Mixed amphoteric oxide ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> as catalyst for the conversion of 2-methyl-3-butyn-2-ol

The TPR spectra of the conversion of 2-methyl-3-butyn-2-ol (MBOH) on mixed ZrO₂-Al₂O₃ oxides with different ZrO₂ contents were obtained by desorption mass spectrometry. It was shown that MBOH is dehydrated to 3-methyl-3-buten-1-yne on the acid centers (H₀ ≥ –3.3) and is decomposed to acetylene and acetone at the basic centers (H_– ≤ +6.8) of this oxide. The formation of acid centers in the amorphous structure of ZrO₂-Al₂O₃ at 1.5 < Al/Zr < 3is explained by the Tanabe rule.     

Kinetic modeling for the conversion of synthesis gas to dimethyl ether on a mixed Cu-ZnO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst with γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

A model is proposed for the kinetics of the direct conversion of synthesis gas to dimethyl ether (DME) on a bifunctional catalyst in a flow reactor. Calculations for the yield of methanol and DME were carried out using literature data for the kinetics of methanol synthesis and methanol dehydration.     

Sol-coated preparation and characterization of macroporous α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> membrane support

A simple approach namely sol-coated technique has been developed for the low cost fabrication of macroporous ceramic under a far below common sintering temperature of alumina with large dimension grains. The prepared green support shows higher sinteractive than the one treated by wet impregnation method under the same sintering conditions. The support possesses great potential applications with 6.63–7.71 μm in pore size, 39% open porosity as well as >45 MPa mechanical strength at the sintering temperature range of 1350°– 1500°C. The results indicate that the nitrogen gas flux and pure water permeation value was 51 252.35 m³ m⁻² h⁻¹ bar⁻¹, 98.43 m³ m⁻² h⁻¹ bar⁻¹, respectively, which were more dependent on the pore structure and pore size distribution than open porosity.     

Promoted porous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for ammonia decomposition

Transition metal catalysts have been considerably used for NH₃ decomposition because of the potential application in CO_x-free H₂ generation for fuel cells. However, most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components. Here, we adopted an efficient method, aerosol-assisted self-assembly approach (AASA), to prepare the optimized cobalt-alumina (Co₃O₄-Al₂O₃) catalysts. The Co₃O₄-Al₂O₃ catalysts exhibited excellent catalytic performance in the NH3 decomposition reaction, which can reach 100% conversion at 600 °C and maintain stable for 72 h at a gaseous hourly space velocity (GHSV) of 18000 cm³ g_cat^?1 h^?1. The catalysts were characterized by various techniques including transmission electron microscope (TEM), scanning electron microscope (SEM), nitrogen sorption, temperature-programmed reduction by hydrogen (H₂-TPR), ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction (XRD) to obtain the information about the structure and property of the catalysts. H₂-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species, which influences the redox properties of the catalysts. It is found that even a low content of alumina (10 at%) is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components, which ensures the high activity and superior stability of the cobalt-alumina catalysts.     

ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> binary oxides as promising supports for palladium catalysts of hydrodechlorination

Deposited palladium catalysts of the hydrodechlorination of 1,3,5-trichlorobenzene were studied. Pure zirconium and aluminum oxides and ZrO₂-Al₂O₃ mixtures with 1, 5, and 10 mol % Al₂O₃ prepared by coprecipitation were used as supports. Palladium was deposited by the precipitation of its hydroxide on supports. Catalysts on binary supports (ZrO₂ + 1% Al₂O₃ and ZrO₂ + 5% Al₂O₃) exhibited higher activity and stability in hydrodechlorination compared with catalysts on pure supports. The suggestion was made that the high activity and stability of these systems in hydrodechlorination was related to the formation of binary oxide in the interaction of ZrO₂ with palladium oxide at the stage of annealing of the catalyst precursor. Binary oxide, which was a center of the activation of the C-Cl bond, was simultaneously a source of active hydrogen. The presence of various palladium states in catalysts was substantiated by the temperature programmed reduction method.     

Effect of chemical modification on oligomerization capacity of alumina support for Pd-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

Effect of modification with an alkali metal on the acid properties of alumina supports and on the oligomerization capacity and working stability of Pd-Al₂O₃ catalysts was studied.     

