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.     

Influence of acid–base properties of cobalt–molybdenum catalysts supported on magnesium orthophosphates in isomerization of 3,3-dimethylbut-1-ene

Synthesis and physico-chemical characterization of a pure magnesium phosphate (MgP) prepared by coprecipitation, and MgP modified by introduction of cobalt–molybdenum (4–12 wt.% of MoO₃ with the Co/Mo ratio fixed at 0.5) have been carried out. The structural properties of these catalysts were characterized by X-ray diffraction, their textural properties were determined by N₂ adsorption–desorption isotherms and the dispersion of cobalt–molybdenum was studied by XPS spectroscopy. Their acid properties have been investigated by in situ FT-IR spectroscopy of adsorbed molecules, often, 2,6-dimethylpyridine (pK_a = 6.7), pyridine (pK_a = 5.3). Co–Mo incorporation leads to a modification in the MgP acid–base properties, especially on the acid sites type and number. Thus, lower loading of cobalt–molybdenum species decreased the number of strong Lewis acid sites whereas higher loading increased it. It was found that Lewis acid sites on magnesium phosphates play an important role in the isomerization of 3,3-dimethylbut-1-ene.The 3,3-dimethylbut-1-ene (33DMB1) conversion increases with the reaction temperature from 493 to 653 K for MgP, but decreases after 573 K for MgP supported by Co–Mo. A linear relationship between both types of acid sites and conversion values was found. The deactivation of the catalysts appears at high reaction temperature (>573 K).     

Phase relations in the system K2MoO4–KPO3–MoO3–Bi2O3: A new phosphate K3Bi5(PO4)6

Phase equilibrium in the pseudo-quaternary system K₂O–MoO₃–P₂O₅–Bi₂O₃ was studied as three-component solvent K₂MoO₄–KPO₃–MoO₃ containing 15 mol% Bi₂O₃ during slow cooling and spontaneous crystallization. The results of the investigation were shown on a composition diagram, which indicates the crystallization fields of K₂Bi(PO₄)(MoO₄), K₅Bi(MoO₄)₄, BiPO₄ and K₃Bi₅(PO₄)₆. New phosphate K₃Bi₅(PO₄)₆ was characterized by single-crystal X-ray diffraction (space group C2/c, a=17.680(4), b=6.9370(14), c=18.700(4) Å, β=113.79(3)°) and FTIR spectroscopy. The possibility of lone electron pair stereoactivity of bismuth was suggested using the calculations of characteristics of the Voronoi–Dirichlet polyhedra for K₃Bi₅(PO₄)₆ and K₂Bi(PO₄)(MoO₄).     

Crystal and Molecular Structures of (Dibenzo-18-Crown-6)(Nitrato-O,O")-Tetrahydrofuranpotassium, [K(DB18C6)(THF)(NO3)]

The (dibenzo-18-crown-6)(nitrato-O,O")tetrahydrofuranpotassium complex [K(DB18C6)(THF)(NO₃)] (I) was synthesized and studied using X-ray diffraction analysis. The crystals are orthorhombic: a= 9.608 Å, b= 9.926 Å, c= 27.234 Å, Z= 4, space group P2₁2₁2₁. The structure was solved by the direct method and refined by the least-squares method in the anisotropic approximation to R= 0.099 over all 2620 measured independent reflections (CAD4 automated diffractometer, MoK radiation). Complex Iin the crystal exists as individual host–guest molecules, the K⁺cation (CN 9) being located in the DB18C6 macrocycle cavity and being coordinated to its six oxygen atoms and to two oxygen atoms of the nitrato ligand on one side of the macrocycle and to the THF oxygen atoms on the other side. The DB18C6 molecule in Ihas a butterfly conformation with approximate C _2V symmetry.     

