Direct synthesis of hydrogen peroxide from H2/O2 using Pd/Al2O3 catalysts

Pd/Al₂O₃ catalysts were prepared by the impregnation method and were used for the direct formation of hydrogen peroxide from H₂ and O₂. The H₂O₂ concentration and selectivity were strongly dependent on the solubility of hydrogen in the reaction medium. The modification of the support by halogenate has a beneficial effect on the selectivity. The state of the active Pd on Pd/Al₂O₃ catalysts was studied using X-ray photoelectron spectroscopy, and Pd(0) was found to be active.     

Formation of C4 Oligomers in Hydrogenation of Acetylene over Pd/Al2O3 and Pd/TiO2 Catalysts

Selectivity of product formation has been tested in hydrogenation of acetylene over 0.3 wt.% Pd/-alumina and 0.5 wt.% Pd/TiO₂catalysts. Non-steady-state regime of catalyst operation was tested in pulse-flow experiments. Significant carbon poisoning appears to be a necessaryrequisite for selective formation of ethylene. The effect of hydrogen and acetylene partial pressure has been tested on the selectivity of C₄products. At 273–298 K the catalysts showed 26–35% selectivity for C₄ hydrocarbons and <2.5% for ethane production at conversionsof 30–40%. Deuterium distribution in ethylene and 1,3-butadiene and the deuterium content of the surface hydrogen pool have been compared and mechanismof diene formation has been discussed.     

Conversion of NO in NO/N2, NO/O2/N2, NO/C2H4/N2 and NO/C2H4/O2/N2 Systems by Dielectric Barrier Discharge Plasmas

An experimental study on the conversion of NO in the NO/N₂, NO/O₂/N₂, NO/C₂H₄/N₂ and NO/C₂H₄/O₂/N₂ systems has been carried out using dielectric barrier discharge (DBD) plasmas at atmospheric pressure. In the NO/N₂ system, NO decomposition to N₂ and O₂ is the dominating reaction; NO conversion to NO₂ is less significant. O₂ produced from NO decomposition was detected by an on-line mass spectrometer. With the increase of NO initial concentration, the concentration of O₂ produced decreases at 298 K, but slightly increases at 523 K. In the NO/O₂/N₂ system, NO is mainly oxidized to NO₂, but NO conversion becomes very low at 523 K and over 1.6% of O₂. In the NO/C₂H₄/N₂ system, NO is reduced to N₂ with about the same NO conversion as that in the NO/N₂ system but without NO₂ formation. In the NO/C₂H₄/O₂/N₂ system, the oxidation of NO to NO₂ is dramatically promoted. At 523 K, with the increase of the energy density, NO conversion increases rapidly first, and then almost stabilizes at 93–91% of NO conversion with 61–55% of NO₂ selectivity in the energy density range of 317–550 J L⁻¹. It finally decreases gradually at high energy density. A negligible amount of N₂O is formed in the above four systems. Of the four systems studied, NO conversion and NO₂ selectivity of the NO/C₂H₄/O₂/N₂ system are the highest, and NO/O₂/C₂H₄/N₂ system has the lowest electrical energy consumption per NO molecule converted.     

Pd(111), Pd(100)及Pd(110)表面H2和O2直接合成H2O2的密度泛函理论研究

采用周期性密度泛函理论研究了H₂和O₂在Pd(111),Pd(100)及Pd(110)表面上直接合成H₂O₂的反应机理,对反应的主要基元步骤进行了计算和分析.结果表明,Pd(111)表面对H₂O₂直接合成的催化选择性最好,表面原子密度较低的Pd(100)表面和Pd(110)表面上含有O-O键的表面物种解离严重,不利于H₂O₂的生成.H₂O₂的选择性与含有O-O键表面物种的O-O键能和表面物种的结合能有关.含有O-O键的表面物种在表面的结合能越大,越容易发生解离,不利于形成H₂O₂.     

