Osmium ligand deficient clusters as catalysts for liquid phase hydrocarbon transformations

Reduction of OsO₄ by molecular hydrogen in alkane (cycloalkane) or benzene media at 20–150 °C yields small osmium clusters of the Os₁C_0.34-0.48H_0-0.6 composition with a specific surface area of 34–46 m²/g. The systems obtained are shown to be ligand deficient osmium clusters (LDC) of 7–16 Å in diameter, stabilized by a small amount of carbonaceous ligands with Os-Os = 2.68-1.70 Å and Os-C = 2.11-2.19 Å. The characteristics of these chemically prepared Os-LDC are similar to those of Ni- and Co-LDC, prepared by a vapour phase synthesis. The novel Os-LDC effectively catalyze hydrogenolysis of alkanes and cycloalkanes at 100–150 ° C and initial H₂ pressure of 5 MPa, hydrogenation of cyclopentadiene and arenes at 20 ° C, multiple H/D exchange between CH₄ and D₂ at 100–120 ° C and methanation of CO₂ at 150–180 ° C.     

A 13C and 15N Solid State NMR Study of the Reactions of Acetone Oxime Adsorbed on FeZSM-5

The reactions of acetone oxime, a proposed reaction intermediate for the SCR (Selective Catalytic Reduction) of NO with propane on FeZSM-5, have been studied with ¹³C and ¹⁵N solid state MAS NMR (magic angle spinning nuclear magnetic resonance). FeZSM-5 with three different loading levels was prepared by the sublimation method. The thermal reactions of acetone [2-¹³C] oxime adsorbed on FeZSM-5 samples with different iron loadings were monitored by ¹³C MAS NMR by heating to the desired temperature and then cooling to room temperature for data acquisition. For the sample with the lowest iron loading (Fe/Al = 0.11), acetic acid and N-methyl-2-propanamine were formed by the decomposition of acetone oxime. For the samples with the higher iron loadings (Fe/Al = 0.69 and 0.91), acetone, N,N-methyl-2,2-propanediamine, and N-methyl-2-propanimine were formed by the decomposition of acetone oxime. ¹⁵N MAS NMR was used to investigate reactions of ¹⁵NO and acetone oxime on the FeZSM-5 samples. The formation of gas phase N₂ and N₂O was observed.     

Solvent Extraction of Li+ using Organophosphorus Ligands in the Presence of Ammonia

In this work, the selective extraction of Li⁺ with the aid of organophosphorus ligands (H-OP) including phenylphosphonic (H-PHO), phenylphosphinic (H-PHI) and bis(2-ethylhexyl) phosphoric (H-BIS) acids in the absence and presence of ammonia was studied. Adding NH₃ to the aqueous phase resulted in significant improvement in the % extraction of Li⁺ into the organic phase containing H-OP ligands. The highest % extraction values obtained in the case of H-PHO, H-PHI, and H-BIS were 43.2%, 45.7%, and 90.0%, respectively. Two mechanisms were inferred; the first was that the extraction equilibrium reaction of LiCl + H-OP ? Li-OP + HCl shifted forward due the reaction of the produced HCl with NH₃. The second mechanism was that the Li⁺/NH₄⁺ exchange of NH₄-OP (produced from the reaction of H-OP with NH₃) was easier than Li⁺/H⁺ exchange of H-OP itself. Competitive extraction experiments indicated that the selectivity factors of Li⁺ over Na⁺ and K⁺ were strongly dependent on the concentration of H-OP ligands which suggested that aggregation of ligand molecules via hydrogen bonding is the limiting factor for selectivity.     

A study of active sites for alkene and alkane oxidation over Mo and V mixed oxide catalysts using 18O tracer and Raman spectroscopy

The oxygen ions of MoO₃, V₂O₅, -VOPO₄, -Mg₂V₂O₇, -CoMoO₄and -Bi₂Mo₃O₁₂were exchanged with ¹⁸O via a reduction–oxidation method and the catalytic oxidation of alkene or alkane using ¹⁸O₂. The Raman bands of the catalysts shifted to lower frequencies by the exchange with ¹⁸O tracer. With MoO₃, V₂O₅, -VOPO₄and -Mg₂V₂O₇, the weak oxygen bonds were active to exchange, i.e., to be active for the oxygen insertion and oxidation reactions, but the strong bonds were less active. The results of exchange features on -Bi₂Mo₃O₁₂catalyst indicate that some sets of two lattice oxygen ions in a twin tetrahedra seem to be good for fitting and bonding with allyl intermediates.     

