Structural characterization of Fe/Ti oxide photocatalysts by X-ray,ESR, and Mössbauer methods

The polycrystalline solids TiO₂Fe₂O₃, with iron contents in the range 0–10 at.%, prepared by coprecipitation and by impregnation, and treated in air at temperatures in the range 500–1000°C, have been studied by X-ray, ESR, and Mössbauer methods. The TiO₂ in the samples treated at 800 and 1000°C always forms the rutile phase and the Fe³⁺ has a rather low solubility in it (～0.1 at.%). The Fe³⁺ in excess forms the antiferromagnetic pseudobrookite phase (Fe₂TiO₅). The samples treated at 500 and 650°C show a dependence on the preparation method. Those prepared by coprecipitation give at 500°C the pure anatase phase in which the Fe³⁺ has a higher solubility (≥ 1%); those prepared by impregnation give the anatase phase accompanied by a variable amount of rutile. The treatment at 650°C provokes the partial transformation of anatase to rutile and the complete development of the Fe₂TiO₅ phase. The relevance of these results to the photocatalytic properties shown by these solids for the photoreduction of dinitrogen to ammonia is discussed.     

Untersuchungen an Metallkatalysatoren. XXXII. Zur Legierungsbildung und Dispersität von Nickel-Rhenium-Katalysatoren

Investigations on Metal Catalysts. XXXII. On Alloying and Dispersion of Nickel-Rhenium Catalysts Unsupported Ni? Re catalysts were prepared by reduction of mixtures from NiO and NH₄ReO₄ at 400°C with hydrogen (1^st series), followed by a heat treatment at 650°C in flowing hydrogen (2^nd series). The bimetallic powders were characterized by DTA investigations, X-ray measurements, N₂ adsorption, and CO chemisorption. The degree of alloying and the changes in dispersion as a result of adding a second metal to a basic one is discussed.     

Some studies on thallium oxalates. I. Thermal decomposition of ammonium bisoxalatothallate(III)

Trivalent thallium is precipitated in the presence of 0.1 M HNO₃ (or 0.05 M H₂SO₄) and O.1 M NH₄NO₃ (or 0.05 M (NH₄)₂SO₄) with oxalic acid. The chemical analysis of the salt obtained correspondens to the formula, NH₄[Tl(C₂O₄)₂]·3H₂O. The thermal decomposition studies of the complex indicate the formation of the intermediates ammonium thallous oxalate (stable from 150° to 160°C) and thallous oxalate (stable up to 290°C) and the final product to be a mixture of 25% of thallous oxide and 75% of thallic oxide (stable from 450° to 650°C). The infrared absorption spectra, X-ray diffraction patterns, microscopic observations and the electrical resistance measurements are used to characterise the complex and the intermediates of its thermal decomposition.     

Untersuchungen an Metallkatalysatoren. XXXIII. Zur Charakterisierung von Nickel-Rhenium-Katalysatoren mittels der ferromagnetischen Resonanz

Investigations on Metal Catalysts. XXXIII. Characterization of Nickel-Rhenium Catalysts by Means of Ferromagnetic Resonance Unsupported nickel-rhenium catalysts (prepared by reduction of NiO? NH₄ReO₄ mixtures at 400°C with hydrogen) were characterized by the method of ferromagnetic resonance. With increasing rhenium content the values of signal intensity, g-factor, and half-width of the resonance line decrease. These facts are indications for the beginning in formation of solid solutions (alloys), which increases by further treatment of the samples at higher temperatures (650°C). The advanced alloying is also indicated by the sign reversal of the anisotropy constant.     

(NH4)3[M2NCl10] (M = Nb,Ta): Synthese,Kristallstruktur und Phasenumwandlung

(NH₄)₃[M₂NCl₁₀] (M = Nb, Ta): Synthesis, Crystal Structure, and Phase Transition The nitrido complexes (NH₄)₃[Nb₂NCl₁₀], and (NH₄)₃[Ta₂NCl₁₀] are obtained in form of moisture-sensitive, tetragonal crystals by the reaction of the corresponding pentachlorides with NH₄Cl at 400 °C in sealed glass ampoules. Both compounds crystallize isotypically in two modifications, a low temperature form with the space group P4/mnc and a high temperature form with space group I4/mmm. In case of (NH₄)₃[Ta₂NCl₁₀] a continuous phase transition occurs between –70 °C and +60 °C. For the niobium compound this phase transition is not yet fully completed at 90 °C. The structure of (NH₄)₃[Nb₂NCl₁₀] was determined at several temperatures between –65 °C und +90 °C to carefully follow the continuous phase transition. For (NH₄)₃[Ta₂NCl₁₀] the structure of the low temperature form was determined at –70 °C, and of the high temperature form at +60 °C. The closely related crystal structures of the two modifications contain NH₄⁺ cations and [M₂NCl₁₀]^3– anions. The anions with the symmetry D_4h are characterized by a symmetrical nitrido bridge M=N=M with distances Nb–N = 184.5(1) pm at –65 °C or 183.8(2) pm at 90 °C, and Ta–N = 184.86(5) pm at –70 °C or 184.57(5) pm at 60 °C.     

