Structural analysis and characterization of doped spinel Co2−xMxTiO4 (M=Mg2+, Mn2+, Ni2+, Cu2+ and Zn2+) coated mica composite pigments

A new kind of composite mica pigments were prepared by coating Co_2−xM_xTiO₄ composite oxide nanoparticles onto mica, to investigate the effects of doping ions Mg²⁺, Mn²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ on the properties of the doped composite pearlescent pigments, such as the crystal structure, color and shading power. The structure, morphology, color and shading power of the coated pigments were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectrophotometer and CIE L*a*b* methods. SEM images of coated pigments showed that mica were coated uniformly with a single layer of dispersed nanoparticles. Research of the doped composite pigments showed that the doping ions had entered into the spinel crystal structure, forming a new kind of composite mica pearlescent pigments coated with Co_2−xM_xTiO₄. For the analysis of color and shading power of the pigments, doping of Ni²⁺ and Zn²⁺ can improve the color and shading power of the doped pigments, but the larger dosage of Zn²⁺ doping can weaken the color and shading power of the doped pigments. Doping of Mg²⁺, Mn²⁺ and Cu²⁺ metal ions can also weaken the color and shading power of the doped pigments.     

Catalytic Ozonation of m-Dinitrobenzene

The efficiency of catalytic ozonation with homogeneous (containing dissolved ions of Fe²⁺, Mn²⁺, Cu²⁺, Ni²⁺, Co²⁺, V⁵⁺, Cr³⁺, Mo⁶⁺) and heterogeneous (MnO₂, Ni₂O_3, Fe₂O₃, CuO, Al₂O₃, CoO, V₂O₅, Cr₂O₃, MoO₃, TiO₂) catalysts and non-accompanied ozonation was compared for degradation of m-dinitrobenzene (m-DNB). Several transition metals in homogeneous and heterogeneous form improved significantly the ozone performance for degradation of m-DNB. This improvement was found to be due to supplementary formation of reactive species (hydroxyl radicals) and better ozone utilization. The effects observed were found to be strongly dependent on the treatment conditions.     

Effect of the calcination temperature on the cation distribution and optical properties of Mg0.5Co0.5CrAlO4 spinel pigment

In this study, a blue-green pigment has been prepared by partially replace Co²⁺ and Cr³⁺ in CoCr₂O₄ spinel structure with Mg²⁺ and Al³⁺ using a gel casting method The gel precursor was calcined at various temperatures (900–1400 °C) to obtain Mg_0.5Co_0.5CrAlO₄ spinel pigment. Combining the Rietveld refinement method of XRD and peak fitting of XPS high-resolution spectra, the relationships between the cation distributions (Co²⁺, Mg²⁺, Al³⁺, and Cr³⁺) in the tetrahedron and octahedron of the spinel structure and the calcination temperature were examined. In the octahedron, the contents of Co²⁺ and Al³⁺ decreased with increasing calcination temperature, and the Mg²⁺ and Cr³⁺ contents exhibited the opposite trend. The bond lengths of A-O and B–O change with increasing calcination temperature, thereby leading to a change in the unit cell. The optical performance of the pigments was investigated via UV–vis and CIE L*a*b* spectrophotometry, and the study shows that the blue-green hue of the pigment powder is caused by the absorption at υ3～υ8 (370 nm–640 nm) in the visible light region. The varied contents of Co²⁺ and Cr³⁺ in the spinel structure among calcination temperatures cause the absorption spectrum intensity change, thereby resulting in various blue-green tones. This study lays the foundations for subsequent investigations of colour modification in Mg_xCo_1-xAl_yCr_2-yO₄ spinel.     

Michael reaction of β-ketoesters with vinyl ketones by iron(III)-exchanged fluorotetrasilicic mica: catalytic and spectroscopic studies

