Bio: Xinyuan Zhang is an academic researcher from University of Virginia. The author has contributed to research in topics: Materials science & Catalysis. The author has an hindex of 1, co-authored 1 publications receiving 9 citations.
TL;DR: In this paper, a spin-polarized gradient corrected density function was used to examine the chemical properties of the model copper chloride and supported copper chloride [CuxCly(OH)z/Alr(OHs)s] clusters.
Abstract: Ethylene chemisorption on model copper chloride [CuxCly, CuxCly(OH)z] and supported copper chloride [CuxCly(OH)z/Alr(OH)s] clusters was examined using spin-polarized gradient corrected density func...
TL;DR: In this article , the influence of spindle speed on the friction and wear properties of a Ni/WC coating in the process of high-temperature assisted ultrasonic rolling (HT/USR) was explored.
Abstract: To improve the friction and wear properties of a plasma-sprayed Ni/WC coating on a #45 steel substrate and explore the influence of spindle speed on the friction and wear properties of the coating in the process of high-temperature assisted ultrasonic rolling (HT/USR), The HT/USR processing of the Ni/WC coating was conducted under various spindle speeds (173, 248, and 360 r/min). The results showed that the pores and cracks in the Ni/WC coating after HT/USR treatment were reduced, giving the coating a compact structure. The surface performance of the coating was the best when the spindle speed was 173 r/min. Compared with the untreated sample, the surface roughness of the coating treated by HT/USR-173 r/min was reduced by 49 %, and the surface hardness was increased by 38.4 %. The residual tensile stress was transformed from tensile stress to compressive stress, reaching −404.2 MPa. The wear mechanism of the coating after HT/USR treatment changed from abrasive and fatigue wear to abrasive and oxidation wear. The friction coefficient and wear amount decreased with decreasing spindle speed. The average friction coefficient and wear amount of the coating with a spindle speed of 173 r/min were the lowest, 0.03094 and 5.4 mg, respectively, which are 69.23 % and 64.23 % lower than those of the untreated sample. Therefore, HT/USR effectively improved the surface properties of the plasma-sprayed Ni/WC coatings, as well as their friction and wear properties.
TL;DR: The design of metal nitrogen carbon (M-N-C) nanocatalysts with increasing durability and activity in the oxygen reduction reaction of fuel cells and metal-air batteries still remains a challenge as mentioned in this paper .
Abstract: The design of metal nitrogen carbon (M-N-C) nanocatalysts with increasing durability and activity in the oxygen reduction reaction of fuel cells and metal-air batteries still remains a challenge. Herein, a...
TL;DR: In this paper , a high-efficiency Co-N-C catalyst, composed of CoOx and N-doped carbon, is successfully constructed by pyrolysis of bimetallic CoZn microspheres and polydopamine (PDA).
Abstract: Although precious metal Pt-based cathodic nanomaterials are extensively considered as the excellent electrocatalysts for overcoming sluggish kinetics in oxygen reduction reaction (ORR), their practical applications are severely impeded by high price, low earth abundance, and poor durability of Pt. Hence, it is highly desired to explore cheaper alternatives with comparable catalytic activity and durability for ORR. Herein, the high-efficiency Co–N–C catalyst, composed of CoOx and N-doped carbon, is successfully constructed by pyrolysis of bimetallic CoZn microspheres and polydopamine (PDA). The N-rich PDA could confer plentiful well-distributed Co–Nx, pyridinic N active sites, and abundant hierarchical pores to the catalyst during pyrolysis. The optimal NC/CoN-2 catalyst manifests an E1/2 of 0.818 V and a JL of 5.27 mA/cm2, as well as excellent MeOH tolerance, long-time durability, and the 4e– reaction pathway in alkaline media. Such a remarkable ORR performance of NC/CoN-2 is attributed to the simultaneous compositional (Co/N co-doping) and structural tailoring (micropore/mesopore/macropore), enabled by PDA surface coating.
TL;DR: An in-depth analysis of the fundamental understanding and applied relevance of halogen chemistry in polymer industries and in the activation of light hydrocarbons and the challenges and directions for future development in this exciting field are provided.
Abstract: Halogen chemistry plays a central role in the industrial manufacture of various important chemicals, pharmaceuticals, and polymers. It involves the reaction of halogens or halides with hydrocarbons, leading to intermediate compounds which are readily converted to valuable commodities. These transformations, predominantly mediated by heterogeneous catalysts, have long been successfully applied in the production of polymers. Recent discoveries of abundant conventional and unconventional natural gas reserves have revitalized strong interest in these processes as the most cost-effective gas-to-liquid technologies. This review provides an in-depth analysis of the fundamental understanding and applied relevance of halogen chemistry in polymer industries (polyvinyl chloride, polyurethanes, and polycarbonates) and in the activation of light hydrocarbons. The reactions of particular interest include halogenation and oxyhalogenation of alkanes and alkenes, dehydrogenation of alkanes, conversion of alkyl halides, an...