Transformation of a Pt/TiO2 catalyst from non-SMSI to SMSI studied by repeated H2-O2 titration

Transformations of Pt/TiO₂ catalyst between non-SMSI and SMSI states have been investigated by repeatedH₂–O₂ titration. The decline of capacity of H₂ and O₂ chemisorption and their reaction on Pt particles is accountable by reduction of superficial labile oxygen species in the temperature range of 298–573 K and an increase of surface oxygen vacancies on TiO₂ above 573 K, respectively.     

Catalytic hydrogenation of C60 fullerene

Catalytic hydrogenation of C₆₀ with H₂ or by hydrogen transfer reactions using Pd/SiO₂, Rh/Al₂O₃ and Ru/Al₂O₃ has been studied. The final products containing partially hydrogenated C₆₀ fullerence C₆₀H₄₂–C₆₀H₄₆ were characterized by FTIR, UV and NMR methods.     

过渡金属改性的Pd/TS-1催化氢、氧直接合成H_2O_2的性能

利用等体积浸渍法制备了M-Pd/TS-1(M=Ce,La,Pt,Fe,Co,Ni,Cr,Mn,Zn,Cd,Cu)系列催化剂,并将制得的催化剂用于常压下氢、氧直接合成过氧化氢的反应。考察了M的类型及负载量对M-Pd/TS-1催化剂催化性能的影响。结果表明,M选Ce时,催化剂的性能最好。Ce的最佳掺入量,n_(Ce)/(n_(Ce)+n_(Pd))=0.5%。对Ce改性与未改性的催化剂进行了TEM及静态化学吸附分析,结果表明,掺入Ce可使Pd在TS-1分子筛表面的粒度及分散度得到改善。考察了n_(O_2)/n_(H_2)比,气体流量,反应时间等反应条件对H_2转化率、H_2O_2选择性及收率的影响。在相对优化的工艺条件下,即n_(O_2)/n_(H_2)=3,气体流量为25 mL·min~(-1),反应时间为3 h时,H_2O_2,的收率可达到25.7%,TOF值为18.7 mol·mol~(-1)·h~(-1),此时溶液中H_2O_2的质量百分数为0.8%。     

The non-perpendicular and non-parallel alkyne bridge in W2(μ-C2H2)(μ-OCH2Bu)2(OCH2Bu)6

The bonding in the ethyne adduct W₂(μ-C₂H₂)(μ-ONp)₂(ONp)₆ (Np=CH₂^tBu) has been examined by various computational methods [Extended Hückel (EHMO), Fenske–Hall, and Gaussian 92 RHF (Restricted Hartree–Fock) and density functional (Becke-3LYP) calculations] employing the model compound W₂(μ-C₂H₂)(μ-OH)₂(OH)₆. EHMO and Fenske–Hall calculations suggest, based on total orbital energy, that a μ-parallel ethyne geometry should have the lowest energy, although traditional frontier orbital arguments agree with the observance of a skewed acetylene bridge. Gaussian 92 computations reproduce the non-perpendicular/non-parallel μ-C₂H₂ geometry in close agreement to that observed in the solid-state (X-ray) structure, which leads us to suggest that the distortion is not sterically imposed by the attendant alkoxide ligands. The observed geometry can be rationalized in terms of Jahn–Teller distortional stabilization from either the μ-parallel or μ-perpendicular mode, i.e., the geometry is favored on electronic grounds, though the potential energy surface is rather shallow. These results are discussed in terms of previous studies of the addition of alkynes to d³–d³ dinuclear complexes of tungsten and in terms of relationships between d²-W(OR)₄ and d⁸-Os(CO)₄ fragments.     

Composite Pd/Pr4O7/C catalysts: Synthesis, dispersity and properties

The catalysts prepared sequentiallyvia the interaction of C₃H₅PdC₅H₅ with the surface of evacuated Pr₄O₇/C and reduction with H₂ at 573 K, contain 20–30 Pd particles and Pr₄O₇ particles<20 . The catalysts obtained have two-order of magnitude higher specific activity in the CH₃OH synthesis than Pd/C.     

