Promotion effect of adsorbed water/OH on the catalytic performance of Ag/activated carbon catalysts for CO preferential oxidation in excess H2

Activated carbon (AC) supported silver catalysts were prepared by incipient wetness impregnation method and their catalytic performance for CO preferential oxidation (PROX) in excess H₂ was evaluated. Ag/AC catalysts, after reduction in H₂ at low temperatures (≤200 °C) following heat treatment in He at 200 °C (He200H200), exhibited the best catalytic properties. Temperature-programmed desorption (TPD), X-ray diffraction (XRD) and temperature-programmed reduction (TPR) results indicated that silver oxides were produced during heat treatment in He at 200 °C which were reduced to metal silver nanoparticles in H₂ at low temperatures (≤200 °C), simultaneously generating the adsorbed water/OH. CO conversion was enhanced 40% after water treatment following heat treatment in He at 600 °C. These results imply that the metal silver nanoparticles are the active species and the adsorbed water/OH has noticeable promotion effects on CO oxidation. However, the promotion effect is still limited compared to gold catalysts under the similar conditions, which may be the reason of low selectivity to CO oxidation in PROX over silver catalysts. The reported Ag/AC-S-He catalyst after He200H₂00 treatment displayed similar PROX of CO reaction properties to Ag/SiO₂. This means that Ag/AC catalyst is also an efficient low-temperature CO oxidation catalyst.     

A new three‐dimensional silver(I) coordination framework with a diamondoid topology constructed from 2‐(pyridin‐4‐yl)‐1H‐imidazole‐4,5‐dicarboxylic acid

The title compound, poly[[μ₄‐5‐carboxy‐4‐carboxylato‐2‐(pyridin‐4‐yl)‐1H‐imidazol‐1‐ido]disilver(I)], [Ag₂(C₁₀H₅N₃O₄)]_n, was synthesized by reacting silver nitrate with 2‐(pyridin‐4‐yl)‐1H‐imidazole‐4,5‐dicarboxylic acid (H₃PyIDC) under hydrothermal conditions. The asymmetric unit contains two crystallographically independent Ag^I cations and one unique HPyIDC²⁻ anion. Both Ag^I cations are three‐coordinated in distorted T‐shaped coordination geometries. One Ag^I cation is coordinated by one N and two O atoms from two HPyIDC²⁻ anions, while the other is bonded to one O and two N atoms from two HPyIDC²⁻ anions. It is interesting to note that the HPyIDC²⁻ group acts as a μ₄‐bridging ligand to link the Ag^I cations into a three‐dimensional framework, which can be simplified as a diamondoid topology. The thermal stability and photoluminescent properties of the title compound have also been studied.     

Reversible high‐temperature phase transition of a manganese(II) formate framework with imidazolium cations

A new metal–formate framework, poly[1H‐imidazol‐3‐ium [tri‐μ₂‐formato‐manganese(II)]], {(C₃H₅N₂)[Mn(HCOO)₃]}_n, was synthesized and its structural phase transition was studied by thermal analysis and variable‐temperature X‐ray diffraction analysis. The transition temperature is around 435 K. The high‐temperature phase is tetragonal and the low‐temperature phase is monoclinic, with a β angle close to 90°. The relationship of the unit cells between the two phases can be described as: a_HT = 0.5a_LT + 0.5b_LT; b_HT = −0.5a_LT + 0.5b_LT; c_HT = 0.5c_LT. In the high‐temperature phase, both the framework and the guest 1H‐imidazol‐3‐ium (HIm) cations are disordered; the HIm cations are located about 2mm sites and were modelled as fourfold disordered. The Mn and a formate C atom are located on fourfold rotary inversion axes, while another formate C atom is on a mirror plane. The low‐temperature structure is ordered and consists of two crystallographically independent HIm cations and two crystallographically independent Mn²⁺ ions. The phase transition is attributable to the order–disorder transition of the HIm cations.     

Structural and Electrical Properties of Be_xZn_(1-x)O Alloys under High Pressure

We conduct extensive research into the structures of Be_xZn_1-xOO ternary alloys in a pressure range of 0-60GPa,using the ab initio total energy evolutionary algorithm and total energy calculations,finding several metastable structures.Our pressure-composition phase diagram is constructed using the enthalpy results.In addition,we calculate the electronic structures of the Be_xZn_1-xOO structures and investigate the bandgap values at varying pressures and Be content.The calculated results show that the bandgap of the Be_xZn_1-xOO ternary alloys increases with an increase in Be content at the same pressure.Moreover,the bandgap of the Be_xZn_1-xOO ternary alloys increases with the increasing pressure with fixed Be content.At the same Be content,the formation enthalpy of the Be_xZn_1-xOO ternary alloys first decreases,then increases with the increasing pressure.     

