Untersuchungen an oxidischen Katalysatoren. XXXVII. Zum Einfluß der Herstellungsbedingungen auf die Eigenschaften röntgenamorpher Al2O3?SiO2-Festkörper

Studies on Oxide Catalysts. XXXVII. On the Influence of Preparation Conditions on the Properties of Silica-Alumina Silica-alumina samples of different composition were prepared by coprecipitation from aqueous solutions at pH = 6 and pH = 9, respectively. Structures and properties of the solids were characterized (i.r., DTA, X-ray, molybdato method, surface acidity, catalytic activity in the cracking reaction of cumene). Solid composition and pH value of the precipitation medium equally exhibit influence on the structure of the silica-alumina (kind of incorporation of the aluminium) and thereby on the acidic and catalytic properties of the solids. Silica-alumina of equal composition but precipitated at different pH values may widely differ in their properties including activity-composition dependency.     

27Al-MAS-NMR- und IR-spektroskopische Untersuchungen zur Aluminium-Koordination in röntgenamorphen SiO2 ?Al2O3-Festkörpern

²⁷Al MAS N.M.R. and I.R. Investigations on the Aluminium Coordination in Amorphous Silica-Alumina Gels Amorphous silica-alumina of different Si/Al ratios have been investigated by ²⁷Al magic-angle spinning n.m.r. (MAS n.m.r.) and i.r. spectroscopy. Aluminosilicate framework structures were found for the Na⁺- and NH₄⁺-exchanged forms of the investigated gels. The thermal deammoniation of the NH₄⁺-exchanged gels, producing the H⁺ forms, causes an irreversible damage of the aluminosilicate framework. This process is accompanied by a change of the coordination state of a part of the aluminium, converting AlO₄ into AlO₆ units. The progress of the solid-state reaction upon further thermal treatment of the H⁺ forms is reflected by a considerable broadening of the n.m.r. spectra and a decrease of the intensity. The possibility that well-known results, including those of nonframework aluminium, obtained for comparable zeolitic systems may also be valid for amorphous solids, is discussed.     

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 oxidischen Katalysatoren. XLIII. Thermoanalytische und katalytische Untersuchungen an platinhaltigen H-ZSM-5-Zeolithen

Studies on Oxide Catalysts. XLIII. Thermoanalytic and Catalytic Investigations of Platinum-Containing Zeolites H-ZSM-5 By impregnation with H₂PtCl₆ from ethanolic solution, after reduction a higher metal dispersion in zeolites Pt/H-ZSM-5 is achieved than by impregnation from aqueous solution. Over such samples, bifunctional catalyzed reactions are more favoured than over zeolites Pt/H-ZSM-5 obtained by impregnation with H₂PtCl₆ from aqueous solution.     

Untersuchungen an oxidischen Katalysatoren. XXIII. Magnetische und Redoxeigenschaften von CrNaY-Zeolithen

Studies on Oxide Catalysts. XXIII. Magnetic and Redox Properties of Zeolites CrNaY After pretreatment in vacuo (110–460°C) and in air (45O°C) CrNaY zeolites with different exchange degrees are characterized by EPR and magnetic measurements. The chromium hyperfinc structure in the EPR spectra shows that stable octahedral [Cr(H₂0)]³⁺ complexes exist up to temperatures of 350–390°C. The decrease of EPR signal intensity with increasing temperature of vacuum pretreatment can be explained by migration of Cr³⁺ ions into the sodalite cage (S_I″, S_II″) and hexagonal prism (S_I), resp. The high values of μ_eff. correspond with the tetrahedra1 environment of Cr³⁺ ions. In the evacuated samples Cr²⁺ ions are present. The oxidizing pretreatment of samples with high Cr³⁺ exchange degrees leads to lattice break down. After pretreatment in air all CrNaY zeolites contain chromium with oxidation number +5 and +6.     

Beiträge zum thermischen Verhalten wasserfreier Phosphate. VII. Darstellung,Struktur und thermisches Verhalten von orthorhombischem NbPO5–δ

Contributions on the Thermal Behaviour of Anhydrous Phosphates. VII Preparation, Structure, and Thermal Behaviour of Orthorhombic NbPO_5–δ By a chemical vapour transport in a temperature gradient (e.g. 1000° → 9000°C) it is possible to prepare the already known forms of NbPO₅ and a new phase as single crystals. Using I₂ or NH₄Cl as transport agents α?NbPO₅ was obtained as colourless crystals, which enabled a refinement of the already known tetragonal crystal structure to R = 1.73%. The dark blue crystals of the up to now unknown orthorhombic phase could only be prepared under reducing conditions (by adding NbP). Their crystall structure is related to monoclinic β-NbPO₅ (single crystall investigation, space group Pna2₁; a = 11.2875 Å; b = 6.6296 Å; c = 5.2871 Å; Z = 4; R = 3.17%), but the crystals are deficient in oxygen according to NbPO_5?δ recognizable by the dark blue colour. When NbPO_5?δ (orthorhombic) is ground in an agate mortar NbPO_5?δ (monoclinic) is formed, which has the already known structure of β-NbPO₅. By heating (340°C) a reversible transformation from NbPO_5?δ (monoclinic) to NbPO_5?δ (orthorhombic) takes place. This is isostructural to WPO₅ and also to an orthorhombic modification of (colourless) NbPO₅, which we also could observe above 340°C.     

