新型重整催化剂的研究——C_6—C_8直链烷烃在Pt/BaKL型沸石上的芳构化反应

本文利用C_■—C_■等纯化合物作原料,用连续微型反应器考察了Pt/BaKL型沸石的芳构化反应性能以及反应条件(如反应温度,载气和原料空速及不同碳数的烷烃等)对催化性能的影响。同时还考察了铂的作用及其粒度在沸石中的分布。实验结果发现,Pt/BaKL型沸石是高活性高选择性的芳构化催化剂,它显示出单功能催化剂特有的催化作用。这可归结于铂粒在沸石中的均匀分布,其粒度为1.5—3.0nm之间。     

新型重整催化剂的研究—Pt／BaKL型沸石中钡的作用

本文采用XRD,NH_3-TPD,IR以及TEM等方法考察了Pt/BaKL沸石中Ba~(2+)的作用。NH_3-TPD结果表明,交换Ba~(2+)后的L型沸石的酸性,由于阳离子的作用仅在弱酸范围内有些改变,但与载铂的沸石的催化活性无明显的对应关系。IR及XRD谱线表明,BaKL沸石中Ba~(2+)在最佳交换度(26.3%)时,随预培烧温度的提高,使Ba~(2+)处于沸石孔道中B、C、D位置,接近于最佳分布,此时IR谱线上1421cm~(-1)处有一新峰。当沸石负载铂后,因铂与Ba~(2+)的相互作用,新峰消失,导致铂粒在沸石上分布更加均匀;铂粒在1.5—3.0nm之间占有最大比例,使得Pt/BaKL沸石呈现芳构化活性及选择性高于Pt/KL沸石,分别为～98%和～95%。     

Biosorption of metal ions with Penicillium chrysogenum

Biosorption of metal ions with Penicillium chrysogenum mycelium is described in this article. Alkaline pretreatment was used to remove proteins and nucleic acids from cells, and this treatment increased the adsorption capacities, for Cr³⁺ from 18.6 mg g⁻¹ to 27.2 mg g⁻¹, for Ni²⁺ from 13.2 mg g⁻¹ to 19.2 mg g⁻¹, for Zn²⁺ from 6.8 mg g⁻¹ to 24.5 mg g⁻¹. The adsorption of metal ions was strongly pH dependent. The mycelium could beused for large-scale removal of Cr³⁺ from tannery wastewater. The results show that this inexpensive mycelium adsorbent has potential in industry because of its high adsorption capacity. The main chelating sites are amino groups (−NH₂) of chitosan in the mycelium. A new model is established, which describes the relation of adsorption of metal ions on pH according to amino group chelating with metal ions and H⁺. The relative errors of simulation for Cu²⁺, Ni²⁺, Zn²⁺, and Cr³⁺ are 4.66%, 5.45%, 11.55%, and 1.69%, respectively.     

Pt/SO42??ZrO2: The state of platinum and its relation with catalytic activity inn-hexane isomerization

Pt/SO₄ ²⁻−ZrO₂ calcined at 873 K shows the same catalytic activity forn-hexane isomerization as the calcined and reduced sample. A platinum reduction peak did not appear in the TPR profile and the presence of Pt⁰ was detected by XPS on the only calcined Pt/SO₄ ²⁻−ZrO₂. Nevertheless, this calcined material does not show hydrogen chemisorption and cyclohexane dehydrogenation activity.     

Theoretical study of the structure and stability of the Na2Cl+, NaCl 2? , Na3Cl 2+ , and Na2Cl 3? ions

