Studies on the thermal decomposition of alkali metal thiosulphatobismuthates(III)

The thermal decomposition of thiosulphatobismuthates(III) of alkali metals was investigated. The general formulae of the thiosulphatobismuthates are M₃[Bi(S₂O₃)₃]·H₂O where M = Na, K, Rb or Cs, and M₂Na[Bi(S₂O₃)₃]·H₂O where M = K or Cs.Typical thermal curves for thiosulphatobismuthates(III) and the results obtained in thermal, X-ray, chemical and spectrophotometrical analyses of the decomposition products are shown. The results were used to determine three stages of the thermal decomposition. At the first stage, at about 200°C, hydrated compounds are dehydrated. At the second stage, above 200°C, there is a rapid decrease in mass which is caused by evolving sulphur dioxide; bismuth sulphide and an intermediate decomposition product are formed. At about 320°C the thermal decomposition products are bismuth sulphide and alkali metal sulphate.     

Thermal decomposition of transition metal carboxylates

Thermal decomposition of anhydrous Cu(HCOO)₂ (1) affords H₂, CO, CO₂, H₂O, HCuOOH, CuHCOO, Cu, and the polymeric product, which contains -CH₂O,-C(O)OH-, and -RCH-0- groups. Dccomposition of1 proceeds in stages with formation of copper(I) formate as an intermediate. Possible pathways of decomposition ofI, including isomeric forms of the HCO₂ radical as intermediates, were analyzed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1406–1412, June, 1996.     

Selective catalytic methanation of CO in hydrogen-rich gases over Ni/ZrO2 catalyst

Ni/ZrO2 catalysts were prepared by the incipient-wetness impregnation method and were investigated in activity and selectivity for the selective catalytic methanation of CO in hydrogen-rich gases with more than 20 vol% CO2. The result showed that Ni loadings significantly influenced the performance of Ni/ZrO2 catalyst. The 1.6 wt% Ni loading catalyst exhibited the highest catalytic activity among all the catalysts in the selective methanation of CO in hydrogen-rich gas. The outlet concentration of CO was less than 20 ppm with the hydrogen consumption below 7%, at a gas-hourly-space velocity as high as 10000 h-1 and a temperature range of 260 °C to 280 °C. The X-ray diffraction （XRD） and temperature programmed reduction （TPR） measurements showed that NiO was dispersed thoroughly on the surface of ZrO2 support if Ni loading was under 1.6 wt%. When Ni loading was increased to 3 wt% or above, the free bulk NiO species began to assemble, which was not favorable to increase the selectivity of the catalyst.     

The nu(CO) vibrational spectra of planar transition metal carbonyl clusters

The nu(CO) vibrational spectra of planar transition cluster carbonyls containing M(CO)(4) groups are studied. It is possible to anticipate qualitatively, both for the infrared and Raman, the band intensity changes associated with increasing metallic nature of the cluster. These enable a unification of the band patterns shown by the species reported. As for (idealized) spherical clusters, the spherical harmonic model (SHM), suitably modified, becomes of more general applicability as cluster size increases, although for smaller species the tensor harmonic model (THM) makes a contribution.     

过渡金属氧化物掺杂对铜锰氧化物催化CO氧化性能的影响

以乙酸铜和乙酸锰为铜锰前驱体,以NH₄HCO₃为沉淀剂,相应金属硝酸盐为掺杂剂,采用共沉淀法制备了不同过渡金属氧化物掺杂的铜锰氧化物催化剂.?采用N₂物理吸附、X射线衍射,氢气-程序升温还原和原位红外漫反射光谱等方法对催化剂进行了表征,考察了系列催化剂上CO反应性能.?结果表明,掺杂过渡金属氧化物可以调变催化剂对CO的吸附能力,进而影响催化剂性能.     

Studies on transition metal murexide complexes

Iron, cobalt, nickel, copper, zinc, cadmium and mercury murexide complexes have been prepared and characterized. The thermal properties of these complexes are studied deeply by DTA technique where their thermal peaks are explained. The multi-stages thermal decomposition mechanism is proposed. The thermodynamic parameters of the decomposition steps are calculated. The entropy change values for all complexes are of the same magnitude and all transition states of the thermal reactions are more ordered than the reactants. The thermal reactions proceed in complicated mechanisms. The fractions appeared in the calculated orders of the thermal reactions confirmed that these reactions proceeded via complex mechanisms.     

