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  • Gold as modifier of metal nanoparticles: effect on structure and catalysis
    Faraday Discuss. (IF 3.588) Pub Date : 2018-02-23
    Laura Prati, Alberto Villa, Andrea Jouve, Andrea Beck, Claudio Evangelisti, Aditya Savara

    Bimetallic gold based catalysts have been prepared by sol immobilisation technique. Despite a very similar metal dispersion different structures are revealed depending on the secon metal, being alloyed systems preferred in the cas of Pd , Pt and Cu while core-shell in the case of Ru. A positive synergistic effect between the metals have been revealed only in the case of Pd and Cu in the oxidation of benzyl alcohol. AuPd/C has been also studied in the hydrogenation of benzaldehyde where the bimetallic catalyst revealed also a different selectivity compared to the monometallic counterpart.

    更新日期:2018-02-24
  • Investigation of modified Nanopore Arrays by FIB/SEM Tomography
    Faraday Discuss. (IF 3.588) Pub Date : 2018-02-23
    Angelika Holzinger, Gregor Neusser, Benjamin J.J. Austen, Alonso Gamero-Quijano, Gregoire Herzog, Damien W.M. Arrigan, Andreas Ziegler, Paul Walther, Christine Kranz

    The investigation of electrochemical processes at the interface of two immiscible electrolyte solutions (ITIES) is of great interest for sensing applications, and serves as surrogates to study biological transport phenomena, e.g. ion channels. Besides e-beam lithography, focused ion beam (FIB) milling is an attractive method to prototype and fabricate nanopore arrays that support nanoITIES. Within this contribution, we explore the capability of FIB combined with scanning electron microscopy (SEM) tomography to visualize the actual pore structure and interfaces at silica-modified nanoporous membranes. The nanopores were also characterized by atomic force microscopy (AFM) using ultra-sharp AFM probes to determine the pore diameter, and by scanning transmission electron microscopy (STEM) and energy dispersive X-ray (EDX) spectroscopy, providing additional information on the elemental composition of deposits within the pore. Si-rich particles could be identified within the pores as well as at the orifice that had faced the organic electrolyte solution during electrochemical deposition. The prospectives of the used techniques for investigating the interface at or within FIB-milled nanopores will be discussed.

    更新日期:2018-02-23
  • A Pb2+ Ionic Gate with Enhanced Stability and Improved Sensitivity Based on a 4'-aminobenzo-18-crown-6 Modified Funnel-Shaped Nanochannel
    Faraday Discuss. (IF 3.588) Pub Date : 2018-02-21
    Yongchao Qian, Zhen Zhang, Wei Chen, Liping Wen, Lei Jiang

    The existence of heavy ions in the external environment such as Pb2+ are potentially hazardous and highly toxic to human bodies. Inspired by the highly efficient ability of biological ion channels to recognize the metal ion, much effort has been devoted to investigate the biomimetic ionic gate based on the engineered solid-state conical nanopores/nanochannels. Howerver, the reported system generally behaves relatively poor functionlity and low stability due to the limited functional region. This article describes an ionic gate with enhanced stability and imporved sensitivity based on the emerging advanced funnel-shaped nanochannel system. The ionic gate is developed by anchoring the Pb2+ ion-responsive functional molecules, 4′-aminobenzo-18-crown-6 (4-AB18C6), onto the inner surface of a funnel-shaped polyethylene terephthalate (PET) nanochannel. The system can selectively recognize Pb2+ with an ultralow concentration to approximately 10-15 M and behaves excellent stability. The Pb2+ will form a positively charged complexes through specific association with the 4-AB18C6, which would screen the negative charge existed on the channel walls, resulting in a decreased ionic current and also an “OFF state”. Since the association ability of EDTA with Pb2+ is much stronger than that of 4-AB18C6, the nanochannel can also achieve reversible switching upon alternative addition of Pb2+ ion and EDTA. The switching behaviors of the system were reflected by the good reproducibility of the tunable rectifying effect. The stability of the conical and funnel-shaped nanochannels is also compared by current scanning under constant voltage. The results have shown that the stability of funnel-shaped nanochannel is much better than that of the conical nanochannel, which can be ascribed to its much longer critical region. Consequently, the funnel-shaped nanochannels with enhanced stability and improved sensitivity can potentially be applied in ion transportation, sensor, drug releasing and energy conversion.

    更新日期:2018-02-21
  • Evaluation of the intrinsic catalytic activity of nanoparticles without prior knowledge of the mass loading
    Faraday Discuss. (IF 3.588) Pub Date : 2018-02-20
    Tobias Löffler, Patrick Wilde, Denis Oehl, Yen-Ting Chen, Kristina Tschulik, Wolfgang Schuhmann

    The quantitative characterisation of electrocatalytic properties of nanoparticle catalyst materi-als is so far only performed for layers typically comprising additionally conducting additives and binders. We propose a method enabling the evaluation of intrinsic catalytic activity of nanoparticles based on the diffusion-limited steady-state current. In a step-after-step process, the influence of coverage on kinetic and diffusion limited current is evaluated to highlight the challenges of sub monolayer electroanalysis. Conclusions are used to point out strategies and their limitations for qualitative and quantitative comparison of intrinsic catalytic properties. Particularly, the impact of coverage, electrode geometry, altered diffusion profile for nanopar-ticles and the catalyst activity and selectivity are discussed. Fundamental information about electrochemical sub monolayer nanoparticle analysis is provided.