A Study of the Zn-based Desulfurization Sorbents for H2S Removal in the IGCC

The various Zn-based sorbents were prepared by physical mixing method and co-precipitation method. The sulfur removing capacity and regeneration properties of the various sorbents were measured in fixed bed reactor at middle temperature condition (sulfidation process 480 °C, regeneration process 580 °C). The sulfur removing capacities of the sorbents were depended on the physical properties such as pore volume, surface area and particle size. The Zn-based sorbents prepared by co-precipitation method were higher pore volume, surface area and smaller particle size resulting in the higher capacities than those prepared by the physical mixing method. To improve the regeneration properties of the sorbents, the various promoters such as cobalt, iron, nickel and cerium were added to the sorbents. The promoters have various roles with the kind of promoter. The roles of promoters could be explained by heat effect and catalytic effect of the promoters. Also, the alloyed structure like spinel structure (ZnTi₂O₄) has been proposed to explain the superior regeneration properties compared to the single ZnO structure. In addition, the simultaneous removals of the H₂S and NH₃ over the Zn–Al-based sorbents were tested at 650 °C. So, the new process for simultaneous removal using the developed Zn-based sorbents could be proposed. The role of promoters, effect of hydrogen potential pressure and the deactivation mechanism including the sulfidation of metal oxide to metal sulfide were also discussed.     

Preparation, structure, morphology, and dc and ac conductivity of the 88SiO2-6Li2O-6Nb2O5 (% mole) sol-gel derived glass-ceramics

The glass composition 88SiO₂-6Li₂O-6Nb₂O₅ (mole %) was successfully prepared by the sol-gel technique. The dried and translucent gel was heat-treated at temperatures between 500°C and 800°C. Lithium niobate crystallites, an important ferroelectric material, were detected in the gel derived glass-ceramics treated above 650°C. In the samples treated at 700 and 800°C the Li₂Si₂O₅ crystalline phase is present. The 800°C treated sample also presents the Li₃NbO₄ phase. The structure and morphology of the samples were studied by X-ray powder diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The SEM revealed that all the samples, heat-treated above 650°C, present crystallites embedded in the glass matrix. The particles detected in the 600°C treated sample are essentially amorphous, or with an incipient structure. The temperature dependence of the dc electrical conductivity (σ _dc ) shows two regions with different activation energies. The conductivity behaviour of the sample is mainly due to the mobile ion number. The ac conductivity (σ _ac ), measured at 1 kHz decreases with the rise of the treatment temperature due to the increase of the LiNbO₃ crystallites amount. The electrical behavior of the glass and glass-ceramics reflects the important role carried out by the treatment temperature in the gel-glass structure.     

Equilibrium,kinetic, and thermodynamic studies of lead ion adsorption from mine wastewater onto MoS2-clinoptilolite composite

This work explored the potential of clinoptilolite, molybdenum sulphide (MoS₂), and MoS₂-clinoptilolite composite in lead (Pb) removal from aqueous medium and industrial mining wastewater. MoS₂-clinoptilolite composite was successfully prepared by a hydrothermal method. The surface properties, structure, and composition of the synthesized composite and the parent compounds were analyzed by scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. The removal efficiency of lead from aqueous solution was studied in batch-mode experiments. The MoS₂-clinoptilolite was used for the removal of Pb ions (50 mg/L) from an aqueous solution: ~100% of the Pb was removed with a MoS₂-clinoptilolite dose of 0.075 g, pH 6 at 328K within 90 min. The adsorption capacities of Pb onto MoS₂-clinoptilolite were found to be higher than those onto clinoptilolite. Metal ion adsorption behavior was well explained by the Freundlich model, that is, multilayer adsorption of Pb molecules occurred on the heterogeneous surface of adsorbents in case of clinoptilolite, while in the case of MoS₂-clinoptilolite, the Langmuir model was suitable, that is, the adsorption occurred on a monolayer surface. The rate of Pb adsorption was explained by pseudo-second-order model suggesting that the adsorption process is presumably chemisorption. Thermodynamic parameters such as ΔH°, ΔS°, and ΔG° were calculated, which indicated that the adsorption was spontaneous and exothermic in nature. The selectivity of each adsorbent for Pb was also tested by adding the adsorbents to real gold mine water which contains competitive metal ions.     