DFT calculations on the catalytic oxidation of CO over Si-doped (6,0) boron nitride nanotubes

The oxidation of carbon monoxide (CO) is important for a series of technological and environmental applications. In this work, the catalytic oxidation of CO on Si-doped (6,0) boron nitride nanotubes (BNNTs) is investigated by using density functional theory calculations. Reaction barriers and corresponding thermodynamic parameters were calculated using the M06-2X, B3LYP and wB97XD density functionals with 6-31G* basis set. Our results indicate that a vacancy defect in BNNT strongly stabilizes the Si adatom and makes it more positively charged. This charging enhances the adsorption of reaction gases (O₂ and CO) and results in the change of the electronic structure properties of the tube. The calculated barrier of the reaction CO + O₂ → CO₂ + O_ads on Si-doped BNNTs following the Langmuir–Hinshelwood is lower than that on the traditional noble metal catalysts. The second step of the oxidation would be the Eley–Rideal reaction (CO + O_ads → CO₂) with an energy barrier of about 1.8 and 10.1 kcal/mol at M06-2X/6-31G* level. This suggests that the CO oxidation catalyzed by the Si-doped BNNTs is likely to occur at the room temperature. The results also demonstrate that the activation energies and thermodynamic quantities calculated by M06-2X, B3LYP and wB97XD functionals are consistent with each other.     

过渡金属替代的CeO_2(111)表面上NO+CO反应机理的理论研究(英文)

采用DFT+U方法研究了过渡金属替代的CeO2(111)表面上的NO+CO反应机理,以探求不同过渡金属对N2选择性的影响.结果表明,在反应过程中,反应活性中心由过渡金属单原子与其最近邻的氧空位组成.NO在过渡金属-氧空位上发生N–O断键,不同过渡金属上该还原步骤的难易程度不同.计算发现,右过渡金属Rh,Pd和Pt替代的CeO2(111)表面可以与吸附物之间形成较强的吸附作用,进而可以达到较高的N2选择性.其主要原因是右过渡金属具有较多的d电子,可以与吸附小分子之间形成有效的反馈键.而左过渡金属拥有较少的d电子,难以有效抓住吸附物,最终导致较低的N2选择性.     

Immobilization of transition metal ion complexes and their catalytic activity towards the activation of hydrogen peroxide

Transition metal ion-imidazole complexes have been immobilized on silica, silica–alumina (25%Al₂O₃), and alumina supports by adsorption and functionalization methods. The catalytic activity of these supported complexes in the decomposition of H₂O₂ has been studied. The reaction exhibits first-order kinetics with respect to [H₂O₂] and the quantity of catalyst. The rate of reaction decreases as [H₂O₂]₀ increases. The order of catalytic reactivity is strongly dependent on the type of metal ion, support, and the immobilization method. The complex anchored via adsorption exhibited a higher activity compared to the corresponding complex anchored via functionalization of the surface. The reaction proceed via formation of the peroxo-intermediate, which has an inhibiting effect on the reaction rate. The reaction is enthalpy-controlled as is concluded from the isokinetic relationship. A mechanism is proposed involving the generation of HO₂ radicals from the peroxo-intermediate in the rate-determining step.     

Alkali metal ion-selective electrodes based on relevant alkali metal ion doped manganese oxides

Potentiometric properties of manganese oxides doped with alkali metal ions (Na⁺, K⁺, Rb⁺ and Cs⁺), which were prepared by heating mixed solutions (starting solution) of each alkali metal and Mn²⁺ ions, were examined. Electrodes based on mixed phases of Nao₄₄MnO₂/Mn₂O₃ and hollandite KMn₈O₁₆/M₂O₃ found by X-ray powder diffraction (XRD) exhibited Na⁺- and K⁺-selective responses with a near-Nernstian slope, respectively, when the molar ratio of alkali metal ion to Mn²⁺ ion in the starting solution was 0.1. When no alkali metal ions were added in the manganese oxide films, no significant potentiometric response was observed to any alkali metal ions. The selectivity coefficients of these electrodes were = 6.7 × 10^–2, = 7.1 × 10^–3, < 9 × 10^–4 and < 9x 10^–4 for the Na_0.44MnO₂/Mn₂O₃, and <4 × 10^–4 <4x 10^–4, =60 × 10^–2 ×10^–4, < 4 × 10^–4, for the KMn₈O₁₆/Mn₂O₃, respectively. Electrodes based on manganese oxides made from mixed solutions of Rb⁺/Mn²⁺ and Cs⁺/Mn²⁺ also responded to the respective primary ions, that is, Rb⁺ and Cs⁺ ions, although XRD patterns for the manganese oxides thus made did not show any peaks except for Mn₂O₃ (bixbyite); it was concluded in these cases that some amorphous type manganese oxides were formed in the Rb⁺/Mn²⁺ and Cs⁺/Mn²⁺ systems and they responded to the respective ions. Conditioning of these electrodes in an aerated indifferent electrolyte solution, 0.1M tetramethylammonium nitrate (TMA-NO₃), for relatively long time, typically more than 2 hours, was found to be a prerequisite for near-Nernstian response to the respective alkali metal ions. During this electrode conditioning, vacant sites (template) suitable in size for selective uptake of primary ions seemed to be formed by releasing the doped alkali metal ions from the solid phase into the adjacent electrolyte solution accompanying oxidation of the manganese oxide film.     