    更新日期:2018-02-21
  • Stability and Mobility of Supported Nin (n = 1-10) Clusters on ZrO2(111) and YSZ(111) Surfaces: a Density Functional Theory Study
    Faraday Discuss. (IF 3.588) Pub Date : 2018-02-20
    Abdelaziz Cadi-Essadek, Alberto Roldan, Nora Henriette De Leeuw

    The performance of supported metal catalysts, such as nickel nanoparticles decorating yttria-stabilized zirconia (YSZ), depends on their microstructure and the metal-support interface. Here, we have used spin polarized density functional theory (DFT) to evaluate different Ni cluster geometries and determined the electronic structure of the most stable configurations. We have described the interaction of Nin (n = 1-10) clusters supported on the cubic ZrO2(111) and YSZ(111) surfaces, which show a preference for pyramidal shapes rather than flat structures wetting the surface. The interfacial interaction is characterized by a charge transfer from the cluster to the surface. We also show how yttrium, present in YSZ, affects the Ni-Ni interaction. By analysing the difference between the cohesive and the clustering energy, we show the preference of Ni-Ni bond formation over Ni-surface interaction; this energy difference decreases with the increase of the Nin cluster size. From the evaluation of the Ni atomic hopping rates on YSZ, we have demonstrated that under different temperature conditions, Ni atoms aggregate with other atoms and clusters which affects the cluster size stability.

    更新日期:2018-02-21
  • Structural behaviour of copper chloride catalysts during the chlorination of CO to phosgene
    Faraday Discuss. (IF 3.588) Pub Date : 2018-02-20
    Shaoliang Guan, Philip Rosser Davies, Emma K Gibson, David Lennon, Giovanni E. Rossi, John Winfield, June Callison, Peter P. Wells, David J Willock

    The interaction of CO with an attapulgite-supported Cu(II)Cl2 catalyst has been examined in a micro-reactor arrangement. CO exposure to the dried, as-received catalyst at elevated temperatures leads to the formation of CO2 as the only identifiable product. However, phosgene production can be induced by a catalyst pre-treatment where the supported Cu(II)Cl2 sample is exposed to a diluted stream of chlorine. Subsequent CO exposure at  370C then leads to phosgene production. In order to investigate the origins of this atypical set of reaction characteristics, a series of x-ray absorption experiments were performed that were supplemented by DFT calculations. XANES measurements establish that at the elevated temperatures connected with phosgene formation, the catalyst is comprised of Cu+ and a small amount of Cu2+. Moreover, the data show that unique to the chlorine pre-treated sample, CO exposure at elevated temperature results in a short-lived oxidation of the copper. On the basis of calculated CO adsorption energies, DFT calculations indicate that a mixed Cu+/Cu2+ catalyst is required to support CO chemisorption.

    更新日期:2018-02-21
  • The deposition of metal nanoparticles on carbon surfaces: the role of specific functional groups
    Faraday Discuss. (IF 3.588) Pub Date : 2018-02-20
    Bethany Bowden, Matthew Davies, Philip Rosser Davies, Shaoliang Guan, David Morgan, Vaughan Roberts, Daniel James Wotton

    The enormous complexity of a typical heterogeneous catalyst makes understanding the development and properties of any active nanoparticles present extremely challenging. In the case of carbon based catalysts that difficulty is compounded by the variability of the carbon powders used. We have previously developed a strategy that addresses these problems by mimicking the catalyst preparation conditions very closely but, by using highly ordered pyrolytic graphite crystals (HOPG) as a model surface, enables us to examine the effects of specific functional groups on nanoparticle formation. We report here an extension of our work characterising functional groups on the HOPG surface, using XPS and AFM to explore the deposition of gold from aqueous solution onto HOPG surfaces treated in a variety of ways to alter the surface functionality. The structure and oxidation state of the resulting nanoparticles depends critically on the nature of the functional groups present and offers some insight into the development of catalysts based on these materials. Hydroyls are identified as key functional species, reducing gold ions to their metallic state whilst being oxidised themselves to carbonyls. Carbonyls meanwhile promote the nucleation of Au3+ creating a network of islands at the HOPG surface. The results have relevance not only to catalysts using activated carbons but also the new generation of materials based on graphene and carbon nanotubes.

    更新日期:2018-02-21
  • Charge Transport at a Molecular GaAs Nanoscale Junction
    Faraday Discuss. (IF 3.588) Pub Date : 2018-02-15
    Andrea Vezzoli, Richard Brooke, Nicoló Ferri, Carly Brooke, Simon Higgins, Walther Schwarzacher, Richard J. Nichols

    In recent years, the use of non-metallic electrodes for the fabrication of single-molecule junctions has developed into an elegant way to impart new properties to nanodevices. Integration of molecular junctions in a semiconducting platform would also speed technological deployment, as it would take advantage of established industrial infrastructures. In a previous proof-of-concept paper,1 we used simple α,ω-dithiol self-assembled monolayers on a gallium arsenide (GaAs) substrate to fabricate molecular Schottky diodes with a STM. In the devices, we were also able to detect the contribution of a single-molecule to the overall charge transport. The prepared devices can also be used as photodiodes, as GaAs is a III-V direct bandgap (1.42 eV at room temperature) semiconductor, and it efficiently absorbs visible light to generate a photocurrent. In this contribution, we demonstrate that fine control can be exerted on the electrical behaviour of a metal-molecule-GaAs junction by systematically altering the nature of the molecular bridge, the type and doping density of the semiconductor and the light intensity and wavelength. Molecular orbital energy alignment dominates the charge transport properties, resulting in strongly rectifying junctions prepared with saturated bridges (e.g. alkanedithiols), with increasingly ohmic characteristics as the degree of saturation is reduced through the introduction of conjugated moieties. The effects we observed are local, and may be observed with electrodes of only a few tens of nanometres in size, hence paving the way to the use of semiconducting nanoelectrodes to probe molecular properties. Perspectives of these new developments for single molecule semiconductor electrochemistry are also discussed.

