Untersuchungen an Nickeloxid-Mischkatalysatoren. XVI. Reduktionsverhalten amorpher NiO?Al2O3/SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. XVI. Reduction Behaviour of Amorphous NiO? Al₂O₃/SiO₂ Catalysts The reduction behaviour of NiO? Al₂O₃/SiO₂ catalysts prepared by precipitationdeposition is influenced by the phase composition (amorphous nickel layersilicates and nickel alumino layersilicates, nickel spinels, nickel oxide) and the differences of the composition between surface and bulk. TPR measurements, determinations of the reduction degree, and the nickel particle sizes by static magnetic measurements showed that the reducibility of the NiO? Al₂O₃/SiO₂ catalysts is enhanced and the nickel dispersity is decreased at low Al₂O₃ contents. The decrease of the reducibility at Al₂O₃ contents >5 mole% is caused by the formation of nickel spinels and the decrease of the Ni^II ion surface concentration.     

Hydrolysis of the uranyl ion in sodium nitrate medium

Studies on Nickel Oxide Mixed Catalysts. VIII. Catalytic Properties of NiO? Al₂O₃/SiO₂ Catalysts Catalytic properties of NiO? Al₂O₃/SiO₂ catalysts prepared by precipitation-deposition and impregnation have been investigated in dimerization of ethene and isomerization of but-1-ene. It was found that the catalytic activity is mainly determined by the interaction between the catalyst components where a X-ray amorphous nickel alumolayersilicate is formed. The dimerization of ethene proceeds by participation of coordinatively unsaturated nickel ions with aluminum ions in the neighbourhood. The catalytic activity in the isomerization of but-1-ene depends on the surface acidic properties of the catalyst.     

Untersuchungen an Nickeloxid-Mischkatalysatoren. XV. Oberflächenchemische Eigenschaften von NiO/Al2O3?SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. XV. Surface Chemical Properties of NiO/Al₂O₃-SiO₂ Catalysts Surface chemical properties of precipitated NiO/Al₂O₃? SiO₂ catalysts different compositions and the corresponding Al₂O₃? SiO₂ carriers have been investigated. Infrared spectroscopic measurements (before and after adsorption of pyridine and ammonia), ¹H-n.m.r. and ammonia adsorption measurements showed that the number of the Lewis-acidic sites are increased mainly by incorporation of the nickel component on the X-ray amorphous Al₂O₃? SiO₂ carriers, whereas the number of the hydroxide groups do not change significantly. With growing alumina content the number and the strength of the Lewis-acidic sites are increased where the part of the Ni^II surface sites decreases and those of the Al^III surface sites increases. Brönsted-acidic sites are detectable at high alumina contents.     

Untersuchungen an Nickeloxid-Mischkatalysatoren. I. Strukturelle Eigenschaften von NiO/SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. I. Structural Properties of NiO/SiO₂ Catalysts Structural properties of NiO/SiO₂ catalysts prepared by precipitation-deposition and impregnation have been investigated. A nickel-layer-silicate like structure is formed only in the precipitated catalysts showed infrared spectroscopic measurements. After thermal treatment at 723 K by means of magnetic measurements and reflectance spectroscopy besides Ni²⁺ ions in octahedral environment tetrahedral coordinated Ni²⁺ions were found. The part of tetrahedral coordinated Ni²⁺ ions is independent of the NiO-content up to 40 mole % NiO. Nickel oxide is formed above a content of 40 mole %. In the case of the impregnated catalysts nickel oxide cluster are formed on the surface after annealing at 723 K.     

Untersuchungen an oxidischen Katalysatoren. XLI. Redoxverhalten des Nickels in NiNa–Y-Zeolithen 3. Reduzierbarkeit von Ni2+ -Ionen und Eigenschaften des reduzierten Nickels in aciden NiNa–Y-Zeolithen

Studies on Oxide Catalysts. XLI. Redox Behavior of Nickel in Zeolites NiNa? Y. 3. Reducibility of Ni²⁺ Ions and Properties of the Reduced Nickel in Acidic Zeolites NiNa? Y The reducibility of nickel ions in zeolites NiNa? Y and the properties of metallic nickel were evaluated by tpr measurements, oxygen chemisorption and conversion of cyclohexane. In NiNa? Y samples which contain NH₄⁺(H⁺) and/or Al³⁺(H⁺) ions the reducibility of Ni²⁺ ions is decreased caused by increasing acidity and the metal dispersion is improved. The electronic interaction between the acidic support and the metallic nickel leads to a decrease of both dehydrogenation and hydrogenolysis activity whereas the dehydrogenation selectivity increases.     