Viscous Shock Wave to an Inflow Problem for Compressible Viscous Gas with Large Density Oscillations

Acta Mathematicae Applicatae Sinica, English Series - This paper is concerned with the inflow problem for one-dimensional compressible Navier-Stokes equations. For such a problem, Huang, Matsumura,...     

Delay driven Hopf bifurcation and chaos in a diffusive toxin producing phytoplankton‐zooplankton model

This paper deals with a diffusive toxin producing phytoplankton‐zooplankton model with maturation delay. By analyzing eigenvalues of the characteristic equation associated with delay parameter, the stability of the positive equilibrium and the existence of Hopf bifurcation are studied. Explicit results are derived for the properties of bifurcating periodic solutions by means of the normal form theory and the center manifold reduction for partial functional differential equations. Numerical simulations not only agree with the theoretical analysis but also exhibit the complex behaviors such as the period‐3, 5, 6, 7, 8, 11, and 12 solutions, cascade of period‐doubling bifurcation in period‐2, 4, quasi‐periodic solutions, and chaos. The key observation is that time delay may control harmful algae blooms (HABs). Moreover, numerical simulations show that the chaotic states induced by the period‐doubling bifurcation are purely temporal, which is stationary in space and oscillatory in time. The investigations may provide some new insights on harmful phytoplankton blooms.     

A Tree-valued Markov Process Associated with an Admissible Family of Branching Mechanisms

Let E?R be an interval. By studying an admissible family of branching mechanisms{ψt,t ∈E} introduced in Li [Ann. Probab., 42, 41-79(2014)], we construct a decreasing Levy-CRT-valued process {Tt, t ∈ E} by pruning Lévy trees accordingly such that for each t ∈E, Tt is a ψt-Lévy tree. We also obtain an analogous process {Tt*,t ∈E} by pruning a critical Levy tree conditioned to be infinite. Under a regular condition on the admissible family of branching mechanisms, we show that the law of {Tt,t ∈E} at the ascension time A := inf{t ∈E;Tt is finite} can be represented by{Tt*,t∈E}.The results generalize those studied in Abraham and Delmas [Ann. Probab., 40, 1167-1211(2012)].     

Characterizations of ( m,n )-Jordan Derivations and ( m,n )-Jordan Derivable Mappings on Some Algebras

Let R be a ring, M be a R-bimodule and m, n be two fixed nonnegative integers with m + n = 0. An additive mapping δ from R into M is called an(m, n)-Jordan derivation if(m +n)δ(A~2) = 2 mAδ(A) + 2nδ(A)A for every A in R. In this paper, we prove that every(m, n)-Jordan derivation with m = n from a C*-algebra into its Banach bimodule is zero. An additive mappingδ from R into M is called a(m, n)-Jordan derivable mapping at W in R if(m + n)δ(AB + BA) =2mδ(A)B + 2 mδ(B)A + 2 nAδ(B) + 2 nBδ(A) for each A and B in R with AB = BA = W. We prove that if M is a unital A-bimodule with a left(right) separating set generated algebraically by all idempotents in A, then every(m, n)-Jordan derivable mapping at zero from A into M is identical with zero. We also show that if A and B are two unital algebras, M is a faithful unital(A, B)-bimodule and U = [A M N B] is a generalized matrix algebra, then every(m, n)-Jordan derivable mapping at zero from U into itself is equal to zero.     

Panisuffrutin A,a highly degraded seco-triterpene derivative from Paeonia suffruticosa var. papaveracea (Andr.) Kerner

Panisuffrutin A (1), a highly degraded seco-triterpene derivative, together with the known palbinone, has been isolated from the whole plant Paeonia suffruticosa var. papaveracea (Andr.) Kerner. The structure with absolute configuration of 1 was determined via comprehensive NMR and MS analyses, as well as NMR and ECD calculations. A plausible biosynthetic pathway for 1 was proposed. Compound 1 showed weak cytotoxicity against Hela cancer cell line with an IC₅₀ value of 26.2 μM, while palbinone exhibited a moderate inhibition on NO production with an IC₅₀ of 18.3 μM.