Direct catalytic decomposition of nitrous oxide gas over rhodium supported on lanthanum silicate

The environmental impacts of nitrous oxide (N₂O) have received much attention, including contributions to the greenhouse effect and ozone depletion. Currently, the direct catalytic decomposition of N₂O is considered to be the simplest and most promising method for N₂O abatement. In this study, we focused on the high activity of rhodium and the oxide-ion conducting property of lanthanum silicate and prepared novel Rh/La₁₀Si_6 − xFe_xO_27 − δ catalysts. From the results of catalytic N₂O decomposition activities, Rh/La₁₀Si_6 − xFe_xO_27 − δ (x = 1.0) exhibited the highest catalytic activity and N₂O was completely decomposed at 600 °C.     

Cyclodextrins as first and second sphere ligands for Rh(I) complexes of lower-rim PTA derivatives for use as catalysts in aqueous phase hydrogenation

The rhodium complex [Rh(cod)Cl(N-tBuBzPTA)]PF₆ (2) was obtained by reacting the appropriate Rh(I) precursor with the lower-rim PTA derivative [N-tBuBzPTA]PF₆ (tBuBz = 4-tert-butylbenzyl; PTA = 1,3,5-triaza-7-phosphaadamantane). The solubility and stability in water of 2 were increased in the presence of native-β-cyclodextrin (β-CD). The interaction of 2 with mono-amino β-cyclodextrin (β-CDNH₂, 2 equiv.) led to a supramolecular Rh assembly (3), identified by ³¹P, ¹H and 2D T-ROESY NMR experiments. The catalytic activity of 3 was evaluated in the water-phase hydrogenation of unsaturated and allylic alcohols and preliminary results are presented here.     

Reduction of N2O by NH3 on polycrystalline copper and Cu(1 1 0): A combined XPS,FT-IRRAS and kinetics investigation

Kinetics of N₂O decomposition and catalytic reduction of N₂O by NH₃ in the presence or absence of oxygen have been studied on polycrystalline Cu planar chip (3 cm × 3 cm × 0.1 cm) or Cu(1 1 0) single crystal, using catalytic test equipment, XPS and FT-IRRAS techniques. It has been shown that N₂O decomposes on metallic Cu, but gives then Cu₂O, which is detrimental to N₂O decomposition. The presence of a reductant, such as NH₃, allowed N₂O to react leading to its catalytic reduction to N₂; 500 °C is the best temperature for catalytic reduction alone, i.e. with low additional self-decomposition of N₂O or NH₃. The presence of oxygen, in amount less than that of NH₃, leads to more efficient NH₃ oxidation, oxygen being observed to be more reactive than N₂O on NH₃. XPS results enabled to identify the active surface as metallic Cu and Cu₃N for NH₃ oxidation and NH₂, NH, N adsorbed species as intermediates of the reaction. At room temperature, in the presence of N₂O, O₂ and NH₃, FT-IRRAS allowed to show the formation of NH₂ and NH species (bands at 1550 and 1440 cm⁻¹, respectively) and of two N₂^δ− species (bands at 2170 and 2204 cm⁻¹), the latter one corresponding to adsorbed N₂^δ− species close to adsorbed electron accepting O or OH species. This study demonstrated that N₂O decomposed to N₂ and O species during SCR reaction; it enabled to identify several adsorbed surface species (N, NH, NH₂, N₂^δ−), both by XPS after catalytic reaction at 500 °C on the polycrystalline Cu chip and by IRRAS on Cu(1 1 0) single crystal in the presence of the reactants at room temperature. In addition, it was shown that N₂ is a powerful IR probe to characterise the surrounding environment of surface sites that cannot be identified by any other way.     

Catalytic properties in N2O decomposition of mixed cobalt–iron spinels

The effect of introduction of iron in the Co_3 − xFe_xO₄ on catalytic activity in N₂O decomposition was investigated. The spinel catalysts were characterized by XRD, SEM, RS, BET methods, work function measurements and Mössbauer spectroscopy. Introduction of iron in the Co_3 − xFe_xO₄ spinel catalysts at the level of x < 1 leads to preferential substitution of Fe³⁺ in tetrahedral sites, whereas for x > 1 also octahedral ones are substituted. A strong correlation between deN₂O activity (T_50%) and work function was observed showing that electronic factor controls the catalytic reactivity of Co–Fe spinels. The results revealed that the active centers for N₂O decomposition are cobalt ions and thus even a low level of their substitution by iron leads to substantial decrease of the deN₂O activity of the cobalt spinel.     