Michael reaction of β-ketoesters with vinylketones at room temperature under solvent-free condition is investigated with various Fe³⁺ catalysts, including FeCl₃ ⋅ 6H₂O supported on various supports (Fe–mica, Fe–mont, Fe–SiO₂, Fe–Al₂O₃, Fe–NaY) and homogeneous catalysts, FeCl₃ ⋅ 6H₂O and Fe(NO₃)₃ ⋅ 9H₂O. Fe³⁺-exchanged fluorotetrasilicic mica (Fe–mica) shows highest activity. Fe–mica exhibits almost quantitative yields of Michael adducts, high turnover numbers (TON = 1000), and a low level of Fe leaching. After simple work-up procedures, Fe–mica can be recycled without a loss in activity. The relationship between catalytic activity and the catalyst structure determined by XRD, UV–vis, and Fe K-edge XANES/EXAFS is discussed in terms of the effect of clay support on the structure and reactivity of Fe³⁺ species. The Fe³⁺ cation, highly dispersed in the interlayer of clay (mica or mont) or on SiO₂, is more active than the cluster-like Fe³⁺ oxide or hydroxide species in Fe–NaY and Fe–Al₂O₃. UV–vis and XAFS results for the catalysts treated with reactants suggest that, during the reaction, the FeCl₂(O)₄ octahedral species in FeCl₃ ⋅ 6H₂O or those on Fe–SiO₂ are converted to the β-diketonato complexes with two β-diketonato ligands, whereas in Fe–mica β-diketonato complexes with one β-diketonato ligand are formed. The formation of β-diketonato complexes results in a slight lowering of the Fe oxidation number from 3+, probably as a result of the electron donation from the β-diketonato ligand to Fe³⁺ as a Lewis acid site. The lower numbers of β-diketonato ligand coordinated with Fe³⁺ in Fe–mica should result in a larger coordination strength for β-diketonato ligand than that in Fe–SiO₂, which was confirmed by acetylacetone-TPD. Thus, the central carbon atom of the β-diketonato ligand in Fe–mica is more reactive toward nucleophilic attack by the coordinated enone, leading to higher activity for the Michael reaction.     

Production of Ceramic Pigments Based on Natural Wollastonite Using the Gel Method

The authors consider the possibility of producing ceramic pigments based on natural wollastonite using the gel method, which contributes to the formation of an amorphous structure in wollastonite under the effect of hydrochloric acid. The chromophores are soluble salts containing Fe³⁺, Ni²⁺, Cr³⁺, Cu²⁺, and Co²⁺ ions. The wollastonite structure is restored under firing; the color characteristics of pigments after the gel-formation stage improve. The use of the gel method does not require a cardinal modification of the technological scheme and equipment but facilitates a significant improvement of the color properties of pigments and paints.__________Translated from Steklo i Keramika, No. 1, pp. 25 – 27, January, 2005.     

Utilization of DTA in determination of crystallization mechanism in SiO2–Al2O3–CaO–MgO(R2O) glasses in presence of various nuclei

The effect of various nuclei on crystallization mechanism of SiO₂–Al₂O₃–CaO–MgO(R₂O) glasses were investigated by differential thermal analysis (DTA) through Matusita, Marotta and modified Kissinger methods. The Avrami constant, n, and the activation energy for crystallization of the most promising specimens containing Cr₂O₃, Fe₂O₃ and TiO₂ in the single, double and triple nuclei series were determined. According to the results the Avrami constants derived from the Marotta method were more consistent with the other experimental observation. While glasses containing TiO₂ as the single nucleant represents surface crystallization and those containing Cr₂O₃ or Fe₂O₃ one-dimensional bulk crystallization, the crystallization mechanism of specimens containing both Cr₂O₃ and Fe₂O₃ and also the glasses containing the triple nuclei, are bulk and two dimensional.     

Synthesis and color properties of the TiO2@CoAl2O4 blue pigments with low cobalt content applied in ceramic glaze

The TiO₂@CoAl₂O₄ complex blue pigments with low cobalt content were synthesized through calcinations of the precursor obtained from coprecipitating Co²⁺ and Al³⁺ to form Co‐Al LDHs (layered double hydroxides) on the surface of TiO₂ particles. The structure and the properties of the synthesized pigments were characterized by XRD, SEM, TEM, UV‐Vis spectroscopy, XPS, and colorimeter. The precursors of the blue TiO₂@CoAl₂O₄ complex pigments were consisted of LDHs shell layer encapsulated TiO₂ microsphere. After calcinations at 1100°C, the LDHs shell layer were absolutely transformed to the spinel CoAl₂O₄, and the pigments presented a core‐shell structure and uniform sphere morphology (the diameter of microsphere was about 780 nm). The absorption bands at around 547, 584, and 624 nm in the Uv‐Vis absorption spectra of the TiO₂@CoAl₂O₄ complex pigments were corresponded to the characteristic absorption bands of the spinel CoAl₂O₄, revealed the pigments with a bright blue hue. In addition, as the mass ratio of CoAl₂O₄/TiO₂ increased to 0.4, the blue component of the pigments reached to 27.89 and slight color variation with the increase in the CoAl₂O₄ content in a range, possessed low cobalt content and exhibited a stabile performance in commercial low‐temperature ceramic glazes. The XGT results showed that the TiO₂@CoAl₂O₄ complex pigments with low cobalt content presented bright color in ceramic glaze. Especially, the synthesized pigments reduced the usage and toxicity of cobalt, which were efficiency for economy and environmental protection.     