The geometrical parameters, normal vibration frequencies, and thermochemical characteristics of the Na₂Cl⁺, NaCl ₂ ⁻ , Na₃Cl ₂ ⁺ , and Na₂Cl ₃ ⁻ ions in saturated vapors over sodium chloride were calculated by the ab initio methods including electron correlation. According to calculations, the Na₂Cl⁺ and NaCl ₂ ⁻ triatomic ions have a linear equilibrium D _∞h configuration. The pentaatomic ions can exist in the form of the D _∞h linear isomer, C _2v planar cyclic isomer, or D _3h bipyramidal isomer. At ∼1000 K the Na₃Cl ₂ ⁺ and Na₂Cl ₃ ⁻ ions exist predominantly in the form of the linear isomers. The energies and enthalpies of the ion-molecule reactions involving the above ions were calculated. The formation enthalpy of the ions Δ_f H ⁰(0 K) was determined: 230 ± 2 kJ/mol (Na₂Cl⁺), −96 ± 4 kJ/mol (Na₂Cl ₃ ⁻ ), −616 ± 2 kJ/mol (NaCl ₂ ⁻ ), and −935 ± 4 kJ/mol (Na₂Cl ₃ ⁻ ). Original Russian Text Copyright ? 2007 by T. P. Pogrebnaya, A. M. Pogrebnoi, and L. S. Kudin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 6, pp. 1053–1061, November–December, 2007.     

Nucleophilic Substitution Reactions at Planar Tetra-coordinate Bis-cationic-platinum(II) Complexes. Kinetics of Displacement of Pyridine from {Pt[2,6-bis(methylthiomethyl)pyridine](py)}2+, {Pt[bis(2-pyridylmethyl)amine] (py)}2+ and {Pt[bis(2-(pyridylmethyl)sulphide](py)}2+ Cations

The kinetics of nucleophilic substitution of pyridine in bis-cationic [Pt(L)(py)]²⁺ complexes (L=SNS, NNN, NSN) [SNS=bis(methylthiomethyl)pyridine, NNN=bis(2-pyridylmethyl)amine, NSN=bis(2-pyridylmethyl)sulphide] by a series of nucleophiles (Cl⁻, Br⁻, I⁻, N₃⁻, (C₂H₅)₂S, NH₃, thiourea (tu), NO₂⁻, C₅H¹0NH, SeCN⁻, SCN⁻, CN⁻ when L=SNS; Cl⁻, Br⁻, I⁻, N₃⁻, (C₂H₅)₂S, SCN⁻, NH₃, NO₂⁻ when L=NNN; Br⁻, N₃⁻, NO₂⁻, NH₃, C₅H₁₀NH when L=NSN) have been measured in MeOH at 25 °C, μ =0.1 mol dm⁻³ (LiClO₄ or LiCF₃SO₃). The logarithms of the second-order rate constants calculated at μ=0, log k° ₂, do not follow the dependence upon the n° _Pt scale. In particular, the reactivity of the biphilic reagents tu, SeCN⁻, SCN⁻ and, to a lesser extent, NO⁻ ₂, towards these doubly charged substrates is largely lower than expected on the basis of the n° _Ptscale. There are good linear relationships between logk° ₂ for the bis-cationic substrate [Pt(SNS)(py)]²⁺, chosen as the standard, and log k° ₂ for the same reactions with [Pt(NNN)(py)]²⁺, [Pt(NSN)(py)]²⁺ and other double charged complexes previously studied. A new wide nucleophilicity scale based on [Pt(SNS)(py)]²⁺, that is appropriate to all the bis-cationic substrates, is here proposed     

Introduction of vanadium species in <Emphasis Type="Italic">β</Emphasis> zeolite by solid-state reaction: spectroscopic study of V speciation and molecular mechanism

V-containing β zeolites were prepared by solid-state reaction between V₂O₅ and β zeolite. The zeolite structure was analysed by XRD and N₂ physisorption. The V speciation was studied by chemical analysis and different spectroscopies (FT-IR, ²⁷Al-NMR, UV-Vis, EPR, photoluminescence). After calcination of V₂O₅-β zeolite mechanical mixtures at 500°C, three kinds of V species were identified: (i) oligomeric vanadates with octahedral V⁵⁺ easily removed by treatment with NH₄OAc, (ii) isolated vanadyl (V=O)²⁺ ions in axially distorted octahedral or square pyramidal environment, interacting with framework and/or extraframework Al nuclei and (iii) isolated V⁵⁺ in tetrahedral and octahedral environments, localized in framework defect sites. The amount of the latter species is higher when water vapor is present during calcination and when parent β zeolite contains a high concentration of defect sites generated by a strong acid pretreatment. Isolated V⁵⁺ are easily reduced to tetrahedral V⁴⁺ or to square pyramidal (V=O)²⁺. Possible models of the mechanism of formation of V species by solid-state reaction and further reduction are proposed.     