Interfacial impedance behaviour of polished and paint platinum electrodes at Na2WO4-Na2MoO4 solid electrolytes

Interfacial impedances of the cell systems polished Pt/Na₂WO₄-Na₂MoO₄ and painted Pt/Na₂WO₄-Na₂MoO₄ were studied as a function of temperature and oxygen partial pressure by a.c. and pulse methods. The impedances are probably related to rate determining surface reactions of oxygen atoms and molecules. With Pt-paint, a particular type of impedance behaviour characterized by a constant phase angle, CPA, is observed: Z_p=K_p(jω)^?p (K_p and p independent of ω). No simple physical models were found to explain this behaviour, which is probably due to highly inhomogeneous current distribution effects.     

Direct Estimation of the Surface Location of Immobilized Functional Groups for Concerted Catalysis Using a Probe Molecule

The location of active sites during concerted catalysis by a metal complex and tertiary amine on a SiO₂ surface is discussed based on the interaction between the functionalized SiO₂ surface and a probe molecule, p‐formyl phenylboronic acid. The interactions of the probe molecule with the surface functionalities, diamine ligand, and tertiary amine, were analyzed by FT‐IR and solid‐state ¹³C and ¹¹B MAS NMR. For the catalyst exhibiting high 1,4‐addition activity, the diamine ligand and tertiary amine base exist in closer proximity than in the catalyst with low activity.     

Thermochemistry of amineborane adduct formation of pyridine and picoline isomers

The enthalpy of reaction of pyridine, 2-, 3-, and 4-picoline with BH₃·THF and the enthalpy of solution of the same amines in THF were determined by reaction-solution calorimetry. From these data, the enthalpies of formation of the corresponding amineborane adducts in solution of THF were also determined. The results can be explained by considering the steric and inductive effects of the methyl group on the pyridine ring and the basicity of amines. The enthalpy of formation of the adducts in solution of THF correlates well with the available literature values of pK _a of amines also determined in THF, and the influence of the solvent on the basicity features of studied amines is verified.     

Nonlinear structure–reactivity correlations. The hydrolysis of 2,4,6-trinitrophenyl acetate catalyzed by general bases

The hydrolysis of 2,4,6-trinitrophenyl acetate was studied in the presence of several carboxylic bases and tertiary amines. Carboxylic bases pyridine and imidazole react as nucleophilic catalysts, while 2,4-dimethyl and 2,4,6-trimethyl pyridine react as general-base catalysts. The nonlinear structure–reactivity correlations (log k_cat versus log k_OH and log k_cat versus pK of the leaving group) for the series of aryl acetates are discussed, and it is suggested that there is a change in transition-state structure along the series.     

An Electron Diffraction and XRPD Study of Superlattice Ordering in the Elpasolite-Related Oxyfluoride K3MoO3F3

A detailed electron diffraction and XRPD study has been made of the room-temperature α polymorph of K₃MoO₃F₃. It is shown that the true symmetry of this polymorph is neither tetragonal, trigonal, nor triclinic as previously reported but rather monoclinic I1a1, a=2a_p−c_p, b=4b_p, c=a_p+2c_p when expressed in terms of the underlying elpasolite (ordered perovskite) parent structure type. A highly structured, three-dimensional, continuous diffuse intensity distribution (presumably arising from local O/F ordering and associated structural relaxation) is shown to coexist with the sharp satellite reflections characteristic of the monoclinic supercell.     

New Molybdenyl Iodates: Hydrothermal Preparation and Structures of Molecular K2MoO2(IO3)4 and Two-Dimensional β-KMoO3(IO3)