Multinuclear magnetic resonance study of equilibria between aluminum(III) and sulfur-containing amino acids in aqueous solutions

Aluminum(III) is generally found in small amounts in living organisms where it interacts with several biomolecules. Low mass biomolecules can form complexes associated with absorption and distribution processes of this toxic ion. However, investigating aluminum(III) complexes in solution poses singular difficulties, because it is highly hydrolyzable. Amino acids constitute possible ligands for aluminum(III). Methionine, cysteine and homocysteine are found in healthy human body. Penicillamine is a drug used in several circumstances, such as in treating metal poisoning. These four biomolecules share similar donor atoms involved in complexation reactions: a carboxylate oxygen, an amine nitrogen and sulfur. In this study, four binary complexes formed by aluminum(III) and amino acids in solution at a metal-to-ligand ratio of 1:1 were analyzed through potentiometry and multinuclear magnetic resonance (¹³C and ²⁷Al). Potentiometry data consistently demonstrated complexion formation. Distributions of species revealed the coexistence of several species in ample pH ranges and pointed out the preferable value to perform the NMR analyses. ¹³C NMR data were used to confirm complexion formation, while ²⁷Al NMR data indicated the geometric arrangement adopted by the complexes. Structures were proposed for each complex.     

NMR study of the role of isopropylsulfates in the two-step “conjunct oligomerization” of propylene and isopentane–propylene alkylation catalyzed by 95% sulfuric acid

“Conjunct oligomerization” of propylene or the isopentane–propylene alkylation catalyzed by an excess of 95% sulfuric acid was performed in two consecutive steps. First di-isopropylsulfate was prepared by interaction of sulfuric acid with propylene. The ester was then either decomposed at room temperature in the presence of the 5–10 molar excess of 95% acid or was used in the acid-catalyzed alkylation of isopentane. In situ ¹H and ¹³C NMR study of the reaction mixture of “conjunct oligomerization” indicated that the diester participates in two equilibria with sulfuric acid. The first one transforms the diester into a monoester. The second equilibrium corresponds to protonation of the monoester with an excess of sulfuric acid. This converts a minor fraction of the mono-alkylsulfate into isopropyl carbenium ions that are only weakly solvated with sulfuric acid: C₃H₇HSO₄ + H₂SO₄ ⇄ C₃H₇ ⁺ H₂SO₄ + HSO₄ ⁻. The subsequent reactions of alkyl carbenium ions with the non-protonated alkylsulfate result in final products of “conjunct oligomerization” while in the presence in the reaction mixture of isopentane, alkylation with the predominant formation of C₈ branched paraffins takes place. A very low yield of propane indicates a minor role of hydride transfer in alkylation. Another unexpected result is the absence in both reaction mixtures of propylene. These findings are in contradiction with the classical mechanism of isoparaffin–olefin alkylation by Schmerling. Therefore, an alternative mechanism of this reaction is suggested via a direct alkylation of isopentane with the mono-alkylsulfate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solvent-Free Selective Oxidation of Benzyl Alcohol and Benzaldehyde by tert-Butyl Hydroperoxide Using MnO- 4-Exchanged Mg–Al–Hydrotalcite Catalysts

MnO^- ₄ (0.4 mmol/g)-exchanged Mg-Al-hydrotalcite is an active and highly selective catalyst for the oxidation of benzyl alcohol to benzaldehyde by tert-butyl hydroperoxide under reflux in the absence of solvent. It also shows high activity for the oxidation of benzaldehyde to benzoic acid. The higher the Mg/Al ratio, the higher is the catalytic activity (in both the reactions) and basicity of the hydrotalcite catalyst.     

