Towards stable single-atom catalysts: Strong binding of atomically dispersed transition metals on the surface of nanostructured ceria

The interaction of a series of different transition metal atoms with nanoparticulate CeO2 has been studied by means of density-functional calculations. Recently, we demonstrated the ability of sites exposed on {100} nanofacets of CeO2 to very strongly anchor atomic Pt, making the formed species exceptionally efficient single-atom anode catalysts for proton-exchange membrane fuel cells. Herein, we analyzed the capacity of these surface sites to accommodate all other group VIII-XI transition metal atoms M = Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Cu, Ag, and Au. The interaction of the M atoms with {100} nanofacets of ceria leads to oxidation of the former and such interaction is calculated to be stronger than the binding of the atoms in the corresponding metal nanoparticles. Comparing the stability of metal-metal and metal-oxide bonds allows one to establish which metals would more strongly resist agglomeration and hence allows the proposal of promising candidates for the design of single-atom catalysts. Indeed, the remarkable stability of these adsorption complexes (particularly for Pt, Pd, Ni, Fe, Co, and Os) strongly suggests that atomically dispersed transition metals anchored as cations on {100} facets of nanostructured ceria are stable against agglomeration into metal particles. Therefore, these sites appear to be of immediate relevance to the preparation of stable catalysts featuring the highest possible metal efficiency in nanocatalysis

Effects of Oxygen Adsorption on the Optical Properties of Ag Nanoparticles

Plasmonic metal nanoparticles are efficient light harvesters with a myriad of sensing- and energy-related applications. For such applications, the optical properties of nanoparticles of metals such as Cu, Ag, and Au can be tuned by controlling the composition, particle size, and shape, but less is known about the effects of oxidation on the plasmon resonances. In this work, we elucidate the effects of O adsorption on the optical properties of Ag particles by evaluating the thermodynamic properties of O-decorated Ag particles with calculations based on the density functional theory and subsequently computing the photoabsorption spectra with a computationally efficient time-dependent density functional theory approach. We identify stable Ag nanoparticle structures with oxidized edges and a quenching of the plasmonic character of the metal particles upon oxidation and trace back this effect to the sp orbitals (or bands) of Ag particles being involved both in the plasmonic excitation and in the hybridization to form bonds with the adsorbed O atoms. Our work has important implications for the understanding and application of plasmonic metal nanoparticles and plasmon-mediated processes under oxidizing environments

In Situ Detection of Active Edge Sites in Single-Layer MoS2_2 Catalysts

MoS2 nanoparticles are proven catalysts for processes such as hydrodesulphurization and hydrogen evolution, but unravelling their atomic-scale structure under catalytic working conditions has remained significantly challenging. Ambient pressure X-ray Photoelectron Spectroscopy (AP-XPS) allows us to follow in-situ the formation of the catalytically relevant MoS2 edge sites in their active state. The XPS fingerprint is described by independent contributions to the Mo3d core level spectrum whose relative intensity is sensitive to the thermodynamic conditions. Density Functional Theory (DFT) is used to model the triangular MoS2 particles on Au(111) and identify the particular sulphidation state of the edge sites. A consistent picture emerges in which the core level shifts for the edge Mo atoms evolve counter-intuitively towards higher binding energies when the active edges are reduced. The shift is explained by a surprising alteration in the metallic character of the edge sites, which is a distinct spectroscopic signature of the MoS2 edges under working conditions

AgPd, AuPd, and AuPt nanoalloys with Ag- or Au-rich compositions: Modeling chemical ordering and optical properties

