Untersuchungen an katalytisch aktiven Oberflächenverbindungen. VII. Katalytische Eigenschaften von Vanadiumoxid-Chromoxid-Aufschicht-Katalysatoren

Studies on Catalytically Active Surface Compounds. VII. Catalytic Properties of Oxidic Vanadium-Chromium Catalysts The catalytic properties of silica supported vanadium-chromium catalysts for the oxidation of ethanol, butane, propene, and butene are described and completed by ESR measurements. Differences in catalytic activity of chromium-free vanadium catalysts which are caused by different values of the silanol group concentration of the support are shown to become levelled by the addition of chromium. V? O? Cr species of medium catalytic activity are considered to be the catalytic active center. ESR spectra taken after the reaction show the existence of Cr³⁺ and VO⁺² species. A correlation between the intensity of the VO²⁺ signal and the catalytic activity of the samples is observed.     

Untersuchungen an katalytisch aktiven Oberflächenverbindungen. XIII. Struktur und katalytische Eigenschaften von Molybdän-oxid/SiO2-Katalysatoren

Studies on Catalytically Active Surface Compounds. XIII. Structure and Catalytic Properties of Molybdenum Oxide/SiO₂ Catalysts The catalytic properties of Mo oxide/SiO₂ catalysts in the selective oxidation of methanol to formaldehyde are described. It is shown that, independently on the preparation conditions, all catalysts showed relative high activity and selectivity values which were however, not constant during the reaction time. The high initial activity could be stabilized to a limited extent both by prereduction with methanol (but not with hydrogen) and by decreasing the oxygen concentration of the reaction gas. ESR measurements showed that in dependence on the means of reduction (methanol or hydrogen) two different coordinated Mo⁵⁺ ions were formed. Evidence was given by IR spectroscopy that prereduction in methanol caused the formation of methoxy groups stabilizing catalytically active Mo⁵⁺ ions. UV-Vis, ESCA, and electron microscopic measurements showed however, that further aggregation and formation of microcrystallites of MoO₃ took place during the catalytic reaction which caused the observed decrease of the activity.     

Untersuchungen an katalytisch aktiven Oberflächenverbindungen. XI. Einfluß der Topologie der Silanolgruppen auf die Bildung von Vanadiumoxidclustern auf SiO2-Oberflächen

Studies on Catalytically Active Surface Compounds. XI. Influence of the Topology of Silanol Groups on the Formation of Vanadium Oxide Clusters on SiO₂ Surfaces Interaction of VOCl₃ dissolved in CCl₄ with silanol groups of Aerosil gives rise to reaction products, the Cl/V-ratio of which depends on thermal pretreatment of Aerosil and the amount of the vanadium fixed on the surface. Geometrically different arrangements of the silanol groups (centers) show kinetically differing behaviour, thus giving the possibility to establish a mathematic model for the interpretation of experimental data. Quantitative estimation of the population with silanol groups depending on the annealing temperature is achieved and correlated with the existence of two vanadium oxide surface species which differ with respect to their catalytic activity.     

Untersuchungen an Nickeloxid-Mischkatalysatoren. XI. Oberflächenchemische Eigenschaften von NiO/SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. XI. Surface Chemical Properties of NiO/SiO₂ Catalysts NiO/SiO₂ catalysts with different composition prepared by precipitation have been investigated which are characterized by a nickel layersilicate-like structure. The determination of the surface chemical properties was carried out by infrared spectroscopy (before and after pyridine adsorption), ¹H-NMR-measurements, chemisorption of ammonia, and titration with n-butylamine. It has been found three kinds of hydroxid groups which are assigned to Ni? OH and Si? OH groups with respect to investigations on definite nickel layersilicates. Furthermore, coordinatively unsaturated Ni^II surface sites were indicated. The number of the OH groups as well as the centers determined by chemisorption of bases increase with increasing NiO content. The obtained results allow the conclusion that the OH groups and the coordinatively unsaturated Ni^II surface sites are weakly acid.     

