Surface fine structure of hydrodesulfurization catalysts. New aspects of promoting effects of Co and Ni

By using the highpressure DRIFT, EXAFS, and TPDDRIFT methods, it is shown that the wellknown effects concerning Co–Mo/Al₂O₃ (i.e., promoting effect of Co or Ni, activating effect of catalyst presulfiding, and inhibiting effect of H₂S) are closely connected to each other. Some direct evidence of the interactions between Mo and Co on sulfided Co–Mo/Al₂O₃ is also shown.     

Elucidation of hydrodesulfurization mechanism on molybdenum‐based catalysts using 35S radioisotope pulse tracer methods

Elucidation of the hydrodesulfurization (HDS) mechanism on molybdenumbased catalysts using radioisotope tracer methods and reaction kinetics is reviewed. Firstly, to investigate the sulfidation state in Mo/Al₂O₃ and Co–Mo/Al₂O₃ catalysts, presulfiding of these catalysts has been performed using a ³⁵S pulse tracer method. Secondly, HDS of radioactive ³⁵Slabeled dibenzothiophene was carried out over a series of sulfided molybdena–alumina catalysts and cobaltpromoted molybdena–alumina catalysts in a pressurized flow reactor to estimate the behavior of sulfur on the working catalysts. Finally, sulfur exchange of a ³⁵Slabeled catalyst with hydrogen sulfide was performed to estimate the relationship between the amount of labile sulfur and catalytically active sites.     

Recent progress in tartaric acid‐modified Raney nickel system for enantio‐differentiating hydrogenation

Tartaric acidmodified Raney nickel (TAMRNi) is an enantiodifferentiating catalyst for hydrogenation of ketones. The stereochemical models explaining the enantiodifferentiation of ketoester and 2alkanone were unified as an extended stereochemical model by the experimental supports. Based on this new model, a working hypothesis to improve the enantiomeric excess (ee) of the ketoester/TAMRNi system was developed, and the ee was improved to 96%. By further fine tuning of this system, almost perfect enantiodifferentiation resulting in over 98% ee was achieved.     

The Chemistry of Methane Remediation by a Non‐thermal Atmospheric Pressure Plasma

The destruction of methane by a nonthermal plasma in atmospheric pressure gas streams of nitrogen with variable amounts of added oxygen has been investigated. The identities and concentrations of the endproducts are determined by online FTIR spectroscopy and the plasma chemistry is interpreted using kinetic modelling. For a deposited energy of 118 kJ m^–3, the destruction is 12% in nitrogen decreasing monotonically to 5% in air. The major endproducts are HCN and NH₃ in nitrogen and CO, CO₂, N₂O, NO and NO₂ for gas streams containing oxygen. The chemistry in pure nitrogen is predominantly due to reactions of electronicallyexcited nitrogen atoms, N(²D). The addition of oxygen converts the excited state nitrogen into nitrogen oxides reducing the methane destruction which then arises by O and OH reactions yielding CO and, to a lesser extent, CO₂. The modelling correctly predicts the magnitude of the methane destruction as a function of added oxygen and the concentrations of the endproducts for processing in both nitrogen and air.     

A new strategy for alkane oxidation with O2 using N‐hydroxyphthalimide (NHPI) as a radical catalyst

A practical catalytic method to convert alkanes into the corresponding oxygencontaining compounds with O₂ under mild conditions using Nhydroxyphthalimide (NHPI) in the presence or absence of a transition metal was developed. Thus, cyclohexane was successfully converted into adipic acid in good conversion and selectivity by a combined catalytic system consisting of NHPI and Mn(acac)₂. Lower alkane such as isobutane was converted into tbutyl alcohol (83%) under 10 atm of air by NHPICo(OAc)₂ system. Alkylbenzene such as toluene was oxidized to benzoic acid in high yield (81%) under normal temperature and pressure of dioxygen in the presence of a catalytic amount of NHPI and Co(OAc)₂. ESR measurements showed that phthalimideNoxyl generated from NHPI under dioxygen atmosphere is a key species in this oxidation and functions as a radical catalyst.     