Two new molybdenyl iodates, K₂MoO₂(IO₃)₄ (1) and β-KMoO₃(IO₃) (2), have been prepared from the reactions of MoO₃ with KIO₄ and NH₄Cl at 180°C in aqueous media. The structure of 1 consists of molecular [MoO₂(IO₃)₄]²⁻ anions separated by K⁺ cations. The Mo(VI) centers are ligated by two cis-oxo ligands and four monodentate iodate anions. Both terminal and bridging oxygen atoms of the iodate anions form long ionic contacts with the K⁺ cations. β-KMoO₃(IO₃) (2) displays a two-dimensional layered structure constructed from ²_∞[(MoO₃(IO₃)]¹⁻ anionic sheets separated by K⁺ cations. These sheets are built from one-dimensional chains formed from corner-sharing MoO₆ octahedra that run along the b-axis that are linked together through bridging iodate groups. K⁺ cations separate the layers from one another and form long contacts with oxygen atoms from both the iodate anions and molybdenyl moieties. Crystallographic data: 1, monoclinic, space group C2/c, a=12.8973(9) Å, b=6.0587(4) Å, c=17.694(1) Å, β=102.451(1)°, Z=4, MoKα, λ=0.71073, R(F)=2.64% for 97 parameters with 1584 reflections with I>2σ(I); 2, monoclinic, space group P2₁/n, a=7.4999(6) Å, b=7.4737(6) Å, c=10.5269(8) Å, β=109.023(1)°, Z=4, MoKα, λ=0.71073, R(F)=2.73% for 83 parameters with 1334 reflections with I>2σ(I).     

Effects of Nonionic, Cationic, and Mixed Nonionic-Cationic Surfactants on the Acid-Base Behavior of Phenyl Salicylate

The effects of Brij 35 micelles, CTABr micelles, and mixed Brij 35–CTABr micelles on the acid–base behavior of phenyl salicylate (PST) have been studied in aqueous solution containing 2% v/v acetonitrile. The apparent pK_b (pK^app_b) of PST is decreased by 1.5 pK units with the increase in [Brij 35] from 0 to 0.02 M which is attributed to micellar medium effect. The values of pK^app_b remain almost independent of [CTABr] within its range 0.01–0.03 M. The increase in [CTABr] from 0 to 0.03 M in aqueous solution containing 0.02 M Brij 35 has not resulted in a change in pK^app_b. This shows that the characeristic structural features of nonionic Brij 35 micelles remain essentially unchanged on addition of CTABr under the present experimental conditions.     

Synthesis, crystal structure and electrical characterization of two new potassium uranyl molybdates K2(UO2)2(MoO4)O2 and K8(UO2)8(MoO5)3O6

Two new potassium uranyl molybdates K₂(UO₂)₂(MoO₄)O₂ and K₈(UO₂)₈(MoO₅)₃O₆ have been obtained by solid state chemistry . The crystal structures were determined by single crystal X-ray diffraction data, collected with MoKα radiation and a charge coupled device (CCD) detector. Their structures were solved using direct methods and Fourier difference techniques and refined by a least square method on the basis of F² for all unique reflections, with R₁=0.046 for 136 parameters and 1412 reflections with I?2σ(I) for K₂(UO₂)₂(MoO₄)O₂ and R₁=0.055 for 257 parameters and 2585 reflections with I?2σ(I) for K₈(UO₂)₈(MoO₅)₃O₆. The first compound crystallizes in the monoclinic symmetry, space group P2₁/c with a=8.250(1) Å, b=15.337(2) Å, c=8.351(1) Å, β=104.75(1)°, ρ_mes=5.22(2) g/cm³, ρ_cal=5.27(2) g/cm³ and Z=4. The second material adopts a tetragonal unit cell with a=b=23.488(3) Å, c=6.7857(11) Å, ρ_mes=5.44(3) g/cm³, ρ_cal=5.49(2) g/cm³, Z=4 and space group P4/n.In both structures, the uranium atoms adopt a UO₇ pentagonal bipyramid environment, molybdenum atoms are in a MoO₄ tetrahedral environment for K₂(UO₂)₂(MoO₄)O₂ and MoO₅ square pyramid coordination in K₈(UO₂)₈(MoO₅)₃O₆. These compounds are characterized by layered structures. The association of uranyl ions (UO₇) and molybdate oxoanions MoO₄ or MoO₅, give infinite layers [(UO₂)₂(MoO₄)O₂]²⁻ and [(UO₂)₈(MoO₅)₃O₆]⁸⁻ in K₂(UO₂)₂(MoO₄)O₂ and K₈(UO₂)₈(MoO₅)₃O₆, respectively. Conductivity properties of alkali metal within the interlayer spaces have been measured and show an Arrhenius type evolution.     

