Observation of [Al(OH) n (H2O)6-n ] n (MoO4) in hydrotreating catalyst precursors by solid-state27 Al NMR

A previously unobserved octahedral²⁷Al MAS NMR resonance has been detected in rehydrated calcined Mo/Al₂O₃ hydrotreating catalyst precursors. This resonance is attributed to the presence of hydrated forms of aluminum molybdate such as [Al(OH) _n (H₂O)_6-n ] _n (MoO₄) (n = 1 or 2). The cross-polarization relaxation parameters, obtained from variable contact time experiments, yielded information on the relative sizes of the [Al(OH) _n (H₂O)_6-n ] _n (MoO₄) domains in the catalysts with different molybdenum loadings. Analysis of the²⁷A1 MAS NMR spectra of P-Mo(8)/Al₂O₃ and P-Mo(12)/Al₂O₃ (wt%P = 0.0–12.0) shows that a function of the phosphate in the 12 wt% Mo catalyst is to prevent the re-hydration of the molybdate phases on the calcined catalysts.     

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.     

Poly(di(ω-alkylphenyl)stannane)s

Poly(di(ω-alkylphenyl)stannane)s, [Sn(C _n H_2n Ph)₂] _m with n = 2–4, and a copolymer of di(3-propylphenyl)stannane and dibutylstannane of weight-average molar masses of 2–8 · 10⁴ g/mol were synthesized by dehydropolymerization of stannanes of the composition H₂SnR₂ using Wilkinson’s catalyst [RhCl(PPh₃)₃]. At least two methylene groups were required as spacers between the phenyl group and the tin atom for polymerization to occur. The polystannanes were characterized by, among other techniques, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy, thermal analysis and X-ray diffraction. The polymers featured properties different from those of the corresponding poly(dialkylstannane)s. Specifically, the [Sn(C _n H_2n Ph)₂] _m family displayed glass transitions at remarkably low temperatures, down to ca. −50 °C, and a lower value for a copolymer (−68 °C). Polymers [Sn(C_nH_2nPh)₂]_m with n = 2 and 3 and a copolymer at room temperature were of a gel-like concistence, which enabled facile orientation with shear forces. Finally, the temperature-dependent electrical conductivity was determined for poly(di(3-propylphenyl)stannane), which followed the law of typical semiconductors, with an activation energy for conduction of 0.12 eV.     

Anion-directed assembly of two novel cadmium(II) complexes constructed by 2,2′-(1,4-butanediyl)bis(1H-benzimidazole) ligand

Depending on the different coordinated anions used, reaction of Cd(II) salt with 2,2′-(1,4-butanediyl)bis(1H-benzimidazole) results in the formation of two coordination polymers: a 1D chain {[Cd(H₂C4BIm)Cl₂] · (H₂C4BIm)}_n (1), and a 2D sheet [Cd(HC4BIm)(NCS)]_n (2) which features distorted 4.8² topology (H₂C4BIm = 2,2′-(1,4-butanediyl)bis(1H-benzimidazole)). The fluorescence properties for both the complexes have been studied.     

Effect of Coordination Modes of HL Ligand on the Molecular Architecture of Its Transition Metal Complexes (HL = 5-Methyl-2-Phenyl-4-[(2-<Emphasis Type="Italic">o</Emphasis>-Tolylamino)-Phenylmethylene]pyrazol-3(2H)-one)

Abstract  Two Ag⁺ complexes [Ag(HL)₂(PF₆)] (1) and [(AgL) _n  · n(CH₂Cl₂) · n(0.5H₂O)] (2) (HL = 5-methyl-2-phenyl-4-[(2-o-tolylamino)-phenylmethylene]pyrazol-3(2H)-one) were synthesized and structurally characterized by EA analysis, IR spectra and X-ray crystallography. The result shows that two expected coordination modes (Modes I and III in Scheme 1) of the HL ligand, can be observed in its Ag⁺ complexes, while not in other transition metal ions (Ni²⁺, Co²⁺ or Cu²⁺) complexes whether deprotonation or not for the HL ligand. Graphical Abstract  Three possible coordination modes (Modes I, II or III in Scheme 1) of the selected HL (HL = 5-methyl-2-phenyl-4-[(2-o-tolylamino)-phenylmethylene]pyrazol-3(2H)-one) ligand, can be adopted, in which Modes I and III can be observed in its two Ag⁺ complexes [Ag(HL)₂(PF₆)](1) and [(AgL) _n  · n(CH₂Cl₂) · n(0.5H₂O)] (2), while Mode II just observed in its transition metal ions (Cu²⁺, Ni²⁺, or Co²⁺) complexes, resulting from the deprotonatd form of the HL ligand and the coordination characters of transition metal ions.      