Ionic liquid as an efficient promoting medium for synthesis of dimethyl carbonate by oxidative carbonylation of methanol

The synthesis of dimethyl carbonate by oxidative carbonylation of methanol using Cu salt catalysts in the presence of various room temperature ionic liquids (RTILs) was reported. Among the ionic liquids used, N-butylpyridinium tetrafluoroborate was the most effective promoter in terms of the conversion of methanol and the selectivity to dimethyl carbonate (DMC). The influences of reaction temperature, pressure, time, molar ratio of CO/O₂, and amount of the ionic liquid on the oxidative carbonylation of methanol were investigated. The results indicated that under the reaction conditions of 120 °C and 2.4 MPa of a 2:1 mixture of CO and O₂, 17.2% conversion of methanol, 97.8% selectivity of DMC and a DMC productivity of 4.6 g g⁻¹ cat h⁻¹ were achieved. The N-butylpyridinium tetrafluoroborate-meditated CuCl catalyst system could be reused at least five recycles with the same selectivity and a slight loss of catalytic activity due to loss of the catalyst during handling and transferring the reaction mixture.     

Two open-framework zinc phosphites constructed from different secondary building units

Presented here are two new zinc phosphites, formulate as Zn₃(dabco)₂(HPO₃)₃ (1, dabco = 1,4-diazabicyclo[2·2·2]octane), and H₂pmdeta ⋅ Zn₃(HPO₃)₄ (2, pmdeta = N,N,N′,N″,N″-pentamethyldiethylenetriamine). Compound 1 has 12-membered-ring (12 MR) channels with a 5-connected bnn topology containing 4 = 1 secondary building units. Compound 2 has multidirectional 10 MR channels with a pcu topology constructed from 6*1 secondary building units. The gas adsorption and fluorescent properties of compound 1 were also investigated.     

Preparation and characterization of CeO2–TiO2 support for Ru catalysts: Application in CWAO of p-hydroxybenzoic acid

The catalytic wet air oxidation of aqueous solutions of p-hydroxybenzoic acid has been carried out over CeO₂–TiO₂ supported ruthenium catalysts (Ru/Ce–Ti) at 140 °C and 50 bar of air. High activity of ruthenium supported catalysts was observed. It was found that the decrease of the molar ratio Ce/Ti from 3 to 1/3, improves the activity of Ru catalysts. The activity of the samples decreases in the following order: Ru/Ce–Ti (1/3) > Ru/CeO₂ ≈ Ru/TiO₂ > Ru/TiO₂DT51. Characterization of samples was performed by means of N₂ adsorption–desorption, XRD, UV–visible, TPR, SEM and TEM.     

Selective oxidation of ethylbenzene by a biomimetic combination: Hemin and N-hydroxyphthalimide (NHPI)

A biomimetic catalytic system consisting of hemin and N-hydroxyphthalimide (NHPI) for the selective oxidation of ethylbenzene with dioxygen is reported. 90.32% conversion of ethylbenzene with 94.30% selectivity for acetophenone (AcPO) can be obtained at 100 °C under 0.3 MPa O₂ for 9 h. Hemin can efficiently decompose in situ formed 1-phenylethyl hydroperoxide (PEHP) with AcPO as the main product.     

Highly enhanced ammonia decomposition in a bimodal catalytic membrane reactor for COx-free hydrogen production

Ammonia decomposition in a bimodal catalytic membrane reactor (BCMR) consisting of a Ru/γ-Al₂O₃/α-Al₂O₃ bimodal catalytic support and a hydrogen-selective silica membrane in a single unit was proposed for CO_x-free hydrogen production in the present study. The bimodal catalytic membrane showed a H₂ permeance of 6.2 × 10^-7 mol/(m² s Pa) at 500 °C, with H₂/NH₃ and H₂/N₂ permeance ratios of 200 and 720, respectively. Ammonia conversion was surprisingly enhanced form 45 to 95% at 450 °C in the BCMR after selective H₂ extraction. The BCMR showed excellent stability with respect to both gas permeation properties and catalytic activities.     

