Interactions between ceria (CeO 2 ) and supported metals greatly enhance rates for a number of important reactions. However, direct relationships between structure and function in these catalysts ...have been difficult to extract because the samples studied either were heterogeneous or were model systems dissimilar to working catalysts. We report rate measurements on samples in which the length of the ceria-metal interface was tailored by the use of monodisperse nickel, palladium, and platinum nanocrystals. We found that carbon monoxide oxidation in ceria-based catalysts is greatly enhanced at the ceria-metal interface sites for a range of group VIII metal catalysts, clarifying the pivotal role played by the support.
Single-atom functionalization of transition-metal dichalcogenide (TMD) nanosheets is a powerful strategy to tune the optical, magnetic, and catalytic properties of two-dimensional materials. In this ...work, we demonstrate a simple solution-phase method to generate nucleophilic sulfide sites on colloidal WS2 nanosheets that subsequently serve as ligands for Ni single atoms. These materials can be controllably functionalized with varying amounts of Ni on the surface ranging from 9% to 47% coverage with respect to W. High-resolution scanning transmission electron microscopy coupled to electron energy loss spectroscopy and X-ray absorption spectroscopy indicate that adsorbed Ni species bind as single atoms at low coverage and a mixture of single atoms and multimetallic clusters at high coverage. The Ni single atoms adsorbed on WS2 show altered electronic properties, and both the electronic perturbation and isolated atom geometry play a role in enhancing the intrinsic catalytic activity of Ni-WS2 samples for the electrochemical oxygen evolution reaction.
Geometric structure of Pt and Pt–In catalysts and crystal structures of the active phase.▪
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•Pt3In and PtIn2 alloys have much high selectivity for ethane dehydrogenation than ...Pt.•Geometric isolation of Pt sites are suggested to be responsible for high olefin dehydrogenation selectivity.•In promotes the turnover rate of Pt and the promotion depends on the specific alloy structure.
The structure of silica supported Pt and Pt–In bimetallic catalysts with nominal In:Pt atomic ratios of 0.7 and 1.4 were determined by in situ synchrotron XAS and XRD. It was seen that the addition of In led to the formation of two different intermetallic alloy phases. At an In:Pt ratio of 0.7 the Pt3In phase with a Cu3Au structure was formed. When the ratio was increased to 1.4 a shell of PtIn2 having a CaF2 structure formed around a core of Pt3In. The catalysts were tested for ethane dehydrogenation at 600°C to determine the effect of alloying on ethylene selectivity and turnover rate (TOR). The monometallic Pt catalysts was 73% selective for ethylene and had an initial TOR of 0.7s−1. Both alloy catalysts were ≈100% selective for dehydrogenation and had higher initial TOR, 2.8s−1 and 1.6s−1 for In:Pt ratio of 0.7 and 1.4, respectively. The increase in selectivity is attributed to the elimination of large Pt ensembles resulting from geometric changes to the catalyst surface upon alloying. Electronic changes due to the formation of Pt–In bonds are thought to be responsible for the increases in TOR in the alloy catalysts.
A non‐noble metal electrocatalyst has been developed for the oxygen reduction reaction. Carbon‐supported cobalt molybdenum oxynitride was simply prepared by impregnation followed by thermal ...ammonolysis. The oxynitride electrocatalytic activity nearly matched that of platinum in 0.1 M KOH solution. The catalyst structure and valence have been characterized using complementary local and bulk probes.