Characterization of zinc-modified lithium tantalate thin films fabricated by chemical solution deposition method

Zinc-substituted lithium tantalate thin films were fabricated for improving the electrical resistivity by compensating the valence of lattice defects in LiTaO₃ crystal. The films with the chemical composition of (Li_1.00-x Zn _x )TaO₃ were fabricated on (111)Pt/TiO₂/SiO₂/(100)Si substrate by a chemical solution deposition technique using metal-organic precursors. Dense films consisting of a ilumenite-type crystalline phase were deposited by spin coating on the substrates, followed by heat-treatment at 650°C for 5 min in air. The leakage current density of the LiTaO₃ film was reduced from approximately 10⁻⁴ to 10⁻⁶ A/cm² by substituting Zn²⁺ ions for Li⁺ ions in the LiTaO₃ films. Polarization–electric field hysteresis loop was improved significantly by partial substitution of Zn²⁺ for Li⁺ ions, which is based on the enhancement of electrical resistivity.     

Does increased chelation enhance the rate of ligand substitution at PtII (N,N,N) centres? A detailed kinetic & mechanistic study

The rate of substitution of the chloride and aqua moieties from the platinum(II)-amine complexes, viz. [Pt(dien)Cl]Cl(Pt1-Chloro) and [Pt(en)(NH₃)Cl]Cl (Pt2-Chloro) and their corresponding aqua analogues, viz. [Pt(dien)(OH₂)] (ClO₄)₂ (Pt1-Aqua) and [Pt(en)(NH₃)(OH₂)](ClO₄)₂ (Pt2-Aqua), by a series of neutral and anionic nucleophiles,viz. thiourea (TU), 1,3-dimethyl-2-thiourea (DMTU), 1,1,3,3-tetramethyl-2-thiourea (TMTU), iodide (I⁻) and thiocyanate (SCN⁻), was determined under pseudo first-order conditions as a function of concentration and temperature using UV/Visible spectrophotometry and standard stopped-flow techniques. The observed pseudo first-order rate constants for the substitution reactions obeyed the simple rate law k _obs = k ₂[Nucleophile]. Second-order kinetics and negative activation entropies, ca. −93 J K⁻¹ mol⁻¹ and −71 J K⁻¹ mol⁻¹, for the chloro and aqua complexes respectively, support an associative mode of activation. The rate of substitution of both the chloro and aqua moieties are observed to decrease with an increase in the steric bulk of the neutral nucleophiles, whilst rate of substitution by SCN⁻ was observed to be faster than that of I⁻, in correlation with the observed nucleophilicities of the two nucleophiles. A comparison of the second-order rate constants, k ₂, at 298 K, obtained for the substitution reactions of Pt1and Pt2 shows that an increase in chelation in moving from Pt2 to Pt1 results in a corresponding increase in the reactivity, by a factor of ca. 3, (28.31 ± 0.15 and 8.02 ± 0.13 m ⁻¹ s⁻¹ for Pt1 and Pt2 respectively, in the case of substitution of the aqua species by TU). Computational analysis of the chloro complexes, viz. Pt1-Chloro, Pt2-Chloro and [Pt(NH₃)₃Cl]Cl (Pt3) support this conclusion by demonstrating that the Pt–N bond trans to the leaving group is shortened and that the Pt–Cl bond is lengthened when chelation is increased from Pt3 to Pt1. Consequently, these results suggest that the increase in reactivity of Pt1 over Pt2, promoted by increased chelation, is as a result of ground state destabilization.     

