Keyan Li

Bio: Keyan Li is an academic researcher from Dalian University of Technology. The author has contributed to research in topics: Catalysis & Electronegativity. The author has an hindex of 32, co-authored 97 publications receiving 3461 citations.

Estimation of Electronegativity Values of Elements in Different Valence States

Abstract: The electronegativities of 82 elements in different valence states and with the most common coordination numbers have been quantitatively calculated on the basis of an effective ionic potential defined by the ionization energy and ionic radius. It is found that for a given cation, the electronegativity increases with increasing oxidation state and decreases with increasing coordination number. For the transition-metal cations, the electronegativity of the low-spin state is higher than that of the high-spin state. The ligand field stabilization, the first filling of p orbitals, the transition-metal contraction, and especially the lanthanide contraction are well-reflected by the relative values of our proposed electronegativity. This new scale is useful for us to estimate some quantities (e.g., the Lewis acid strength for the main group elements and the hydration free energy for the first transition series) and predict the structure and property of materials.

High-Density Ultra-small Clusters and Single-Atom Fe Sites Embedded in Graphitic Carbon Nitride (g-C3N4) for Highly Efficient Catalytic Advanced Oxidation Processes

Abstract: Ultra-small metal clusters have attracted great attention owing to their superior catalytic performance and extensive application in heterogeneous catalysis However, the synthesis of high-density metal clusters is very challenging due to their facile aggregation Herein, one-step pyrolysis was used to synthesize ultra-small clusters and single-atom Fe sites embedded in graphitic carbon nitride with high density (iron loading up to 182 wt %), evidenced by high-angle annular dark field-scanning transmission electron microscopy, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and 57Fe Mossbauer spectroscopy The catalysts exhibit enhanced activity and stability in degrading various organic samples in advanced oxidation processes The drastically increased metal site density and stability provide useful insights into the design and synthesis of cluster catalysts for practical application in catalytic oxidation reactions

Electronegativity identification of novel superhard materials.

Abstract: We show that electronegativity can be used to effectively identify the hardness of crystal materials on the basis of a new microscopic model for hardness. Bond electronegativity is proposed to characterize the electron-holding energy of a bond, which is the intrinsic origin of hardness. Applying this model to c-BC(2)N materials, we confirm the proper bond composition of the experimentally observed phase of c-BC(2)N, in which the bond ratio N(C-C):N(B-N):N(B-C):N(C-N) is 3:3:1:1. A number of bonds that can or cannot form a superhard material are qualitatively distinguished, which enables us to explore novel superhard materials by screening possible elemental combinations.

Crystallization design of MnO2 towards better supercapacitance

Abstract: Nanostructured manganese oxides with different crystallization behaviors were fabricated by a simple redox reaction between KMnO4 and NaNO2 aqueous solution. MnO2 nanostructures with sphere-, rod-, wire-, plate- and flower-like morphologies were crystallized, and the relationship between crystallization characteristics and their electrochemical performances were studied. The electrochemical energy storage behaviors of these samples were investigated by cyclic voltammetry and galvanostatic charge–discharge measurements processed using noncorrosive Na2SO4 as the electrolyte. A maximum specific capacitance 200 F g−1 was obtained for poorly crystallized α-MnO2 at a current density of 1 A g−1. For different crystallographic MnO2 phases, their specific capacitance values increase in the order: β < γ < δ < α, meanwhile, for any particular MnO2 phase, their electrochemical energy storage performances decrease with increasing crystalline nature and particle size.

Recent developments in the methods and applications of the bond valence model.

Abstract: In the paragraph following eq 28, the average bond valence was incorrectly referred to as V/R. It has been corrected to V/N. The paper originally posted to the web on September 3, 2009, and was reposted on September 24, 2009.

Defect Engineering: Tuning the Porosity and Composition of the Metal–Organic Framework UiO-66 via Modulated Synthesis

Abstract: Presented in this paper is a deep investigation into the defect chemistry of UiO-66 when synthesized in the presence of monocarboxylic acid modulators under the most commonly employed conditions. We unequivocally demonstrate that missing cluster defects are the predominant defect and that their concentration (and thus the porosity and composition of the material) can be tuned to a remarkable extent by altering the concentration and/or acidity of the modulator. Finally, we attempt to rationalize these observations by speculating on the underlying solution chemistry.

Microscopic theory of hardness and design of novel superhard crystals

Abstract: Hardness can be defined microscopically as the combined resistance of chemical bonds in a material to indentation. The current review presents three most popular microscopic models based on distinct scaling schemes of this resistance, namely the bond resistance, bond strength, and electronegativity models, with key points during employing these microscopic models addressed. These models can be used to estimate the hardness of known crystals. More importantly, hardness prediction based on the designed crystal structures becomes feasible with these models. Consequently, a straightforward and powerful criterion for novel superhard materials is provided. The current focuses of research on potential superhard materials are also discussed.