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.     

Spektroskopische und röntgenographische Untersuchungen an Dichlormethyl-Quecksilberverbindungen

Spectroscopic and X-Ray Structural Investigations on Dichloromethyl Mercury Compounds Bis(dichloromethyl)mercury, Hg(CHCl₂)₂, and mixed alkyl compounds RHgCHCl₂ (with R = CH₃, C₂H₅) have been synthesized by known methods from CH₂Cl₂, lithium butanide and HgCl₂, CH₃HgCl or C₂H₅HgCl, respectively. The ¹H-, ¹³C-NMR as well as the IR and Raman spectra of the liquid alkyls RHgCHCl₂ and the high melting Hg(CHCl₂)₂ have been measured and assigned. According to the X-ray structure determination Hg(CHCl₂)₂ crystallizes in the monoclinic space group P2₁/c with 4 non-symmetric molecules per unit cell (R = 0.046).     

Untersuchungen an oxidischen Katalysatoren. XVII. Zum Zusammenhang zwischen elektrischen und katalytischen Eigenschaften dotierter Zinkoxidkatalysatoren

Studies on Oxide Catalysts. XVII. On the Relations between Electric and Catalytic Properties of Doped Zinc Oxide Catalysts The electric conductivity and thermo EMF of zinc oxide catalysts doped with Li₂O, Ga₂O₃ and Fe₂O₃, and, on the other hand, their activity of dehydrogenation in the catalytic decomposition of isopropanol have been studied. The electric measurements were carried out preferably in an atmosphere of isopropanol. In washed single-phase catalysts doped with Li₂O (n-type semiconductors) the relation between the catalytic activity of dehydrogenation and the FERMI level position postulated by VOL'KEN?TEJN was verified quantitatively. The absorption of the isopropanol is considered to be the rate-determining acceptor step. In unwashed zinc oxide catalysts doped with Li₂O, however, the inversion from n- to p-type (between 0.3 and 0.5 mole-% Li₂O) causes a change in the character of the rate-determining step from an acceptor to a donor step. For the two-phase and three-phase solid systems of ZnO? Ga₂O₃ and ZnO? Fe₂O₃, respectively, it was not possible to find quantitative relations according to the electron theory of catalysis.     

Untersuchungen an oxidischen Katalysatoren. XXIV [1]. Adsorptions- und katalytische Eigenschaften von CeNaY- und CrNaY-Zeolithen

Studies on Oxide Catalysts. XXIV. Adsorption and Catalytic Properties of CeNaY and CrNaY Zeolites The adsorption of benzene, n-butylamine and ammonia(isotherms and heats of adsorption) on CeNaY and CrNaY zeolites of different exchange degrees has been measured. The acidic properties were characterized by titration with n-butylamine. As function of exchange degree the adsorption and catalytic properties (cracking of cumene) both change in the same manner. Whereas the reaction rate constants up to exchange degrees of 40–50% change only insignificantly, they are exponentially increasing at higher exchange degrees. The energies of activation are nearly independent of the degree and run to 23–25 kcal mol^?1.     

Nonanatrium-bis(hexahydroxoaluminat)-trihydroxid-hexahydrat (Na9[Al(OH)6]2(OH)3 · 6H2O) – Kristallstruktur,NMR-Spektroskopie und thermisches Verhalten

Nonasodium Bis(hexahydroxoaluminate) Trihydroxide Hexahydrate (Na₉[Al(OH)₆]₂(OH)₃ · 6H₂O) – Crystal Structure, NMR Spectroscopy and Thermal Behaviour The crystal structure of the nonasodium bis(hexahydroxoaluminate) trihydroxide hexahydrate Na₉[Al(OH)₆]₂(OH)₃ · 6H₂O (4.5 Na₂O Al₂O₃ · 13.5 H₂O) (up to now described as 3 Na₂O · Al₂O₃ · 6H₂O, 4Na₂O · Al₂O₃ · 13 H₂O and [3 Na₂O · Al₂O₃ · 6H₂O] [xNaOH · yH₂O], respectively) was solved. The X-ray single crystal diffraction analysis (triclinic, space group P1 , a = 8.694(1) Å, b = 11.344(2) Å, c = 11.636(3) Å, α = 74.29(2)°, β = 87.43(2)°, γ = 70.66(2)°, Z = 2) results in a structure, consisting of monomeric [Al(OH)₆]^3? aluminate anions, which are connected by NaO₆ octahedra groups. Furthermore the structure contains both, two hydroxide anions only surrounded by water of crystallization and OH groups of [Al(OH)₆]^3? aluminate anions and a hydroxide anion involved in three NaO₆ coordination octahedra directly and moreover connected with a water molecule by hydrogen bonding. The results of ²⁷Al and ²³Na-MAS-NMR investigations, the thermal behaviour of the compound and possible relations between the crystal structure and the conditions of coordination in the corresponding sodium aluminate solution are discussed as well.     