Synthesis of NiO/Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites as substrate for the construction of electrochemical biosensors

The exploration of substrate materials to construct electrochemical biosensors for glucose monitoring in the field of clinical diagnosis, especially for diabetes is still being investigated extensively. In this paper, NiO/Fe₂O₃ nanocomposites are designed and synthesized by two-step hydrothermal approach in combination with calcinations. The morphology and microstructure are studied by SEM, XRD, XPS, and TEM systematically. Optimized NiO/Fe₂O₃ nanocomposites are employed as substrate to construct glucose biosensors, and the electrochemical properties are carried out by cyclic voltammetric and chronoamperometric techniques. The results indicate as-prepared biosensors achieve a high sensitivity of 230.5 μA cm^?2 mM^?1, wide linear range between 50 and 2867 μM, and low detection limit of 3.9 μM towards glucose detection. The synergistic effect between NiO and Fe₂O₃ as substrate to construct glucose biosensors is elucidated. The selectivity is acceptable based on the detection of glucose concentration for diabetics.     

Hydrothermal synthesis of nanosized and amorphous alumina in the ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-H<Subscript>2</Subscript>O system

The reciprocal influence of components on the chemical and structural transformations in the ZrO₂-Al₂O₃-H₂O system during nanoparticle formation under hydrothermal conditions is considered. The possibility of formation of amorphous aluminum oxide under hydrothermal conditions is found as a result of the influence of zirconia nanoparticles on the crystallization.     

Sol–gel synthesis,characterization and photocatalytic activity of mesoporous TiO<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3 </Subscript>granules

Mesoporous TiO₂/γ-Al₂O₃ composite granules were prepared by combining sol–gel/oil-drop method, using various titania solution. The product granules can be used as a photocatalyst or adsorbent in moving, fluidized bed reactors. The phase composition and pore structure of the granules can be controlled by calcination temperature and using different titania solution. In the photocatalysis of NH₃ decomposition, TiO₂/γ-Al₂O₃ granules using Degussa P25 powder treated thermally at 450 °C showed the highest catalytic ability. However, TiO₂/γ-Al₂O₃ granules using titania made by hydrothermal method had comparable performance in NH₃ decomposition.     

Sorption of phosphate and arsenate ions from solutions by sorbents of the system TiO<Subscript>2</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-H<Subscript>2</Subscript>O

Hydrated nanosize oxides of the system TiO₂-Fe₂O₃-Al₂O₃-H₂O were tested as sorbents for recovery of phosphate and arsenate ions from aqueous solutions in a wide range of pH values. The optimal compositions of the sorbents were found, their ion-exchange functions were studied, and limiting sorption capacities were determined.     

Synthesis and study of solid acid materials SnO<Subscript>2</Subscript>/B<Subscript>2</Subscript>O<Subscript>3</Subscript>

SnO₂/B₂O₃ samples were produced by a reaction between SnCl₄, H₃BO₃, and (NH₂)₂CO in a boiling aqueous solution. The Sn: B molar ratio in these samples was 1: 1, 1: 2, and 1: 3. The phase composition and degree of crystallinity of these materials was studied. The surface acidity of the samples was analyzed by the method based on a temperature-programmed reaction of dehydration of 2-methyl-3-butyn-2-ol. Thermal transformations of SnO₂/B₂O₃ samples were examined by means of differential-thermal analysis.     

Solid solutions in the MgO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Coexisting solid solutions with spinel and corundum structure were synthesized at 1773 K and two pressures, 1 bar and 25 kbar. Samples were analyzed by electron microprobe analysis and X-ray powder diffraction. Pressure and temperature were shown to affect the properties of the solid solutions in different ways. Pressure governs the composition of the defect spinel Mg_1−xAl₂O₄, and temperature changes the cation distribution between coexisting phases. This allows one to separate the effects of cation exchange and magnetic contribution to the heat capacity in thermodynamic modeling. The defect spinel itself can form only because γ-Al₂O₃ exists, polymorph with spinel structure.     

Phase relations in the MgO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Phase relations in the MgO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction analysis and DTA. No ternary compounds have been found in the system. Quasi-binary sections have been the 600°C determined and isothermal section of the system has been constructed.     