Oxidative dehydrogenation of ethane by carbon dioxide over sulfate‐modified Cr2O3/SiO2 catalysts

The oxidative dehydrogenation of ethane into ethylene by carbon dioxide over unsupported Cr₂O₃, Cr₂O₃/SiO₂ and a series of Cr₂O₃/SiO₂ catalysts modified by sulfate was investigated. The results show that Cr₂O₃/SiO₂ is an effective catalyst for dehydrogenation of ethane and CO₂ in the feed promotes the catalytic activity. Sulfation of silica will influence the catalytic behavior of Cr₂O₃/SiO₂ in dehydrogenation of ethane with carbon dioxide depending on the amount of sulfate. Cr₂O₃/6 wt% SO ₄ ^2- –SiO₂ catalysts exhibit an excellent performance for this reaction, giving an ethylene yield of 55% at 67% ethane conversion at 650°C. Characterizations indicate that addition of sulfate changes the bulk and surface properties of Cr₂O₃/SiO₂, promoting the reduction of Cr⁶⁺ to Cr³⁺ and favoring the catalytic conversion. This revised version was published online in July 2006 with corrections to the Cover Date.     

Decomposition of Carboxylic Acids in Water by O3, O3/H2O2, and O3/Catalyst

This paper studies the decomposition of formic, oxalic and maleic acids by O₃, O₃/catalyst, and O₃/H₂O₂. The catalytic effect of Co²⁺, Ni²⁺, Cu²⁺, Mn²⁺, Zn²⁺, Cr³⁺, and Fe²⁺ ions is investigated. The results showed that—Co²⁺ and Mn²⁺ have the highest catalytic activity for the decomposition of oxalic acid while the catalytic effect of the studied ions is insignificant on the rate of decomposition of formic acid. Maleic acid decomposes by ozone into formic acid and glyoxylic acid, which subsequently oxidizes to oxalic acid. Though the studied ions have no effect on the decomposition of maleic acid, they have a significant effect on the produced oxalic and glyoxylic acids. In the presence of Cu²⁺ ions glyoxylic acid is mainly transformed into formic acid and traces of oxalic acid. In such case, a complete decomposition of maleic acid and its degradation products is achieved within 45 min. The results also show that combining H₂O₂ with O₃ results in an increase in the rate of decomposition of oxalic acid. However, O₃/H₂O₂ system is less active than O₃/Co²⁺ or O₃/Mn²⁺.     

Synthesis and characterization of Co5Cr2(P2O7)4 - New pyrophosphate as a colouring substance

A new pyrophosphate(V) of the formula Co₅Cr₂(P₂O₇)₄ was obtained in the system Co₂P₂O₇–Cr₄(P₂O₇)₃ as a result of solid-state reactions taking place between different reactants. The new compound crystallizes in the orthorhombic system and belongs to the family of pyrophosphates of the general formula M₅²⁺M₂³⁺(P₂O₇)₄ and is probably isostructural with Fe₅²⁺Fe₂³⁺(P₂O₇)₄. Powder diffraction pattern, infrared spectrum and SEM image of the new compound were presented. As a new potential inorganic pigment, Co₅Cr₂(P₂O₇)₄ was tested for its thermal stability, particle size distribution and colour properties, which were studied both for powder and after introduction into organic matrix and leadless ceramic glaze. The colour of Co₅Cr₂(P₂O₇)₄ powder was defined as deep grey with the colour coordinates L*/a*/b* = 60.63/-1.42/-3.41 and according to the hue angle (h° = 247.39°) it belongs to the blue region. Co₅Cr₂(P₂O₇)₄, with its relatively high thermal stability (t _m = 1230 ± 10 °C) and appropriate colour properties, is a good candidate to be used as inorganic pigment for colouring of acrylic paints. In the case of leadless glaze, the obtained compound acts as a dye.     