Isomerization of α-pinene over dealuminated ferrierite-type zeolites

Isomerization of α-pinene was performed on a series of dealuminated ferrierite (FER)-type zeolites in liquid phase at 363 K using a batch reactor. The course of zeolite dealumination was followed in detail using ²⁹Si, ²⁷Al, ¹H MAS NMR, XRD, FTIR, and sorption of nitrogen. The ammonium form of FER was dealuminated with aqueous solutions of HCl. While retaining the crystallinity of the zeolite particles, the treatments removed up to 53% of the tetrahedrally coordinated aluminum atoms from the FER framework. According to ²⁹Si MAS NMR studies, the framework aluminum atoms located at the 10-membered rings in the main channels of FER (T_B sites) were depleted preferentially from their positions. Even relatively mild dealumination of FER led to an active catalyst containing both Brønsted and Lewis centers, yielding up to 97% conversion of α-pinene at 363 K, in contrast to the 72% observed for the parent hydrogen form. Such catalytic behavior was discussed in terms of the conversion of a reactant inside micropores of the zeolite catalyst, on Brønsted acid centers with enhanced strength located probably in the vicinity of Lewis sites. The selectivity toward camphene and limonene changed smoothly with the dealumination level; thus, a higher selectivity toward limonene was observed at the expense of camphene formation with increasing the n_Si/n_Al ratio of the catalysts. The selectivity toward camphene and limonene was close to 85% for all of the materials studied. The initial rates of α-pinene transformations over FER-type materials exceeded those observed for other catalytic systems, heteropoly acid/SiO₂ and H₂SO₄/ZrO₂. This study demonstrates the successful application of a medium-pore zeolite for the catalytic transformation of α-pinene in liquid phase.     

Electronic Switch in the Carbon-Centered [Re12CS17(CN)6] n− Nanocluster

An abrupt change in internuclear Re–Re distances between {Re₆} subunits in the carbon-centered [Re₁₂μ₆-CS₁₇(CN)₆] ⁿ⁻ complexes caused by the change of the oxidation state (n = 6, 8) is first theoretically shown to be possibly controlled by an external electric field. ¹³C NMR signal is shown to change over ~400 ppm (~37G) for μ₆-C atom together with n. Thereby, the metal cluster [Re₁₂μ₆-CS₁₇(CN)₆] ⁿ⁻ can be considered as a perspective model of a molecular switch.     

Competitive mechanisms ofn-butane isomerization on sulfated zirconia catalysts

Isotopic analysis ofn-butane isomerization over sulfated zirconium oxide, using double¹³C-labelledn-butane, shows that at low temperature this isomerization is an inter-molecular process. Probably, a C₈ surface intermediate is formed which isomerizes and undergoes -fission; the iso-C₄ fragments are desorbed asi-butane. Previously, the same mechanism was indicated for Fe, Mn promoted catalysts. The isomerization rate at 130°C is drastically lowered by gaseous H₂, because the concentration of the unsaturated species, required for the formation of the C₈ intermediate, is low under such conditions. Whereas₁₃C-scrambledi-butane is a true primary product, isotopic scrambling ofn-butane continues after chemical equilibrium betweenn-butane andi-butane has almost been reached; i.e.¹³C scrambledn-butane is a secondary product. Intra-molecular rearrangement of carbon atoms inn-butane precedes intermolecular scrambling. The similarity of the isomerization mechanism over unpromoted sulfated zirconia and Fe, Mn promoted sulfated zirconia is paralleled by an equal strength of the acid sites in both catalysts. The shift in the FTIR band of CO adsorbed on the Lewis sites indicates that these sites, presumably surface Zr⁴⁺ ions, are weaker acids than A1³⁺ in dehydrated alumina.     

