Untersuchungen an Nickeloxid-Mischkatalysatoren. XV. Oberflächenchemische Eigenschaften von NiO/Al2O3?SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. XV. Surface Chemical Properties of NiO/Al₂O₃-SiO₂ Catalysts Surface chemical properties of precipitated NiO/Al₂O₃? SiO₂ catalysts different compositions and the corresponding Al₂O₃? SiO₂ carriers have been investigated. Infrared spectroscopic measurements (before and after adsorption of pyridine and ammonia), ¹H-n.m.r. and ammonia adsorption measurements showed that the number of the Lewis-acidic sites are increased mainly by incorporation of the nickel component on the X-ray amorphous Al₂O₃? SiO₂ carriers, whereas the number of the hydroxide groups do not change significantly. With growing alumina content the number and the strength of the Lewis-acidic sites are increased where the part of the Ni^II surface sites decreases and those of the Al^III surface sites increases. Brönsted-acidic sites are detectable at high alumina contents.     

Oberflächenchemie,Sintern und Redispergieren von Pd/Al2O3-Katalysatoren

Surface Chemistry, Sintering, and Redispersion of Pd/Al₂O₃ Catalysts Surface chemistry of Pd/Al₂O₃ has been investigated by temperature-programmed reduction, O₂ chemisorption, and u.v.-vis spectroscopy. Depending on conditions of different thermal pretreatments especially in O₂, different chlorine-free and chlorine-containing Pd compounds exist on the alumina. Sintering and redispersion of Pd are governed by properties of chlorine-free Pd oxide. The mechanism of Pd sintering consists in the thermal decomposition of a two-dimensional PdO phase; redispersion consists in formation of this phase by spreading of bulk PdO. There is no direct connection between Pd oxidation and redispersion. The discussion compares properties of Pd/Al₂O₃ and Pt/Al₂O₃.     

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.     

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.     

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.     

Untersuchungen an Metallkatalysatoren. 37. Zum Einfluß der Beladung auf Aktivität und Selektivität von Nickel/Träger-Katalysatoren

Investigations on Metal Catalysts. 37. On the Influence of the Loading on Activity and Selectivity of Supported Nickel Catalysts Strong metal-support interactions effect a distinct decrease of the hydrogenolysis activity. They can be detected with diminishing metal loading in the following order: Ni/TiO₂ > Ni/Al₂O₃ > Ni/SiO₂. Strong metal-support interactions mean an influence on the electronic properties of the metal crystallites. On the other hand a mechanical mixture of nickel and η-Al₂O₃ is more active in hydrogenolysis than nickel.     

Untersuchungen an oxidischen Katalysatoren. XIV. Die katalytische Aktivität verschiedener Übergangsformen des Aluminiumoxids bei der Dehydratisierung von Isopropanol

Studies on Oxide Catalysts. XIV. The catalytic Activity of some transient Forms of Alumina in the Dehydration of Isopropanol In order to give statements about the influence of the method of preparation of aluminum hydroxides and oxide hydroxides on the catalytic properties of alumina obtained from these compounds in the dehydration of ispropanol, bayerite, nordstrandite, and boehmite were prepared by several methods, carefully excluding impurity ions. Also, hydrargillite containing alkali was included in the investigations. By calcination in oxygen at 550 and 950°C, respectively, two groups of alumina were obtained. The catalytic properties of the oxides in the dehydration of isopropanol were examined by an apparatus working according to the dynamic principle. The specific activities of the different transient forms of alumina were found to vary according to the sequence η-;≈γ->?-≈δ->??(>??-)Al₂O₃.     

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.     

Characterization of new catalysts based on uranium oxides

Catalysts based on uranium oxides were systematically studied for the first time. Catalysts containing various amounts of uranium oxides (5 and 15%) supported on alumina and mixed Ni-U/Al₂O₃ catalysts were synthesized. The uranium oxide catalysts were characterized using the thermal desorption of argon, the low-temperature adsorption of nitrogen, X-ray diffraction analysis, and temperature-programmed reduction with hydrogen and CO. The effects of composition, preparation conditions, and thermal treatment on physicochemical properties and catalytic activity in the reactions of methane and butane oxidation, the steam and carbon dioxide reforming of methane, and the partial oxidation of methane were studied. It was found that a catalyst containing 5% U on alumina calcined at 1000°C was most active in the reaction of high-temperature methane oxidation. For the Ni-U/Al₂O₃ catalysts containing various uranium amounts (from 0 to 30%), the introduction of uranium as a catalyst constituent considerably increased the catalytic activity in methane steam reforming and partial oxidation.     

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.     

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.     

Préparation et caractérisation des catalyseurs Rh/Al2O3 et Rh/ZnO–Al2O3

A series of rhodium (1 and 5 wt%) deposited on alumina and alumina modified by Zn was prepared by impregnation of Al₂O₃ and ZnO–Al₂O₃ with two different precursors, Rh(NO₃)₂·xH₂O and RhCl₃, followed by calcination at 723 K, and characterized after reduction at different temperatures, in the range 500–800 °C. Catalysts were analysed by Hydrogen Chemisorption (Hc), Temperature-Programmed Reduction (TPR), Temperature-Programmed Desorption (TPD), X-ray diffraction (RDX), and Scanning Electron Microscopy methods. The results show that the metal dispersion depends strongly on the Zn/Rh atomic ratio and on the metal loading. The presence of Zn and high reduction temperature decrease the capacity to chemisorb hydrogen, whereas the metal particles' size increase is probably due to the sintering effect. Temperature-programmed studies (TPR) of catalysts show that the temperature of maximal reduction is lower with nitrate-prepared catalysts, which is explained by metal–support interactions.     