Preparation of glass-ceramics with diopside as the main crystalline phase from low and medium titanium-bearing blast furnace slag

Because of the low content of TiO₂, the utilization of low and medium Ti-bearing blast furnace slag is a difficult problem. In this study, glass-ceramics with diopside as the main crystalline phase was made by using TiO₂ in the blast furnace slag as the nucleating agent and adding additional elements of TiO₂, Fe₂O₃ and Cr₂O_3. The effects of these three nucleating agents on the phase composition and structural properties of the prepared glass-ceramics were evaluated by DSC, XRD, and SEM to determine their optimal dosage. Research results show that the suitable mass percentages of the TiO₂, Fe₂O₃ and Cr₂O₃ crystal nucleation agents of the glass-ceramics are 7.69%, 0.96%, and 2.88%, respectively. The prepared glass-ceramics have excellent physical and chemical properties, e.g., a bending strength of 114.74 MPa, a bulk density of 2.77 g/cm³, a water absorption rate of 0, and a mass-loss rate of only 0.085%.     

Effective removal of Fe(II) impurity from rare earth solution using surface imprinted polymer

Rare earth is a very important resource. But, impurities, such as Fe²⁺, have great influence on the properties of rare earth material. In this paper, a novel Fe²⁺-ionic imprinted polyamine functionalized silica gel adsorbent was prepared by a surface imprinting technique for selective adsorption of Fe²⁺ from rare earth solution. Firstly, functional macromolecule polyethyleneimine (PEI) was grafted onto the surfaces of silica gel particles, and the PEI/SiO₂ was formed. Secondly, the ionic imprinting process was carried out using Fe²⁺ ion as a template, and Cr³⁺ ionic imprinting polyamine IIP-PEI/SiO₂ was prepared. The adsorption and recognition properties of IIP-PEI/SiO₂ for Fe²⁺ were studied in detail, and the effects of main imprinting conditions, such as the amount of crosslinking agent and reaction time, on the adsorption property of the imprinted material IIP-PEI/SiO₂ were examined. The experimental results showed that the IIP-PEI/SiO₂ possesses strong adsorption affinity, specific recognition ability, and excellent selectivity for Fe²⁺. The adsorption capacity could reach to 0.334 mmol g⁻¹, and relative selectivity coefficients to Pr³⁺ and Ce³⁺ are 23.25 and 18.42, respectively. Besides, the IIP-PEI/SiO₂ was regenerated easily using diluted hydrochloric acid solution as eluent and IIP-PEI/SiO₂ possesses better reusability.     

Magnetic Properties of FeMn<Subscript>y</Subscript>Co<Subscript>y</Subscript>Fe<Subscript>2−2y</Subscript>O<Subscript>4</Subscript>@Oleylamine Nanocomposite with Cation Distribution

In this study, oleylamine (OAm) capped FeMn_yCo_yFe_2?2yO₄ (0.0?≤?y?≤?0.4) nanocomposites (NCs) were prepared via the polyol route and the impact of bimetallic Co³⁺ and Mn³⁺ ions on the structural and magnetic properties of Fe₃O₄ was investigated. The complete characterization of FeMn_yCo_yFe_2?2yO₄@OAm NCs were done by different techniques such as XRD, SEM, TGA, FT-IR, TEM, and VSM. XRD analyses proved the successful formation of mono-phase MnFe₂O₄ spinel cubic products free from any impurity. The average crystallite sizes were calculated in the range of 9.4–26.4 nm using Sherrer’s formula. Both SEM and TEM results confirmed that products are nanoparticles like structures having spherical morphology with small agglomeration. Ms continued to decrease up to Co³⁺ and Mn³⁺ content of y?=?0.4. Although Mössbauer analysis reveals that the nanocomposites consist three magnetic sextets and superparamagnetic particles are also formed for Fe₃O₄, Co_0.2Mn_0.2Fe_2.6O₄ and Co_0.4Mn_0.4Fe_2.2O₄. Cation distributions calculation was reported that Co³⁺ ions prefer to replace Fe²⁺ ions on tetrahedral side up to all the concentration while Mn³⁺ ions prefer to replace Fe³⁺ ions on the octahedral.     