    更新日期:2018-02-15
  • The electronic properties of Au clusters on CeO2(110) surface with and without O-defects
    Faraday Discuss. (IF 3.588) Pub Date : 2018-02-13
    Arunabhiram Chutia, David J Willock, C. Richard A. Catlow

    We use density functional theory with Hubbard corrections (DFT+U) to understand the local electronic properties of Au adatom and Au2 dimer adsorption on the CeO2(110) surface. We show that, based on the initial geometries, we can observe Au species in a variety of charge states including Au+, Au—, Auδ— and Auδ+—Auδ—. We present a detailed discussion using Bader charge analysis and partial density of states to support our observations. We also discuss the influence of solvent on the adsorption of Au adatoms adsorbed on top of an O-vacancy, which shows interesting geometrical and electronic properties.

    更新日期:2018-02-13
  • The role of water molecules in phototransduction of retinal proteins and G protein-coupled receptors
    Faraday Discuss. (IF 3.588) Pub Date : 2017-11-20
    Elena Lesca, Valérie Panneels, Gebhard F. X. Schertler
    更新日期:2018-02-07
  • A QM/MM study of the initial excited state dynamics of green-absorbing proteorhodopsin
    Faraday Discuss. (IF 3.588) Pub Date : 2017-11-03
    Veniamin A. Borin, Christian Wiebeler, Igor Schapiro
    更新日期:2018-02-02
  • Effect of point mutations on the ultrafast photo-isomerization of Anabaena sensory rhodopsin
    Faraday Discuss. (IF 3.588) Pub Date : 2017-11-15
    D. Agathangelou, Y. Orozco-Gonzalez, M. del Carmen Marín, P. P. Roy, J. Brazard, H. Kandori, K.-H. Jung, J. Léonard, T. Buckup, N. Ferré, M. Olivucci, S. Haacke
    更新日期:2018-02-01
  • Excited-state dynamics of mononucleotides and DNA strands in a deep eutectic solvent
    Faraday Discuss. (IF 3.588) Pub Date : 2017-11-06
    Yuyuan Zhang, Kimberly de La Harpe, Mahesh Hariharan, Bern Kohler
    更新日期:2018-01-31
  • Direct observation of the external force mediated conformational dynamics of an IHF bound Holliday junction
    Faraday Discuss. (IF 3.588) Pub Date : 2017-11-01
    Subhas C. Bera, Tapas Paul, A. N. Sekar Iyengar, Padmaja P. Mishra
    更新日期:2018-01-31
  • Probing the excited state dynamics of Venus: origin of dual-emission in fluorescent proteins
    Faraday Discuss. (IF 3.588) Pub Date : 2017-11-06
    Shaina Dhamija, Bhisham Thakur, Purnananda Guptasarma, Arijit K. De
    更新日期:2018-01-30
  • Effects of the dipolar double layer on elemental electrode processes at micro- and macro-interfaces
    Faraday Discuss. (IF 3.588) Pub Date : 2018-01-29
    Jingyuan Chen, Koichi Aoki

    Determination of heterogeneous rate constants of redox reactions or charge transfer resistances always involves ambiguities due to participation in double layer (DL) capacitances and solution resistances. The rate constants determined by the steady-state voltammograms at ultra-microelectrodes are inconsistent with time-dependent voltammograms, implying participation of the DL impedance. We examine controlling factors of DLs through the frequency-dependence of the capacitance on the basis of the definition of the current and the capacitance. The capacitance is obeyed by the power law of the frequency. It is controlled by orientation of limited amount of solvent dipoles, independent of salts. Redox species, of which dipoles are oriented oppositely to the solvent dipoles, decrease the DL capacitance and make the value negative at high concentration of the specie. The decrease in the capacitance increases the real impedance, as predicted from the phase angle, yielding an extra resistance. This may be a ghost charge transfer resistance. However, there are a number of actually well-defined charge transfer resistances, which are observed as transferring rates through films on electrodes.