Visible-light-induced photocatalytic activity of TiO2−xNy prepared by solvothermal process in urea–alcohol system

Nitrogen-doped anatase, rutile and brookite titania photocatalyst TiO_2−xN_y which can be excited by visible light were prepared by mixing aqueous TiCl₃ solutions with urea ((NH₂)₂CO) and various type of alcohols followed by solvothermal treatment at 190 °C. The phase composition, crystallinity, microstructure and specific surface area of titania powders greatly changed depending on the pH and type of solvents. Violet, yellowish and grayish TiO_2−xN_y with excellent visible light absorption and photocatalytic activity were prepared. The TiO_2−xN_y powders prepared in urea–methanol solution showed excellent photocatalytic ability for the oxidative destruction of nitrogen monoxide under irradiation of visible light λ > 510 nm.     

Palladium-catalyzed Mizoroki–Heck coupling reactions using sterically bulky phosphite ligand

A new catalytic system based on palladium-phosphite for Mizoroki–Heck coupling reactions of aryl iodide and bromide is described. An air-stable phosphite ligand afforded the desired products with high yields in the palladium-catalyzed Mizoroki–Heck reactions. The coupling of aryl iodides was optimized with 0.5 mol% Pd(OAc)₂, 1 mol% phosphite 2, and K₂CO₃ in DMF solvent. For the coupling of aryl bromides, 1 mol% Pd(OAc)₂ and 5 mol% phosphite 2 were required with Na₂CO₃ as base. As a coupling partner alkene, n-butyl acrylate, t-butyl acrylate, styrene and N-t-butyl acrylamide all showed good yields.     

Synthesis and electrocatalytic function for hydrogen generation of cobalt and nickel complexes supported by phenylenediamine ligand

To study the effect of different metal centers on catalytic function, two complexes [L-M] (M = Co, 1; Ni, 2) were prepared by the reactions of N,N′-bis(2-amino-3,5-di-tert-butylphenyl)-o-phenylenediamine, H₂L, with Co(ClO₄)₂·6H₂O or Ni(ClO₄)₂·6H₂O, respectively. Electrochemical investigations show 1 and 2 can electrocatalyze hydrogen generation both from acetic acid and aqueous buffer. Complexes 1 and 2 afford a turnover frequency (TOF) of 738.23 and 1331.23 mol of hydrogen per mole of catalyst per hour (mol h^− 1) at an overpotential (OP) of 0.838 V from a neutral buffer, respectively, indicating that the nickel center constitutes the better active catalyst.     

Highly active SO2-resistant ex-framework FeMFI catalysts for direct N2O decomposition

Ex-framework FeMFI catalysts, prepared by isomorphous substitution of iron in the aluminosilicate or gallosilicate MFI-type framework and activation by calcination at 823 K and steaming (300 mbar H₂O in N₂) at 873 K, show high activity and stability in N₂O decomposition in the presence of O₂, CO₂, H₂O, and SO₂. The N₂O conversion of the ex-framework catalysts in simulated tail-gas mixtures was >80% at 800 K and 75,000 h⁻¹. The specific activity per mole of Fe (turnover frequency, TOF) of the ex-framework catalysts in N₂O–He is four to nine times higher than observed for catalysts prepared by conventional solid and liquid-ion exchange, and sublimation methods. The stability of ex-framework catalysts for the direct N₂O decomposition, in the absence of any reductant, is remarkable, showing no significant deactivation (at N₂O conversion levels ranging from 20 to 65%) after 600 h on stream. Sublimed and especially ion-exchanged FeZSM-5 catalysts show a strong irreversible deactivation in feed mixtures containing H₂O and SO₂. The effect of SO₂ on the catalytic performance of FeMFI catalysts is discussed, as well as the applicability of the ex-framework FeMFI catalysts in fluid-bed combustion facilities.     