Über die Dispersität von Metallen in Trägerkatalysatoren. II. Röntgenkleinwinkeluntersuchungen an Platin- und Palladium-Tonerde-Katalysatoren

On the Dispersion of Metals in Supported Catalysts. II. Small Angle X-ray Investigation. on Platinum/Alumina and Palladium/Alumina Catalysts The metal dispersion in 0.5% Pd/A1₂O₃. 0.5°% Pt/Al₂O₃ abd 1.5% Pt/Al₂O₃ catalysts was investigated by small angle X-ray scattering, Using a Kratky camera the difference scattering curves catalyst-carrier were evaluated. The assumption was made that the scattering centres are globular and that there is no interparticular scattering. From the Guinier approximation the Guinier radii R_G of the metal particles were determined. With the Pd catalyst always positive difference scattering curves were found, whereas negative values were found with the Pt catalysts at a scattering angle greater than 0.022 rad. Therefore only for the sample with 0.5% Pd the Porod invariant \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \tilde Q}$\end{document} and the Porod radius R_P could be determined. From R_G and R_P the parameters of a two- and of a one-parametric distribution were calculated. The results are in good agreement with data from wide angle X-ray diffraction measurements.     

Microporous Crystalline γ‐Al2O3 Replicated from Microporous Covalent Triazine Framework and Its Application as Support for Catalytic Hydrolysis of Ammonia Borane

Significant progress has been made on the synthesis and application of mesoporous γ‐alumina. To date, little attention has been paid to the synthesis of microporous crystalline alumina. Here, fabrication of microporous crystalline γ‐alumina using a microporous covalent triazine framework (CTF‐1) as a template is described. Microporous crystalline γ‐alumina with a micro‐meso binary pore system was replicated by infiltration of aluminum nitrate into the micropores of the CTF‐1 template through a NH₃/water‐vapor‐induced internal hydrolysis method, followed by thermal treatment, and subsequent removal of the CTF‐1 template with a 30 % H₂O₂ aqueous solution. The obtained crystalline γ‐alumina material exhibits a large surface area (349 m² g⁻¹) with micropore distribution centered at about 1.27 nm. Ru supported on microporous γ‐Al₂O₃ can be employed as catalyst for hydrolytic dehydrogenation of ammonia borane, and it exhibits high catalytic activity and good durability. This finding provides a new benchmark for preparing well‐defined crystalline microporous alumina materials by a template method, which can be applied in a wide range of fields.     

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.     

Catalytic properties of Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in the aqueous-phase reforming of ethylene glycol: Effect of the alumina support

The influence of the alumina support on the catalytic activity of Pt/Al₂O₃ catalysts in aqueous phase reforming of ethylene glycol to hydrogen was studied. The catalysts were prepared by impregnation of γ-, δ-, and α-alumina with H₂PtCl₆. The highest rate of hydrogen production (452 μmol min⁻¹ g⁻¹) obtained with the Pt/α-Al₂O₃ catalyst can be related to the highest extent of dispersion of Pt on α-Al₂O₃. XPS, TEM-EDX and TPR-H₂ measurements showed the absence of chloride-containing surface complexes in the Pt/α-Al₂O₃ catalyst. However, chloride-containing entities were found on the surface of Pt/γ-Al₂O₃ and Pr/δ-Al₂O₃ catalysts. When chloride ions are removed chlorinated Pt species facilitate the sintering of Pt crystallites and in this way affect the extent of Pt dispersion. Moreover, depending upon the particular crystalline form, alumina atoms have different coordination and alumina surfaces contain varying amounts of OH groups of different nature which affect the interaction between Pt and the support.     

Ferromagnetic resonance investigation of dispersed Ni catalysts: epitaxial and textural effects from the support

Catalysts consisting of dispersed Ni particles supported on silica and alumina, with sizes ranging from 6 to 20 nm, have been studied by ferromagnetic resonance. For the Ni on Al₂O₃ catalyst, a textural promotion effect is shown to be present and it is attributed to the possible presence of NiAl₂O₄. The FMR data confirm the epitaxial growth of Ni on SiO₂ when Ni antigorite is reduced and show that some anisotropy is still present after sintering of the catalyst at about 1200K.     

Dehydrogenative activity of catalysts with low palladium content

Catalysts containing as little as 0.5 mass. % Pd are highly active in the dehydrogenation of cyclohexane when Sibunite® or active alumina (for gas dehumidification) are used as catalyst supports. Dehydrogenative activity of the Pd/Al₂O₃ catalyst is further increased upon surface sulfidation and addition of 0.25–0.5 mass. % Re.Translated fromIzvestiya Akademii Nauk. Seriya Khmicheskaya, No. 2, pp. 422–423, February, 1993.     

Untersuchungen an Metallkatalysatoren. XXVII. Zum Einfluß verschiedener Träger auf die Dispersität von Nickel

Investigations on Metal Catalysts. XXVII. On the Influence of Several Carriers on the Dispersion of Nickel Nickel supported catalysts (carrier: η-, ?-, α-Al₂O₃, TiO₂) were characterized by chemically determined degree of reduction, CO chemisorption, magnetic susceptibility measurements and FMR. The influence of interaction between carrier and active component in the unreduced state on the size and number of Ni crystallites is discussed.     

Thermal analysis of binary system Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SnO<Subscript>2</Subscript> obtained by sol-gel technique

Summary A series of Al₂O₃-SnO₂ catalysts with Al₂O₃ to SnO₂ molar ratio of 1:1, 1:0.5, 1:0.2 and 1:0.1 were synthesized by sol-gel technique and characterized by thermal analysis and FTIR. In the case of binary gels - addition of tin component leads to better crosslinking than in pure alumina gel and as a result to a much uniform texture structure.