TL;DR: In this paper, the chemistry of coinage-metal-ethylene adducts that have been synthesized and characterized by X-ray crystallography is discussed, and bidentate and tridentate donors based on nitrogen appear to be the ligands of choice for stabilizing species with an M-C2H4 (M = CuI, AgI, and AuI) moiety.
Abstract: Despite the interest in them, easily isolable and thermally stable CuI, AgI, and AuI complexes of ethylene are stilllimited and get increasingly sparse as one descends the group 11 triad towards gold. Recently, there have been some notable developments in this field, including the isolation of gold–ethylene complexes and coinage-metal adducts with more than one ethylene molecule on a metal center. This article focuses on the chemistry of coinage-metal–ethylene adducts that have been synthesized and characterized by X-ray crystallography. Thus far, bidentate and tridentate donors based on nitrogen appear to be the ligands of choice forstabilizing species with an M–C2H4 (M = CuI, AgI, and AuI) moiety. Weakly donating ligands and anions are also commonly used, as they do not interfere with and displace the ethylene from the metal center. The ethylene 13C NMR chemical shift provides useful information about the nature of the metal–ethylene interaction. In some adducts (especially those with relatively weak M–C2H4 interactions), the change in the C=C bond length upon coordination to the metal site is difficult to discern because it falls within the errors associated with the crystallographically determined C=C bond length value. IR and Raman C=C stretching data would be useful but, probably due to the very weak nature of the IR band and the lack of convenient access to the Raman instruments, are often not reported. In this microreview, results from some computational and gas-phase spectroscopic studies are also provided for comparison.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
TL;DR: In this article, the authors present a methodology that allows them to extract quantitative information from EXAFS data collected on complex samples where the absorbing species is present in more than one phase.
Abstract: We present a methodology that allows us to extract quantitative information from EXAFS data collected on complex samples where the absorbing species is present in more than one phase. We have chosen as our case study the CuCl2/Al2O3 material, which represents the basic catalyst for the ethylene oxychlorination reaction (a fundamental intermediate step in PVC production). In previous studies [J. Catal. 2000, 189, 91, and J. Catal. 2000, 189, 105], it has been shown that three different copper species are present on CuCl2/Al2O3a Cu-aluminate phase, a highly dispersed copper chloride phase, and an aggregated paratacamite (Cu2(OH)3Cl) phase, whose relative fraction depends on copper loading, sample aging, and heating conditions. In this work, we extract from the EXAFS spectra the fraction of the three phases on a quantitative ground. A study of the corresponding XANES spectra allows us to qualitatively support the EXAFS results. This methodology represents a generalization of the standard EXAFS procedure that...
TL;DR: In the adsorption of naphthalene and quinoline on Pt and Pd, an antibonding state lies below the Fermi energy, while on Rh all antibonding states are empty, in agreement with the larger interaction energies.
Abstract: The adsorption of naphthalene and quinoline on Pt(111), Pd(111) and Rh(111) surfaces is studied using density functional theory. The metal surfaces are simulated by means of large confined clusters and for Pt by means of a slab with periodic boundary conditions (PBC). Calculation parameters such as basis set convergence, basis set superposition error and effects of cluster relaxation and size are analyzed in order to assess the aptness of the cluster model. For all the metals, the preferred sites of adsorption are analyzed, thus revealing their different behaviors concerning structure and stability of adsorption modes. On Pt, the molecules have the richest theoretical configurational variety. Naphthalene and quinoline are found to adsorb preferentially on di-bridge sites on the three metals, and Rh exhibits higher adsorption energies than Pt and Pd. Structural features of the adsorbed molecules are correlated to the calculated adsorption energies. The di-bridge adsorption modes are studied in deeper detail decomposing the adsorption energies in two terms arising from molecular distortion and binding interaction to the metal. Molecular distortion is correlated to the HOMO-LUMO energy gap. The larger adsorption energies found for interactions with Rh result from the lower contribution of the distortion term. Binding interactions are described by analyzing the wave functions of naphthalene and quinoline adsorbed on a subunit of the large clusters in order to reduce the complexity of the analysis. Molecular orbitals are studied using concepts of Frontier Molecular Orbitals theory. This approach reveals that in the adsorption of naphthalene and quinoline on Pt and Pd, an antibonding state lies below the Fermi energy, while on Rh all antibonding states are empty, in agreement with the larger interaction energies. In addition, further insight is gained by projecting the density of states on the d band of the clean surfaces and of the adsorbed systems. This results in the rationalization of the structural features in terms of the concepts of electronic structure theory. The distributions of electronic density are described by means of Hirshfeld charges and isosurfaces of differential electron density. The net electron transfer from the metals to the molecules for most of the sites correlates with the trends of the adsorption energies.