Untersuchungen an oxidischen Katalysatoren. XXVIII. Einfluß der Vorbehandlungsbedingungen auf Die katalytischen Eigenschaften von NiNaY- und NiCoNaY-Zeolithen

Studies on Oxide Catalysts. XXVIII. Influence of Pretreatment on Catalytic Properties of Zeolites NiNaY and NiCoNaY The influence of the pretreatment conditions on the acidic properties, the reduction degree of nickel, and the catalytic activity and selectivity of zeolites NiNaY and NiCoNaY in the alkylation of benzene with ethylene has been investigated. From the experimental results can be concluded that sec. buthylbenzene from benzene and ethylene is only formed on zeolite samples which contain both together BRÖNSTED acidic centres and Ni²⁺ cations or NiO. Catalysts which contain only metallic nickel are inactive for this reaction. Catalysts with nickel in different forms are active in the formation of ethylbenzene, diethylbenzene, butane and sec. buthylbenzene, the yields depending on the relation of Ni°, Ni²⁺, and NiO. Changing this relation makes possible to regulate the selectivity in the alkylation of benzene with ethylene.     

Oberflächenverbindungen von Übergangsmetallen. XXX. Fischer-Tropsch-analoge Umsetzung von CO/H2 bzw. CO2/H2 an Oberflächen-Chrom(II)

Surface Compounds of Transition Metals. XXX. Fischer-Tropsch Analogous Reactions of CO/H₂ and CO₂/H₂ on Surface Chromium(II) Surface chromium(II)/silicagel catalyzes the reduction of CO and CO₂ by hydrogen to CH₄, C₂H₆ and C₃H₈. The catalyst is partially desactivated by this reaction, but a permanent activity of ca. 30% remains. – The reaction can be formulated via the sequence formaldehyde complex → <CH₂>-complex → alkane. If cycloalkenes or chlorobenzene are added simultaneously, these scavenger molecules are methylated by <CH₂>.     

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.     

Über Glasbildung und Eigenschaften von Chalkogenidsystemen. IV. Bleithiogermanat (II,IV)-Gläser und ihre Eigenschaften

On Glass-Forming and Properties of Chalkogenide Systems. IV. Leadthiogermanate(II, IV) Glasses and their Properties PbS forms with GeS₂ in the presence of GeS stable glasses in a large range of composition. Melts containing an excess of sulphur yield inhomogenious products. Substituting PbS for GeS, the values of the atomic volume of the glasses at first decrease. The glass transition points as well as the optical and electrical properties are noticed and the crystalline phases received on annealing are discussed with respect to the glass-forming region. The results give the fundamentals to consider the vitreous materials of the system PbS? GeS? GeS₂ as leadthiogermanate(II, IV) glasses.     

Oberflächenverbindungen von Übergangsmetallen. XVIII. Der Einfluß der Cr-Konzentration auf Oxydationszahl und „Qualität”︁ von Cr-Oberflächenverbindungen auf Silicagel

Surface Compounds of Transition Metals. XVIII. The Influence of Cr Concentration on Oxidation Number and “Quality” of Cr Surface Compounds on Silicagel Mean oxidation number (OZ ) and mean unsaturated character (q ) of reduced Cr surface compounds on silicagel depend on the concentration of Cr in the product. The first effect is caused by the decrease of thermally stable surface Cr^VI with increasing Cr concentration in the activated product, since surface Cr^VI is the only precursor of surface Cr^II (constant yield of reduction～90%); consequently OZ _red shifts to higher values with increasing concentration. — The measured decrease of q with increasing Cr content cannot be correlated with a possible coordination of neighbouring SiOH groups, as it was suggested for the influence of T_act and T_red; other explanations are proposed. For the analyzed product, the results support the postulated model of an ensemble of topologically different individual surface species of typical reactivity.     

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.     

