Molecular dynamics simulation and energy minimization of O2 adsorbed on a graphite surface

Simulation studies of O₂ on graphite show that the quadrupole interaction strongly affects the orientational correlation between neighbouring molecules in the adsorbed solid. The energy minimization study shows two non-equivalent competing structures with nearest neighbours arranged parallel and at an angle of 60°. The precise value of the quadrupole moment stabilises one structure with respect to the other. For Θ = 0 the simulated structure agrees with experiment. For values of the quadrupole close to the experimental value there is a significant discrepancy between experiment and theory. This discrepancy can be understood in terms of the neglect of the magnetic forces arising from the exchange interaction. The best effective σ₀₀ is 5% higher than the value recommended by bulk solid studies. The minimum energy structure is incommensurate and molecules are aligned preferentially parallel to the surface at the coverage in this study.     

Inelastic electron tunneling spectroscopy of a model catalyst: CO on Rh/Al2O3

Using tunneling spectroscopy we have studied the preparation and behavior of dispersed rhodium model catalysts supported on alumina. Samples were prepared by vacuum evaporation from Rh metal or Rh₂O₃ sources onto an oxidized Al film and CO was adsorbed in-situ. The tunnel junctions were formed by adding a Pb top electrode and the vibrational spectra of the adsorbed species were measured. We observed qualitatively different spectra when the preparation procedure was varied. Special care was taken to monitor and control background gases. We obtained different results from Rh of Rh₂O₃ sources and the presence of oxygen or water affects the vibrational spectra of the adsorbed CO. We also study the effect of the Rh thickness on the spectral intensity. Other experiments were measurement of the superconducting tunneling spectra of the Pb and a TEM study of Rh particle size. Previously reported data from tunneling and IR measurements are compared with the present work. Based on these results, we conclude that there are two species present, either a linear Rh-CO or doubly (geminal) adsorbed Rh(CO)₂ depending upon the degree of dispersion and oxidation of the Rh. The evidence also indicates that in both instances a dispersed form of Rh, rather than relatively large Rh metal particles, is responsible for the observed spectra.     

Silver(I) ion induced formation of 2-D ternary lead(II)-silver(I)-4-tolythiolate [PbAg2(μ-Stol)2(μ4-Stol)2]n from 1-D binary lead(II)-4-tolythiolate [(μ-Cl)Pb2(Stol)(μ-Stol)2]n (tol = 4-tolyl)

Treatment of [Pb(Stol)₂]_n with an equiv of [Et₄N]Cl in DMF afforded a new 1-D polymeric complex, [(μ-Cl)Pb₂(Stol)(μ-Stol)₂]_n (1), with Pb–Cl–Pb links. Interaction of 1 with a suspension of [Ag(Stol)] in DMF resulted in formation of a 2-D polymeric complex, [PbAg₂(μ-Stol)₂(μ₄-Stol)₂]_n (2), with the planar four-membered Ag₂S₂ and PbAgS₂ rings bridged by μ-Stol and μ₄-Stol ligands. Both polymeric complexes were structurally characterized by single-crystal X-ray diffraction analysis.     

Cp Me5P6C5[M(CO)5]3: Ungewöhnliche reaktion des tricyclischen hexaphosphans Cp2P6 mit M(CO)5thf (M = Cr,W)

3,4-Bis[pentamethylcyclopentadienyl]tricyclo-[3.1.0.0^2,6] hexaphosphane 1 reacts with Cr(CO)₅thf or W(CO)₅thf to give the zwitterionic chromium complex 1,9,10-tris(pentacarbonylchromium)−3,4,5,6,11-pentamethyl-7-pentamethylcyclopentadienyl-3,4,5,6,11-pentacarba-penta-cyclo-[6.1. 1.^1,8.1^3,6.O^2,7.0^10,11 ]-4-en-7-ium-9-id-undeca-phosphane 2 and the analogous tungsten compound 3, respectively. The basic structures of 2 and 3 are similar to the cunean-moiety of the Hittorf-modification of phosphorus.     

磁性Fe3O4纳米粒子的功能化修饰研究进展

Fe₃O₄纳米粒子因其独特的磁学性能和良好的生物相容性,在生物医药、催化剂、环境治理等领域具有良好的应用前景。然而,磁性Fe₃O₄纳米粒子易团聚、在潮湿的空气中易氧化,制约了Fe₃O₄纳米粒子的深度应用。本文结合课题组在磁性Fe₃O₄纳米粒子应用方面的研究成果,综述了磁性Fe₃O₄纳米粒子的功能化修饰,并讨论了磁性Fe₃O₄复合纳米材料发展面临的机遇和挑战。      

Grain Boundary Electronic Insulation for High-Performance All-Solid-State Lithium Batteries

Sulfide electrolytes with high ionic conductivities are one of the most highly sought for all-solid-state lithium batteries (ASSLBs). However, the non-negligible electronic conductivities of sulfide electrolytes (≈10⁻⁸ S cm⁻¹) lead to electron smooth transport through the sulfide electrolyte pellets, resulting in Li dendrite directly depositing at the grain boundaries (GBs) and serious self-discharge. Here, a grain-boundary electronic insulation (GBEI) strategy is proposed to block electron transport across the GBs, enabling Li−Li symmetric cells with 30 times longer cycling life and Li−LiCoO₂ full cells with three times lower self-discharging rate than pristine sulfide electrolytes. The Li−LiCoO₂ ASSLBs deliver high capacity retention of 80 % at 650 cycles and stable cycling performance for over 2600 cycles at 0.5 mA cm⁻². The innovation of the GBEI strategy provides a new direction to pursue high-performance ASSLBs via tailoring the electronic conductivity.     

Ethanol synthesis from syngas on Mn- and Fe-promoted Rh/γ-Al2O3

The catalytic hydrogenation of CO was studied over Mn- and/or Fe-promoted Rh/γ-Al₂O₃ catalysts. The catalysts were characterized by means of XRD, BET, H₂-TPR·H₂-TPD, XPS and DRIFTS. CO hydrogenation results showed that the doubly Mn- and Fe-promoted Rh/γ-Al₂O₃ catalysts exhibited superior catalytic activity and better ethanol selectivity. The DRIFTS results showed that Mn promoter stabilized the adsorbed CO on Rh⁺ and Fe stabilized adsorbed CO on Rh⁺ and Rh⁰, especially Rh⁰. The fact that doubly Mn- and Fe-promoted Rh/γ-Al₂O₃ owned more (Rhx⁰–Rhy⁺)–O–Fe³⁺·(Fe²⁺) active species was proposed to be a crucial factor accounting for its higher ethanol selectivity.