Mesoporous Ga-MCM-41 as support for metallocene catalysts: Acidity–activity relationship

Several Ga-MCM-41 materials, prepared using different synthesis and template removal procedures, were used for the immobilisation of Cp₂ZrCl₂ by a direct impregnation method. Supports were carefully characterised by XRD, N₂ adsorption, ICP-AES, AAS, XPS and FTIR (using pyridine as probe molecule for acid sites), in order to assess their structural features, chemical composition (bulk and surface) and surface acidity properties.Supported catalysts were tested for the polymerisation of ethylene, using methylaluminoxane (MAO) as cocatalyst/activator. The relationships established between concentration/strength of acid sites of Ga-MCM-41 and the catalytic performance of zirconocene dichloride supported in these materials demonstrate that the behaviour of the catalytic systems analysed in this paper is compatible with existing models for the interaction of single-site olefin polymerisation catalysts with other inorganic acidic oxides.     

Effect of the physico-chemical properties of vanadia/praseodymia on cyclohexanol decomposition

Vanadia supported on praseodymia (2, 6 and 10 wt.% V₂O₅) were prepared by wet impregnation and characterized by energy dispersive X-ray analysis (EDAX), X-ray diffraction (XRD), TGA/DTA and BET surface area measurements. Decomposition of cyclohexanol was conducted over these catalysts in the vapor phase. Acidity of the catalysts was measured by temperature programmed desorption using ammonia as a probe molecule. The structural and acidic properties were correlated to the total conversion and cyclohexene selectivity.     

TiO2和Mg-Fe型类水滑石特征电离/络合平衡常数研究

The intrinsic surface reaction constants, pKa1^int, pKa2^int, p^＊KC^int and p^＊KA^int , were evaluated by a modifieddouble extrapolation （MDE） for TiO2 without structural charge and Mg-Fe hydrotalcite-like compounds （HTlc） with structural charge, respectively. The results of intrinsic surface reaction constants for TiO2 were compared with those obtained by class double extrapolation （CDE） in literature. Furthermore, the values of intrinsic surface reaction constants obtained by MDE were used to simulate the charging behaviors of the materials. The following conclusions were obtained. For TiO2 without structural charge, the pKa1^int and pKa2^int evaluated by MDE are equal to those by CDE, however the p^＊KC^int and p^＊KA^int evaluated by MDE are much different from those by CDE. In principle, the results of the p^＊KC^int and p^＊KA^int evaluated by MDE are more accurate than those by CDE. The values of intrinsic surface reaction constants obtained by MDE can excellently simulate the charging curves for TiO2 with the triple layer model （TLM）. For HTlc with positive structural charge, the results of ^＊KC^int=0 and ^＊KA^int →∞ were obtained by MDE, which means the inert electrolyte chemical binding does not exist; the point of zero net charge （PZNC） of c-independence also exist as the same as solid without structural charge, and the PHPZNC obtained by the acid-base titration can excellently be simulated and the surface charging tendency can be simulated to a great extent using the pKa1^int and pKa2^int evaluated by MDE and the diffuse layer model （DLM）.     

Oxidation of Alcohols by Hydroperoxides in the Presence of Polymer-Supported Catalysts: Tetrabromooxomolybdate Supported on a Cationic Polymer

The immobilization of Br₄MoO^? in both poly-p-vinyipyridine with a flexible backbone and silica as a rigid polymer support was carried out. The oxidation of alcohols by t-butyl hydroperoxide (t-BuOOH) was then studied in the presence of the polymer-supported complexes obtained. The differences of the reactivity between catalysts supported by organic and inorganic polymers are discussed. The best carrier for Br₄MoO^? as an oxidation catalyst is a silica modified with silane coupling reagent (dimethyloctadecyl-[3-(trimethoxysilyl)propyl] ammonium chloride).     