    更新日期:2018-01-29
  • Photochemical relaxation pathways of S6-methylthioinosine and O6-methylguanosine in solution
    Faraday Discuss. (IF 3.588) Pub Date : 2017-11-07
    Brennan Ashwood, Luis A. Ortiz-Rodríguez, Carlos E. Crespo-Hernández
    更新日期:2018-01-26
  • Adenine radicals generated in alternating AT duplexes by direct absorption of low-energy UV radiation
    Faraday Discuss. (IF 3.588) Pub Date : 2017-09-12
    Akos Banyasz, Tiia Ketola, Lara Martínez-Fernández, Roberto Improta, Dimitra Markovitsi
    更新日期:2018-01-26
  • 更新日期:2018-01-25
  • In situ formation of the active sites in Pd-Au bimetallic nanocatalysts for CO oxidation: NAP (near ambient pressure) XPS and MS study
    Faraday Discuss. (IF 3.588) Pub Date : 2018-01-24
    Andrey Bukhtiyarov, Igor Prosvirin, Andrey A. Saraev, Alexander Yu. Klyushin, Axel Knop-Gericke, Valerii Bukhtiyarov

    The model bimetallic Pd-Au/HOPG catalysts have been investigated in CO oxidation reaction using combination of NAP XPS and MS techniques. The samples have shown catalytic activity at temperatures above 150C. The redistribution of Au and Pd on the surface depending on the reaction conditions has been demonstrated using NAP XPS. The Pd enrichment of the bimetallic particles surface under reaction gas mixture has been shown. Apparently, CO adsorption induces the Pd segregation on the surface. Heating the sample under reaction conditions above 150C decomposes Pd-CO state due to CO desorption and reaction and simultaneous Pd-Au alloy formation on the surface takes place. Cooling down back to RT results in reversible Pd segregation due to Pd-CO formation and the sample becomes inactive. It has been shown that the in situ studies are necessary for the investigation of the active sites in Pd-Au bimetallic systems.

    更新日期:2018-01-25
  • Protein charge transfer absorption spectra: an intrinsic probe to monitor structural and oligomeric transitions in proteins
    Faraday Discuss. (IF 3.588) Pub Date : 2017-11-13
    Mohd. Ziauddin Ansari, Amrendra Kumar, Dileep Ahari, Anurag Priyadarshi, Padmavathi Lolla, Rashna Bhandari, Rajaram Swaminathan
    更新日期:2018-01-24
  • Optically sensing phospholipid induced coil–helix transitions in the phosphoinositide-binding motif of gelsolin
    Faraday Discuss. (IF 3.588) Pub Date : 2017-11-01
    Samsuzzoha Mondal, Amitava Chandra, Ravindra Venkatramani, Ankona Datta
    更新日期:2018-01-24
  • Engineered photoproteins that give rise to photosynthetically-incompetent bacteria are effective as photovoltaic materials for biohybrid photoelectrochemical cells
    Faraday Discuss. (IF 3.588) Pub Date : 2017-11-01
    Juntai Liu, Vincent M. Friebe, David J. K. Swainsbury, Lucy I. Crouch, David A. Szabo, Raoul N. Frese, Michael R. Jones
    更新日期:2018-01-24
  • Mechanistic insights into photoinduced damage of DNA and RNA nucleobases in the gas phase and in bulk solution
    Faraday Discuss. (IF 3.588) Pub Date : 2017-09-18
    Pratip Chakraborty, Tolga N. V. Karsili, Barbara Marchetti, Spiridoula Matsika
    更新日期:2018-01-24
  • Fluorescent excimers and exciplexes of the purine base derivative 8-phenylethynyl-guanine in DNA hairpins
    Faraday Discuss. (IF 3.588) Pub Date : 2017-09-01
    Kristen E. Brown, Arunoday P. N. Singh, Yi-Lin Wu, Lin Ma, Ashutosh K. Mishra, Brian T. Phelan, Ryan M. Young, Frederick D. Lewis, Michael R. Wasielewski
    更新日期:2018-01-24
  • Computational studies on ground and excited state charge transfer properties of peptidomimetics
    Faraday Discuss. (IF 3.588) Pub Date : 2018-01-23
    Sherin Joy, Vommina V Sureshbabu, Ganga Periyasamy
    更新日期:2018-01-23
  • CO adsorption and oxygen activation on group 11 nanoparticles – a combined DFT and high level CCSD(T) study about size effects and activation processes
    Faraday Discuss. (IF 3.588) Pub Date : 2018-01-23
    Wilke Dononelli, Thorsten Klüner

    The focus of this study lies on the activation of molecular oxygen and reaction with CO within density functional theory (DFT) and high level CCSD(T) calculations. Therefore, we use M13 and M55 nanoparticles (NPs) and periodic M(321) surfaces as model systems and compare the catalytic activity of gold substrates to Ag and Cu based NP catalysts. In a first step, the adsorption energies of CO were compared for nanoparticles of different size for Au, Ag and Cu, respectively. The adsorption energies on M(321) and M55 NPs (M=Au, Ag, Cu) are virtually identical. For smaller M NPs the adsorption energies differ by ~0.2 eV for Ag, ~0.4 eV for Au, and ~0.6 eV for Cu at the PBE level of theory. This can be explained by size effects, as the M13 NPs show a more molecule-like character. Presumingly, CO binds stronger to this very small NPs at the PBE level of theory. However, a benchmark calculation in the framework of CCSD(T)-theory reveals an adsorption energy of CO on Au13 of -0.88 eV, comparable to the adsorption energies calculated at the PBE level for Au55 and Au(321). For Au55, the adsorption energy calculated at the CCSD(T) level is -0.85 eV. It is in perfect agreement with the PBE result. In addition to adsorption energies, dissociation barriers have been calculated on M(321) surfaces. The dissociation energies of O2 on coinage metal catalysts are high, so that direct CO-oxidation reactions with molecular oxygen should be the dominant reaction mechanism compared to a dissociation and reaction of CO and atomic oxygen at least for silver and copper catalysts.