Studies on the thermal decomposition of the silver group of alkali metal nitritocobaltates(III)

The thermal decomposition of nitritocobaltate(III) of the silver group of general formula M₂Ag[Co(NO₂)₆] (where M = K⁺, NH⁺₄, Rb⁺ or Cs⁺) has been investigated. Based on the thermal curves of the investigated compounds and chemical and diffractometric analysis, the mechanism of thermal decomposition has been determined. The results obtained indicate that the decomposition proceeds in three stages. As a result of decomposition in the first stage (300°C), nitrates of alkali metals, metallic silver and Co₃O₄ are formed. In the second stage (500°C), a partial decomposition of nitrates to alkali metal oxides occurs, and in the third stage the products are alkali metal oxides, silver and Co₃O₄. This paper also presents the dependence of the decomposition temperature of nitritocobaltates(III) of the silver group on the ionic radius of the outer-sphere cation.     

Calculation of catalytic activity of transition metal complexes

A method is proposed for calculation of the catalytic activity of the complexes of transition metals. An effective Hamiltonian describing the behavior of the reagents in the presence of the catalyst is formulated, and a catalytic activity index tan2 is introduced. The isomerization of quadricyclane to norbornadiene is considered. It is shown that the index in the case of the catalytically active low-spin complex CoTPP is two orders of magnitude larger than in the case of the catalytically inactive high-spin complex MnTPP and the analogous Fe(III)TPP and MnPc complexes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 398–406, July–August, 1988.     

Characterization of the redox-reactivity of transition metal oxides by temperature-programmed limited thermal decomposition (TPLTD)

The concept of labile lattice oxygen (LLO) as a consequence of the Mars-Van Krevellen model was reminded, and contrasted with the surface oxygen species. Methods of characterizing of the Me-O bond strength were reviewed emphasizing the temperature-programmed limited thermal decomposition (TPLTD). A series of Ag_xV₂Mo_yO_z was characterized by TPLTD. Two forms of LLO were distinguished. The weaker form is independent on Ag-doping, in contrast to the stronger one. Activation energy of TPLTD of the stronger bound LLO was a linear function of the anion vacancy concentration.

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Zusammenfassung Aus dem Konzept des labilen Gittersauerstoffs (LLO) als Konsequenz des Mars-Van Krevellen-Modells wird die Rolle der Oberflächen-Sauerstoff-Spezies hervorgehoben. Ein Überblick über die Methoden zur Charakterisierung der Me-O-Bindung wird unter besonderer Betonung der temperaturprogrammierten begrenzten thermischen Zersetzung (TPLTD) gegeben.Eine Reihe Ag _x V₂Mo _y O₂ wurde mittels TPLTD charakterisiert, dabei konnten zwei Arten von LLO unterschieden werden. Die schwächere Form ist im Gegensatz zu der stärkeren unabhängig vom Silbergehalt. Die Aktivierungsenergie der TPLTD der stärker gebundenen LLO hängt linear von der Konzentration der Anionenfehlstellen ab.

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, - , . Me- . Ag_xV₂Mo_yO_z, . , , . n.

     

Study on the catalytic reduction mechanism of SO2 by CO over doped copper perovskite catalyst in presence of oxygen

Summary The reduction mechanism of SO₂ by CO using LaCoO₃ and doped copper as catalysts was investigated. The activity, selectivity of sulfur and the COS amount under various reaction conditions were tested. The results showed that the Cu doped catalysts were better than the undoped catalyst and 10% copper-doping gave the optimum catalyst.     

Microwave assisted solvent free amination of halo-(pyridine or pyrimidine) without transition metal catalyst

A solvent free direct amination of halo-(pyridine or pyrimidine) has been developed in good to high yields under computer-controlled microwave irradiation without transition metal catalyst. This reaction is a solvent and metal free, useful method for coupling of halo-(pyridine or pyrimidine) with pyrrolidine and piperidine derivatives by nucleophilic aromatic substitution (S_NAr).     

不同制备方法对铬掺杂NiFe2O4分解CO2的活性影响

采用共沉淀法和柠檬酸络合法分别制备掺杂4%Cr3 的N iFe2O4,运用XRD、DTA-TG、BET等手段对其结构进行表征,并探讨其直接催化分解CO2成C反应活性影响。研究结果表明,采用共沉淀法和柠檬酸络合法均能制备具有单一尖晶石结构的纳米晶的铬掺杂N iFe2O4。共沉淀法制备的铬掺杂N iFe2O4晶粒很小,平均晶粒只有8.3nm,比表面积为160.2 m2g-1,H2还原后其分解CO2成C的转化率为96%;而柠檬酸络合法制备的铬掺杂N iFe2O4晶粒比前者大,平均晶粒37.5nm左右,比表面积为51.6 m2g-1,其CO2分解成C的转化率只有82%。