Influence of Pd precursors on the catalytic performance of Pd–H4SiW12O40/SiO2 in the direct oxidation of ethylene to acetic acid

The effects of palladium precursors (PdCl₂, (NH₄)₂PdCl₄, Pd(NH₃)₂Cl₂, Pd(NO₃)₂ and Pd(CH₃COO)₂) on the catalytic properties in the selective oxidation of ethylene to acetic acid have been investigated for 1.0 wt% Pd–30 wt% H₄SiW₁₂O₄₀/SiO₂. The structures of the catalysts were characterized using X-ray diffraction, N₂ adsorption, H₂-pulse chemical adsorption, infrared spectrometry of the adsorbed pyridine, H₂ temperature-programmed reduction and X-ray photoelectron spectroscopy. The present study demonstrates that the different palladium precursors can lead to the significant changes in the dispersion of palladium. It is found that Pd dispersion decreases as follows: PdCl₂ > (NH₄)₂PdCl₄ > Pd(NO₃)₂ > Pd(NH₃)₂Cl₂ > Pd(C₂H₃O₂)₂, which is nearly identical to the catalytic activity. This indicates that the dispersion of palladium plays an important role in the catalytic activity. Furthermore, density of Lewis (L) and Brönsted (B) acid sites are also strongly dependent on the palladium precursors. It is also demonstrated that an effective catalyst should possess a well combination of Brönsted acid sites with dispersion of palladium.     

Hydrocarbon production from synthesis gas over ZnO?Cr2O3+SA physical mixtures and Pd/SA impregnated catalysts

The performances of ZnO–Cr₂O₃+silica-alumina physically mixed and Pd impregnated on silica-alumina catalysts in the transformation of synthesis gas to hydrocarbons are compared in the present work. ZnO–Cr₂O₃ or Pd and silicaalumina are used as methanol synthesis and the hydrocarbon formation catalysts, respectively. The highest CO conversion corresponds to the highest relative amount of methanol synthesis active sites. The highest proximity between both types of active sites in the Pd imprenated on silica-alumina produces higher hydrocarbon selectivity and higher C₁ fraction than when using the physically mixed ZnO–Cr₂O₃+silica-alumina catalysts.     

XAFS characterization of supported PdCl2?CuCl2 catalysts for CO oxidation

A heterogenized Wacker catalyst system in which pores of a high surface area alumina were filled with an aqueous solution of PdCl₂–CuCl₂ was active for the oxidation of CO near room temperature. The structure of thecatalyst was studied by XRD and XAFS. The active phase of Pd was a molecular Pd species whose structure was similar to PdCl₂, probably modified by a carbonyl ligand. The active phase of copper was found to be solid Cu₂Cl(OH)₃ particles. The presence of Cu was essential to keep the Pd in the Pd(II) state during the reaction.     

Coordination Polymers of Scandium Sulfate. Crystal Structures of (H2Bipy)[Sc(H2O)(SO4)2]2 · 2H2O and (H2Bipy)[HSO4]2

Compounds with the general formula Cat_x[Sc(H₂O)_z(SO₄)_y] · nH₂O (Cat = NH₄, H₂Bipy (Bipy is 4,4′-bipyridine), and HEdp (Edp is ethylenedipyridine) are synthesized and identified by elemental analysis and IR spectral data. The X-ray diffraction analysis of (H₂Bipy)[Sc(H₂O)(SO₄)₂]₂ · 2H₂O shows that in the structure of this compound, the chains of ScO₆ octahedra and SO₄ tetrahedra are united to form ribbons due to the tridentate coordination of the sulfate ion. The ribbons form a framework, whose infinite cavities contain H₂Bipy²⁺ cations.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 8, 2005, pp. 576–582.Original Russian Text Copyright © 2005 by Petrosyants, Ilyukhin, Sukhorukov.     