    更新日期:2018-01-23
  • 更新日期:2018-01-23
  • Photoinduced formation mechanism of the thymine–thymine (6–4) adduct in DNA; a QM(CASPT2//CASSCF):MM(AMBER) study
    Faraday Discuss. (IF 3.588) Pub Date : 2017-10-24
    Angelo Giussani, Irene Conti, Artur Nenov, Marco Garavelli
    更新日期:2018-01-23
  • Two-dimensional electronic spectroscopy as a tool for tracking molecular conformations in DNA/RNA aggregates
    Faraday Discuss. (IF 3.588) Pub Date : 2017-10-24
    Javier Segarra-Martí, Vishal K. Jaiswal, Ana Julieta Pepino, Angelo Giussani, Artur Nenov, Shaul Mukamel, Marco Garavelli, Ivan Rivalta
    更新日期:2018-01-23
  • Exploring oligomeric state of the serotonin1A receptor utilizing photobleaching image correlation spectroscopy: implications for receptor function
    Faraday Discuss. (IF 3.588) Pub Date : 2017-10-06
    Hirak Chakraborty, Md. Jafurulla, Andrew H. A. Clayton, Amitabha Chattopadhyay
    更新日期:2018-01-23
  • Chiral self-assembly of fullerene clusters on CT-DNA templates
    Faraday Discuss. (IF 3.588) Pub Date : 2017-10-05
    Sandeepa Kulala Vittala, Joshy Joseph
    更新日期:2018-01-23
  • Operando study of palladium nanoparticles inside UiO-67 MOF for catalytic hydrogenation of hydrocarbons
    Faraday Discuss. (IF 3.588) Pub Date : 2018-01-22
    Aram L Bugaev, Alexander Alexandrovich Guda, Kirill A. Lomachenko, Elizaveta G. Kamyshova, Mikhail A Soldatov, Gurpreet Kaur, Sigurd Øien-Ødegaard, Luca Braglia, Andrea Lazzarini, Maela Manzoli, Silvia Bordiga, Unni Olsbye, Karl Petter Lillerud, Alexander V Soldatov, Carlo Lamberti

    Functionalization of metal-organic frameworks with metal nanoparticles (NPs) is a promising way for producing advanced materials for catalytic applications. We present synthesis and in situ characterization of palladium NPs encapsulated inside functionalized UiO-67 metal-organic framework. The initial structure was synthesized with 10% of PdCl2bpydc moieties with grafted Pd ions replacing standard 4,4'-biphenyldicarboxylate linkers. This material exhibits the same high crystallinity and thermal stability of standard UiO-67. Formation of palladium NPs was initiated by sample activation in hydrogen and monitored by in situ X-ray powder diffraction and X-ray absorption spectroscopy (XAS). The reduction of PdII ions to Pd0 occurs above 200 °C in 6% H2/He flow. The formed palladium NPs have the average size of 2.1 nm as limited by the cavities of UiO-67 structure. The resulting material showed high activity towards ethylene hydrogenation. In reaction conditions, palladium was found to form carbide structure indicated by operando XAS, while formation of ethane was monitored by mass spectroscopy and infra-red spectroscopy.

    更新日期:2018-01-22
  • 更新日期:2018-01-22
  • Gold nanorods decorated with a cancer drug for multimodal imaging and therapy
    Faraday Discuss. (IF 3.588) Pub Date : 2017-09-12
    Resmi V. Nair, Hema Santhakumar, Ramapurath S. Jayasree
    更新日期:2018-01-22
  • Modelling Free and Oxide-supported Nanoalloy Catalysts: Comparison of Bulk-immiscible Pd-Ir and Au-Rh Systems and Influence of a TiO2 Support
    Faraday Discuss. (IF 3.588) Pub Date : 2018-01-19
    Ilker Demiroglu, Tian'e Fan, Ziyou Li, Jun Yuan, Tun-dong Liu, Laurent Piccolo, Roy L Johnston

    The relative stabilities of different chemical arrangements of Pd-Ir and Au-Rh nanoalloys (and their pure metal equivalents) are studied, for a range of compositions, for fcc truncated octahedral 38- and 79-atom nanoparticles (NPs). For the 38-atom NPs, comparisons are made of pure and alloy NPs supported on a TiO2(110) slab. The relative energies of different chemical arrangements are found to be similar for Pd-Ir and Au-Rh nanoalloys, and depend on the cohesive and surface energies of the component metals. For supported nanolloys on TiO2, the interaction with the surface is greater for Ir (Rh) than Pd (Au): most of the pure NPs and nanoalloys preferentially bind to the TiO2 surface in an edge-on configuration. When Au-Rh nanoalloys are bound to the surface through Au, the surface binding strength is lower than for the pure Au NP, while the Pd-surface interaction is found to be greater for Pd-Ir nanoalloys than for the pure Pd NP. However, alloying leads to very little difference in Ir-surface and Rh-surface binding strength. Comparing the relative stabilities of the TiO2-supported NPs, the results for Pd-Ir and Au-Rh nanoalloys are the same: supported Janus NPs, whose Ir (Rh) atoms bind to the TiO2 surface, bind most strongly to the surface, becoming closer in energy to the core-shell configurations (Ir@Pd and Rh@Au) which are favoured for the free particles.