Microorganisms and their hosts communicate with each other through an array of signals. The plant hormone auxin (indole-3-acetic acid; IAA) is central in many aspects of plant development. ...Cyclodipeptides and their derivative diketopiperazines (DKPs) constitute a large class of small molecules synthesized by microorganisms with diverse and noteworthy activities. Here, we present genetic, chemical, and plant-growth data showing that in Pseudomonas aeruginosa, the LasI quorum-sensing (QS) system controls the production of three DKPs--namely, cyclo(L-Pro-L-Val), cyclo(L-Pro-L-Phe), and cyclo(L-Pro-L-Tyr)--that are involved in plant growth promotion by this bacterium. Analysis of all three bacterial DKPs in Arabidopsis thaliana seedlings provided detailed information indicative of an auxin-like activity, based on their efficacy at modulating root architecture, activation of auxin-regulated gene expression, and response of auxin-signaling mutants tir1, tir1 afb2 afb3, arf7, arf19, and arf7arf19. The observation that QS-regulated bacterial production of DKPs modulates auxin signaling and plant growth promotion establishes an important function for DKPs mediating prokaryote/eukaryote transkingdom signaling.
Large-area icosahedral-AB13-type Pt–Pd binary superlattices (BNSLs) are fabricated through self-assembly of 6 nm Pd nanocrystals (NCs) and 13 nm Pt octahedra at a liquid–air interface. The Pt–Pd ...BNSLs enable a high activity toward electrocatalysis of oxygen reduction reaction (ORR) by successfully exploiting the shape effects of Pt NCs and synergistic effects of Pt–Pd into a single crystalline nanostructure. The Pt–Pd BNSLs are promising catalysts for the oxygen electrode of fuel cells.
Planar Josephson junctions (JJs) made in semiconductor quantum wells with large spin-orbit coupling are capable of hosting topological superconductivity. Indium antimonide (InSb) two-dimensional ...electron gases (2DEGs) are particularly suited for this due to their large Landé g-factor and high carrier mobility, however superconducting hybrids in these 2DEGs remain unexplored. Here we create JJs in high quality InSb 2DEGs and provide evidence of ballistic superconductivity over micron-scale lengths. A Zeeman field produces distinct revivals of the supercurrent in the junction, associated with a 0-π transition. We show that these transitions can be controlled by device design, and tuned in-situ using gates. A comparison between experiments and the theory of ballistic π-Josephson junctions gives excellent quantitative agreement. Our results therefore establish InSb quantum wells as a promising new material platform to study the interplay between superconductivity, spin-orbit interaction and magnetism.
Well-controlled synthesis of nanocrystals is necessary to unambiguously correlate the structural properties of nanocrystals with the catalytic properties. The most common low-index surfaces are (111) ...and (100). Therefore, model materials with {111} and {100} facets are highly desirable, in order to understand the catalytic properties of (111) and (100) surfaces for various structure-sensitive reactions. We report a solution-phase synthesis using metal carbonyls as additives. This synthetic method produces highly monodisperse Pt octahedra and icosahedra as the model of Pt{111}, Pt cubes as the model of Pt{100}, respectively. Several other morphologies, such as truncated cubes, cuboctahedra, spheres, tetrapods, star-shaped octapods, multipods, and hyper-branched structure, are produced, as well. A bifunctional role of metal carbonyl in the synthesis is identified: zerovalent transition metal decomposed from metal carbonyl acts as a shape-directing agent, while CO provides the reducing power. These high-quality shape-controlled Pt nanocrystals are suitable for model catalyst studies.
Formic acid is a promising chemical fuel for fuel cell applications. However, due to the dominance of the indirect reaction pathway and strong poisoning effects, the development of direct formic acid ...fuel cells has been impeded by the low activity of existing electrocatalysts at desirable operating voltage. We report the first synthesis of Pt3Pb nanocrystals through solution phase synthesis and show they are highly efficient formic acid oxidation electrocatalysts. The activity can be further improved by manipulating the Pt3Pb–Pt core–shell structure. Combined experimental and theoretical studies suggest that the high activity from Pt3Pb and the Pt–Pb core–shell nanocrystals results from the elimination of CO poisoning and decreased barriers for the dehydrogenation steps. Therefore, the Pt3Pb and Pt–Pb core–shell nanocrystals can improve the performance of direct formic acid fuel cells at desired operating voltage to enable their practical application.
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