Synthesis and Structure of the Supramolecular Adduct Formed by the [Mo3S4(H2O)7Cl22+ Cluster Complex with Cucurbituril: {[Mo3S4(H2O)7Cl2](C36H36N24O12)} Cl2·10H2O

Slow crystallization of an HCl solution containing cucurbituril (C₃₆H₃₆N₂₄O₁₂) and a triangular molybdenum cluster aqua complex [Mo₃S₄(aq)]⁴⁺ yielded a supramolecular adduct of { [Mo₃S₄(H₂O)₇Cl₂]×(C₃₆H₃₆N₂₄O₁₂₎Cl₂·10H₂O composition. The molecular and crystal structure of the adduct were established by single crystal X-ray diffraction. Monoclinic crystal system, space group P2₁/c, a = 21.4762(2) Å, b = 14.6853(1) Å, c = 24.6480(3) Å; β = 112.8366(5)°, V _cell = 7164.26(12) ų, Z = 4, ρ_calc = 1.725 g/cm³.Original Russian Text Copyright © 2004 by E. V. Chubarova, D. G. Samsonenko, J. H. Platas, M. N. Sokolov, and V. P. Fedin__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 950–954, September–October, 2004.     

Temperature-programmed desoprtion of H2 from the surfaces of pd/support and Pd-Ag/support catalysts (support = Al2O3, SiO2)

Thermal desorption of H₂ from the surface of Pd/support and Pd-Ag/support (support = Al₂O₃, SiO₂) catalysts has been investigated. Two wide desorption peaks can be observed for the 5% Pd/support catalyst. The presence of these peaks in the thermogram indicates that several adsorption states exist, which is the result of occurrance of different adsorption centers of specific bond strengths for hydrogen. The addition of silver to the palladium catalysts causes a considerable decrease in the size of the high temperature desorption peak. It is also worth noting that the temperature of the maximum of the desorption rate remains practically constant for all bimetallic catalysts studied. This means that the activation energy of the hydrogen desorption process does not change after the introduction of silver to the palladium catalyst.     

Study on a new single flow acid Cu–PbO2 battery

The present paper reports a new single flow acid battery, Cu–H₂SO₄–PbO₂ battery, in which smooth graphite is employed as negative electrode, lead dioxide as positive electrode and the intermixture of H₂SO₄–CuSO₄ as electrolyte. The reaction CuCu²⁺ takes place on the negative electrode. The working process of the battery is only the circulation of H₂SO₄–CuSO₄ intermixture by means of a single pump. No cationic membrane is needed. A miniature acidic copper single flow battery with a rated capacity of 2000 mAh can offer a discharge voltage of 1.29 V, an average coulombic efficiency of 97% and an energy efficiency of 83% during 450 cycles at a charge/discharge current of 1000 mA.     

Structures Of Tetraammine Salts [Pt(NH3)4](N03)2, [Pd(NH3)4](N03)2, and [Pd(NH3)4]F2 H20

This contribution presents the results of a single crystal X-ray diffraction study of three ammine complexes of bivalent platinum and palladium: [Pt(NH₃)₄](N0₃)2, [Pd(NH₃)₄](N0₃)₂ and [Pd(NH₃)₄]F₂H₂O. The first two compounds are isostructural; metal atoms are located on inversion centers, all other atoms are in general positions. A three-dimensional framework is built from planar-square complex cations and nitrate ions joined by N-H...O hydrogen bonds. In [Pd(NH₃)₄]F₂H₂O, palladium atoms, as in the previous cases, are located on inversion centers, while oxygen atoms of water molecules are on the two-fold symmetry axis. A network of strong N-H...F and O-H...F hydrogen bonds linking the cations, anions, and crystallization water molecules is present in the structure.     