Über Oberflächenverbindungen von Übergangsmetallen. X [1]. Zum Stöchiometrie-Problem der Bindung von Oberflächen-Chrom(II) an Silicagel

On Surface Compounds of Transition Metals. X. The stoichiometry Problem of Fixation of Surface Chromium (II) on Silicagel. Thermogravimetric analysis of a reduced Philips catalyst (support: silicagel “Merck 7733”) shows that the metal is bound prediminantly (if not only) in chromate-like units up to a concentration of 2,8% Cr^II. At higher Cr^II contents. up to the maximum of 3.5%, the additionally fixed chromium does not consume further OH^s, within the scope of the thermogravimetric method formation of polychromatelike structures and/or use of not-neighbouring OH groups. The analysis further demonstrates that not all the Si? Oh groups comprised by the method are able to accommodate surface chromium. The fixation of the metal seems to proceed most likely by reaction with the vicinal pairs of Si? OH, as a correlation of our data with silica models shows.     

Über Oberflächenverbindungen von Übergangsmetallen. VIII. Die Komplexbildung von koordinativ ungesättigtem Oberflächen-Chrom (II) mit Oxiden des Stickstoffs

On Surface Compounds of Transition Metals. VIII. Complex Formation of a Coordinatively Unsaturated Cr^II Surface Compound with Nitrogen Oxides N₂O forms with surface-Cr(II) a relatively unstable light blue compound of the stoichiometry 1:1, while addition of NO results in formation of a very stable dark brown, diamagnetic surface complex . By reaction with O₂ this complex undergoes — depending on reaction temperature — either replacement of NO unter reoxidation of the metal (→Cr(VI)) or/and reaction of the ligand (→NO₂). Direct reaction of NO₂ with results in the same products as stepwise addition of NO and 1/2 O₂. reacts with HCl/ROH under formation of the soluble, paramagnetic kation [Cr(NO)(ROH)_n]²⁺, which is formulated as [Cr(II)(NO)]²⁺ ? [Cr(I)(NO⁺)]²⁺ accordingly to the e.s.r. spectra.     

Synthese,Kristallstruktur und Eigenschaften von Vanadium(II)‐tetrachloroaluminat

Synthesis, Crystal Structure, and Properties of Vanadium(II) Tetrachloroaluminate The reaction of vanadium dichloride and aluminium trichloride yields vanadium(II) tetrachloroaluminate. Amber cuboid crystals can be obtained by slow cooling of the melt. V(AlCl₄)₂ crystallizes in the monoclinic space group I2/c (a = 1284.6(3), b = 776.3(2), c = 1163.5(2) pm, β = 92.376(10)°) and is therefore isotypic to Co(AlCl₄)₂. The structure contains chains build of VCl₆ octahedra and AlCl₄ tetrahedra sharing corners and edges with each other. The temperature dependence of the magnetic susceptibility follows Curie‐Weiss behaviour (μ = 3.88(2) μ_B, Θ = ?9(1) K) complying with the spin‐only paramagnetism expected of d³ ions.     

Untersuchungen on Thoriumoxid-Katalysatoren. II [8] Über den Einfluß Oberflächenchemischer Eigenschaften von ThO2− Katalysatoren auf die selektive Dehydratisierung von 2-Butanol

Studies on Thoria Catalysts. II. On the Influences of Surfacechemical Properties Tho₂-Catalysts on the Selective Dehydration of 2-Butanol Acid and basic properties as well as the interaction of 2-butanol with the surfaces of some ThO₂catalysts were studied. Sites of low acidity and basic sites of medium strength were found on the catalysts. After CO₂ adsorption we have shown by i.r. spectroscopy the formation of monodentate and bidentate carbonate as well as hydrocarbonate. There were indications of Lewis-type acid sites. Bands of alcoxide and carboxylate structure were observed in the i.r. spectra by interaction with 2-butanol and thoria. A mechanism is proposed for dehydration of 2-butanol.     