Fischer-Tropsch synthesis. Evidence for two chain growth mechanisms

The results show that n-pentanol serves to initiate Fischer-Tropsch synthesis reactions. Product accumulation in the CSTR is not adequate to explain the deviation from a constant¹⁴C activity/mole with increasing carbon number for alkane products. A second Fischer-Tropsch synthesis mechanism that produces only alkanes is needed to explain the deviation of the C activity/mole with increasing carbon number for n-alkanes. Furthermore, the two chain growth pathways must be completely independent without the possibility of a carbon number species that is common to both mechanisms. It is suggested that the pathway that incorporates added¹⁴C labeled alcohol has an oxygen containing surface intermediate while the other reaction pathway involves an oxygen-free reaction intermediate.     

NO – oxygen scavenger or reaction intermediate in the decomposition of N2O?

Nitric oxide and nitrogen dioxide were found during the thermal desorption of surface species left on Fe-ferrierites after the decomposition of nitrous oxide. This demonstrates the formation of surface NOx species during N₂O decomposition. Repeated decomposition and subsequent desorption of surface species confirm the active role of surface NOx species. Addition of NO up to a fraction of 0.1 times the amount of N₂O increased the decomposition of nitrous oxide as well as the amount of surface NOx species. The use of nitrous oxide labeled with ¹⁸O demonstrated that the zeolite oxygens participate in the reaction and that the presence of NO enhances this participation.     

ESR of Gd3+: a surrogate for the study of lanthanide dispersion in zeolitic and amorphous catalysts

Gd³⁺-ESR spectroscopy can be used as a sensitive method for the study of lanthanide additives in catalysts. Here we present the results of a comparative study of Gd/SiO₂-Al₂O₃ and Gd/HZSM-5. ESR gives evidence of rigid bonding of isolated Gd³⁺ ions into both amorphous silica-alumina and into HZSM-5. In addition, the zeolitic matrix stabilizes very small Gd³⁺-clusters (containing only a few ions) capable of interacting with water molecules. Excess Gd is present as non-dispersed, particulate oxide. Strong bonding of PO₃^3- anionic ligands irreversibly changes the local environment and reactivity towards H₂O of the Gd³⁺-clusters in HZSM-5. The Gd³⁺ ions do not block the cationic positions of HZSM-5 from further interaction with paramagnetic Cu²⁺ or Rh²⁺ cations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Change in the structure of poly(tetramethylene succinate) under tensile stress monitored with solid state C NMR

A new solid-state NMR experimental equipment was developed to monitor the structural change of polymer and protein fibers under active uniaxial deformation. The equipment was applied to monitoring change in the structure of a biodegradable aliphatic polyester fiber, poly(tetramethylene succinate) (PTMS; [-O(CH₂)₄OCO-(CH₂)₂CO-]_n), as a function of tensile stress. The crystal transition from α to β forms for PTMS was induced by stress and monitored by the change of the methylene region in the ¹³C NMR spectra. The ¹³C chemical shielding constant for the model compound of poly(tetramethylene succinate) was calculated using the GIAO-CHF (gauge invariant atomic orbitals-coupled Hartree-Fock) with ab initio 6-311G^∗∗ basis set. This calculation acceptably explains the experimental results.     

NMR study of the gamma radiolysis of poly(dimethyl siloxane) under vacuum at 303 K

The structural changes which occur on the γ-radiolysis of poly(dimethyl siloxane) (PDMS) under vacuum at 303 K have been investigated using ²⁹Si and ¹³C NMR. New structural units consistent with main chain scission and crosslinking through both H-linking and Y-linking reactions have been identified. The results obtained at various absorbed doses have been used to calculate the G-values for scission and crosslinking. G-values for scission of G(S)=1.3±0.2, for H-linking of G(D^CH₂-R)=0.34±0.02 and for Y-linking of G(Y)=1.70±0.09 were obtained for radiolysis under vacuum at 303 K. Thus crosslinking predominates over scission for radiolysis of PDMS under these conditions, and, by contrast with previous studies, Y-links have been shown to be the predominant form of crosslinks.     