Modification of inorganic supports with nickel acetylacetonate: The effect of their surface properties

The mesostructured silica SBA-15, γ-Al₂O₃, and amorphous silica-alumina are modified with Ni(acac)₂ in the liquid and gas phases. This process depends crucially on the nature of active sites on the support surface. In the modification of materials containing weakly acidic or weakly basic hydroxyl groups, it is necessary to use low-polarity solvents. The dominant Ni(acac)₂ chemisorption sites on amorphous silica-alumina are the acid hydroxyls of ≡Si-OH-Al= bridges. The covalent bonding resulting from the replacement of the acetylacetonate ligand favors the fixation of the adsorbed complex on the support surface. The coordinatively unsaturated sites formed by Al³⁺ ions play an insignificant role in Ni(acac)₂ chemisorption. The degree of dispersion of the oxide phase in the resulting catalysts depends strongly on the strength of the interaction between the modifier molecules and the active sites of the support. This is not the case with the aluminum acetylacetonate complexes that form upon the modification of the Al-containing supports. Gas-phase modification affords finer NiO particles than liquid-phase modification.     

Cu/NiO-V2O5/SiO2催化剂光催化CO2和甲醇合成碳酸二甲酯的研究

采用表面改性法和等体积浸渍法制备了NiO-V₂O₅/SiO₂和Cu/NiO-V₂O₅/SiO₂光催化剂. 用TPR, XRD, UV-Vis DRS, IR和TPD-MS技术对催化剂的结构、吸光性能和化学吸附性能进行了表征, 研究了催化剂上CO₂和甲醇光促表面催化反应的反应性能. 结果表明, 半导体NiO和V₂O₅复合后部分形成了Ni^2＋—O—V^5＋键联, 而且NiO和V₂O₅在催化剂表面有相互修饰作用, NiO的加入有助于提高V₂O₅在载体SiO₂表面的分散程度, 抑制V₂O₅的聚集, 而且金属Cu和NiO的引入扩展了催化剂的光响应范围. 在催化剂表面存在多种活性吸附位, 催化剂对CO₂和甲醇的有效吸附使得其在较低温度下就能促进碳酸二甲酯的紫外光化学合成. 用Cu/NiO-V₂O₅/SiO₂催化剂, 在常压、空速300 h^－1、140 ℃和125 W紫外灯辐照的情况下, CH₃OH的转化率为14.2%, 碳酸二甲酯的选择性可达89.9 %.     

Untersuchungen an oxidischen Katalysatoren. XXVIII. Einfluß der Vorbehandlungsbedingungen auf Die katalytischen Eigenschaften von NiNaY- und NiCoNaY-Zeolithen

Studies on Oxide Catalysts. XXVIII. Influence of Pretreatment on Catalytic Properties of Zeolites NiNaY and NiCoNaY The influence of the pretreatment conditions on the acidic properties, the reduction degree of nickel, and the catalytic activity and selectivity of zeolites NiNaY and NiCoNaY in the alkylation of benzene with ethylene has been investigated. From the experimental results can be concluded that sec. buthylbenzene from benzene and ethylene is only formed on zeolite samples which contain both together BRÖNSTED acidic centres and Ni²⁺ cations or NiO. Catalysts which contain only metallic nickel are inactive for this reaction. Catalysts with nickel in different forms are active in the formation of ethylbenzene, diethylbenzene, butane and sec. buthylbenzene, the yields depending on the relation of Ni°, Ni²⁺, and NiO. Changing this relation makes possible to regulate the selectivity in the alkylation of benzene with ethylene.     