Additive telluromolybdates. Structure and catalysis in oxidation

Additive telluromolybdates, MoO₃·2TeO₂ and M^IIO·TeO₂·MoO₃ (M^IITeMoO₆; M^II = Co, Mn, Zn), converted ethyl lactate selectively to pyruvate in a vaporphase fixedbed flow system at 250–300 °C. A synergy in activity was observed for binary TeO₂–MoO₃, and crystalline Te₂MoO₇ was suggested as the active species. The Rietveld analysis of powder XRD patterns of ternary CoTeMoO₆ revealed the layer structure quite different from that of the reference Te₂MoO₇, but tellurium was again located adjacent to molybdenum linked through lattice oxygen.     

Synthesis of β‐Chlorinated Macrocyclic [Au(C14H20N4Cl2)]X (X = AuCl2, ClO4, AuCl4) Gold(III) Complexes. Crystal and Molecular Structures of [Au(C14H20N4Cl2)]ClO4

A squareplanar [AuL₂]⁺ gold(III) complex [L₂ = 6.13dichloro5,7,12,14tetramethyl1,4,8,11tetraaza4,6,11,13tetraenato(2-)] containing two chlorine atoms in the position of the ligand hexacyclic ring was first synthesized by the reaction of the [AuL₁]⁺ tetraiminate complex [L₁ = 5,7,12,14tetramethyl1,4,8,11tetraaza4,6,11,13tetraenato(2-)] with HAuCl₄ in an acetone – DMFA solution. The complex was isolated in the form of dichloroaurite (I), perchlorate (II), and tetrachloroaurate (III). Compounds I–III were studied by elemental and Xray diffraction analyses and IR and NMR spectroscopies. Single crystals of [AuL₂]ClO₄ were obtained, and the crystal structure of this compound was determined from Xray diffraction patterns. The crystals are monoclinic: a = 10.147(2), b = 7.260(1), c = 12.519(2), = 96.70(1)°, V = 915.9(3)³, Z = 2, space group P2/c, d_calc = 2.218, d_meas = 2.209 g/cm³ The crystal structure is built of nearly planar [Au(C₁₄H₂₀N₄Cl₂)]⁺ cations and [ClO₄]^- anions. Introduction of chlorine atoms into the positions of the hexacyclic rings of the tetraazamacrocycle hardly changes the lengths of the delocalized C N and C C bonds.     

The Preparation and Characterization of Highly Dispersed PdO over Alumina for Low‐temperature Combustion of Methane

PdO/Al₂O₃ catalysts prepared by glow discharge plasma treatment followed by thermal calcination show a much higher dispersion and a better catalytic activity for methane combustion at relatively low temperatures. The dispersion of palladium active species by such plasma prepared catalysts is 29.7%, 5.4 times higher than that of conventional catalysts. XPS analysis indicates that a surface enrichment of Pd active species (PdO) has been achieved after plasma treatment. The surface atomic composition of PdO of plasma prepared catalysts reaches 10.5%. XRD characterization also confirms a wellcrystallized PdO phase present on the plasma prepared catalyst. The lightoff temperature of the plasma prepared catalyst is 370°C, 50°C lower than that obtained from the conventional catalyst.     

Disordered Crystal Structure of 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacozane perchlorate

Crystals of the ionic complex (salt) of 4,7,13,16,21,24hexaoxa 1,10diazabicyclo[8.8.8]hexacozane perchlorate, [H₂(Crypt2.2.2)]²⁺ · 2ClO₄ ^-, were synthesized and studied by Xray structural analysis: space group C2/c, a = 20.198(3), b = 10.119(2), c = 12.938(2), = 90.97(1)°, Z = 4, 3030 measured independent reflections, R = 0.067. In these crystals, all atoms of the 2.2.2 dication are disordered over two positions with occupancies of 0.518(4) and 0.482(4). Two conformations of the disordered 2.2.2 dication are such that two H atoms at two nodal N atoms point to its cavity.     

Reaction characteristics of cellulose in the LiCl/1,3‐dimethyl‐2‐imidazolidinone solvent system

In order to elucidate the nature of the LiCl/1,3dimethy2imidazolidinone (DMI) solvent system as one of the homogeneous reaction media of cellulose, cellulose acetate (CA) and Omethylcellulose (MC) were prepared using this solvent system, and the distribution of substituents within anhydroglucose units was examined by ¹³CNMR. It was found that (i) homogeneous cellulose solutions can be easily prepared by heating 2, 5–12 and 100 parts of weight of cellulose, LiCl, and DMI, respectively, and (ii) the relative reactivity of hydroxyl groups is in the order C6 > C2 > C3 for both CA and MC. A remarkable feature of this solvent system is that the reaction efficiency in etherification is very high compared with other homogeneous solvent systems.     