Untersuchungen an Beliten und Dicalciumsilicaten. II. Phasen-, Wertigkeits- und Reaktivitätsänderungen von Mn-dotiertem Ca2SiO4 bei thermischer Behandlung

Investigations on Belites and Dicalcium Silicates. II. On the Changes of Phases, Valency, and Reactivity during Heat Treatment of Mn-doped Ca₂SiO₄ Annealing of blue Mn-doped single crystals of Ca₂SiO₄ at T > 1450°C causes decolorization. The Mn profile in the crystals, formed during the process of crystal growth, vanishes. The experimental results suggest a causal connection between

• — the change of valency of the doping component (Mn)
• — its mobility between tetrahedral positions, and
• — the reactivity of the Ca₂SiO₄

and the phase transformation α′ _H → α of dicalcium silicate (Hedvall effect).     

Beziehungen zwischen Lumineszenzspektrum und Struktur von Seltenerdkomplexen. III. Zur Existenz unterschiedlicher Polyedertypen bei Alkalitetrakis(dibenzoylmethanato)europat(III)-Komplexen

The luminescence spectra of alkali tetrakis(dibenzoylmethido)europate(III) complexes in the crystalline state at 77°K have been measured in the spectral region 510–640 nm. The spectra show the existence of different modifications of these compounds. The spectra of the β-forms are consistent with a site symmetry D₂ at the Eu(III) ion, the spectra of the corresponding α-forms with a site symmetry D₄. A conversion from the β-form into the α-form on heating is observed in some cases. The conversion involves a change from dodecahedral into antiprismatic coordination around the Eu(III) ion.     

Über Oxidsysteme mit Übergangsmetallionen in verschiedenen Oxydationsstufen. XIX. Darstellung und Eigenschaften Vanadium(II)-haltiger und damit n-leitender Vanadium(III)-Spinelle

On Oxide Systems with Transition Metal Ions in Different States of Oxidation. XIX. Preparation and Properties of Vanadium(II) Containing n-type Vanadium(III) Spinels Solid solutions of the general formulae and have been prepared by solid state reaction. The lattice constants, distributions of cations, and the oxygen parameter have been evaluated by X-ray diffraction. The IR spectra, resistivities, and thermo-EMF have been studied. The thermoelectrical properties can be described by the hopping model.     

Untersuchungen an Beliten und Dicalciumsilicaten. I. Untersuchungen über Gitterposition und Oxidationszahl des Mangans in Mn-dotiertem Ca2SiO4

Investigations on Belites and Dicalcium Silicates. I. Investigations of the Oxidation Number and the Crystallographic Position of Mn-Ions in the Crystal Lattice of Mn-doped Ca₂SiO₄ Light-blue Mn-doped monocrystals of Ca₂SiO₄ were grown from a CaCl₂ flux using raw mixes (2 CaCO₃ + 1 SiO₂) with different contents of MnCO₃. The MnO content in these crystals ranges up to ～0.50% and decreases with increasing duration of crystal growth thus generating a Mn profile in the crystals obtained. The oxidation number of Mn is predominantly 2+, but a little amount of Mn with a higher oxidation degree is also present. Some experiments suggest the existence of Mn⁵⁺ ions in the crystals. Mn²⁺ ions substitute Ca²⁺ ions in their irregular coordination polyhedra (coordination number 7 and 8), whereas Mn ions of higher valency substitute Si⁴⁺ ions in tetrahedra.     

Darstellung und Eigenschaften einiger Molybdän(II)-Thiocarboxylate

Preparation and Properties of Some Molybdenum (II) Thiocarboxylates The binuclear thiocarboxylates Mo₂(CH₃COS)₄, Mo₂(COS)₄, and Mo₂(C₆H₅CSS)₄ have been prepared and characterized by their spectroscopic properties. With the exception of Mo₂(C₆H₅CSS)₄ investigations of vapourization (mass spectrometer) show the binuclear molecules in the vapour phase. For the u. v.- and i. r.-spectra an assignment of the observed bands is given. The magnetic measurements of the three compounds show no systematic differences.