Zeit- und temperaturaufgelöste Röntgenpulverdiffraktometrie: Die Reaktion von (NH4)2SnF6 mit Ammoniak

Time and Temperature Resolved in situ X-Ray Powder Diffractometry. The Reaction of (NH₄)₂SnF₆ with Ammonia The thermal decomposition of (NH₄)₂SnF₆ under an atmosphere of ammonia is reported. The complicated reaction paths were illucidated by time and temperature resolved in situ x-ray powder diffractometry. It is shown that this technique is a powerful tool to observe structural changes during reaction. It offers also a valuable access to thermodynamic and kinetic data for solid state and gas phase reactions. (NH₄)₂SnF₆ decomposes under ammonia below room temperature to NH₄F and amorphous SnF₄ · x NH₃. At a temperature of 80°C an intermediate product, (NH₄)₄SnF₈, is formed, which decomposes at 140°C into (NH₄)₂SnF₆ and NH₄F. At 250°C (NH₄)[Sn(NH₃)F₅] and Sn(NH₃)₂F₄ are formed. The latter crystallises C-centered monoclinic with lattice constants a = 844.1(5) pm, b = 630.5(3) pm, c = 520.2(3) pm and b? = 114.02(7)°. At 330°C a further decomposition yields SnF₂(NH₂)₂ with a C-centered monoclinic cell and lattice constants a = 1 069(7), b = 325.3(2), c = 504.8(3) pm and b? = 105.83(7)°. Finally above 500°C tin metal is formed.     

The thermal decomposition of (NH4)4V2O11 in a nitrogen atmosphere and the kinetics of the first decomposition step

Although the reaction products are unstable at the reaction temperatures, at a heating rate of 2 deg·min^?1 ammonium peroxo vanadate, (NH₄)₄V₂O₁₁, decomposes to (NH₄)[VO (O₂)₂ (NH₃)] (above 93°C); this in turn decomposes to (NH₄) [VO₃ (NH₃)] (above 106°C) and then to ammonium metavanadate (above 145°C). On further heating vanadium pentoxide is formed above 320°C. The first decomposition reaction occurs in a single step and the Avrami-Erofeev equation withn=2 fits the decomposition data best. An activation energy of 148.8 kJ·mol^?1 and a ln(A) value of 42.2 are calculated for this reaction by the isothermal analysis method. An average value of 144 kJ·mol^?1 is calculated for the first decomposition reaction using the dynamic heating data and the transformation-degree dependence of temperature at different heating rates.     

Catalytic reforming of methane by carbon dioxide over nickel-exchanged zeolite catalysts

A series of nickel-exchanged catalysts based on ZSM-5, USY, and Mordenite zeolites has been prepared by the ionic exchange method. The NiZeol catalysts have been characterized by XRD and BET. The exchange levels and nickel contents of the catalysts have been determined by chemical analysis. The acidity of the zeolite supports has been investigated using NH₃ adsorption microcalorimetry. The number of acidic sites was found to decrease according to the following sequence: HUSY > HZSM-5 > HMOR. The temperature programmed reduction studies showed that the most reducible catalyst is NiZSM-5. The Ni-exchanged zeolites presented good catalytic performance in the methane reforming by CO₂. At a temperature of 650°C, CH₄ conversions of 71 and 54% were achieved on NiUSY and NiZSM-5 respectively. At 400°C, CO₂ FTIR adsorption has shown that CO₂ decomposes into CO and oxygen on NiZSM-5 which explains its reactivity at such a low temperature, while no decomposition of this probe molecule was observed on the NiUSY catalyst. The catalytic performance was found to vary in the following sequence at 650°C: NiUSY > NiZSM-5 > NiMOR. Moreover, the catalytic performances were found to depend strongly on the CO₂/CH₄ ratio in the feed and were markedly improved for CO₂/CH₄ greater than 1.     