Crystal and Molecular Structure of 2‐nitro‐1‐ureidoguanidine

An Xray structural investigation of 2nitro1ureidoguanidine has been carried out. The crystals are monoclinic: a = 4.4690(2), b = 15.566(1), c = 9.4131(7), = 94.896(5)°, V = 652.4(3)> ³, space group P2₁/n, Z = 4, _calc = 1.650 g/cm³. The molecule consists of two planar fragments: carbamide and nitroguanidine. The geometrical characteristics of the molecule are analyzed. The system of intra and intermolecular hydrogen bonds in the crystal is considered.     

Effect of H2S-uptake on the conversion of cyclohexene on Ru- and Pd-promoted molybdena-alumina catalysts

The effect of H₂S on the activity and selectivity of catalysts (Ru/Al₂O₃, Pd/Al₂O₃ and Ru and Pd promoted molydena-alumina) was different (on differnt catalysts and different conversions of cyclohexene). Ru-containing catalysts showed higher sulfur sensitivities than the Pd-containing ones. The sequence of catalysts by their H₂S uptake related to mass of catalyst was PdMo/Al₂O₃RuMo/Al₂O₃Mo/Al₂O₃>Pd/Al₂O₃Ru/Al₂O₃.     

Crystal Structures of [Ni(Phen)(i‐Bu2PS2)2] and [Ni(Phen)3](i‐Bu2PS2)2 Complexes and Interaction between Coordinated 1,10‐Phenanthroline Molecules

Single crystals of [Ni(Phen)(iBu₂PS₂)₂] (I) and [Ni(Phen)₃](iBu₂PS₂)₂ (III) compounds were grown, and their structures were determined by Xray diffraction analysis (CAD4 diffractometer, MoK radiation, 3336 F _hkl , R = 0.0373 for I and 2575 F _hkl for III). The crystals of complex I have a triclinic unit cell with the following parameters: a = 11.097(1) , b = 14.903(2) , c = 22.650(3); = 75.18(1)°, = 80.50(1)°, = 75.07(1)°, V = 3479.2(7)³, Z = 4, _calc = 1.255 g/cm³, and space group 1; the crystals of III have a monoclinic unit cell with the following parameters: a = 19.010(3), b = 15.481(1) , c = 17.940(3); = 97.58(1)°, V = 5233.5(12)³, Z = 4, _calc = 1.292 g/cm³, and space group C2/c. The structure of complex I is built from mononuclear molecules, and the structure of III, from [Ni(Phen)₃]²⁺ complex cations and i Bu₂PS₂ ^- outersphere anions. The NiN₂S₄ coordination polyhedra in the structure of I and NiN₆ in the structure of III are distorted octahedra. Based on structural data, the interaction between the coordinated Phen molecules of complexes I, [Ni(Phen)₂(iBu₂PS₂)](iBu₂PS₂) (II), and III is considered, as well as the packing modes of these complexes.     

Crystal Structure of Ammonium(2.2.2‐cryptand) Thiocyanate Monohydrate

Crystals of the ammonium (2.2.2cryptand) thiocyanate monohydrate complex, [NH₄(2.2.2Crypt)]⁺ × SCN^- · H₂O, were studied by Xray structural analysis: space group P2/c, a = 11.303(2)*angst;, b = 8.313(1), c = 14.392(3), = 110.39(2)°, Z = 2, 3680 independent measured reflections, R = 0.064. This complex is of the guest–host type: the cryptand ligand cavity contains the NH₄ ⁺ cation with statistically disordered H atoms forming H bonds with each of its O and N heteroatoms. The SCN^- anions and H₂O molecules are linked by H bonds to form chains that are infinite along the z axis.     

