Untersuchungen an oxidischen Katalysatoren. XVI. Über Zusammensetzung und Struktur dotierter Zinkoxidkatalysatoren

Studies on Oxide Catalysts. XVI. Composition and Structure of Doped Zinc Oxide Catalysts Analytical, x-ray, textural, IR-spectroscopic, and MÖSSBAUER investigations of zinc oxide catalysts doped with Li₂O, Ga₂O₃ and Fe₂O₃ were conducted in order to reveal relations between electronic and catalytic properties. The mixtures ZnO/Li₂CO₃, ZnO/Ga₂O₃, ZnO/Fe₂O₃, and ZnO/⁵⁷Fe(NO₃)₃, after the thermal pretreatment, always exist in the state of a polyphase solid system. In the ZnO/Li₂O system, only a very small part of the added lithium oxide is incorporated into the zinc oxide lattice by substitution. A second part of the Li₂O volatizes during the thermal pretreatment, and the greater part of it exists in the state of a separate solid phase in the catalyst and can be washed out by water. During the pretreatment, according to its temperature and duration, two-phase systems (ZnO, ZnMe₂O₄) or three-phase systems (ZnO, ZnMe₂O₄, Me₂O₃) are formed in the solid systems ZnO/Ga₂O₃ and ZnO/Fe₂O₃. For the reaction of both oxides forming a spinel, an electronic model is proposed.     

Untersuchungen an Metallkatalysatoren. XI. Untersuchungen an eisen-, kobalt- und nickelmodifizierten Pt-η-Al2O3-Katalysatoren

Investigations on Metal Catalysts. XI. Investigations on Pt? η-Al₂O₃ Catalysts Modifieded by Iron, Cobalt, and Nickel Pt? Me? η-Al₂O₃ catalysts (M: Fe, Co, Ni) were characterized by magnetic investigations, reflectance spectra and determination of dispersity (chemisorption of CO, oxygen-hydrogen titration), respectively. The phase structure of platinum-rich catalysts is composed of a high degree by Pt₃Fe super-structure. All the Pt? Fe? η-Al₂O₃ catalysts contained Fe^III ions in octahedral symmetry. The dispersity of the metallic components is determined essentially by their phase structure.     

Untersuchungen an Nickeloxid-Mischkatalysatoren. XVI. Reduktionsverhalten amorpher NiO?Al2O3/SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. XVI. Reduction Behaviour of Amorphous NiO? Al₂O₃/SiO₂ Catalysts The reduction behaviour of NiO? Al₂O₃/SiO₂ catalysts prepared by precipitationdeposition is influenced by the phase composition (amorphous nickel layersilicates and nickel alumino layersilicates, nickel spinels, nickel oxide) and the differences of the composition between surface and bulk. TPR measurements, determinations of the reduction degree, and the nickel particle sizes by static magnetic measurements showed that the reducibility of the NiO? Al₂O₃/SiO₂ catalysts is enhanced and the nickel dispersity is decreased at low Al₂O₃ contents. The decrease of the reducibility at Al₂O₃ contents >5 mole% is caused by the formation of nickel spinels and the decrease of the Ni^II ion surface concentration.     

Catalytic activity of solid solutions of nickelous and zinc oxides

Summary A comparison of the change in the rules of chemisorption of gas-acceptors and donors of electrons with catalytic activity for processes with gases of the same type showed that the change in the catalytic properties of NiO and ZnO and their solid solutions may be explained by the effect of dissolved oxides Li₂O, Ga₂O₃, Fe₂O₃, etc., on chemisorption. The change in chemisorption is considered to be connected with the effect of cations with an anomalous charge in the lattice points on the statistics of the active centers on the surface.     

Hydrolysis of the uranyl ion in sodium nitrate medium

Studies on Nickel Oxide Mixed Catalysts. VIII. Catalytic Properties of NiO? Al₂O₃/SiO₂ Catalysts Catalytic properties of NiO? Al₂O₃/SiO₂ catalysts prepared by precipitation-deposition and impregnation have been investigated in dimerization of ethene and isomerization of but-1-ene. It was found that the catalytic activity is mainly determined by the interaction between the catalyst components where a X-ray amorphous nickel alumolayersilicate is formed. The dimerization of ethene proceeds by participation of coordinatively unsaturated nickel ions with aluminum ions in the neighbourhood. The catalytic activity in the isomerization of but-1-ene depends on the surface acidic properties of the catalyst.     

n-Octane Dehydrocyclization on Cr2O3/La2O3/ZrO2 Catalyst Elucidated by H–D-Tracer Experiments

H–D tracer experiments during n-octane aromatization on Cr₂O₃/La₂O₃/ZrO₂ catalysts allow conclusions to be drawn on the reaction mechanism. The rate-determining step is the dissociative adsorption of the paraffin molecule. The following dehydrogenation steps seem to proceed predominantly reversibly.     

