307 research outputs found
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Strain to alter the covalency and superconductivity in transition metal diborides
Among layered metal diborides, MB2, only MgB2 is a superconductor. However, a strategically applied mechanical stress that removes metal–boron covalency can turn ScB2 into a superconductor with the same mechanism
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Dynamic Phase Diagram of Catalytic Surface of Hexagonal Boron Nitride under Conditions of Oxidative Dehydrogenation of Propane.
Partially oxidized surfaces of hexagonal boron nitride (hBN) and several metal borides are unexpectedly excellent catalysts for oxidative dehydrogenation of alkanes to olefins, but the nature of the active site(s) on these B-containing interfaces remains elusive. We characterize the surface of the partially oxidized B-rich hBN surface under reaction conditions from first principles. The interface has thermal access to multiple different stoichiometries and multiple structures of each stoichiometry. The size of the thermal ensemble is composition-dependent. The phase diagram of the interface constructed on the basis of the statistical ensembles of many accessible states is very different from the one based on global minima. Phase boundaries shift and blur, and phases consist of several stoichiometries and structures. The BO layer transiently exposes the reactive -B═O motifs in the metastable states. The fluxionality and structural diversity emerging under reaction conditions must be taken into account in theoretically descriptions of the catalytic interface
Photo-driven Molecular Wankel Engine B
We report a molecular Wankel motor, the dual-ring structure B13+, driven by
circularly-polarized infrared electromagnetic radiation, under which a guided
uni-directional rotation of the outer ring is achieved with rotational
frequency of the order of 300 MHz.Comment: 5 pages, 4 figure
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Germanium as key dopant to boost the catalytic performance of small platinum clusters for alkane dehydrogenation
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Interpreting the Operando XANES of Surface-Supported Subnanometer Clusters: When Fluxionality, Oxidation State, and Size Effect Fight
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Preparation of Size- and Composition-Controlled PtnSnx/SiO2 (n=4, 7, 24) Bimetallic Model Catalysts with Atomic Layer Deposition
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Coking-Resistant Sub-Nano Dehydrogenation Catalysts: PtnSnx/SiO2 (n=4, 7)
We present a combined experimental/theoretical study of Pt/SiO and
PtSn/SiO (n = 4, 7) model catalysts for the endothermic
dehydrogenation of hydrocarbons, using the ethylene intermediate as a model
reactant. Supported pure Ptn clusters are found to be highly active toward
dehydrogenation of C2D4, quickly deactivating due to a combination of carbon
deposition and sintering, resulting in loss of accessible Pt sites. Addition of
Sn to Ptn clusters results in the complete suppression of C2D4 dehydrogenation
and carbon deposition, and also stabilizes the clusters against thermal
sintering. Theory shows that both systems have thermal access to a multitude of
cluster structures and adsorbate configurations that form a statistical
ensemble. While Pt4/SiO2 clusters bind ethylene in both di-sigma and pi-bonded
configurations, PtSn/SiO binds C2H4 only in the pi-mode, with
di-sigma bonding suppressed by a combination of electronic and geometric
features of the PtSn clusters. Dehydrogenation reaction profiles on the
accessible cluster isomers were calculated using the climbing image nudged
elastic band (CI-NEB) method
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