Some contributions to the characterization of active sites in Mg-supported Ziegler–Natta catalysts

The contribution of different MgO supports to the coordination polymerization of ethylene was studied by x-ray diffractometry and infrared (IR) and electron spin resonance (ESR) spectroscopy of the supports and their products after treatment with TiCl₄. It was concluded that TiCl₄ was bonded on the surface OH groups of MgO mainly in inactive form, whereas the majority of the active sites was associated with the coordinatively unsaturated O^2? ions.     

CH Activation of Benzene by a Photoactivated NiII(azide): Formation of a Transient Nickel Nitrido Complex

Photochemical activation of nickel‐azido complex 2 [Ni(N₃)(PNP)] (PN^HP=2,2′‐di(isopropylphosphino)‐4,4′‐ditolylamine) in neat benzene produces diamagnetic complex 3 [Ni(Ph)(PN^PN^H)], which is crystallographically characterized. DFT calculations support photoinitiated N₂‐loss of the azido complex to generate a rare, transient Ni^IV nitrido species, which bears significant nitridyl radical character. Subsequent trapping of this nitrido through insertion into the Ni? P bond generates a coordinatively unsaturated Ni^II imidophosphorane P?N donor. This species shows unprecedented reactivity toward 1,2‐addition of a C? H bond of benzene to form 3 . The structurally characterized chlorido complex 4 [Ni(Cl)(PN^PN^H)] is generated by reaction of 3 with HCl or by direct photolysis of 2 in chlorobenzene. This is the first report of aromatic C? H bond activation by a trapped transient nitrido species of a late transition metal.     

A 3D Porous Metal Organic Framework Based on Infinite 1D Nickel(II) Chains with Rutile Topology Displaying Open Metal Sites

The reaction of Ni^II with a tetra‐benzoate pyrene ligand produces a 3D porous framework based on infinite 1D Ni^II chains. The Ni^II–O connectivity and the formation of a hydroxo‐bridge (μ₃‐OH) responsible for the connection of the central Ni^II atoms within the 1D Ni^II–(μ₃‐OH)₂–Ni^II chains can be straightforwardly compared with the Ti^IV–O–Ti^IV connectivity seen in TiO₂. The arrangement of the TBAPy ligand around the 1D rutile‐based chains leads in the generation of a porous framework with two distinct types of pores; based on the chemistries of these two types of pores, one can be labelled as hydrophobic and the other as hydrophilic. The use of different activation methods results in the generation of either a porous framework free of guest molecules or a completely solvent‐free material, in which the terminal H₂O molecules bound to Ni^II were removed, leading thus to a framework with open Ni^II sites. CO₂ isotherms collected on both frameworks at 195 K and one barshowed type I isotherms characteristic of microporous materials (BET surface areas for: guest‐free framework: 257(3) m² · g^–1; solvent‐free framework: 362(2) m² · g^–1). The affinity of both networks at zero coverage for both CO₂ and CH₄ was found to be greater when the unsaturated Ni^II sites are available within the void space.     

State of Supported Nickel Nanoparticles during Catalysis in Aqueous Media

The state of Ni supported on HZSM‐5 zeolite, silica, and sulfonated carbon was studied during aqueous‐phase catalysis of phenol hydrodeoxygenation using in situ extended X‐ray absorption fine structure spectroscopy. On sulfonated carbon and HZSM‐5 supports, NiO and Ni(OH)₂ were readily reduced to Ni⁰ under reaction conditions (≈35 bar H₂ in aqueous phenol solutions containing up to 0.5 wt. % phosphoric acid at 473 K). In contrast, Ni supported on SiO₂ was not stable in a fully reduced Ni⁰ state. Water enables the formation of Ni^II phyllosilicate, which is more stable, that is, difficult to reduce, than either α‐Ni(OH)₂ or NiO. Leaching of Ni from the supports was not observed over a broad range of reaction conditions. Ni⁰ particles on HZSM‐5 were stable even in presence of 15 wt. % acetic acid at 473 K and 35 bar H₂.     