Hydroisomerization of benzene-containing gasoline fractions on a Pt/SO 42? -ZrO2-Al2O3 catalyst: II. Effect of chemical composition on acidic and hydrogenating and the occurrence of model isomerization reactions

The acidic and hydrogenating of Pt/SO₄²⁻-ZrO₂-Al₂O₃ samples containing from 18.8 to 67.8 wt % Al₂O₃ as a support constituent were studied by the IR spectroscopy of adsorbed CO and pyridine, and the model reactions of n-heptane and cyclohexane isomerization on these catalysts were examined. The total catalyst activity in the conversion of n-heptane decreased with the concentration of Al₂O₃; this manifested itself in an increase in the temperature of 50% n-heptane conversion from 112 to 266°C and in an increase in the selectivity of isomerization to 94.2%. In this case, the maximum yield of isoheptanes was 47.1 wt %, which was reached on a sample whose support contained 67.8 wt % Al₂O₃. A maximum yield (69.6 wt %) and selectivity (93.7%) for methylcyclopentane formation from cyclohexane were also reached on the above catalyst sample. This can be explained by lower concentrations of Lewis and Br?nsted acid sites in the Pt/SO₄²⁻-ZrO₂-Al₂O₃ system, as compared with those in Pt/SO₄²⁻-ZrO₂. The experimental results allowed us to make a preliminary conclusion that the Pt/SO₄²⁻-ZrO₂-Al₂O₃ catalyst whose support contains 67.8 wt % Al₂O₃ is promising for use in the selective hydroisomerization of benzene-containing gasoline fractions in the thermodynamically favorable process temperature range of 250–300°C.     

High resolution adsorption isotherms of N2 and Ar for nonporous silicas and MFI zeolites

The high resolution adsorption isotherms of N₂ (77.4 K) and Ar (87.3 K) have been measured for two nonporous silicas with different silanol contents (3.3 and 0.35 OH/nm²) and for two MFI zeolite with different Al contents (Si/Al=12.5 and 500). Silanol groups and Al sites (acid sites) gives the significant effect on the N₂ isotherms at submonolayer, but the Ar isotherms are independent of silanols and Al sites. The Ar isotherms, therefore, are preferable in calculation of microporosity of zeolites. The N₂ and Ar isotherms for MFI zeolite (Si/Al=500) have been measured at temperatures of 77–94 K, from which the differential adsorption energies of N₂ and Ar are calculated. The interaction of N₂ with channel surface of MFI zeolite is greater than that of Ar in the range of α _s =0.1–0.7. The hystereses are detected for the N₂ isotherm in p/p ^o=0.1–0.3 at 77.4 K and for the Ar isotherm in p/p ^o=3×10⁻⁴–2×10⁻³ at 87.3 K. However, it is difficult to explain the hysteresis phenomenon using differential adsorption energy.     

A study of samarium ions electroreduction at various electrodes in KCl-NaCl-CsCl melt at <Emphasis Type="Italic">T</Emphasis> = 823 K

Samarium ions electroreduction mechanism was studied on the supporting of KCl-NaCl-CsCl eutectic melt at 823 K on various electrodes (W, Mo, Al, Ni, Pt, and Ag). The diffusion coefficients of SmCl₆³⁻ chloride complexes and Sm³⁺ → Sm²⁺ heterogeneous recharge stage rate constant K _fh⁰ were calculated in KCl-NaCl-CsCl melt at T = 823 K.     

Toward total structural analysis of cardiolipins: multiple-stage linear ion-trap mass spectrometry on the [M − 2H + 3Li]<Superscript>+</Superscript> ions

ESI multiple-stage linear ion-trap (LIT) mass spectrometric approaches for a near-complete structural characterization of cardiolipins (CLs), including identification of the fatty acyl substituents, assignment of the fatty acid substituents on the glycerol backbone, and location of the double-bond(s) or cyclopropyl group along the fatty acid chain are described. Upon collisionally activated dissociation (CAD) on the [M − 2H + 3Li]⁺ ions of CL in an ion-trap (MS²), two sets of fragment ions (designated as (a + 136) and (b + 136) ions) analogous to those previously reported for the [M − 2H + 3Na]⁺ ions were observed, leading to assignment of the phosphatidyl moieties attached to 1′- or 3′-position of the central glycerol. Further dissociation of the (a + 136) (or (b + 136)) ions (MS³) gives rise to the (a + 136 − R_{1(or 2)}CO₂Li) (or b + 136 − R_{1(or 2)}CO₂Li) ion pairs that identify the fatty acid moieties and their position on the glycerol backbone. This is followed by MS⁴ on the (a + 136 − R_{1(or 2)}CO₂Li) (or b + 136 − R_{1(or 2)}CO₂Li) ion to eliminate a tricylic glycerophosphate ester residue (136 Da) to yield the (a − R_{1(or 2)}CO₂Li) ion, which is then subjected to MS⁵. The MS5 spectrum contains the structural information that locates the double-bond(s) or cyclopropyl group of the fatty acid substituents. Finally, the subsequent MS⁶ on the dilithiated fatty acid ions generated from MS⁵ also yields feature ions that confirm the assignment.     