Solution properties and mesophase formation of 4‐phenyl‐benzoylcellulose

Cellulose samples were derivatized in dimethylacetamide/LiCl (DMAc/LiCl) to give 4phenylbenzoylcelluloses (PBCs). The process is quantitative and leads to an highly substituted product, as verified by elemental analysis, IR and ¹³CNMR spectroscopy. PBC samples were characterized by viscometric and light scattering measurements in DMAc. The persistance length q is used to evaluate the theoretical critical volume fraction for mesophase formation (v _th, which has been found higher than the experimental critical one (v _exp)     

Crystal and Molecular Structure of Monoammonium Salt of 5‐nitroaminotetrazole

Xray structural investigation of the monoammonium salt of 5nitroaminotetrazole was performed. The crystals are orthorhombic: a = 10.077(1), b = 17.009(1), c = 6.6472(6), V = 1139.33(17)³, space group Pbca, Z =8, _calc = 1.715 g/cm³. Monodeprotonation of 5nitroaminotetrazole during formation of the salt occurs at the N(4) nitrogen atom of the heterocycle. The anion has an almost flat structure; the bond lengths suggest delocalization of electron density in the molecule. The negative charge is distributed among three nitrogen atoms and two oxygen atoms of the anion. Changes in the geometrical parameters of 5nitroaminotetrazole on monodeprotonation are considered.     

Types of Inorganic Fluorocarbon Polymer Materials and Structure–Property Correlation Problems

The paper reviews published data on the structure and composition of two large classes of inorganic polymer fluorocarbon materials (IP FCMs), including hightemperature (HT) and lowtemperature (LT) modifications of graphite fluorides and fluorographitelike compounds CF _x (x = 0.5 – 1.12$) and CF_1+y (y = 0.08 – 1.33$) and intercalated fluorographite compounds (IFGCs) based on C _x F (x < 2) matrices. According to Xray diffraction data, C1s and F1s Xray photoelectron spectroscopy (XPS), ¹³C and ¹⁹F NMR, CK and FK Xray spectroscopy, and IR and Raman spectroscopy, as well as MNDO calculations, the structure of monolayers and the properties of IP FCMs of C₂F – CF_1+y composition depend on the combination of C(sp ³) – F fragments bonded to the sp ² fragments of the starting carbon matrices. The structure of hightemperature CF_1+y is specified by the presence of structurally isolated external and internal C(sp ³)F₂ groups located on the boundaries of C(sp ³) – F skeleton monolayers and in the holes of their nanostructures, respectively. The enthalpy of formation of HT FCMs does not depend on the type of starting carbon material and is linearly proportional to the F/C atomic ratio; C(sp ³)F and C(sp ³)F₂ groups are chemically indistinguishable in HT FCMs. Six models for the structure of C₂F and C₄F monolayers in LT FCMs are considered. The best agreement with spectroscopy and MNDO data is obtained using modified Yudanov–Gornostaev's model for C₂F, in which alternating rows of graphitelike sp ² carbon fragments coexist with rows of bonded perfluorocyclohexane sp ³ cells. For lowtemperature C₂₄F–C₂F, electric conductivity and C1s and F1s XPS data are generalized and composition–property diagrams are constructed. In this case, the conductivity, C1s and F1s XPS, and the interplanar distances in monolayers are explained using the concept of planarity of C _x F monolayers and the ensuing ideas of semiionic and semicovalent C=F bonds. For C₄F · yA–C₂F · zA compositions, ¹³C and ¹⁹F NMR data, C1s and F1s XPS, and IR data are accounted for by the predominant sp ³ nature of the structureforming C=F bonds.     

Heterogeneous Asymmetric Reactions, 22. β-Isocinchona Alkaloids in Enantioselective Hydrogenations

The enantioselective hydrogenation of ethyl pyruvate to (S)-ethyl lactate over Pt/Al₂O₃ catalyst was investigated using the new modifier -isocinchonine (40% ee) which has oxazatwistane structure. These studies supply additional evidence for the widely accepted reaction mechanism.     

Effect of Oxygen Redistribution on the Normal and Superconducting Properties of Yttrium High‐Temperature Superconductors

An anomaly is found in the vicinity of T_max 560$ K on electric resistance versus temperature curves for yttrium hightemperature superconductors of the 123 phase. Xray phase analysis suggests a structural phase transition in the vicinity of T_max due to oxygen redistribution in the mobile sublattice of this compound. Investigation of samples with Y partially replaced by Ca has shown that the structural phase transition does not depend on carrier concentration in the conduction band.