Untersuchungen an Metallkatalysatoren. XXXII. Zur Legierungsbildung und Dispersität von Nickel-Rhenium-Katalysatoren

Investigations on Metal Catalysts. XXXII. On Alloying and Dispersion of Nickel-Rhenium Catalysts Unsupported Ni? Re catalysts were prepared by reduction of mixtures from NiO and NH₄ReO₄ at 400°C with hydrogen (1^st series), followed by a heat treatment at 650°C in flowing hydrogen (2^nd series). The bimetallic powders were characterized by DTA investigations, X-ray measurements, N₂ adsorption, and CO chemisorption. The degree of alloying and the changes in dispersion as a result of adding a second metal to a basic one is discussed.     

A new oxamato-bridged heterotrinuclear NiIICuIINiII complex: synthesis,structure and properties

A new oxamato-bridged Ni^IICu^IINi^II species, [Ni(iprtacn)]₂[Cu(pba)(H₂O)_0.5](BPh₄)₂ (1), (iprtacn?=?1,4,7-triisopropyl-1,4,7-triazacyclononane; pba?=?1,3-propylenebis(oxamato)) has been synthesized and structurally as well as magnetically characterized. Complex 1 has a discrete trinuclear Ni^IICu^IINi^II structure: Two nickel(II) ions are bridged by [Cu(pba)]^2? with the macrocyclic ligand iprtacn a terminal ligand of nickel(II). Fitting the magnetic data of 1 led to g _Cu?=?2.16, g _Ni?=?2.18, J?=??112.5?cm^?1, D?=?±7.78?cm^?1. The irregular spin state structure and interaction of complex 1with DNA are described here.     

Synthesis of Ni-poor NiO nanoparticles for p-DSSC applications

To improve the performances of p-Dye Sensitized Solar Cell (p-DSSC) for the future, the synthesis of modified p-type nickel oxide semiconductor, commonly used as photocathode in such devices, was initiated with Ni₃O₂(OH)₄ as precursor. This specific nickel oxyhydroxide was first characterized by X-ray photo-electron spectroscopy and magnetic susceptibility measurements. Then its thermal decomposition was thoroughly studied in order to control the particles size of the as-prepared NiO nanopowders. Low temperature decomposition in air of this precursor allows the formation of Ni_1−xO nanoparticles with a large amount of Ni vacancies and specific surface areas up to 250 m² g⁻¹. Its ammonolysis at 250 °C leads to nanostructured N-doped NiO (NiO:N) materials.     

Energetic properties of nio surface examined by heat-of-adsorption measurement

Heat of adsorption and isotherm of water vapor on NiO samples were measured simultaneously at 301 K to examine the energetic properties of the surface. They revealed that NiO has a relatively uniform surface. The heat of adsorption ranging 80–90 kJ·mol^–1 indicates the production of surface hydroxyl groups on the (100) plane of NiO. It is relatively small compared with that of other metal oxides, which suggests a weak nature of the Ni²⁺ ion sites for chemisorption of water. It is suspected that half of the surface Ni²⁺ ions are covered with hydroxyl groups and the remainings act as relatively strong physisorption sites for water molecules.The authors are grateful for the help of Prof. S. Kittaka of Okayama University of Science in taking electron micrographs. This work was partly supported by Grant-in-Aid for Scientific Research No. 02640348 from the Ministry of Education, Science and Culture of Japanese Government.     

A characterization of the surface acidity of HfO2by FTIR spectroscopy of adsorbed species,electron microscopy and adsorption microcalorimetry

A preparation of HfO₂, derived from the hydrolysis of hafnium isopropylate, has been characterized by XRD, (HR)TEM, MR and adsorption microcalorimetry. The thermal destruction of the amorphous hafnium hydroxide starting phase is complete at ≈700 K, and leads to the crystalline (monoclinic) phase of HfO₂. The latter exhibits a particle morphology which, upon thermal treatment, evolves quickly from one of large and loose aggregates of tiny microcrystallites (microcrystalline HfO₂) to one made of large single crystallites or of large polyaggregates, in which relatively small ordered microcrystals stack together in a rather disordered fashion (partially sintered HfO₂). The evolving morphology of HfO₂ is monitored, on a microscopic surface scale, by a varying IR spectrum of surface OH groups and by a varying surface Lewis acidic activity (e.g. towards CO chemisorption), due to coordinatively unsaturated Hf⁴⁺ surface centres produced upon vacuum activation. CO uptake, both at ambient temperature and at low temperature (≈78 K), is mainly due to two families of adsorbing sites: sites in structurally and/or coordinatively highly defective configurations, onto which CO adsorbs with an adsorption enthalpy of ≈65 kJ mol⁻¹, and sites located in relatively extended patches of regular crystallographic planes, onto which CO adsorbs with an adsorption enthalpy of ≈50 kJ mol⁻¹. The relative population of the two families of adsorbing sites depends to some extent on the degree of sintering of the material, but it is observed that, unlike other similar systems, the early sintering process causes a rather limited destruction of the crystallographically/coordinatively defective configurations. Both families of adsorbed CO species exhibit a strong dependence of their spectral features on several parameters, among which of primary importance are the degree of surface hydration/dehydration and the surface concentration of charge withdrawing/releasing adsorbed species which, through surface inductive effects, affect the strength of the CO adsorption process.     