    更新日期:2018-01-19
  • Correlating structural dynamics and catalytic activity of AgAu nanoparticles with ultrafast spectroscopy and all-atom molecular dynamics simulations
    Faraday Discuss. (IF 3.588) Pub Date : 2018-01-19
    Guilherme F Ferbonink, Thenner Rodrigues, Diego Pereira dos Santos, Pedro Camargo, Rodrigo Q Albuquerque, RENE NOME

    In this study, we investigated hollow AgAu nanoparticles with the goal of improving our understanding of the composition-dependent catalytic activity of theses nanoparticles. AgAu nanoparticles were synthesized via the galvanic replacement method with controlled size and nanoparticle compositions. We studied extinction spectra with UV-Vis spectroscopy and simulations based on Mie theory and the boundary element method, and ultrafast spectroscopy measurements to characterize decay constants and the overall energy transfer dynamics as a function of AgAu composition. Electron-phonon coupling times for each composition were obtained from pump-power dependent pump-probe transients. These spectroscopic studies showed how nanoscale surface segregation, hollow interiors and porosity affect the surface plasmon resonance wavelength and fundamental electron-phonon coupling times. Analysis of the spectroscopic data was used to correlate electron-phonon coupling times to AgAu composition, and thus to surface segregation and catalytic activity. We have performed all-atom molecular dynamics simulations of model hollow AgAu core-shell nanoparticles to characterize nanoparticle stability and equilibrium structures, besides providing atomic level views of nanoparticle surface segregation. Overall, the basic atomistic and electron-lattice dynamics of core-shell AgAu nanoparticles characterized here thus aid the mechanistic understanding and performance optimization of AgAu nanoparticle catalysts.

    更新日期:2018-01-19
  • The challenge of catalyst prediction
    Faraday Discuss. (IF 3.588) Pub Date : 2018-01-15
    Rutger A van Santen, Aditya Sengar, Erik Steur

    New insights and successful use of computational catalysis is highlighted. This within the context of remaining issues that prevent theoretical catalysis to be fully predictive of catalyst performance. A major challenge is to include in modelling studies the transient initiation as well as deactivation processes of the catalyst. We will illustrate this using as an example for solid acid catalysis, the alkylation process, and for transition metal catalysis, the Fischer-Tropsch reaction. For the alkylation reaction of isobutane and alkene, an important reaction for high octane gasoline, we will present a deactivation model. For the Fischer-Tropsch reaction, that converts synthesis gas into gasoline grade molecules, we discuss structural reorganization of the catalyst induced by reaction.

    更新日期:2018-01-15
  • Time-resolved operando studies of carbon supported Pd nanoparticles under hydrogenation reactions by X-ray diffraction and absorption
    Faraday Discuss. (IF 3.588) Pub Date : 2018-01-15
    Aram L Bugaev, Oleg A. Usoltsev, Andrea Lazzarini, Kirill A. Lomachenko, Alexander Alexandrovich Guda, Riccardo Pellegrini, Michele Carosso, Jenny Grazia Vitillo, Elena Groppo, Jeroen van Bokhoven, Alexander V Soldatov, Carlo Lamberti

    Formation of palladium hydride and carbide phases in palladium-based catalysts is a critical process which changes the catalytic performance and selectivity of the catalysts in important industrial reactions, such as selective hydrogenation of alkynes or alkadienes. We present a comprehensive study of a 5 wt.% carbon supported Pd nanoparticles (NPs) catalyst under various environments by in situ and operando X-ray absorption spectroscopy and diffraction, to determine structure and evolution of palladium hydride and carbide phases, and their distribution over the volume of the NPs. We demonstrate how the simultaneous analysis of extended X-ray absorption fine structure (EXAFS) spectra and X-ray powder diffraction (XRPD) patterns allows discriminating between the inner “core” and outer “shell” regions of the nanoparticle during hydride phase formation at different temperatures and under different hydrogen pressures, indicating that the amount of hydrogen in the shell region of the nanoparticle is lower than that in the core. For palladium carbide, advanced analysis of X-ray absorption near-edge structure (XANES) spectra allows detecting Pd-C bonds with carbon-containing molecules adsorbed at the surface of the nanoparticles. In addition, H/Pd and C/Pd stoichiometries of PdHx and PdCy phases were obtained by theoretical modelling and fitting of XANES spectra. Finally, the collection of operando time-resolved XRPD patterns (with a time resolution of 5 s) allowed highlighting, during ethylene hydrogenation reaction, periodic oscillations in the NPs core lattice parameter, which are in phase with the MS signal of the ethane (product) and in antiphase with the MS signal of the H2, highlighting an interesting direct structural-reactivity relationship. The presented studies show how a careful combination of X-ray absorption and diffraction can highlight the structure of core, shell and surface of the palladium nanoparticles and prove their relevant roles in catalysis.

    更新日期:2018-01-15
  • Step-edge structures on the anatase TiO2 (001) surface studied by atomic-resolution TEM and STM
    Faraday Discuss. (IF 3.588) Pub Date : 2018-01-11
    Martin Ek, Igor Beinik, Albert Bruix, Stefan Wendt, Jeppe Vang Lauritsen, Stig Helveg

    Low-coordinate surface sites, such as those present on high-index step edges, often exhibit chemical reactivity that markedly differs from more close-packed facets. To understand the site-specific reactivity, insight into the three-dimensional atomic arrangment of step-edges is needed. Here, we employ atomic-resolution transmission electron microscopy (TEM) of nanoparticles in combination with scanning tunneling microscopy (STM) of a single crystal surface to uncover the structure of prevalent step edges on the anatase TiO2 (001) surface.