SCR of NOx with NH3 over Cu/NaZSM-5 and Cu/HZSM-5 in the presence of decane

The selective catalytic reduction of NO_x with NH₃ in the presence of decane over Cu/ZSM-5 catalysts prepared from H⁺ and Na⁺ZSM-5 precursors were investigated. Cu/NaZSM-5 catalyst showed significantly higher NO_x conversion compared to Cu/HZSM-5. However, the presence of decane decreased the activity of both the catalysts, due to coke formation. Cu/HZSM-5 catalyst showed a larger decline in NO_x conversion with time on stream compared to Cu/NaZSM-5. The higher activity of Cu/NaZSM-5 is attributed, to the promoting effect of Na⁺ cations in the formation of active Cu⁺ and nitrite and nitrate intermediates species and retardation of coke formation.     

Preparation and characterization of titanium suboxides as conductive supports of IrO2 electrocatalysts for application in SPE electrolysers

A novel chemical route for the preparation of titanium suboxides (Ti_nO_2n−1) with Magneli phase was developed. The ceramic powders were prepared from TiCl₄ by complexation of Ti ions and successive decomposition of the complex to form an amorphous oxide. A high temperature reduction (1050 °C) of the amorphous oxide was carried out by using diluted hydrogen. IrO₂ electrocatalysts supported on Ti-suboxides were prepared by incipient wetness. The chemistry, morphology and structure of the materials were studied by TPR, XRF, XPS, BET, TEM and XRD. The electrochemical activity for oxygen evolution in a solid polymer electrolyte (SPE) electrolyser of IrO₂ catalysts supported on a commercial titanium suboxide (Ebonex^®) and Ti_nO_2n−1 prepared in-house was investigated by ac-impedance spectroscopy, linear sweep and cyclic voltammetry. The results showed proper electronic conductivity for both electrocatalysts and superior electrocatalytic activity of the catalyst based on the Ti-suboxides prepared in-house compared to the commercial support. In situ cyclic voltammetry and ac-impedance analyses showed larger voltammetric charge and double layer capacitance for the catalyst based on the Ti-suboxides prepared in-house with respect to the catalyst supported on Ebonex^®. These results were attributed to the better dispersion and larger occurrence of active catalytic sites on the surface of the suboxide prepared in-house based anode compared to the anode based on the commercial support.     

Photooxidation of Polycyclic Aromatic Hydrocarbons over NaBiO3 under Visible Light Irradiation

The NaBiO₃ samples (NaBiO₃ · nH₂O) used in photooxidation of polycyclic aromatic hydrocarbon were obtained through heating NaBiO₃ · 2H₂O. The samples were characterized by X-ray diffractometer and ultraviolet-visible spectrophotometer. The photooxidation of anthracene and Benz[a]anthracene over NaBiO₃ · nH₂O was investigated, respectively. The intermediates were analysed by gas chromatography-mass spectrometer. The results indicated that the prepared NaBiO₃ samples showed considerable photooxidation activity and stability for PAHs degradation under visible light irradiation. The possible reaction pathways of the decomposition of the two polycyclic aromatic hydrocarbons were proposed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Intermediates and isomers in the substitution of cobalt carbonyl hydride with tertiary phosphorous ligands

Mono- and disubstitution of HCo(CO)₄ with tertiary phosphines and phosphites was studied by IR and¹H-NMR spectroscopy. It was found that these substitutions proceed through phosphonium tetracarbonylcobaltate intermediates, leading to a mixture of isomers. The crystal and molecular structure of trans-HCo(CO)₃[P(O-p-C₆H₄Ph)₃] was determined by X-ray diffraction.GDR research fellow at the University of Veszprém.     

Effects of Water and Ion-Exchanged Counterion on the FTIR Spectra of ZSM-5. II. (Cu+–CO)-ZSM-5: Coordination of Cu+–CO Complex by H2O and Changes in Skeletal T–O–T Vibrations

The 2157 cm^–1 (strong) and 2108 cm^–1 (very weak) (CO) IR bands due to Cu⁺–CO in ZSM-5 zeolite with ¹²C and ¹³C isotopes, respectively, are reversibly red-shifted by subsequent adsorption of H₂O at 293 K. On the contrary, the locally perturbed internal (T–O–T) asymmetric stretching framework vibration [ _as ^int (TOT)(Cu⁺–CO)=965 cm^–1] is reversibly blue-shifted. The courses of the band shifts revealed notable features. Charge transfers from water to Cu⁺ ions, changes in coordination spheres of Cu⁺(CO)(H₂O) _n aqua complexes and secondary (solvent-like) effects were considered to explain the results.     