Effects of Temperature and Common Ions on Binding of Puerarin to BSA

The effects of temperature and common ions on binding of puerarin to bovine serum albumin (BSA) are investigated. The binding constants (K _a) between puerarin and BSA are 1.13×10⁴ L⋅mol⁻¹ (20 °C) and 1.54×10⁴ L⋅mol⁻¹ (30 °C), and the number of binding sites (n) is (0.95±0.02). However, at a higher temperature (40 °C) the stability of the puerarin–BSA system decreases, which results in a lower binding constant (1.58×10³ L⋅mol⁻¹) and number of binding sites (n=0.73) of the puerarin–BSA system. However, the presence of Cu²⁺ and Fe³⁺ ions increases the binding constants and the number of binding sites in the puerarin–BSA complex.     

Application of an extended solvation theory to study on the binding of magnesium ion with myelin basic protein

Binding properties of myelin basic protein (MBP) from bovine central nervous system due to the interaction by divalent magnesium ion (Mg²⁺) was investigated at 27°C in aqueous solution using isothermal titration calorimetry (ITC) technique. An extended solvation model was used to reproduce the enthalpies of Mg²⁺-MBP interaction over the whole Mg²⁺ concentrations. It was found that there is a set of two identical and noninteracting binding sites for Mg²⁺ ions. The dissociation equilibrium constant is K _d=45.5 μM. The molar enthalpy of binding site is identical for both sites; ΔH=−15.24 kJ mol⁻¹. The solvation parameters recovered from the solvation model were attributed to the structural change of MBP due to the metal ion interaction.     

Effect of polyether diamine on gas permeation properties of organic-inorganic hybrid membranes

The quantitative incorporation and high dispersion of platinum nanoparticles into MCM-41 has been carried out by the coordination between Pt(IV) ion and APTMS-anchored MCM-41. Before and after calcination of Pt/APTMS/MCM41 samples, the Pt content in samples was evaluated from home-made photoacoustic spectrometer (PAS). The PAS bands at 350 nm and 450 nm can be assigned to d–d transition bands of Pt complexes. By increasing the concentration of Pt solution, the PAS intensity of Pt/APTMS/MCM41 was increased proportionally up to 1.0×10⁻² M, and remained constant above 1.0×10⁻² M. It can be attributed to the saturation of Pt content within Pt/APTMS/MCM41. The Pt content in the saturated Pt/APTMS/MCM41 was 8.5 wt% (the theoretical value), 9.7 wt% (measured by EDX) and 9.2 wt% (measured by ESCA), respectively. This indicates that the content of Pt precursor within MCM-41 could be controlled by the concentration of Pt precursor solution. The PAS intensity of calcined Pt/APTMS/MCM41's in H₂ flow was increased up to 1.0×10⁻² M and remained nearly constant above 1.0×10⁻² M. Therefore, we suggest that the formation of Pt complexes with APTMS-anchored MCM-41 made it possible to incorporate quantitatively Pt nanoparticles in the range of 0.5–9.2 wt% within MCM-41 channels.     

Rubidium-cationic conductance in the systems Rb2 ? 2xAl2 ? xAxO4 (A = P, V)

RbAlO₂-based solid solutions are synthesized in the systems Rb_{2 − x} Al_{2 − x} A _x O₄ (A = P, V). Temperature and concentration dependences of their conductance are studied; the rubidium-cationic character of the conductance is corroborated. The high ionic conductivity of the synthesized phases (∼5 × 10⁻³ S cm⁻¹ at 300°C, ∼2 × 10⁻² S cm⁻¹ at 700°C) is caused by (a) formation of rubidium vacancies as a result of the replacing of Al³⁺ ions by fivefold-charged cations of phosphorus or vanadium and (b) disordered crystal structure of γ-KAlO₂ type. The obtained data are compared with the results of the studying of similar systems. Original Russian Text ? G.Sh. Shekhtman, E.I. Volegova, E.I. Burmakin, 2009, published in Elektrokhimiya, 2009, Vol. 45, No. 4, pp. 495–499.     

