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Direct diabatization and analytic representation of coupled potential energy surfaces and couplings for the reactive quenching of the excited (2)sigma(+) state of OH by molecular hydrogen
No full textWe have employed extended multiconfiguration quasidegenerate perturbation theory, fourfold-way diabatic molecular orbitals, and configurational uniformity to develop a global three-state diabatic representation of the potential energy surfaces and their couplings for the electronically nonadiabatic reaction OH* + H-2 -> H2O + H, where * denotes electronic excitation to the A (2)sigma(+) state. To achieve sign consistency of the computed diabatic couplings, we developed a graphics processing unit-accelerated algorithm called the cluster-growing algorithm. Having obtained consistent signs of the diabatic couplings, we fit the diabatic matrix elements (which consist of the diabatic potentials and the diabatic couplings) to analytic representations. Adiabatic potential energy surfaces are generated by diagonalizing the 3 x 3 diabatic potential energy matrix. The comparisons between the fitted and computed diabatic matrix elements and between the originally computed adiabatic potential energy surfaces and those generated from the fits indicate that the current fit is accurate enough for dynamical studies, and it may be used for quantal or semiclassical dynamics calculations
Nanodisperse gold catalysts in oxidation of benzyl alcohol: comparison of various supports under different conditions
No full textMonodisperse gold particles (ca. 2 nm) were prepared and deposited on various supports (SiO2, Al2O3, HAP, MgAl2O4 and MgO). The acid/base properties of supports were characterized by NH3 and CO2 sorption. The size of the gold nanoparticles spans in the 1.7-6.5 nm mean diameter range after calcination as determined from TEM measurements. The amounts of accessible surface sites were estimated by binary concentration pulse chromatography of CO with Kr adsorption. The data are in agreement with the results of CO adsorption obtained by DRIFT spectroscopy. The activities of the catalysts were compared in the oxidation of benzyl alcohol in stirred batch reactors under two different conditions: in xylene solvent with atmospheric oxygen at 60 degrees C (in presence and in absence of K2CO3), and in a solvent-free mixture at elevated pressure and temperature (5 bar O-2, 150 degrees C, 5 h). The activities of catalysts in benzyl alcohol conversion are described in two variants, namely related to (i) active catalytic sites (ASNA), and (ii) number of Au atoms on the geometric surface of particles (GSNA). The activities of catalysts in xylene solvent at 60 degrees C were excellent, with 0.28-1.11 s(-1) characteristic GSNA(ini) values (initial reaction rates related to surface Au atoms, Au-surf) in presence of K2CO3. The observed order of activities under these conditions is Au/SiO2 < Au/Al2O3 < Au/HAP < Au/MgAl2O4 < Au/MgO. In the experiments performed at 150 degrees C under solvent-free conditions, the reaction partners are depleted in greater extents (with the exception of Au/Al2O3), thus the obtained average GSNA(ave) (average reaction rate during 5 h reaction related to Au-surf) values are less reliable, however selectivity data provide useful information as well. These estimated average GSNA(ave) values (0.14-0.83 s(-1)) attest still good activities. For the interpretation of the obtained data, the roles of active sites on gold nanoparticles of various dispersion and the accessibility of their surfaces as well as the acid-base properties and surface hydroxyl concentration of supports, water ad- and desorption phenomena are considered simultaneously
Reductive methylation labeling, from quantitative to structural proteomics
No full textReductive methylation is a highly reactive and selective chemical labeling method and plays an important role in proteomic analysis. Various applications of reductive methylation have been developed and have substantially promoted the scope of proteomic analysis to date. Aside from a well-known method for introducing isotopes, this reaction could also be conducted under biological conditions and has little structural perturbations. In this paper, we reviewed the recent developments and applications of reductive methylation in quantitative proteomics and protein N-terminal profiling, along with the emerging applications in structural proteomics for monitoring protein structural/conformational changes under various conditions. (C) 2019 Elsevier B.V. All rights reserved
Dynamic Interplay between Copper Tetramers and Iron Oxide Boosting CO2 Conversion to Methanol and Hydrocarbons under Mild Conditions
No full textAtomically precise subnanometer catalysts are of significant interest because of their remarkable efficiency in a variety of catalytic reactions. However, the dynamic changes of active sites under reaction conditions, in particular, the transition of cluster-oxide interface structure have not yet been well-elucidated, lacking in situ measurements. By using multiple state-of-the-art in situ characterizations, here we show a dynamic interplay between copper tetramers and iron oxides in a single-size Cu-4/Fe2O3 catalyst, yielding an enrichment of surface Cu-4-Fe2+ species under reaction conditions that boosts CO2 hydrogenation at near-atmospheric pressures. During reaction, Cu-4 clusters facilitate the reduction of Fe2O3 producing surface-rich Fe2+ species in the proximate sites. The as-formed Fe2+ species in return promotes CO2 activation and transformation over Cu4 cluster, resulting in strikingly high methanol synthesis at low temperatures and C-1/C-3 hydrocarbon production in a high-temperature regime. The discovery of highly active Cu-4-Fe2+ sites thus provides new insights for the atomic-level design of copper catalyst toward high-efficiency CO2 conversion under mild conditions
Boosting the rate capability of multichannel porous TiO2 nanofibers with well-dispersed Cu nanodots and Cu2+-doping derived oxygen vacancies for sodium-ion batteries
No full textThe use of TiO2 as an anode in rechargeable sodium-ion batteries (NIBs) is hampered by intrinsic low electronic conductivity of TiO2 and inferior electrode kinetics. Here, a high-performance TiO2 electrode for NIBs is presented by designing a multichannel porous TiO2 nanofibers with well-dispersed Cu nanodots and Cu2+-doping derived oxygen vacancies (Cu-MPTO). The in-situ grown well-dispersed copper nanodots of about 3 nm on TiO2 surface could significantly enhance electronic conductivity of the TiO2 fibers. The one-dimensional multichannel porous structure could facilitate the electrolyte to soak in, leading to short transport path of Na+ through carbon toward the TiO2 nanoparticle. The Cu2+-doping induced oxygen vacancies could decrease the bandgap of TiO2, resulting in easy electron trapping. With this strategy, the Cu-MPTO electrodes render an outstanding rate performance for NIBs (120 mAh center dot g(-1) at 20 C) and a superior cycling stability for ultralong cycle life (120 mAh center dot g(-1) at 20 C and 96.5% retention over 2,000 cycles). Density functional theory (DFT) calculations also suggest that Cu2+ doping can enhance the conductivity and electron transfer of TiO2 and lower the sodiation energy barrier. This strategy is confirmed to be a general process and could be extended to improve the performance of other materials with low electronic conductivity applied in energy storage systems