Amino-group excites vitality in nitrogen-rich energetic salts of triazolium

Incorporating amino groups is an efficient strategy for the tuning properties of energetic materials. However, there is no unanimous conclusion on the effect of the number of amino groups (−NH₂) on performance. Therefore, in this study, different number of −NH₂ of four energetic salts of triazolium based on oxadiazole and triazole were designed and synthesized. The structure features of energetic salts 4 – 6 were then investigated by single-crystal X-ray diffractions and Hirshfeld surfaces analyses. Afterward, the effects of −NH₂ were evaluated by thermal stability, impact sensitivity and detonation performance. All these energetic salts were insensitive to mechanical stimulation (IS >40 J), but the thermal decomposition temperatures of energetic salt 5 – 7 with −NH₂ are 24 °C to 54 °C higher than energetic salt 4 without −NH₂. Moreover, energetic salt 5 with one −NH₂ has the highest theoretical detonation properties compared to those without −NH₂ ( 4 ) and with two −NH₂ ( 6 , 7 ). These observations revealed that appropriate amount of −NH₂ can lead to desirable increase in the energetic properties, and this work can offer guidance for the design and synthesis of further energetic salts.     

Effect of synthesis parameters on the composition and properties of the product silica

The properties of two silica samples were studied; one sample precipitated by ammonia from a saturated (NH₄)₂SiF₆ solution and the other washed out from the sublimate obtained by joint evaporation of (NH₄)₂SiF₆ and SiO₂. These silicas are fundamentally different compounds. Their chemical composition was determined. Evolution of samples during heating to 1000°C was interpreted using chemical analysis, IR spectroscopy, and X-ray powder diffraction. A possibility of removing fluorine and ammonia from test samples by heat and chemical treatment is demonstrated. Fluorine impurities in the form of fluoroammonium salts are removed completely during heating to 300–400°C; surface fluoride ions are removed only upon heating to 800°C.     

Determination of the optimum conditions for the synthesis of praseodymium(III) chloride

In the present work, we have synthesized praseodymium(III) chloride, PrCl₃, from the praseodymium oxide, Pr₆O₁₁, by dry method in the presence of ammonium chloride, NH₄Cl. This study includes the establishment of an assembly synthesis under inert gas. The thermal decomposing process of pure NH₄Cl was investigated by TG–DTG. The results showed that NH₄Cl begins to lose weight at 188 °C, large loss of weight ending at 302 °C when NH₄Cl is heated at the rate of 10 °C/min under N₂ atmosphere. For chlorination, NH₄Cl participates directly in the reaction, and HCl decomposed from NH₄Cl also contributes to the chlorination reaction. The influence of various synthesis parameters (temperature, contact time and chemical composition) on the reaction yield was studied, and the optimum conditions for synthesis were, thus, determined and discussed.     

Electrochemical properties of single-phase LiFePO4 synthesized using LiF as Li precursor and hydrogen and carbon gel as reducing agents

LiFePO₄ samples have been synthesized by mixing stoichiometric amounts of (NH₄)₂HPO₄, FeC₂O₄·2H₂O, and LiF. During synthesis, carbon gel was used as the carbon source. Single-phase LiFePO₄ can be formed when the heating temperature ranges from 650 to 800 °C and it is decomposed into Li₄P₂O₇, Li₃PO₄, Fe₂P, and Li₃P₇ when the temperature comes to 850 °C. We find that the ratio of the lattice parameter (a/c) decreases with the increasing temperature, thereby increasing the Li⁺ diffusion channel length. Both the decrease of a/c and the abrupt crystal growth are expected to contribute to the monotonic decrease of the initial capacity of the samples. The sample heated at 650 °C with a smaller uniform particle size and relative higher specific surface area (8.2 m²/g) shows an excellent electrochemical performance. The initial specific capacity of 156.7(3) mAh/g is obtained at the rate of C/10.     

Synergetic Effects of In Situ Formed CaH2 and LiBH4 on Hydrogen Storage Properties of the Li–Mg–N–H System

Hydrogen storage properties and mechanisms of the Ca(BH₄)₂‐doped Mg(NH₂)₂–2 LiH system are systematically investigated. It is found that a metathesis reaction between Ca(BH₄)₂ and LiH readily occurs to yield CaH₂ and LiBH₄ during ball milling. The Mg(NH₂)₂–2 LiH–0.1 Ca(BH₄)₂ composite exhibits optimal hydrogen storage properties as it can reversibly store more than 4.5 wt % of H₂ with an onset temperature of about 90 °C for dehydrogenation and 60 °C for rehydrogenation. Isothermal measurements show that approximately 4.0 wt % of H₂ is rapidly desorbed from the Mg(NH₂)₂–2 LiH–0.1 Ca(BH₄)₂ composite within 100 minutes at 140 °C, and rehydrogenation can be completed within 140 minutes at 105 °C and 100 bar H₂. In comparison with the pristine sample, the apparent activation energy and the reaction enthalpy change for dehydrogenation of the Mg(NH₂)₂–2 LiH–0.1 Ca(BH₄)₂ composite are decreased by about 16.5 % and 28.1 %, respectively, and thus are responsible for the lower operating temperature and the faster dehydrogenation/hydrogenation kinetics. The fact that the hydrogen storage performances of the Ca(BH₄)₂‐doped sample are superior to the individually CaH₂‐ or LiBH₄‐doped samples suggests that the in situ formed CaH₂ and LiBH₄ provide a synergetic effect on improving the hydrogen storage properties of the Mg(NH₂)₂–2 LiH system.     