A Thermodynamic Study on the Binding of Calcium Ion with Myelin Basic Protein

The interaction of myelin basic protein (MBP) from the bovine central nervous system with divalent calcium ion was studied by isothermal titration calorimetry at 27 °C in aqueous solution. The extended solvation model was used to reproduce the enthalpies of Ca²⁺-MBP interaction over the whole range of Ca²⁺ concentrations. The solvation parameters recovered from the solvation model were attributed to the structural change of MBP due to the metal ion interaction. It was found that there is a set of two identical and non-interacting binding sites for Ca²⁺ ions. The association equilibrium constant is 0.021 μmol⋅dm⁻³. The molar enthalpy of binding is ΔH=−15.10 kJ⋅mol⁻¹.     

In-source decay and fragmentation characteristics of peptides using 5-aminosalicylic acid as a matrix in matrix-assisted laser desorption/ionization mass spectrometry

The use of 5-aminosalicylic acid (5-ASA) as a new matrix for in-source decay (ISD) of peptides including mono- and di-phosphorylated peptides in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is described. The use of 5-ASA in MALDI-ISD has been evaluated from several standpoints: hydrogen-donating ability, the outstanding sharpness of molecular and fragment ion peaks, and the presence of interference peaks such as metastable peaks and multiply charged ions. The hydrogen-donating ability of several matrices such as α-cyano-4-hydroxycinnamic acid (CHCA), 2,5-dihydroxybenzoic acid (2,5-DHB), 1,5-diaminonaphthalene (1,5-DAN), sinapinic acid (SA), and 5-ASA was evaluated by using the peak abundance of a reduction product [M + 2H + H]⁺ to that of non-reduced protonated molecule [M + H]⁺ of the cyclic peptide vasopressin which contains a disulfide bond (S-S). The order of hydrogendonating ability was 1,5-DAN > 5-ASA > 2,5-DHB > SA = CHCA. The chemicals 1,5-DAN and 5-ASA in particular can be classified as reductive matrices. 5-ASA gave peaks with higher sharpness for protonated molecules and fragment ions than other matrices and did not give any interference peaks such as multiply-protonated ions and metastable ions in the ISD mass spectra of the peptides used. Particularly, 1,5-DAN and 5-ASA gave very little metastable peaks. This indicates that 1,5-DAN and 5-ASA are more “cool” than other matrices. The 1,5-DAN and 5-ASA can therefore be termed “reductive cool” matrix. Further, it was confirmed that ISD phenomena such as N-Cα bond cleavage and reduction of S-S bond is a single event in the ion source. The characteristic fragmentations, which form a− and (a + 2)-series ions, [M + H − 15]⁺, [M + H − 28]⁺, and [M + H − 44]⁺ ions in the MALDI-ISD are described.     

Chromium uptake from tricomponent solution in zeolite fixed bed

Removal of Cr³⁺,Ca²⁺,Mg²⁺ and K⁺ in equilibrium isotherms and in tricomponent solutions (Cr/Ca/K, Cr/Ca/Mg and Cr/Mg/K) were investigated in NaX and NaY packed beds at 30^∘C. The equilibrium selectivity was obtained as Cr⁺³ > Mg²⁺ > Ca²⁺≈K⁺ for zeolite NaY and Ca^{2 +}≫Cr^{3 +} > Mg^{2 +}≈K⁺ for zeolite NaX. The breakthrough curves showed sequential ion exchange where chromium ions are able to replace the competing cations. Some mass transfer parameters, such as length of unused bed and overall mass transfer coefficient, were investigated. Chromium retention was also investigated through a mass balance. Based on the breakthrough results, it was concluded that chromium-uptake mechanism was hardly influenced by the competition and interaction between the entering ions. NaY showed a higher affinity towards Cr³⁺ for both equilibrium and dynamic systems and its sites were more efficiently used in the ion exchange process. Chromium was less retained in NaX due to the high selectivity towards calcium ions.