Mechanism of Butane Transformation

Catalytic activity and aromatic selectivity of n‐butane transformation were studied over various MFI type zeolites. From the data obtained, a reaction mechanism is suggested for different catalyst systems. It is visualized that in gallium doped catalysts, Ga³⁺ directly takes part both in cracking and dehydrogenation. The [Ga CH₃]²⁺ and [GaH]²⁺ species formed during cracking and dehydrogenation require protonic sites for regeneration of Ga³⁺ species. An alternative mechanism was suggested for dehydrogenation and cracking by Ga³⁺ without the involvement of protonic sites. However a protonic site would be required for aromatization. In case of gallosilicates a one step mechanism is suggested for cracking and dehydrogenation reaction which does not require the presence of protonic sites in the catalyst system.     

Solid state properties and catalytic behavior of the α- and β-vanadium bronzes

Decomposition of isopropanol (IPA) on V₂O₅, Li_0.02V₂O₅, Na_0.02V₂O₅, Na_0.06V₂O₅, Li_0.33V₂O₅, and Na_0.33V₂O₅ has been studied in the temperature range 186–300°C. The first four catalysts (α-phase) show predominately dehydration, whereas the last two (β-phase) have comparable dehydration and dehydrogenation activity. Dehydration activity increases with alkali metal concentration within the α-phase, but falls sharply on the β-phase catalysts. This difference is attributed to the different rate determining steps for the reaction on the α- and β-phase catalysts. X-ray and ir spectral data show that the β-phase catalysts are much more stable than the α-phase. A mechanism for the dehydration of IPA based on the electrical resistivity, ESR spectra, and kinetic data has been proposed.     

Untersuchungen an oxidischen Katalysatoren. XIX. Über die thermische Alterung eines Al2O3/Cr2O3/K2O-Tränkkatalysators für die Dehydrocyclisierung und seine Regenerierung

Studies on Oxide Catalysts. XIX. On the Thermal Aging of an Al₂O₃/Cr₂O₃/K₂O Dehydrocyclization Catalyst Made by Impregnation and its Regeneration An Al₂O₃/Cr₂O₃/K₂O catalyst was aged at different temperatures in hydrogen flow. These samples and the regenerated ones (prepared by oxidation and subsequent reduction under mild conditions of the aged samples) were investigated by means of reflectance spectroscopy, EPR, oxygen chemisorption, determination of oxidizability and microcatalytic measurements of the activity in the dehydrocyclization of n-hexane. The reversible and irreversible processes occurring during the thermal aging are discussed. The importance of the oxidizability of the chromia for the regenerability of the catalysts is explained.     

Study of oxidative dehydrogenation of ethylbenzene with CO2 on supported CeO2-Fe2O3 binary oxides

Nano-sheets Al₂O₃ supported CeO₂-Fe₂O₃ binary oxides were prepared by the vacuum impregnation method. The structural and textural properties were characterized by pertinent techniques, and the materials were evaluated as catalysts for the oxidative dehydrogenation of ethylbenzene with carbon dioxide (CO₂-ODEB). The characterization results show that all samples maintain the hierarchical structure, and CeO₂-like and Fe₂O₃-like solid solutions were formed when changing the Ce-to-Fe molar ratio. The catalytic performances indicate that CeO₂-Fe₂O₃ binary oxides were effective for CO₂-ODEB, and the activity is determined by mobile oxygen, which can facilitate the dehydrogenation process. The DFT studies further identified the reaction pathway and rate-determining step. The inter-transmission of oxygen species and the presence of CO₂ refill the oxygen vacancies and restore the redox cycle of CeO₂-Fe₂O₃ binary oxides.     