    更新日期:2018-01-12
  • Looking for the active hydrogen species in a 5wt% Pt/C catalyst: a challenge for Inelastic Neutron Scattering
    Faraday Discuss. (IF 3.588) Pub Date : 2018-01-05
    Michele Carosso, Andrea Lazzarini, Andrea Piovano, Riccardo Pellegrini, Sara Morandi, Maela Manzoli, Jenny Grazia Vitillo, Monica Jimenez-Ruiz, Carlo Lamberti, Elena Groppo

    We looked at the active hydrogen species in a highly dispersed and very homogeneous 5wt% Pt/C industrial catalyst (Pt particle mean diameter of 2.0 ± 0.5 nm) for hydrogenation reactions, by coupling H2 adsorption measurements with Inelatic Neutron Scattering (INS). Taking advantage of the enormous progresses undergone by the INS instruments, we succedeed in collecting INS spectra of unprecedented quality that allowed us: 1) demonstrating that the Pt nanoparticles are mainly located at the regular edges of the sp2 graphitic domains on the activated carbon; 2) validating that most of the H2 physisorbed on the carbon is side-on adsorbed; 3) detecting for the first time H2 molecules adsorbed on hydride-covered Pt nanoparticles; 4) observing Pt-hydrides (on the Pt/C catalyst with the lowest Pt loading among those investigated by INS so far) and 5) providing evidences for the occurrence of spillover of atomic hydrogen from the Pt surface to unsaturated reactive sites located at the irregular borders of the sp2 domains on the activated carbon.

    更新日期:2018-01-05
  • DFT calculation of oxygen adsorption on platinum nanoparticles: Coverage and size effects
    Faraday Discuss. (IF 3.588) Pub Date : 2018-01-03
    Lucas Garcia Verga, Jolyon Aarons, Misbah Sarwar, David Thompsett, Andrea E Russell, Chris-Kriton Skylaris

    Catalysts made of Pt nanoparticles and Pt alloys are considered state-of-the-art catalysts for the anodic and cathodic reactions involved in hydrogen fuel cells. The optimal size of such nanoparticles for each chemical reaction is an unsolved problem, which depends on environmental variables, such as reactant concentration, solvent, temperature, etc. From a theoretical point of view, this problem has been tackled mainly by observing how single key adsorbates react with different nanoparticles in controlled conditions. In this work, we use large-scale DFT calculations to examine the interplay between the Pt nanoparticle size and O coverage effects. We examine single O adsorptions for three adsorption sites on cuboctahedral platinum nanoparticles with different sizes. As we grow the nanoparticle size, the binding strength decreases and we observed a quick convergence of the adsorption energies with increasing nanoparticle size, which correlates with the calculated d-band centre for (111) Pt facets on such nanoparticles. We also carried out a detailed study of the effect of oxygen coverage with varying fractions of O monolayer coverage, computing adsorption energies per O atom for Pt 55 , Pt 147, and Pt309 nanoparticles with several O coverages. In general, the increase of O coverage led to weaker adsorption energies per O atom, and when analysing the results in terms of oxygen monolayers, this effect is more pronounced for larger nanoparticles. The O coverage dependency of the adsorption energy per O atom is analysed in terms of the O distribution for each nanoparticle size and electronic changes that the adsorbed oxygen causes to the Pt nanoparticle. In studying nanoparticle size and oxygen coverage effects simultaneously, we offer insights with DFT accuracy to help on heterogeneous catalyst design

    更新日期:2018-01-03
  • Insights into structure and dynamics of (Mn,Fe)Ox-promoted Rh nanoparticles
    Faraday Discuss. (IF 3.588) Pub Date : 2017-12-20
    Maria Dimitrakopoulou, Xing Huang, Jutta Kröhnert, Detre Teschner, Sebastian Praetz, Christopher Schlesiger, Wolfgang Malzer, Christiane Janke, Ekkehard Schwab, Frank Rosowski, Harry Kaiser, Stephan A Schunk, Robert Schlögl, Annette Trunschke

    The mutual interaction between Rh nanoparticles and manganese/iron oxide promoters in silica-supported Rh catalysts for hydrogenation of CO to higher alcohols was analyzed by applying a combination of integral techniques including temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), X-ray absorption (XAS) and Fourier transform infrared (FTIR) spectroscopy with local analysis by using high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) in combination with energy dispersive X-ray spectroscopy (EDX). The promoted catalysts show reduced CO adsorption capacity as evidenced by FTIR spectroscopy, which is attributed to a perforated core-shell structure of the Rh nano-particles in accordance with the microstructural analysis by electron microscopy. Iron and manganese occur in low formal oxidation states between 2+ and zero in the reduced catalysts as shown by TPR and XAS. Infrared spectroscopy measured in diffuse reflectance at reaction temperature and pressure indicates that partial coverage of the Rh particles is maintained at reaction temperature under operation and that the remaining accessible metal adsorption sites might be catalytically less relevant because hydrogenation of adsorbed carbonyl species at 523 K and 30 bar hydrogen essentially failed. It is concluded that Rh0 is poisoned due to adsorption of CO under reaction conditions of CO hydrogenation. The active sites are associated either with a (Mn,Fe)Ox (x<0.25) phase or species at the interface between Rh and its co-catalyst (Mn,Fe)Ox.