Fe effect on the optical properties of TiO2:Fe2O3 nanostructured composites supported on SiO2 microsphere assemblies

The effect of Fe ion concentration on the morphological, structural, and optical properties of TiO₂ films supported on silica (SiO₂) opals has been studied. TiO₂:Fe₂O₃ films were prepared by the sol-gel method in combination with a vertical dip coating procedure; precursor solutions of Ti and Fe were deposited on a monolayer of SiO₂ opals previously deposited on a glass substrate by the same procedure. After the dip coating process has been carried out, the samples were thermally treated to obtain the TiO₂:Fe₂O₃/SiO₂ composites at the Fe ion concentrations of 1, 3, and 5 wt%. Scanning electron microscopy (SEM) micrographs show the formation of colloidal silica microspheres of about 50 nm diameter autoensembled in a hexagonal close-packed fashion. Although the X-ray diffractograms show no significant effect of Fe ion concentration on the crystal structure of TiO₂, the μ-Raman and reflectance spectra do show that the intensity of a phonon vibration mode and the energy bandgap of TiO₂ decrease as the Fe⁺³ ion concentration increases.     

Characterization of Fischer–Tropsch Cobalt-Based Catalytic Systems (Co/SiO<Subscript>2</Subscript> and Co/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) by X-ray Diffraction and Magnetic Measurements

Results of the characterization of six Co-based Fischer–Tropsch (FT) catalysts, with 15% Co loading and supported on SiO₂ and Al₂O₃, are presented. Room temperature X-ray diffraction (XRD), temperature and magnetic field (H) variation of the magnetization (M), and low-temperature (5 K) electron magnetic resonance (EMR) are used for determining the electronic states (Co⁰, CoO, Co₃O₄, Co²⁺) of cobalt. Performance of these catalysts for FT synthesis is tested at reaction temperature of 240 °C and pressure of 20 bars. Under these conditions, 15% Co/SiO₂ catalysts yield higher CO and syngas conversions with higher methane selectivity than 15% Co/Al₂O₃ catalysts. Conversely the Al₂O₃ supported catalysts gave much higher selectivity towards olefins than Co/SiO₂. These results yield the correlation that the presence of Co₃O₄ yield higher methane selectivity whereas the presence of Co²⁺ species yields lower methane selectivity but higher olefin selectivity. The activities and selectivities are found to be stable for 55 h on-stream.     

Preparation of monolayers of [MnIII6CrIII]3+ single-molecule magnets on HOPG,mica and silicon surfaces and characterization by means of non-contact AFM

We report on the characterization of various salts of [Mn^III₆Cr^III]³⁺ complexes prepared on substrates such as highly oriented pyrolytic graphite (HOPG), mica, SiO₂, and Si₃N₄. [Mn^III₆Cr^III]³⁺ is a single-molecule magnet, i.e., a superparamagnetic molecule, with a blocking temperature around 2 K. The three positive charges of [Mn^III₆Cr^III]³⁺ were electrically neutralized by use of various anions such as tetraphenylborate (BPh₄^-), lactate (C₃H₅O₃^-), or perchlorate (ClO₄^-). The molecule was prepared on the substrates out of solution using the droplet technique. The main subject of investigation was how the anions and substrates influence the emerging surface topology during and after the preparation. Regarding HOPG and SiO₂, flat island-like and hemispheric-shaped structures were created. We observed a strong correlation between the electronic properties of the substrate and the analyzed structures, especially in the case of mica where we observed a gradient in the analyzed structures across the surface.     

Influence of Cr3+ on yellowish-green UC emission and energy transfer of Er3+/Cr3+/Yb3+ tri-doped zinc silicate glasses

In this paper, we study the influence of Cr³⁺ on yellowish-green upconversion (UC) emission and the energy transfer (ET) of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in SiO₂–ZnO–Na₂O–La₂O₃ (SZNL) zinc silicate glasses under excitation of the 980 nm laser diode (LD). The influence of Cr³⁺ on enhancing the red UC emission of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in SiO₂–ZnO–Na₂O–La₂O₃ zinc silicate glasses under the excitation of 980nm LD was also investigated. The ET processes between Yb³⁺, Cr^3+, and Er³⁺, together with the combination of Yb³⁺-Cr³⁺-Er³⁺, which led to the green UC emission intensity of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in SiO₂–ZnO–Na₂O–La₂O₃ zinc silicate glasses bands centered at ~546 nm have been significantly enhanced. By increasing the concentration of Cr³⁺ from 0 up to 5 mol.%, we can locate the Commission Internationale de l'éclairage (CIE) 1931 (x; y) chromaticity coordinates for UC emissions of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in the central position of the yellowish-green color region of CIE 1931 chromaticity diagram. Besides, the ET processes between the Yb³⁺, Cr³⁺, and Er³⁺ are also proposed and discussed.     