Optimization of Process Parameters for Controlled Ring-Opening Polymerization of Lactide to Produce Poly(L-Lactide) Diols as Precursor for Polyurethanes

Series of poly(L-Lactide) diols with molecular weights (M_n) in 2,069–4,811?g mol^?1 were synthesized from L-Lactide using stannous octoate catalyst and 1,4-butanediol chain extender. Operating conditions, i.e., temperature, catalyst concentration, chain extender concentration, and reaction time, were optimized. Maximum monomer conversion and M_n were observed at 0.5?mol% SnOct₂ and 1.0?mol% 1,4 butanediol (BDO) at 145°C. Poly(L-Lactide) diols were analyzed by Fourier transform infrared, proton nuclear magnetic resonance, end-group analysis, and X-ray diffraction techniques. Fourier transform infrared confirmed the formation of poly(L-Lactide) diols. Poly(L-Lactide) diols’ % degree of crystallinity was determined by X-ray diffraction. M_n was calculated by proton nuclear magnetic resonance and end-group analysis.     

Influence of template on Si distribution of SAPO-11 and their performance for n-paraffin isomerization

SAPO-11 molecular sieves were synthesized using single agent (i.e. diethylamine (DEA), di-iso-propylamine (DIPA) and di-n-propylamine (DPA)) or a mixture of DEA and DIPA (named DEPA) as the template under hydrothermal conditions. XRD indicated that the directing effect of different templates for AEL structure decreased in the order of DEPA > DPA > DIPA > DEA. ²⁹Si MAS NMR showed that although all SAPO-11 samples synthesized at same Si content, that prepared with the mixed template contained more Si (4Al) sites, whereas Si (nAl, 4-nSi, 0 < n < 4) environments were predominant in the samples synthesized with single template. The results indicated that the mixed template led to a better Si dispersion and then increased the number of total acid sites of SAPO-11. In the isomerization of n-tetradecane over different Pt/SAPO-11 catalysts, the sample prepared with DEPA showed high catalytic activity and selectivity for i-C₁₄, which were related to the most abundant weak acid sites of the sample.     

New catalyst of SO 4 2− /Al2O3–ZrO2 for n-butane isomerization

The catalytic behavior of Al-promoted sulfated zirconia for n-butane isomerization at low temperature in the absence of H₂ and at high temperature in the presence of H₂ was studied. The addition of Al enhances the activity and stability of the catalysts for reaction at 250°C and in the presence of H₂ significantly. After on stream for 120 h, the n-butane conversion of the catalyst containing 3 mol% Al₂O₃ keeps steadily at 88% of its equilibrium conversion and no observable trend of further deactivation has been observed. The difference in behavior of the promoted and unpromoted catalysts at low and high temperature is associated with a change of reaction mechanism from bimolecular to monomolecular. Experimental evidence is presented to show that the promoting effect of Al is different from that of the transition metals. Microcalorimetric measurements of NH₃ adsorption on catalysts reveal that the remarkable activity and stability of the Al-promoted catalysts are caused by an enhancement in the number of acid sites effective for the isomerization reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

A novel 3D Cd-coordination framework with helical units in a mixed flexible ligand system: Encapsulating right-handed helical water chains

In flexible co-ligand system, the P-handed [Cd(bpb)]_n and the M-handed [Cd(pda)]_n helical chains interweave mutually into a novel 3D coordination framework with diamondoid skeleton, namely, {[Cd(1,4-pda)(bpb)(H₂O)]·H₂O}_n (1) [bpb = 1,4-bi(4-pyridyl)butane , 1,4-H₂pda = 1,4-phenylenediacetic acid ]. Interestingly, 1D hydrophilic tunnel of 1 acts as a template for the formation of the P-handed 1D helical water chains, displaying molecular recognition and chirality transfer. The photoluminescent property and thermal stability of 1 were also discussed.     