    更新日期:2017-12-20
  • 更新日期:2017-12-15
  • Selective separation of furfural and hydroxymethylfurfural from an aqueous solution using a supported hydrophobic deep eutectic solvent liquid membrane
    Faraday Discuss. (IF 3.588) Pub Date : 2017-09-21
    Carin H. J. T. Dietz, Maaike C. Kroon, Michela Di Stefano, Martin van Sint Annaland, Fausto Gallucci
    更新日期:2017-12-15
  • Brønsted acidity in deep eutectic solvents and ionic liquids
    Faraday Discuss. (IF 3.588) Pub Date : 2017-09-19
    Andrew P. Abbott, Sahar S. M. Alabdullah, Azhar Y. M. Al-Murshedi, Karl S. Ryder
    更新日期:2017-12-15
  • New dimensions in salt–solvent mixtures: a 4th evolution of ionic liquids
    Faraday Discuss. (IF 3.588) Pub Date : 2017-09-11
    Douglas R. MacFarlane, Alison L. Chong, Maria Forsyth, Mega Kar, R. Vijayaraghavan, Anthony Somers, Jennifer M. Pringle
    更新日期:2017-12-15
  • Design principles from multiscale simulations to predict nanostructure in self-assembling ionic liquids
    Faraday Discuss. (IF 3.588) Pub Date : 2017-07-18
    Benjamin T. Nebgen, Harsha D. Magurudeniya, Kevin W. C. Kwock, Bryan S. Ringstrand, Towfiq Ahmed, Sönke Seifert, Jian-Xin Zhu, Sergei Tretiak, Millicent A. Firestone
    更新日期:2017-12-15
  • Structure and lifetimes in ionic liquids and their mixtures
    Faraday Discuss. (IF 3.588) Pub Date : 2017-07-11
    Sascha Gehrke, Michael von Domaros, Ryan Clark, Oldamur Hollóczki, Martin Brehm, Tom Welton, Alenka Luzar, Barbara Kirchner
    更新日期:2017-12-15
  • Biredox ionic liquids: new opportunities toward high performance supercapacitors
    Faraday Discuss. (IF 3.588) Pub Date : 2017-06-29
    C. Bodin, E. Mourad, D. Zigah, S. Le Vot, S. A. Freunberger, F. Favier, O. Fontaine
    更新日期:2017-12-15
  • Molecular scale structure and dynamics at an ionic liquid/electrode interface
    Faraday Discuss. (IF 3.588) Pub Date : 2017-06-27
    Peter Reichert, Kasper Skov Kjær, Tim Brandt van Driel, Julian Mars, Jannis Walther Ochsmann, Diego Pontoni, Moshe Deutsch, Martin Meedom Nielsen, Markus Mezger
    更新日期:2017-12-15
  • Exploring the bulk-phase structure of ionic liquid mixtures using small-angle neutron scattering
    Faraday Discuss. (IF 3.588) Pub Date : 2017-06-26
    Christopher P. Cabry, Lucía D’Andrea, Karina Shimizu, Isabelle Grillo, Peixun Li, Sarah Rogers, Duncan W. Bruce, José N. Canongia Lopes, John M. Slattery
    更新日期:2017-12-15
  • Determining the composition of the vacuum–liquid interface in ionic-liquid mixtures
    Faraday Discuss. (IF 3.588) Pub Date : 2017-06-14
    E. J. Smoll, Jr., M. A. Tesa-Serrate, S. M. Purcell, L. D’Andrea, D. W. Bruce, J. M. Slattery, M. L. Costen, T. K. Minton, K. G. McKendrick
    更新日期:2017-12-15
  • Exfoliation of graphene and fluorographene in molecular and ionic liquids
    Faraday Discuss. (IF 3.588) Pub Date : 2017-06-13
    Émilie Bordes, Joanna Szala-Bilnik, Agílio A. H. Pádua
    更新日期:2017-12-15
  • Nano-mechanics of ionic liquids at dielectric and metallic interfaces
    Faraday Discuss. (IF 3.588) Pub Date : 2017-06-09
    Léo Garcia, Léa Jacquot, Elisabeth Charlaix, Benjamin Cross
    更新日期:2017-12-15
  • Atomic charges of sulfur in ionic liquids: experiments and calculations
    Faraday Discuss. (IF 3.588) Pub Date : 2017-06-08
    Richard M. Fogarty, Rebecca Rowe, Richard P. Matthews, Matthew T. Clough, Claire R. Ashworth, Agnieszka Brandt, Paul J. Corbett, Robert G. Palgrave, Emily F. Smith, Richard A. Bourne, Thomas W. Chamberlain, Paul B. J. Thompson, Patricia A. Hunt, Kevin R. J. Lovelock
    更新日期:2017-12-15
  • 更新日期:2017-12-15
  • Interfacial structure and structural forces in mixtures of ionic liquid with a polar solvent
    Faraday Discuss. (IF 3.588) Pub Date : 2017-05-30
    Samuel W. Coles, Alexander M. Smith, Maxim V. Fedorov, Florian Hausen, Susan Perkin
    更新日期:2017-12-15
  • 更新日期:2017-12-15
  • Low-temperature and high-pressure phases of a room-temperature ionic liquid and polyiodides: 1-methyl-3-propylimidazolium iodide
    Faraday Discuss. (IF 3.588) Pub Date : 2017-05-24
    Hiroshi Abe, Hiroaki Kishimura, Mayumi Takaku, Mai Watanabe, Nozomu Hamaya
    更新日期:2017-12-15
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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