Untersuchungen an Metallkatalysatoren. XIV. Zu physikalisch-chemischen und katalytischen Eigenschaften von Palladium–Rhenium-Katalysatoren

Investigations on Metal Catalysts. XIV. Physico-chemical and Catalytical Properties of Palladium-Rhenium Catalysts Characterization of carrier-free Pd? Re catalysts with regard to their phase structure, dispersity and catalytical activity were performed by X-ray measurements, sorption methods (adsorption of N₂, chemisorption of CO, sorption of H₂), and catalytical investigations (dehydrogenation of cyclohexane, hydrogenation of benzene). The dispersity of the catalysts is influenced by thenium to a remarkable extent. There are references, that the composition of the bulk phase and the surface layer of the crystallites differs from each other. Also a synergistic effect in catalytical activity is caused by rhenium. The similarities between Pd? Re and Pt? Re catalysts are discussed briefly.     

Untersuchungen an Metallkatalysatoren. XXVIII [1]. Zur Aktivität und Selektivität von Nickel/Träger-Katalysatoren

Investigations on Metal Catalysts. XXVIII. Activity and Selectivity of Supported Nickel Catalysts Titania and alumina supported nickel catalysts (with 1 and 10 wt.-% Ni, resp.) have been tested in ethane hydrogenolysis and conversion of cyclohexane. Titania supported nickel and nickel on high surface aluminas are characterized by small hydrogenolysis activities and high dehydrogenation selectivities. The behaviour of the Ni/Al₂O₃ catalysts is discussed in terms of an interaction between small nickel crystallites and unreduced nickel. In the case of the Ni/TiO₂ catalysts the interpretation is based on the partial poisoning of the nickel surface by titanium cations.     

Zeolite-supported silver and silver�Ciron nanoclusters and their activities as photodecomposition catalysts

Catalysts containing nanoclusters of Ag(I) and Fe₂O₃ as dopants with sodalite and Y zeolite supports have been investigated in order to develop a more efficient catalyst for photodecomposition of the pesticide carbaryl and to gain insight about the reaction mechanism. Ag(I)?Csodalite, Ag(I)/Fe₂O₃?Csodalite, Ag(I)?CY zeolite, and Ag(I)/Fe₂O₃?CY zeolite were synthesized by ion-exchange techniques and characterized by powder X-ray diffraction (XRD), solid-state luminescence, UV?Cvisible absorption, and atomic absorption spectroscopy measurements. The luminescence activity of the sodalite-supported and Y zeolite-supported catalysts was significantly different. Catalyst performance studies were conducted using carbaryl as the target compound and specific wavelengths of UV light as photon sources for the experiments. The studies showed that each catalyst??s performance was determined primarily by the specific wavelength of the UV light with which the system was irradiated. The studies also showed that inclusion of Fe₂O₃ as dopant enhanced the reactivity of the catalysts in several instances, with the Ag(I)/Fe₂O₃?Csodalite catalyst and 298 nm irradiation being the most reactive of the systems studied. Additional reactions using each catalyst and 298 nm irradiation, and including either sodium bicarbonate as hydroxyl radical scavenger or D₂O as solvent, showed that hydroxyl radicals were likely intermediates in the catalyzed photodecomposition reaction.     

Catalytic transformations of 1-octanol and 2-ethyl-1-hexanol over oxide catalysts, 1. Transition metal oxides as catalysts

A comparative study of 1-octanol and 2-ethyl-1-hexanol transformations over silica supported NiO, MnO₂, Cr₂O₃, Fe₂O₃, and ZnO has been performed. Zinca containing catalyst was found to be the most active in dehydrogenation and dehydration of the alcohols studied. ZnO dehydrogenating activity increased with supported oxide load.     

Elaborated Reaction Pathway of Photothermal Catalytic CO2 Conversion with H2O on Gallium Oxide-Decorated and -Defective Surfaces

Ga₂O₃-decorated and -defective surface models based on anatase TiO₂ have been established. The thermodynamic reaction pathways, including protonation, deoxygenation and hydroxylation steps, during CO₂ conversion with H₂O to C₁ products were calculated. The calculation results demonstrate that a Ga₂O₃ cocatalyst enhances the selective adsorption of CO₂ and slightly weakens the competitive adsorption of H₂O. The promotion effect of Ga₂O₃ on the subsequent reaction depends on the availability of protons and electrons. Free-energy calculations revealed that the basic functional site generated by Ga₂O₃ not only suppresses the back reaction of the OH group after H₂O directly provides protons but also maintains the surface defect oxygen vacancy (V_O), which promotes the reaction thermodynamics but tends to be consumed in the process. Additionally, Ga₂O₃ decoration promotes V_O formation, and the coexistence of Ga₂O₃ and V_O further decreases the reaction rate-determining step energy barrier, promoting C₁ production.     