Effects of K/Na ratio on the phase structure and electrical properties of 0.98(KxNa1−x)NbO3–0.02BiScO3 lead-free ceramics

Lead-free piezoelectric ceramics 0.98(K_xNa_1?x)NbO₃–0.02BiScO₃ (0.98 K_xN_1?xN–0.02BS) (x = 0.30–0.60) doped with 0.8 mol% Mn were prepared by conventional solid-state sintering. The effects of K/Na ratio on the phase structure and electrical properties of the Mn doped 0.98 K_xN_1?xN–0.02BS (0.98 K_xN_1?xN–0.02BS–Mn) were mainly studied. It is experimentally demonstrated that the electrical properties strongly depend on K/Na ratio in the 0.98 K_xN_1?xN–0.02BS–Mn ceramics and when x = 0.45 the ceramics exhibit optimum electrical properties: d₃₃ ～ 308 pC/N, k_p ～ 0.495, ?_r ～ 1577, tan δ ～ 0.028. These results show that the 0.98 K_xN_1?xN–0.02BS–Mn ceramic with x = 0.45 is a promising lead-free piezoelectric material.     

Solvothermal in situ synthesis of (Schiff-base)-containing dinuclear cobalt compound

A new dinuclear cobalt compound, namely Co₂(L)(H₂O)Cl₂ (1, H₂L = N,N′-o-phenylenebis(salicylide-neimine) was obtained by one-pot solvothermal self-assembly of CoCl₂, 1,2-phenylenediamine, and salicylaldehyde in C₂H₅OH. The magnetic studies suggest weak antiferromagnetic behavior and the magnetic data were interpreted by means of a dinuclear cobalt model with the parameters of g = 2.12, J = ?1.25 cm^?1, θ = ?3.12 K.     

Rod-like eutectic structure of arc-melted TiB2–TiCxN1−x composite

TiB₂–TiC_xN_1−x composites were synthesized by arc-melting mixtures of TiB₂, TiC and TiN powders in a N₂ atmosphere at 60 kPa. TiB₂–TiC_xN_1−x composites were obtained at TiN contents below 20 mol%, whereas TiB formed in the composites at higher TiN contents. TiB₂–TiC_xN_1−x composites with a nominal composition of 36TiB₂–44TiC–20TiN (mol%) had a rod-like eutectic structure, where the TiC_xN_1−x single-crystal rods dispersed in the TiB₂ single-crystal matrix. The crystal orientation relationship between the TiB₂ matrix and the TiC_xN_1−x rods was TiB₂ (0 0 0 1)//TiC_xN_1−x (1 1 1). Vickers hardness (H_v) of the rod-like eutectic composite was 22.5 GPa.     

Synthesis,reactivity, and X-ray structural characterization of a vanadium(III) oxidation pre-catalyst, (CpPOEtCo)VCl2(DMF)

Vanadium complexes are extensively used in the chemical industry as oxidation catalysts. During the course of our investigations into vanadium oxidation catalysis, the rich reactivity of a vanadium(III) scorpionate analogue complex, (CpP^OEtCo)VCl₂(DMF) (1), was investigated. The octahedrally coordinated 1 was prepared by mixing vanadium(III) chloride with Na(CpP^OEtCo) in DMF. The crystal structure of 1 has been determined through X-ray diffraction. Complex 1, C₂₀H₄₂Cl₂CoNO₁₀P₃V, crystallizes in the monoclinic space group P2₁/c with a = 38.566(9) Å, b = 9.499(2) Å, c = 18.149(4) Å, and β = 100.485(4)° with Z = 8. Complex 1 was found to be an effective pre-catalyst for the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone. The reactivity studies, oxidative catalytic ability, as well as X-ray structural characterization of (CpP^OEtCo)VCl₂(DMF) will be discussed. ((CpP^OEtCo) = [η⁵-cyclopentadienyltris(diethylphosphito-κ¹P) cobaltate(III)⁻; DMF = N,N-dimethylformamide).     