An efficient method for a numerical description of virgin olive oil color with only two absorbance measurements

Four polynomial expressions are obtained that provide a good approximation and an easy, rapid calculation of the chromatic coordinates and the chroma—L ^*, a ^*, b ^*, and C—for the illuminant C and the standard observer, for a virgin or extra virgin olive oil; absorbance is measured at only 480 and 670 nm. These are as follows: L ^*=0.556458(A₄₈₀)²−2.51145A₄₈₀+0.55504(A₆₇₀)²−8.53016A₆₇₀+98.4089; a ^*=0.177372(A₄₈₀)²+2.1363A₄₈₀+1.43254(A₆₇₀)²−0.789231A₆₇₀−13.9246; b ^*=−16.0277(A₄₈₀)²+79.8932A₄₈₀−5.06558(A₆₇₀)²+3.36169A₆₇₀+31.9405; C=−15.8439(A₄₈₀)²+78.9312A₄₈₀−5.26784(A₆₇₀)²+3.56917A₆₇₀+33.3927. These give acceptable results, making the method a practical alternative to the extremely laborious Commission Internationale d’Eclairage (CIE) L ^* a ^* b ^* system, by which 391 absorbance values must be measured individually, nanometer by nanometer, before applying more complex equations. The validity of the proposed method has been confirmed by comparison, using a set of 20 sample oils different from the set of 25 oils used to generate the order of the equations. The variations between the values provided by the proposed and standard methods, respectively, had a mean of 0.00 for each of the chromatic variables—L ^* , a ^* , b ^* , and C; SD were moderate (0.71, 0.52, 1.22, and 1.22, respectively); the root mean square and the R ²-terms also confirmed the validity of the method.     

Structure and molecular weight of catenapoly [diphenoxy-λ5-phosphazene-co-bis(sulfophenoxy)-λ5-phosphazene] obtained from catenapoly (diphenoxy-λ5-phosphazene) in very strong acid medium

Acid polymers, –[N=P(OC₆H₅)_2–x (OC₆H₄SO₃H) _x ] _n (II), having an entirely inorganic chain of fifth-group elements, with acid equivalent values between 2.90 and 5.19 mEq/g and molecular weights (M _w) of 10⁵–10⁶ (205n3582), have been obtained from –[N=P(OC₆H₅)₂]– _n (I), 4325n 20,300, in very strong acid medium (SO₃/–P=N –=1.15–3.10 mol/mol). Sulfonation of the pendant substituents occurs first in the meta position and successively at the para carbons, presumably due to reduced conformational mobility as the degree of substitution (x) in II increases.     

Ship-in-Bottle synthesis of Pt9-Pt15 carbonyl clusters inside NaY and NaX zeolites,in-situ FTIR and EXAFS characterization and the catalytic behaviors in13CO exchange reaction and NO reduction by CO

[Pt₉(CO)₁₈]^2–/NaY (orange-brown, 2056 and 1798 cm^–1), [Pt₁₂(CO)₂₄]^2–/NaY (dark-green, 2080 and 1824 cm^–1 and [Pt₁₅(CO)₃₀]^2–/NaX (yellow-green, 2100 and 1865 cm^–1) were stoichiometrically synthesized by the reductive carbonylation of [Pt(NH₃)₄]²⁺/NaY, Pt²⁺/NaY and Pt²⁺/NaX, respectively. The IR bands characteristic of their linear carbonyls shift to higher frequencies whereas the bridging CO bands to lower frequencies, compared with those on the external zeolites and in solution. In-situ FTIR studies suggested that the subcarbonyl species such as PtO(CO) and Pt₃(CO)₃(₂ –CO)₃ are formed as the proposed intermediates towards [Pt₁₂(CO)₂₄]^2–/NaY in the reductive carbonylation of Pt²⁺/NaY.¹³CO exchange reaction preceded with the different intrazeolite Pt carbonyl species in the following order of activity at 298–343 K: Pt₃(CO)₃(₂ –CO)₃/NaY PtO(CO)/NaY>[Pt₉(CO)₁₈]^2–/NaY >[Pt₁₂(CO)₂₄]^2–/NaY. Pt-L₃-edge EXAFS measurment for these synthesized samples demonstrated that they are consistent with the Pt carbonyl clusters having trigonal prismatic Pt₉ and Pt₁₂ frameworks infered to a series of the Chini complexes such as [NEt₄]₂[Pt₃(CO)₆] _n ( _n = 3–5). The intrazeolite Pt₉ and Pt₁₂ carbonyl clusters exhibited higher cataytic activity in NO reduction by CO towards N₂ and N₂O at 473 K, compared with those on the conventional Pt/Al₂O₃ catalysts. The mechanism of intrazeolite Pt₉-Pt₁₅ carbonyl cluster formation are discussed in terms of the intrazeolite basicity and acidity.On leave from National Laboratory for Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 129 Street, China.