the methanation reaction is extremely structure dependent. Simulations of the flow, temperature, and product distributions in the high pressure cell are furthermore presented as supplementary information. 相似文献
943.
Doping CeO(2) with Pd or Pt increases the oxygen storage capacity (OSC) and catalytic activity of this environmentally important material. To date, however, an understanding of the mechanism underlying this improvement has been lacking. We present a density functional theory analysis of Pd- and Pt-doped CeO(2), and demonstrate that the increased OSC is due to a large displacement of the dopant ions from the Ce lattice site. Pd(II)/Pt(II) (in a d(8) configuration) moves by ~1.2 ? to adopt a square-planar coordination due to crystal field effects. This leaves three three-coordinate oxygen atoms that are easier to remove, and which are the source of the increased OSC. These results highlight the importance of rationalizing the preferred coordination environments of both dopants and host cations when choosing suitable dopants for next generation catalysts. 相似文献
944.
Carroll L Boldon S Bejot R Moore JE Declerck J Gouverneur V 《Organic & biomolecular chemistry》2011,9(1):136-140
The Staudinger ligation of phosphine-substituted thioesters with (18)F-fluoroethylazide has been successfully applied to access (18)F-labelled molecules in radiochemical yields superior to 95%; the first fluorous variant of a Staudinger radio-ligation has been validated. 相似文献
945.
Mimi Y. Keating Feng Gao Jane B. Ramsey 《Journal of Thermal Analysis and Calorimetry》2011,106(1):207-211
The phosphorus-containing ionic liquids (IL) decompose where ion pairs fall apart. Trihexyl(tetradecyl)phosphonium decanoate,
sold as Cyphos IL 103, and Trihexyltetradecylphosphonium bis[(trifluoromethyl)sulfonyl] amide, sold as Cyphos IL 109, decompose
in 200–475 °C range in air and the fragments containing organophosphorus are found here among other major fragments of hydrocarbon
arms. Black residues are found after heating in air to 740 °C in TG in 5.0 and 0.6 mass/% for Cyphos IL 103 and 109, respectively.
They were presumably containing P2O5 after oxidation. Not all the phosphorus can be counted for at 740 °C and falls short of calculated values of 10.9 and 9.3
mass/%, if residues contain nothing else but P2O5. Among the fragments the authors found in MS the organophosphorus fragments from decomposition of the cationic C32 H68 P + including P with 3–4 hydrocarbon attached as well as the major fragments of linear hydrocarbon arms. Water evolves early
at lower temperature and continues to 740 °C. CO2 comes from oxidation of carbon at high temperatures. The SO, SO2, CF3, CF2CF2 evolve in sulfur and fluorine containing anion in Cyphos IL 109. H3PO4 is detected, which is most likely from the reaction product of P2O5 and water. No P2O5 was found. Ash content examined by inductively coupled plasma spectroscopy (ICP) found that the phosphorus P in the ashes
after burning in air to 700 °C and found 3200 ppm (or 0.62 mass/%) and 30 ppm (0.003 mass/%) in Cyphos IL 103 and 109, respectively. 相似文献
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947.
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949.
Janez Konc Matjaž Depolli Roman Trobec Kati Rozman Dušanka Janežič 《Journal of computational chemistry》2012,33(27):2199-2203
The ProBiS algorithm performs a local structural comparison of the query protein surface against the nonredundant database of protein structures. It finds proteins that have binding sites in common with the query protein. Here, we present a new parallelized algorithm, Parallel‐ProBiS, for detecting similar binding sites on clusters of computers. The obtained speedups of the parallel ProBiS scale almost ideally with the number of computing cores up to about 64 computing cores. Scaling is better for larger than for smaller query proteins. For a protein with almost 600 amino acids, the maximum speedup of 180 was achieved on two interconnected clusters with 248 computing cores. Source code of Parallel‐ProBiS is available for download free for academic users at http://probis.cmm.ki.si/download . © 2012 Wiley Periodicals, Inc. 相似文献
950.
Using molecular dynamics simulations in conjunction with home-developed Split Integration Symplectic Method we effectively decouple individual degrees of freedom of water molecules and connect them to corresponding thermostats. In this way, we facilitate elucidation of structural, dynamical, spectral, and hydration properties of bulk water at any given combination of rotational, translational, and vibrational temperatures. Elevated rotational temperature of the water medium is found to severely hinder hydration of polar molecules, to affect hydration of ionic species in a nonmonotonous way and to somewhat improve hydration of nonpolar species. As proteins consist of charged, polar, and nonpolar amino-acid residues, the developed methodology is also applied to critically evaluate the hypothesis that the overall decrease in protein hydration and the change in the subtle balance between hydration of various types of amino-acid residues provide a plausible physical mechanism through which microwaves enhance aberrant protein folding and aggregation. 相似文献