Selective hydrogenation of phenylacetylene on Pd/Al2O3: Effect of the addition of Pt and particle size

Phenylacetylene hydrogenation on Pd, Pt and Pd–Pt/Al₂O₃ catalysts has been studied. In all catalysts activity was found not to depend on particle size. However, selectivity to styrene was found to depend on Pd/Al₂O₃ catalysts. Carbon deposition in both metal and support explains such a behavior. Nevertheless, in small Pd particles a longer residence time of styrene may control the selectivity.     

Nanosized Au4Pd32(CO)28(PMe3)14 Containing a Highly Distorted Encapsulated Au4 Tetrahedron: Proposed Multi-Twinned Growth-Pattern from Two Deformed Au-Centered Double Icosahedral-Based Fragments*

As part of an extensive effort to synthesize a variety of nanosized gold–palladium carbonyl phosphine clusters, the neutral Au₄Pd₃₂(CO)₂₈(PMe₃)₁₄ (1) was isolated and unambiguously characterized by low-temperature CCD X-ray diffraction and IR measurements. This nanosized Au₄Pd₃₂ cluster was prepared in low yields (<5%) from the room-temperature reaction of Pd₁₀(CO)₁₂(PMe₃)₆ (2) with Au(SMe₂)Cl in THF/acetone. The heretofore unknown molecular geometry of 1 of pseudo-D₂ (222) symmetry (without methyl substituents) may be viewed to arise from a relatively strong (Au–Au)-bonded linkage (2.64 Å (av)) of two pentagonal-bipyramidal (μ₅-Au)(μ₅-Pd)Pd₅ polyhedra; this generated 14-atom Au₂Pd₁₂ unit may be considered as a markedly deformed part of a 19-atom Au-centered double icosahedron without the inner pentagon (corresponding to five missing inner atoms). In turn, two Au₂Pd₁₂ units form a central composite-twinned Au₄Pd₂₂ kernel via vertex-fusion of two common Pd atoms along with additional formation of four Pd–Pd bonding, four Au–Pd bonding, and two weaker secondary Au–Au bonding interactions at 2.90 Å (av) (versus the other two diagonal Au–Au nonbonding ones at 3.51 Å (av)); this resulting Au₄Pd₂₂P₈ kernel is augmented by the addition of two triangular Pd₃P core-fragments and four exopolyhedral PdP groups to give the Au₄Pd₃₂P₁₄ framework of 1. This cluster is stabilized by 28 bridging COs, of which 20 are doubly bridging and 8 triply bridging. The largest metal-core diameter of 1 along one pseudo C₂ axis is 1.1 nm. This new type of multi-twinned metal cluster has direct relevance to both ligated and non-ligated (naked) non-crystalline metal nanoparticles, many of which possess multiple twinning and/or disorder.^*Dedicated to Professor F. A. Cotton on the occasion of his 75th birthday in recognition of numerous seminal contributions to modern Inorganic Chemistry. Professor Cotton has a truly unparalleled scientific career in Inorganic Chemistry in terms of the overall composite effects of his highly prolific research productivity, his tremendous impact on former graduate students, postdoctoral associates, and collaborators, and his matchless textbooks/monographs.     

Système ternaire : H2O–Fe(NO3)3–Co(NO3)2 isotherme : 30 °C

Ternary system: H₂O–Fe(NO₃)₃–Co(NO₃)₂ isotherm: 30 °C. The H₂O–Co(NO₃)₂ binary system has been investigated in the –28 to 50 °C temperature range. The solid–liquid equilibria of the ternary system H₂O–Fe(NO₃)₃–Co(NO₃)₂ were studied by using a synthetic method based on conductivity measurements. One isotherm is established at 30 °C, and the stable solid phases that appear are iron nitrate nonahydrate: Fe(NO₃)₃·9 H₂O, iron nitrate hexahydrate: Fe(NO₃)₃·6 H₂O, cobalt nitrate hexahydrate: Co(NO₃)₂·6 H₂O, and cobalt nitrate trihydrate: Co(NO₃)₂·3 H₂O. To cite this article: B. El Goundali et M. Kaddami, C. R. Chimie 9 (2006).