Untersuchungen an oxidischen Katalysatoren. XLI. Redoxverhalten des Nickels in NiNa–Y-Zeolithen 3. Reduzierbarkeit von Ni2+ -Ionen und Eigenschaften des reduzierten Nickels in aciden NiNa–Y-Zeolithen

Studies on Oxide Catalysts. XLI. Redox Behavior of Nickel in Zeolites NiNa? Y. 3. Reducibility of Ni²⁺ Ions and Properties of the Reduced Nickel in Acidic Zeolites NiNa? Y The reducibility of nickel ions in zeolites NiNa? Y and the properties of metallic nickel were evaluated by tpr measurements, oxygen chemisorption and conversion of cyclohexane. In NiNa? Y samples which contain NH₄⁺(H⁺) and/or Al³⁺(H⁺) ions the reducibility of Ni²⁺ ions is decreased caused by increasing acidity and the metal dispersion is improved. The electronic interaction between the acidic support and the metallic nickel leads to a decrease of both dehydrogenation and hydrogenolysis activity whereas the dehydrogenation selectivity increases.     

The effect of Fe2O3 dopants on electrophysical and sorption properties of ZnO

The effect of Fe₂O₃ dopants (0–0.8 mol.%) on ZnO conductivity and its chlorine chemisorption ability has been studied in the temperature range of 20–250 °C. Introduction of dopants increases the activation energy of ZnO conductivity and decreases the conductivity. The effective charge of the chemisorbed chlorine species as well as the strength of their bonding to the surface in samples containing Fe₂O₃ are considerably lower than in initial ZnO, which leads to a decrease of reactivity of the doped catalysts in chlorination.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1196–1199, July, 1993.     

Dehydrogenation of propane in the presence of carbon dioxide over oxide-based catalysts

In the present study, we show the advantages of CO₂ use for the dehydrogenation of propane to propene on the basis of thermodynamic considerations and some experimental results. Several metal oxides Ga₂O₃, Cr₂O₃, Fe₂O₃ unsupported and supported on g- Al₂O₃ and SiO₂ were tested. Ga₂O₃ catalyst was found to be an effective agent for dehydrogenation of propane to propene. The yield of propene at 873 K was 30.1 %. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of iron ions on the structural properties of Zn-borosilicate glasses

The effects of iron on the structural properties of Zn-borosilicate glasses have been studied using X-ray diffraction, IR spectroscopy and⁵⁷Fe Mössbauer spectroscopy. Zn-borosilicate glasses were doped with α?Fe₂O₃. In the systems Na₂O?ZnO?B₂O₃?SiO₂?Fe₂O₃ the presence of only one crystalline phase, ZnFe₂O₄, was detected. X-ray diffraction showed that crystallization is more pronounced in the systems ZnO?B₂O₃?SiO₂?Fe₂O₃. In these systems the presence of different crystalline phases, such as ZnO, γ?Fe₂O₃, Fe₃O₄, ZnFe₂O₄ and Fe₃BO₅, was detected. The crystallization of α?Zn₂SiO₄ in the system ZnO?B₂O₃?SiO₂ was confirmed by X-ray diffraction and IR spectroscopy. The valence state and coordination of iron in Zn-borosilicate glasses were determined by⁵⁷Fe Mössbauer spectroscopy.     

Zur Kenntnis der μ-Peroxo-bis(pentacyanokobaltate(III)). Neuartige Darstellung,Beschreibung eines μ-Hydroperoxo-komplexes K5[Co2OOH(CN)10] · 2 H2O und eines μ-Peroxo-Carbonato-Komplexes K6[Co2CO4(CN)10] · 2 H2O

Investigations on Metal Catalysts. XXII. Chemisorption of Hydrogen on Pt? Ru and η-Al₂O₃ Supported Pt? Ru Catalysts Measurements of the H₂ chemisorption by volumetric method were carried out on several series of Pt? Ru and η-Al₂O₃ supported Pt? Ru catalysts. Addition of Ru to Pt and vice versa effects a remarkable influence on the sorption behaviour of the starting samples. For mixtures of carrier-free catalysts and η-Al₂O₃ as well as Pt? Ru/η-Al₂O₃ catalysts a hydrogen-spillover effect was found.