低温燃烧法制备Mn-CeO_x催化剂及其NH_3-SCR脱硝性能

通过低温燃烧法(LCS)制备了不同金属硝酸盐与柠檬酸物质的量比的系列Mn-CeO_x(LCS)锰铈催化剂,将其与共沉淀法(CP)制备的Mn-CeO_x(CP)锰铈催化剂相对比,结合XRD、XPS、FESEM和H2-TPR等技术表征,对其NH_3-SCR脱硝催化性能进行了研究。结果表明,金属硝酸盐与柠檬酸的物质的量比是影响Mn-CeO_x(LCS)催化剂脱硝性能的重要因素。虽然两种催化剂中的锰氧化物组分均为无定型,但相较于Mn-CeO_x(CP),Mn-CeO_x(LCS)表面具有较高的锰含量与Oα/(Oα+Oβ)比,其脱硝催化性能也较高;同时,Mn-CeO_x(LCS)锰铈催化剂上有更多的多级孔,有利于气体在催化剂上的吸附和反应。硝酸盐与柠檬酸物质的量比为36∶22的Mn-CeO_x(LCS)锰铈催化剂在80-180℃下脱硝率可达75%-100%;即使通入SO2,180℃下的脱硝率仍可稳定于74%。     

Single crystal synthesis and magnetism of the BaLn2O4 family (Ln = lanthanide)

The series of compounds in the BaLn₂O₄ family (Ln = La–Lu, Y) has been synthesized for the first time in single crystalline form, using a molten metal flux. The series crystallizes in the CaV₂O₄ structure type with primitive orthorhombic symmetry (space group Pnma, #62), and a complete structural study of atomic positions, bonds, angles, and distortions across the lanthanide series is presented. With the exception of the Y, La, Eu, and Lu members, magnetic susceptibility measurements were performed between 2 K and 300 K. BaCe₂O₄ and BaYb₂O₄ display large crystal fields effects and suppression of magnetic ordering. All compounds show signs of magnetic frustration due to the trigonal arrangements of the trivalent lanthanide cations in the structure.     

Reduced magnetic disorder at low temperature in Ca3Co2O6 via zinc substitution

ABSTRACT

The compound Ca₃Co₂O₆ undergoes a transition into a spin-density wave (SDW) state near 24?K. Below ～10?K, this unstable SDW state coexists with a nearly- degenerate commensurate antiferromagnetic state as well as short-range magnetic order. Clear signatures of this strong magnetic disorder have been observed in the response of entropy to changing magnetic field and temperature. We performed a calorimetry study of Ca₃Co₂O₆ and Ca₃Co_1.9Zn_0.1O₆ in order to compare their entropic responses at low temperature. Our results for Ca₃Co₂O₆ reveal that ΔS(T, H)?≡?S(T, H)?S(T, H?=?0) increases as either temperature or magnetic field increase. In contrast, ΔS data for Ca₃Co_1.9Zn_0.1O₆ were relatively unresponsive to changes in temperature or field, suggesting that Zn substitution may reduce the low-temperature magnetic disorder observed in Ca₃Co₂O₆. These results are discussed within the context of two cases (Ca₃Co₂O₆ under applied pressure and Ca_2.75R_0.25Co₂O₆ (R?=?Dy, Lu)) in which a single magnetic ground state is stabilised.     

Ultrasound-assisted synthesis of ZnO photocatalysts for gas phase pollutant remediation: Role of the synthetic parameters and of promotion with WO3

The synthesis of ZnO photocatalysts by ultrasound-assisted technique was here investigated. Several experimental parameters including the zinc precursor (acetate, chloride, nitrate), sonication conditions (amplitude, pulse) and post-synthetic thermal treatment (up to 500 °C) were studied. Crystalline ZnO samples were obtained without thermal treatments due to the adopted reactant ratios and synthesis temperature. Sonication plays a major role on the morphological oxide features in terms of particle size and surface area, the latter showing a 20-fold increase with respect to conventional synthesis. Interestingly, 1 and 3 s sonication pulses led to morphological properties similar to continuous sonication. A thermal treatment at moderate temperatures (400–450 °C) promoted the loss of surface hydroxylation and the formation of lattice defects, while higher temperatures were detrimental for the sample morphology. The prepared ZnO was decorated with WO₃ particles comparing an ultrasound-assisted technique using 1 s pulses with a conventional approach, giving rise to composites with promoted visible light absorption. Samples were tested towards the photocatalytic degradation of nitrogen oxides (500–1000 ppb) in humidified air under both UV and visible light. By carefully controlling the synthetic procedure, better performance were observed with respect to the commercial benchmark. Samples from ultrasound-assisted syntheses, also in the case of pulsed sonication, showed consistently better results than conventional references, in particular for ZnO-WO₃ composites. The composite by ultrasound-assisted synthesis showed > 95% degradation in 180 min and doubled NO_x degradation under visible light with respect to the conventional composite.     

Cu chemistry of YBa2Cu3O6+x investigated by nuclear quadrupole resonance

The nuclear quadrupole resonance (NQR) technique has been utilized to characterize the local oxygen coordination of inequivalent Cu sites in YBa₂Cu₃O_6+x(0 ≤ x ≤ 0.91). Essentially, four distinct NQR lines which correspond to 2, 3,4 oxygen coordinated Cu sites in the Cu-O chains and 5 oxygen coordinated Cu sites in the Cu-O planes have been observed. The zero-field NQR frequencies of these are centered at about 30.1, 24.0, 22.0 and 31.5 MHz for ⁶³Cu, respectively. For the antiferromagnetic ordered state (x ≤ 0.3), antiferromagnetic nuclear resonance (AFNR) has been observed at 90 MHz with quadrupole splittings associated with the moment-bearing Cu sites in the Cu-O planes. The relative intensities of these resonance lines depend on the oxygen content, and this gives us a microscopic understanding of the Cu chemistry of this system.     

Influence of the Coulomb forces on the thermodynamic and transport properties of non stoichiometric cerium dioxide

Abstract

In this study, it is demonstrated that the Coulomb interactions explains the essential of experimental thermodynamic and transport thermodynamic results.     

Extraction Properties of Oligodentate Carbamoylmethylphosphine Oxides and β-Aminophosphine Oxides Toward Lanthanides and Rhenium(VII)

Abstract

The extraction properties of a series of carbamoylmethylphosphine oxides and β-aminophosphine oxides with lanthanide metal ions is presented. Tris[bis(2-diphenyl- phosphorylethyl)-aminoethyl]amine is shown to be highly effective for extraction of Re(VII).     

Sigmatropic Rearrangements in Phosphorylated 2-Azaallylic Systems

Abstract

Allylic and heteroallylic compounds are classical objects of organic chemistry and can serve as models in the investigation of various theoretical problems. The anions and 1,3-dipoles generated from azaallylic derivatives are widely used in the synthesis of cyclic and acyclic nitrogen-containing compounds.     

Sulfur Ligands. from β-Lactam Antibiotics to Contrast Agents for MRI

Abstract

NMR, IR and semi empirical Molecular Orbital PM3 studies on selected β-lactam antibiotics are reported. The role of sulfur in β-lactam antibiotics is discussed.