Transition metal doped chalcogenides are one of the most important classes of catalysts that have been attracting increasing attention for petrochemical and energy related chemical transformations due to their unique physiochemical properties. For practical applications, achieving maximum atom utilization by homogeneous dispersion of metals on the surface of chalcogenides is essential. Herein, we report a detailed study of a deposition method using thiourea coordinated transition metal complexes. This method allows the preparation of a library of a wide range of single atoms including both noble and non-noble transition metals (Fe, Co, Ni, Cu, Pt, Pd, Ru) with a metal loading as high as 10 wt % on various ultrathin 2D chalcogenides (MoS2, MoSe2, WS2 and WSe2). As demonstrated by the state-of-the-art characterization, the doped single transition metal atoms interact strongly with surface anions and anion vacancies in the exfoliated 2D materials, leading to high metal dispersion in the absence of agglomeration. Taking Fe on MoS2 as a benchmark, it has been found that Fe is atomically dispersed until 10 wt %, and beyond this loading, formation of coplanar Fe clusters is evident. Atomic Fe, with a high electron density at its conduction band, exhibits a superior intrinsic activity and stability in CO2 hydrogenation to CO per Fe compared to corresponding surface Fe clusters and other Fe catalysts reported for reverse water–gas-shift reactions.

It is well established that the inclusion of small atomic species such as boron (B) in powder metal catalysts can subtly modify catalytic properties, and the associated changes in the metal lattice implies that the B atoms are located in the interstitial sites. However, there is no compelling evidence for the occurrence of interstitial B atoms, and there is a concomitant lack of detailed structural information describing the nature of this occupancy and its effects on the metal host. In this work, we use an innovative combination of high-resolution 11 B magic-angle-spinning (MAS) and 105 Pd static solid state NMR nuclear magnetic resonance (NMR), synchrotron X-ray diffraction (SXRD), in-situ X-ray pair distribution function (XPDF), scanning transmission electron microscopy-annular dark field imaging (STEM-ADF), electron ptychography and electron energy loss spectroscopy (EELS) to investigate the B atom positions, properties and structural modifications to the palladium lattice of an industrial type interstitial boron doped palladium nanoparticle catalyst system (Pdint B/C NPs). In this study we report that upon B incorporation into the Pd lattice, the overall face centered cubic (FCC) lattice is maintained, however short range disorder is introduced. The 105 Pd static solid-state NMR illustrates how different types (and levels) of structural strain and disorder are introduced in the nanoparticle history. These structural distortions can lead to the appearance of small amounts of local hexagonal close packed (HCP) structured material in localized regions. The short range lattice tailoring of the Pd framework to accommodate interstitial B dopants in the octahedral sites of the distorted FCC structure can be imaged by electron ptychography. This study describes new toolsets that enables the characterization of industrial metal nanocatalysts across length scales from macro-analysis to micro-analysis, which gives important guidance to structure-activity relationship of the system.

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The low-temperature specific heat C(T,H) of a new superconductor MgCNi 3 has been measured in detail. ∆C/γ n T c =1.97 is estimated from the anomaly at T c . At low temperatures, the electronic contribution in the superconducting state follows C es /γ n T c ≈7.96exp(-1.46T c /T).The magnetic field dependence of γ(H) is found to be linear with respect to H. T c estimated from the McMillan formula agrees well with the observed value. All the specific heat data appear to be consistent with each other within the moderate-coupling BCS context. It is amazing that such a superconductor unstable to ferromagnetism behaves so conventionally.The Debye temperature Θ D =287 K and the normal state γ n =33.6 mJ/mol K 2 are determined for the present sample.

Magnetic field dependence of low temperature specific heat of spinel oxide superconductor LiTi 2 O 4 has been elaborately investigated. In the normal state, the obtained electronic coefficient of specific heat ã n = 19.15 mJ/mol K 2 , the Debye temperature È D = 657 K and some other parameters are compared with those reported earlier. The superconducting transition at T c~1 1.4 K is very sharp (∆T c ~ 0.3 K) and the estimated äC/ã n T c is ~1.78. In the superconducting state, the best fit of data leads to the electronic specific heat C es /ã n T c = 9.87 exp (-1.58 T c /T) without field and ã(H) ∝ H 0.95 with fields. In addition, H c2 (0) ~ 11.7 T, H c (0)~0.32 T, ξ GL (0) ~ 55 Å , λ GL (0) ~ 1600 Å , and H c1 (0) ~ 26 mT are estimated from Werthamer-Helfand-Hohenberg (WHH) theory or other relevant relations. All results from the present study indicate that LiTi 2 O 4 can be well described by a typical type-II, BCS-like, moderate coupling, and fully gapped superconductor in the dirty limit. It is further suggested that LiTi 2 O 4 is a moderately electron-electron correlated system. 74.25.Bt, 74.25.Ha PACS number(s):