Controlled synthesis,characterization and thermal properties of Mg<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>

Optimum conditions for synthesizing monoclinic and triclinic Mg₂B₂O₅ compounds by high-temperature solid-state reactions were investigated. Mixtures composed of boric acid and magnesium oxide at MgO:B₂O₃ mole ratios of 1:0.25, 1:0.5 and 1:1.5 were heated for 1 hour at temperatures between 600–1050°C and the formed phases were identified by XRD analysis. Monoclinic Mg₂B₂O₅ was formed by heating at 850°C for 4 hours together with minimum amounts of triclinic Mg₂B₂O₅, while triclinic Mg₂B₂O₅ was formed as a single phase at 1050°C for the same reaction time. The products obtained at optimum conditions were subjected to a series of tests to determine their chemical compositions, particle size distributions, surface area values, IR spectra and TG/DTA patterns.      

Glass formation in the CaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> and SrO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> systems

A physicochemical study of glasses based on the MO-Bi₂O₃-B₂O₃ and SrO-Bi₂O₃-B₂O₃ systems was performed. Glass formation regions were found. The structural and optical properties, as well as the thermal behavior of the glasses, were studied.     

Hydrothermal synthesis and thermodynamic properties of 2CaO·3B<Subscript>2</Subscript>O<Subscript>3</Subscript>·H<Subscript>2</Subscript>O

2CaO·3B₂O₃·H₂O which has non-linear optical (NLO) property was synthesized under hydrothermal condition and identified by XRD, FTIR and TG as well as by chemical analysis. The molar enthalpy of solution of 2CaO·3B₂O₃·H₂O in HCl·54.572H₂O was determined. From a combination of this result with measured enthalpies of solution of H₃BO₃ in HCl·54.501H₂O and of CaO in (HCl+H₃BO₃) solution, together with the standard molar enthalpies of formation of CaO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of −(5733.7±5.2) kJ mol⁻¹ of 2CaO·3B₂O₃·H₂O was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method.     

A comparative study of Ir/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>, Pt/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>, and Ru/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in selective hydrogenation of crotonaldehyde

Catalytic performance of gallia-supported iridium catalysts in the reaction of selective hydrogenation of crotonaldehyde in the gas phase was studied and compared to that of platinum and ruthenium catalysts. The best catalytic properties in terms of the selectivity to crotyl alcohol are shown by 5 wt % Pt/α-Ga₂O₃ and 5 wt % Ir/α-Ga₂O₃ catalysts prepared from nonchlorine precursors: Pt(acac)₂ and Ir(acac)₃, but for the 5 wt % Pt/α-Ga₂O₃ a very high selectivity of 75% at the high conversion (ca. 60%) is observed. A high selectivity of galia-supported iridium and platinum catalysts was explained by the surface reducibility of gallium oxide leading to covering (decoration) of platinum and iridium by gallium suboxides and the promoting effect of gallium.     

Phase relations in the CaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system in the subsolidus region

Phase relations in the CaO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction and differential thermal analyses, and the isothermal section at 600°C has been constructed. The formation of ternary compounds at the component ratios 1CaO: 1Bi₂O₃: 1B₂O₃ (CaBi₂B₂O₇) and 1CaO: 1Bi₂O₃: 2B₂O₃ (CaBi₂B₄O₁₀) has been established X-ray diffraction characteristics of these phases are presented.     

Investigation of catalyst Ni/K<Subscript>2</Subscript>O-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for vapor conversion of methane

An effect of raw material (aluminum oxide and hydroxide), of amount, and of technique of KOH feed (solid or solution) on a composition of potassium aluminates formed at calcination. Reactivity of the obtaining catalysts at the vapor conversion of methane was studied.     

Mass spectrometric investigation of vaporization in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The thermodynamics of vaporization in the Bi₂O₃-Fe₂O₃ quasibinary system was studied by high-temperature mass-spectrometry. The partial pressures of the constituents of a saturated vapor over the system at 1100 K were determined. Based on the experimental data, the following parameters were calculated: the activities of the components of the Bi₂O₃-Fe₂O₃ system condensed phase, the standard enthalpies of some heterogeneous reactions, and standard enthalpies of formation and enthalpies of formation for crystalline BiFeO₃ and Bi₂Fe₄O₉ from individual oxides. An optimal temperature for the solid-phase synthesis of bismuth ferrites from simple oxides is recommended.