Olefin as an Intermediate in n-Butane Isomerization on Sulfated Zirconia. An In Situ 13C MAS NMR Study of n-Octene-1 Conversion

By using in situ ¹³C MAS NMR and ex situ GC-MS, the analysis of hydrocarbon products formed from n-octene-1 adsorbed on sulfated zirconia catalyst (SZ) has been performed. It is shown that a mixture of alkanes and stable alkyl substituted cyclopentenyl cations (CPC) is formed as the basic reaction products. Formation of both alkanes and CPC from n-octene-1, a precursor of C₈ ⁺ cation, the key intermediate in n-butane isomerization via a bimolecular pathway, implies that formation of the isomerized alkane occurs by a complex process of conjunct polymerization, rather than isomerization itself. CPC deposited on the SZ surface can be in charge of the catalyst deactivation.     

Influence of precursor Bi/Fe ion concentration on hydrothermal synthesis of BiFeO3 crystallites

In this study we investigated the effect of precursor Bi³⁺/Fe³⁺ ion concentration on the hydrothermal synthesis of BiFeO₃ crystallites. It is demonstrated that the phase-purity and morphology of the products is highly dependent on the metal ion concentration. Phase-pure BiFeO₃ crystals can be prepared at the Bi³⁺/Fe³⁺ ion concentration ranging from 0.025 to 0.0625 M. The samples prepared at n(Bi³⁺/Fe³⁺)=0.025, 0.0375, 0.05, and 0.0625 M, are composed, respectively, of cuboid-like particles (100–200 nm), regular spherical agglomerates (30–40 μm) made up of irregular grains with size about several hundred nanometers, irregular flower-like clusters formed from irregular grains of several hundred nanometers in size, and octahedron-shaped particles (500–600 nm). These samples have a similar bandgap energy of 2.20 eV and exhibit a typical antiferromagnetic behavior at room temperature.     

Preparation, characterization and electrocatalytic properties of poly(luminol) and polyoxometalate hybrid film modified electrodes

Hybrid films composed of poly(luminol) and nanometer-sized clusters of polyoxometalate, SiMo₁₂O₄₀⁴⁻ and PMo₁₂O₄₀³⁻ have been prepared in acidic aqueous solutions. These films are stable and electrochemically active, and produced on glassy carbon, platinum, gold and transparent semiconductor tin oxide electrodes. The electrochemical quartz crystal microbalance and cyclic voltammetry were used to study in situ growth of the hybrid poly(luminol)/SiMo₁₂O₄₀⁴⁻ and poly(luminol)/PMo₁₂O₄₀³⁻. Both the poly(luminol)/SiMo₁₂O₄₀⁴⁻ and poly(luminol)/PMo₁₂O₄₀³⁻ hybrid films showed four redox couples and the electrochemical properties were compared to SiMo₁₂O₄₀⁴⁻ and PMo₁₂O₄₀³⁻. When transferred to various acidity aqueous solutions, the four redox couples and the formal potentials of two hybride film were observed to be pH-dependent. The electrocatalytic reduction of ClO₃⁻, BrO₃⁻, IO₃⁻, S₂O₈²⁻ and NO₂⁻ by a poly(luminol)/PMo₁₂O₄₀³⁻ hybrid film in an acidic aqueous solution showed an electrocatalytic reduction activity of IO₃⁻ > BrO₃⁻ and ClO₃⁻. The electrocatalytic oxidation of dopamine and epinephrine by a poly(luminol)/PMo₁₂O₄₀³⁻ hybrid film was also investigated.     

Study on the photocatalytic degradation of trichlorfon in suspension of titanium dioxide

In this paper, the photocatalytic degradation of trichlorfon, an organophosphorous pesticide, was studied by using TiO₂ as a photocatalyst. The effects of various parameters, such as the amount of the photocatalyst, illumination time, reaction temperature, electron acceptors, metal ions, anions, and initial pH value on the photocatalytic degradation of trichlorfon were investigated. The best conditions for the photocatalytic degradation of trichlorfon were obtained. The results show that the optimum amount of the photocatalyst used is 8.0 g L^− 1. The photodegradation efficiency of trichlorfon increases with the increase of the illumination time or reaction temperature. The photodegradation efficiency of trichlorfon is increased rapidly by adding a small amount of H₂O₂, K₂S₂O₈, KBrO₃, Fe³⁺ and Cu²⁺, however, with the addition of Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Co²⁺ and Ni²⁺, or with the addition of trace amount of SO₄²⁻, Cl⁻, Br⁻, there are no obvious effects on the photocatalytic degradation reactions. Alkaline mediums are favorable for the photocatalytic degradation of trichlorfon. The possible roles of the additives on the reactions and the possible mechanisms of effect were also discussed.     