Bimetallic nanoparticles have a myriad of technological applications, but investigations of their chemical and physical properties are precluded due to their structural complexity. Here, the chemical ordering and optical properties of AgPd, AuPd, and AuPt nanoparticles have been studied computationally. One of the main aims was to clarify whether layered ordered phases similar to L11 one observed in the core of AgPt nanoparticles [Pirart, J.; Nat. Commun. 2019, 10, 1982] are also stabilized in other nanoalloys of coinage metals with platinum-group metals, or the remarkable ordering is a peculiarity only of AgPt nanoparticles. Furthermore, the effects of different chemical orderings and compositions of the nanoalloys on their optical properties have been explored. Particles with a truncated octahedral geometry containing 201 and 405 atoms have been modeled. For each particle, the studied stoichiometries of the Ag- or Au-rich compositions, ca. 4:1 for 201-atomic particles and ca. 3:1 for 405-atomic particles, corresponded to the layered structures L11 and L10 inside the monatomic coinage-metal skins. Density functional theory (DFT) calculations combined with a recently developed topological (TOP) approach [Kozlov, S. M.; Chem. Sci. 2015, 6, 3868−3880] have been performed to study the chemical ordering of the particles, whose optical properties have been investigated using the time-dependent DFT method. The obtained results revealed that the remarkable ordering L11 of inner atoms can be noticeably favored only in small AgPt particles and much less in AgPd ones, whereas this L11 ordering in analogous Au-containing nanoalloys is significantly less stable compared to other calculated lowest-energy orderings. Optical properties were found to be more dependent on the composition (concentration of two metals) than on the chemical ordering. Both Pt and Pd elements promote the quenching of the plasmon

Aromatic polymers obtained by precipitation polycondensation: 4*. Synthesis of poly(ether ketone ketone)s

High molecular weight aromatic poly(ether ketone ketone)s were synthesized by the Friedel-Crafts polyacylation condensation of iso- and terephthaloyl chlorides with diphenyl ether, 1,4- and 1,3-bis(4- phenoxybenzoyl)benzenes. Depending on the monomers used for polycondensation, polyketones of regular structure with different iso-/tereisomer repeating unit ratio (100/0, 50/50, 0/100) in the main chain were obtained. Polymers of each repeating isomer unit were prepared in two different ways. All the polymer syntheses were performed as precipitation polycondensations and the resulting polymers were obtained in particle form. The influence of reaction conditions and preparation route on the polymer properties were examined. The monomer concentration and monomer stoichiometric ratio were found to affect the polymer viscosity. The size and shape of the polyketone particles obtained were also found to be governed by reaction conditions and preparation route.Peer reviewe

Spin Structure of K Valleys in Single-Layer WS2 on Au(111)

The spin structure of the valence and conduction bands at the K\u304 and K\u304\u2032 valleys of single-layer WS2 on Au(111) is determined by spin- and angle-resolved photoemission and inverse photoemission. The bands confining the direct band gap of 1.98 eV are out-of-plane spin polarized with spin-dependent energy splittings of 417 meV in the valence band and 16 meV in the conduction band. The sequence of the spin-split bands is the same in the valence and in the conduction bands and opposite at the K\u304 and the K\u304\u2032 high-symmetry points. The first observation explains "dark" excitons discussed in optical experiments; the latter points to coupled spin and valley physics in electron transport. The experimentally observed band dispersions are discussed along with band structure calculations for a freestanding single layer and for a single layer on Au(111)

Chemical ordering in Pt-Au, Pt-Ag and Pt-Cu nanoparticles from density functional calculations using a topological approach

Bimetallic alloys are actively investigated as promising new materials for catalytic and other energy-related applications. However, the stable arrangements of the two metals in prevailing nanostructured systems, which define their structure and surface reactivity, are seldom addressed. The equilibrium chemical orderings of bimetallic nanoparticles are usually different from those in the corresponding bulk phases and hard to control experimentally, which hampers assessment of the relations between composition, structure, and reactivity. Herewith, we study mixtures of platinum an essential metal in catalysis alloyed with coinage metals gold, silver, and copper. These systems are interesting, for instance, for reducing the costly Pt content and designing improved multifunctional catalysts, but the chemical orderings in such mixtures at the nanoscale are still debated. We therefore explore chemical orderings and properties of Pt-containing nanoalloys by means of a topological method based on density functional calculations. We determine the lowest-energy chemical orderings in 1.4 to 4.4 nm large Pt-Au, Pt-Ag and Pt-Cu particles with different contents of metals. Chemical ordering, bonding, and charge distribution in the nanoparticles are analyzed, identifying how peculiar structural motifs relevant for catalysis and sensing applications, such as monometallic skins and surface single-atom sites, emerge. We compare these results with previous data for the corresponding Pd-based particles, identifying trends in chemical ordering, deepening understanding of the behaviour of catalytically relevant bimetallic compositions, and establishing appropriate models for studying the bimetallic nanoalloys