Studies on Polymerization of Vinyl Compounds Initiated by Metal Chelate II Kinetics of Polymerization of Methyl Methacrylate Initiated by Nickel Ethyl Acetoacetate in the Presence and the Absence of Aromatic Amines

The kintetic studies of polymerization of methyl methacrylate initiated with nickel ethyl acetoacetate gave the following equations. R_p=K₁[Monomer]^1.4[Chelate]^0.5, in the absence ox aniline R_p=K₂[Monomer]^1.2[Chelate]^0.5 [Aniline]^0,5, in the presence of aniline. Some aromatic amines such as aniline markedly accelerated the polymerization, while pyridine had no such effect. The activation energy of initiation was 24.8 kcal/mol in the absence of aniline, and 8.8 kcal/mol in the presence of aniline. Both the kinetic data and the infrared spectra of the polymer indicated that the polymerization was radical in nature. The reaction order against monomer varied, as the temperature differed. The spectrophotometric investigation indicated formation of a complex between the chelate and the monomer, or amines. It also showed that the formation of a complex was not a factor which controlled the rate of initiation. A scheme of initiation mechanism was presented on the basis of the above experimental evidence.     

Aggregation of polythiophene homopolymer and block copolymer in solution utilizing the characteristics of pyridine at the side chain

Poly[3‐(5′‐hexylpyridine‐2′‐yl)thiophene] ( P3PT ) (M_n = 13900, H‐T content = 90%) was prepared by the regioselective Grignard metathesis reaction and the subsequent Kumada coupling polymerization. Likewise, poly(3‐hexylthiophene)‐b‐poly[3‐(5′‐hexylpyridine‐2′‐yl)thiophene] ( P3HT‐b‐P3PT ) (M_n = 17,300) was synthesized in the one‐pot and successive monomer addition protocol, in which the segment ratio was calculated to be 56 ( P3HT )/44 ( P3PT ) base on the ¹H NMR spectrum. The absorption and emission spectra of homopolymer P3PT(H) , obtained by the protonation of the pyridine nitrogen, in THF/cyclohexane shifted to the longer wavelength as compared with those collected in THF, suggesting the aggregation in poor solvent. The aggregation of P3PT induced by the addition of Sc(OTf)₃ could be controlled by the molar ratio of pyridine and scandium complex. The protonated block copolymer P3HT‐b‐P3PT(H) was also subjected to the aggregate formation. The absorption maximum in THF/CH₃OH showed a bathochromic shift and the fluorescence emission was almost quenched. From the ¹H NMR spectra and DLS measurements, P3HT‐b‐P3PT(H) forms nanometer scale aggregates particularly with the insolubility and stacking of non‐ionic P3HT in alcohol as the driving force. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3383–3389     

Base-Modified Nucleosides Related to 2-Chloro-2′-deoxyadenosine

Derivatives of 2-chloro-2′-deoxyadenosine ( 1a ) containing secondary 6-NH₂ groups ( 5a-c ) or a 8-Br substituent ( 9 ) were synthesized. They were tested together with ring-modified congeners containing a pyrrolo[2,3-b]pyridine, pyrrolo[3,2-c]pyridine, or pyrazolo[3,4-d]pyrimidine ring system as inhibitors of various leukemic cell lines. Only the 8-Br derivatives 9 showed inhibitory activity, whereas the base-modified congeners were not active. Compound 1a was protonated at a pK_a = 1.4 (2′-deoxyadenosine at pK_a = 3.8). Protonation occurred at N(7) and not at N(1) as observed for dA.     

不同锌盐改性的HZSM-5催化剂上甲醇芳构化反应

分别用ZnSO4,Zn(AcO)2,Zn(NO3)2和ZnCl2溶液对HZSM-5分子筛浸渍改性得到不同Zn盐改性的HZSM-5催化剂.采用X射线衍射、N2物理吸附、热重-质谱分析、氨程序升温脱附和吡啶吸附红外光谱等方法对改性后的催化剂进行了表征,并在固定床反应装置上考察了其甲醇芳构化反应性能.结果表明,不同Zn盐改性的HZSM-5催化剂上Zn物种的存在形式不同会导致其表面酸中心强度与分布具有较大差异,经ZnSO4改性的HZSM-5催化剂表面上强B酸中心和Zn物种的存在使其表现出最佳的甲醇芳构化反应性能.