Extraction of Uranium and Thorium from Nitric Acid Solution by TODGA in Ionic Liquids

Extraction of uranium (UO₂²⁺) and thorium (Th⁴⁺) from a nitric acid solution into an imidazolium-type ionic liquids (ILs) of 1-alkyl-3-methylimidazolium hexafluorophosphate ([C_nmim][PF₆], n = 6 or 8) was carried out using N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TODGA) as an extractant. It was found that the extraction efficiencies of UO₂²⁺ and Th⁴⁺ ions are higher in comparison with that done in n-dodecane. The extraction mechanism was deduced by the slope analysis and extraction experiment. Transfer of both ions is assumed to proceed predominantly through the neutral solvation mechanism from nitric acid solution into ILs. The UO₂²⁺ ion forms a 1:2 complex with TODGA in ILs at lower acidity, and a 1:1 complex in ILs and in n-dodecane at higher acidity. The Th⁴⁺ ion forms a 1:2 complex with TODGA in C₆mimPF₆ IL or a 1:1 complex in C₈mimPF₆ IL at lower acidity and a 1:1 complex in both ILs, and n-dodecane at higher acidity. Stripping studies were conducted using sodium salt of EDTA as a stripping ligand. The thermodynamics of extracting UO₂²⁺ ions and Th⁴⁺ ions from a 3 M HNO₃ solution was also studied. The results indicated that the extraction reactions are spontaneous and go through an exothermic process.     

Semiquantitative analysis of thiophenic compounds in light cycle oil (LCO) using C NMR spectroscopy

S-methyltetrafluoroborate salts of the thiophenic compounds (CH₃-S⁺:BF₄⁻) present in LCO petroleum fractions were obtained and analyzed by ¹H and ¹³C NMR spectroscopy. The methylation of the samples was carried out using 99.5% ¹³C enriched methyl iodine, to improve the sensitivity of the technique. The amount of the methylated derivatives was determined by the internal standard method; using dioxane as a reference, 37 sulphur compounds were detected. Among them, benzo[b]thiophene, dibenzo[b,d]thiophene, and several isomers of methyl, dimethyl and trimethyl[b]benzothiophenes were the most abundant. With this research, it was demonstrated that NMR spectroscopy can be used to analyze thiophenic compounds from petroleum medium fractions.     

Reactivity of disulfide peptide l-cystine with iodido (diethylenetriamine)platinum(II) and synthesis of products in the presence of an iodide ion

Substitution reactions of complex [PtI(dien)]⁺ (where, dien=diethylenetriamine ) with sulfur-containing peptide l-cystine has been studied in 1.0×10^?1 M aqueous perchlorate or acetate medium between 298≤T (K)≤323 and 2.30≤pH≤4.45 using a UV–visible spectrophotometer. Products obtained have characterized from their physico-chemical and spectroscopic methods at various pH and temperatures. From this characterization, products have indicated that [PtI(dien)]⁺ has formed a complex with l-cystine and acts as a bidentate ligand, through Pt–S bond at 2.30≤pH≤3.30 and through Pt–N and Pt–S bond of cystine in 3.95≤pH≤4.45. At 2.30≤pH≤3.30, ring opening and closing of dien have occurred at 308 and 323 K, respectively, and the same has happened at pH≥3.95. All reactions have followed the rate law – d[mixture]/dt=(k ₁+k ₂ [cystine]) [Pt(II)], where k ₂ denotes the second-order rate constant. Activation parameters E _a , Δ H ^# and Δ S ^# have been determined. Product formation and reversible and forward reaction rate constants have also been evaluated.