Multimodality Treatment with Conventional Transcatheter Arterial Chemoembolization and Radiofrequency Ablation for Unresectable Hepatocellular Carcinoma

Background/Aims: To evaluate the efficacy of multimodality treatment consisting of conventional transcatheter arterial chemoembolization (TACE) and radiofrequency ablation (RFA) in patients with non-resectable and non-ablatable hepatocellular carcinoma (HCC). Methods: In this retrospective study, 85 consecutive patients with HCC (59 solitary, 29 multifocal HCC) received TACE followed by RFA between 2001 and 2010. The mean number of tumors per patient was 1.6 +/- 0.7 with a mean size of 3.0 +/- 0.9 cm. Both local efficacy and patient survival were evaluated. Results: Of 120 treated HCCs, 99 (82.5%) showed a complete response (CR), while in 21 HCCs (17.5%) a partial response was depicted. Patients with solitary HCC revealed CR in 91% (51/56); in patients with multifocal HCC (n = 29) CR was achieved in 75% (48 of 64 HCCs). The median survival for all patients was 25.5 months. The 1-, 2-, 3- and 5-year survival rates were 84.6, 58.7, 37.6 and 14.6%, respectively. Statistical analysis revealed a significant difference in survival between Barcelona Clinic Liver Cancer (BCLC) A (73.4 months) and B (50.3 months) patients, while analyses failed to show a difference for Child-Pugh score, Cancer of Liver Italian Program (CLIP) score and tumor distribution pattern. Conclusion: TACE combined with RFA provides an effective treatment approach with high local tumor control rates and promising survival data, especially for BCLC A patients. Randomized trials are needed to compare this multimodality approach with a single modality approach for early-stage HCC. Copyright (C) 2011 S. Karger AG, Base

NMR characterisation of the minimal interacting regions of centrosomal proteins 4.1R and NuMA1: effect of phosphorylation

<p>Abstract</p> <p>Background</p> <p>Some functions of 4.1R in non-erythroid cells are directly related with its distinct sub-cellular localisation during cell cycle phases. During mitosis, 4.1R is implicated in cell cycle progression and spindle pole formation, and co-localizes with NuMA1. However, during interphase 4.1R is located in the nucleus and only partially co-localizes with NuMA1.</p> <p>Results</p> <p>We have characterized by NMR the structural features of the C-terminal domain of 4.1R and those of the minimal region (the last 64 residues) involved in the interaction with NuMA1. This subdomain behaves as an intrinsically unfolded protein containing a central region with helical tendency. The specific residues implicated in the interaction with NuMA1 have been mapped by NMR titrations and involve the N-terminal and central helical regions. The segment of NuMA1 that interacts with 4.1R is phosphorylated during mitosis. Interestingly, NMR data indicates that the phosphorylation of NuMA1 interacting peptide provokes a change in the interaction mechanism. In this case, the recognition occurs through the central helical region as well as through the C-terminal region of the subdomain meanwhile the N-terminal region do not interact.</p> <p>Conclusions</p> <p>These changes in the interaction derived from the phosphorylation state of NuMA1 suggest that phosphorylation can act as subtle mechanism of temporal and spatial regulation of the complex 4.1R-NuMA1 and therefore of the processes where both proteins play a role.</p