Organic–inorganic hybrid oxides: Structure and magnetic properties of [{Cu(terpy)}2Mo6O17(H2O)(O3PCH2NH2CH2PO3)2] · H2O,a bimetallic oxide constructed from novel {Mo6O17(H2O)(O3PCH2NH2CH2PO3)2}4− clusters

The hydrothermal reaction of MoO₃, CuSO₄ · 5H₂O, 2,2′:6′:2″-terpyridine (terpy) and bis-N,N-(methylphosphonic acid) amine (H₂O₃PCH₂NHCH₂PO₃H₂) provided blue crystals of the bimetallic oxide [{Cu(terpy)}₂Mo₆O₁₇(H₂O)(O₃PCH₂NH₂CH₂PO₃)₂] · H₂O (1 · H₂O). The three-dimensional structure of 1 is constructed from {Mo₆O₁₇(H₂O)(O₃PCH₂NH₂CH₂PO₃)₂}⁴⁻ clusters linked through {Cu(terpy)}²⁺ subunits. The cluster consists of three pairs of edge-sharing {MoO₆} octahedra linked through corner-sharing interactions into a {Mo₆O₆} ring. One phosphonate ligand spans the diameter of the ring, bridging four molybdenum sites and leaving at a pendant {PO} group at each terminus. The second diphosphonate ligand exploits one {–PO₃} unit to cap the hexamolybdate ring and bridge all six molybdenum sites while the second {–PO₃} terminus bridges two molybdenum sites, leaving a pendant {PO} unit. Crystal data: C₃₄H₄₅Cu₂Mo₆N₈O₃₅P₄: monoclinic, P2₁/n, a = 11.9431(7) Å, b = 17.382(1) Å, c = 27.524(2) Å, β = 90.429(1)°, V = 5713.7(6) Å³, Z = 4, D_calc = 2.270 g cm⁻³, R₁ = 0.0466.     

Catalytic nitridation preparation of high-performance Si3N4(w)-SiC composite using Fe2O3 nano-particle catalyst: Experimental and DFT studies

The complete conversion from Si into Si₃N₄ was achieved after 2 h nitridation at 1400 °C by using in-situ formed Fe₂O₃ nano-particles (NPs) as a catalyst. Such a synthesis condition was remarkably milder than that (>1450 °C for many hours) required by the conventional Si nitridation method. Density functional theory (DFT) calculations suggest that Fe₂O₃ catalyst accelerates the Si nitridation via weakening the bond strength of absorbed N₂ molecule. Furthermore, Si₃N_4(w)-SiC composites prepared by the present catalytic nitridation method showed excellent high-temperature properties including modulus of rupture (MOR of 29.9 MPa at 1400 °C), thermal shock resistance (residual MOR percentage of 50% at ΔT = 1300 °C), as well as good oxidation resistance and cryolite corrosion resistance against molten cryolite. It can be concluded that, Fe₂O₃ NPs not only greatly accelerated the Si nitridation and Si₃N₄ formation, but also facilitated the epitaxial growth of reinforcement phase of Si₃N₄ whisker in the Si₃N_4(w)-SiC composites.     

Synthesis,luminescence, and structural characterization of Zn and Cd coordination polymers of flexible bis(imidazolyl) derivatives

Coordination polymers [Zn(imc)(L¹)] · H₂O, (1, imc = iminodiacetate, L¹ = bis(N-imidazolyl)methane) [Zn(hba)₂(L²)]₂ · EtOH · 3H₂O, (2, hba = p-hydroxybenzoate, L² = bis(N-benzimidazolyl)methane), [Cd(mal)(H₂O)(L³)](3, L³ = 1,4-bis(N-imidazolyl)butane, mal = maleate) have been prepared and structurally characterized. Complex 1 consists of hexa-coordinated central Zn ions and exhibits 2D network structure. The Zn atoms in 2 have tetrahedral coordination geometry, and are linked by bis(imidazolyl) ligands into 1D chain structure. The cadmium ions in 3 are hepta-coordinated with pentagonal bipyramidal geometry. Complex 3 displays 2D grid structure. The TGA showed that the coordination polymers are stable up to 200 °C. All the three complexes are emissive at room temperature in their solid state.