Effective synthesis of green nano-sized ceramic pigments by co-doping Zn2+, Cr3+ and Sm3+ into the cobalt-aluminate

A green nano-sized ceramic pigment Co_0.6Zn_0.4Al_0.8Cr_1.2-xSm_xO₄ has been successfully prepared by doping ions Zn²⁺, Cr³⁺, and Sm³⁺ into the crystalline CoAl₂O₄ spinel and using the complex-gel method along with agar as complexing and combustion agent. The Infrared Spectroscopy, X-ray diffraction, Thermo-gravimeter, High resolution transmission electron microscopy, Automatic color reader, and UV Vis diffuse reflectance were applied to characterize the pigment power and its gel precursor. The results reveal that the introduction of Zn²⁺, Cr³⁺, and Sm³⁺ could change the occupation status of ions in the tetrahedral and octahedral framework of CoAl₂O₄ spinel, leading to the colorant variation of the blue cobalt pigment CoAl₂O₄, With increasing the content of Sm³⁺ ion, the reflection peak position of the pigments in visible spectrum appeared a red-shift, ie the color transition from blue green to yellow green, and the average reflectivity in the violet region decreased to 13.31%, and the band gap energy also changed from 3.47 to 3.20 eV. This illustrates the better UV absorption of this green pigment and can be used as UV shielding material. With the hydrochloric acid or sodium hydroxide solution treatment, this pigment was found to be durable in chemical stability.     

The effect of foreign ions on the reactivity of the CaO-SiO2-Al2O3-Fe2O3 system: Part II: Cations

The subject of this paper is the effect of foreign cations on the reactivity of the CaO-SiO₂-Al₂O₃-Fe₂O₃ system. One reference mixture and eighteen modified mixtures, prepared by mixing the reference sample with 1% w/w of chemical grade MnO₂, CuO, V₂O₅, PbO, CdO, ZrO₂, Li₂O, MoO₃, Co₂O₃, NiO, WO₃, ZnO, Nb₂O₅, CrO₃, Ta₂O₅, TiO₂, BaO₂ and H₃BO₃ were studied. The effect on the reactivity is evaluated on the basis of the free lime content in samples sintered at 1200 and 1450 °C. At 1200 °C, the reactivity of the mixture is greatly increased in the presence of Cu and Li oxides. Based on their effect at 1450 °C, the added elements can be divided into three groups. W, Ta, Cu, Ti and Mo show the most positive effect, decreasing the free CaO (fCaO) content by 30-60%, compared with the pure sample. Cr and B cause an increase of fCaO content, while the rest of the elements exhibit a marginal positive effect. According to their volatility at 1450 °C, the added compounds can be subdivided into three groups of low (Ti⁴⁺, Cu²⁺, Mo⁶⁺, W⁺⁶, V⁵⁺, Zn²⁺, Zr⁴⁺), moderate (Cr⁶⁺, Co³⁺, Ni²⁺, Mn⁴⁺) and high volatility (Cd²⁺, Pb²⁺). All burned samples, analyzed by means of X-ray diffraction, have a final mineralogical composition, which corresponds to the structure of a typical clinker.     

Zum promotierenden Einfluß von Molybdaten in Multikomponent-Molybdat-Katalysatoren

The Mutual Promotion Effect of Molybdates in Multicomponent Molybdate Catalysts Multicomponent molybdate catalysts (e.g. of the composition Bi₂Fe_1,5Co₇Cr₁₀Mo₁₉O_y) are produced by coprecipitation, drying and calcination. These catalysts exhibit high activity and selectivity in the ammoxidation of propene to acrylonitrile. The individual molybdates (Co-, Fe- and Cr-molybdate) exhibit no selectivity in the ammoxidation of propene. Therefore a mutual promotion effect of these molybdates exists. The cause of the promotion effect is the formation of the active and selective phase from the β-phase of Co-molybdate by exchange of protons with ions of Fe³⁺ and Cr³⁺ from the molybdates of Fe and Cr. The structure of this catalytic active and selective phase is similar to the structure of the β-phase of Co-molybdate.