Photocatalytic degradation of metoprolol in water suspension of TiO<Subscript>2</Subscript> nanopowders prepared using sol–gel route

Nanocrystalline titanium dioxide (TiO₂) powders have been synthesized by sol–gel method using titanium tetrachloride (TiCl₄) or tetrabutyl titanate (Ti(OC₄H₉)₄ as precursors, different alcohols and calcination temperatures in the range from 400 to 650 °C. The photocatalytic activity of as-prepared powders has been tested for the degradation of metoprolol tartrate salt, a selective β-blocker used to treat a variety of cardiovascular diseases, and compared to photocatalytic activity obtained from Degussa P25. Nanosized TiO₂ powders prepared from TiCl₄ and amyl-alcohol, calcined at 550 °C, displayed an activity comparable to Degussa P25, whereas the sample from the same series, calcined at 650 °C, showed higher photocatalytic activity in the whole range of the catalyst loading. Structural, morphological and surface properties of synthesized TiO₂ nanopowders have been investigated by XRD, SEM, EDS and BET measurements, as well as FTIR and Raman spectroscopy, in order to find out the material properties which enable rapid an efficient decomposition of metoprolol under UV radiation.     

Study of crystallization process of soda lead silicate glasses by thermal and spectroscopic methods

The crystallization process of some glasses in the ternary Na₂O–SiO₂–PbO system with good chemical stability that can be used for waste inertization was studied using X-ray diffraction (XRD), infrared spectroscopy (FT-IR), differential thermal analysis (DTA) and scanning electron microscopy. The parent glasses were characterized by XRD and FT-IR, and their vitreous state was determined. DTA measurements evidenced glass transition (T _g) and crystallization temperatures (T _c). The thermal treatments were conducted at vitreous transition temperature (400 °C) and at highest effect of crystallization (650 °C). XRD evidenced the lead and sodium silicate crystalline phases in samples treated at 650 °C for 12 h. Micrometer crystallites dispersed in the glass matrices have affected the transparence of glasses and made them opaque after treatment at 650 °C. The influence of oxide quantities in compositions on the crystallization tendency was revealed. A PbO higher content than that of SiO₂ as well as lower Na₂O content decreased the tendency of crystallization.     

An aqueous solution-gel method for low temperature synthesis of nanocrystalline NaNbO<Subscript>3</Subscript> and their ceramics

Nano-sized NaNbO₃ powder has been successfully prepared by aqueous solution-gel method. The phase evolution of NaNbO₃ powder is investigated by TG/DSC, X-rays spectra, FT-IR, and Raman spectra. The results show that the pure NaNbO₃ phase has been obtained at about 375 °C, which is lowered by about 100 °C comparing to others’ work. In TEM studied, it shows the average particle size of ~ 70 nm for the powders heat-treated at 750 °C for 4 h. The powders heat-treated below 650 °C for 4 h shows a Pmnm symmetry, then change from O₃ orthorhombic to O₁ orthorhombic with the heat-treatment temperature above 650 °C.     

The X‐ray Crystal Structures of Hg(C6F4X‐p)2 (X = NH2, OMe,or Me) – Two Examples of Supramolecular Lewis Acid/Base Complexes

The X‐ray crystal structures of Hg(C₆F₄X‐p)₂ (X = NH₂, OMe, or Me) show the compounds to have almost linear C–Hg–C stereochemistry (X = NH₂, 176.3(4)°; X = OMe, 179.5(2)°; X = Me, 176.3(2)°), and the two tetrafluoroaryl rings rotated ca. 52–62° with respect to each other. Substantial conjugation of NH₂ and OMe groups with the aromatic rings is evident from N–C and O–C(Ar) distances. For X = NH₂ or OMe, two weak N(O)–Hg coordination interactions per mercury lead to a two dimensional supramolecular chain structure containing pairs of π‐stacked aromatic rings at near van der Waals contact distances rotated at 62.2° (X = NH₂) or 52.9° (X = OMe) to each other. In Hg(C₆F₄Me‐p)₂, which does not have potential donor atoms, no supramolecular structure is obtained, the molecules being laterally displaced from one another.