Untersuchungen an oxidischen Katalysatoren. XLII. Redoxverhalten des Nickels in NiNa?Y-Zeolithen 4. Einfluß der Zusammensetzung auf die Reduzierbarkeit von Nickel in NiNa?Y-Zeolithen

Studies on Oxide Catalysts. XLii. Redox Behaviour of Nickel in Zeolites NiNa? Y. 4. Influence of Composition on the Reducibility of Nickel in Zeolites NiNa? Y By chemical analysis (reaction with K₂Cr₂O₇) and ESCA investigations we determined the degree of reduction in reduced samples NiNa-Y as function of the mole ratio SiO₂/Al₂O₃ (module), of the Ni²⁺ degree of exchange and the kind of the second cations. (NH₄₊, Ca²+, Co²+, and Nd³+) in the temperature region of 620–770 K. The degree of nickel reduction increases with increasing module, decreasing degree of exchange and decreasing number of Brönsted acidic centres. This behaviour is caused by the influence of the interaction between cations Ni²⁺ and zeolite lattice on the reduction equilibrium.     

Über grünes Bis-(2-Iminoisopropyl-thiophenolato)-nickel(II) und weitere, ähnliche NiII-Komplexe

Green Bis-(2-iminoisopropyl-thiophenolato)nickel(II) and other Similar Ni^II Complexes The compounds [Ni^II(iitp)₂] 1 (iitp = 2-iminoisopropyl-thiophenolate), [Ni(imptp)₂] · 2 CH₃OH 2 , a dinuclear compound with an Ni? Ni distance of 276 pm, and [PPh₄] · [Ni^II(imptp)(SCN)] 3 (imptp = 2-(2-iminopentane-4-on)-thiophenolate) have been prepared by the reaction of nickel(II)-acetate-tetrahydrate with 2-iminoisopropyl-thiophenole and 2-(2-iminopentane-4-on)-thiophenole in methanol, respectively. They have been characterized by single-crystal X-ray structure analysis and other physical methods. The redox behaviour of 1–3 has been studied in detail (chemically as well as by cyclovoltammetry and ESR spectroscopy). Particularly interesting are the electronic properties of 1 and its reduction with NaBH₄ and the following reaction of the product with O₂. The complexes are model compounds for some Ni-containing enzymes. For details of the crystal structure determination see “Inhaltsübersicht”.     

Complexing reactions in the Ni(II)-5-methyl-4-amino-3-thiooxo-1,2,4-triazapentene-1-methanal and Ni(II)-5-methyl-4-amino- 3-thiooxo-1,2,4-triazapentene-1-propanone triple systems

Complexing processes in the Ni^II-TTA-methanal (A) and Ni^II-TTA-propanone (B) triple systems (TTA–5-methyl-4-amino-3-thiooxo-1, 2, 4-triazapentene-1) in ethanol solution and nickel(II)hexacyanoferrate(II) gelatin-immobilized matrix have been studied. In the Ni^II-TTA- methanal system, formation of Ni^II oligomeric coordination compounds in which metal chelate cycles are connected by–H₂C–O–CH₂–structural groups, takes place. In the Ni^II-TTA-propanone triple system, formation of only Ni^II complexes with TTA takes place. No complexing process in the triple systems in nickel(II)hexacyanoferrate(II) gelatin-immobilized matrix was found.