Die Kristallstrukturen der hexagonalen Elpasolithe Ba3NiSb2O9 und Ba3CuSb2O9 – röntgenographische und spektroskopische Ergebnisse

The Structures of the Hexagonal Elpasolite-Type Compounds Ba₃NiSb₂O₉ and Ba₃CuSb₂O₉ The results of an X-ray single crystal study of the hexagonal elpasolite Ba(NiSb₂)⁽⁶⁾O₉ are given. (Space group: C; a = b = 5.837 Å, c = 14.392 Å; Z = 2). The structure can be described by close-packed BaO₃ layers alternating in the sequence c c h c c h … (hex. BaTiO₃ type). Groups of two octahedra with common faces are connected by SbO₆ octahedra via common corners. They are occupied alternately by Ni and Sb. The final reliability index was R = 3.0%. The Cu²⁺-compound is of the same structural type. The ligand field and EPR spectra are discussed in comparison with related Ni²⁺ and Cu²⁺ compounds.     

Untersuchungen an Reaktionsprodukten von Dinatriumdihydrogensilicathydraten – Na2H2SiO4 · xH2O – und Dinatriumsilicat – (Na2SiO3)x – mit Wasserstoffperoxid. III1. Über den Abbau von Dinatriumsilicat-3-Wasserstoffperoxid

Na₂SiO₃ · 3 H₂O₂ is an instable compound, delivering oxygen on storing at room temperature. The decomposition is of a radicalic nature. An intermediate resulting from this decomposition is Na₂SiO₃ · H₂O₂ · 2 H₂O; it slowly looses elemental oxygen yielding two hydrates: Na₂SiO₃ · 3 H₂O₂ und Na₂SiO₃ · H₂O, depending on the experimental conditions. Thermal decomposition of Na₂SiO₃ · 3 H₂O₂ leads to (Na₂SiO₃)_x or Na₂SiO₃ · H₂O. The latter is stable up to 480°C, above this temperature being converted to (Na₂SiO₃)_x by exothermic reaction. The existence of these compounds have been proved analytically and by X-ray powder diffraction.     

Tribochemische und thermische Umwandlungen von LnTa3O9 (Ln = Pr,Nd) – röntgenographische und elektronenmikroskopische Untersuchungen

Tribochemical and Thermal Transitions of LnTa₃O₉ (Ln = Pr, Nd) — X-ray and Electron Microscopic Investigations Upon grinding crystals of M1? LnTa₃O₉ (Ln = Pr, Nd) [3] undergo a tribochemical phase transition. This leads to a new modifikation M2? LnTa₃O₉ with a significant higher density. We tried to find out more about the structure with high resolution electron microscopic investigations. According to electron diffraction and powder patterns the lattice parameters are (CuKα₁, λ = 1,54051 Å): M2? PrTa₃O₉: a = 6.2545(7) Å, b = 7.6736(7) Å, c = 6.5316(8) Å, β = 93.93(9)°; M2? NdTa₃O₉: a = 6.2552(5) Å, b = 7.6598(7) Å, c = 6.5103(4) Å, β = 94.096(7)°; (Z = 2). Using the intensities of powder patterns two structure models were calculated (space group P2₁/m, P2/m; R < 20%, heavy metal positions only). A through focus series of high resolution images was in better agreement with the first model (space group P2₁/m). Both models show a remarkable similarity to the structure of M? CeTa₃O₉ [4]. A thermal phase transition leads to M? PrTa₃O₉ and M? NdTa₃O₉ which are both isostructural to M? CeTa₃O₉.     

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.     

Struktur und thermisches Verhalten von Gadolinium(III)-sulfat-Octahydrat Gd2(SO4)3 · 8 H2O

Structure and Thermal Behaviour of Gadolinium(III)-sulfate-octahydrate Gd₂(SO₄)₃ · 8 H₂O . Gd₂(SO₄)₃ · 8 H₂O crystallizes monoclinic with space group C2/c and the lattice constants a = 13.531(7), b = 6.739(2), c = 18.294(7) Å, β = 102.20(8)°. In the structure Gd is coordinated by 4 oxygen atoms of crystal water and 4 oxygens of sulfate giving rise to a distorted square antiprism. During DTA-TG-experiments the title compound first loses crystal water in a two-step mechanism in the temperature range 130–306°C. The resulting Gd₂(SO₄)₃ is amorphous and recrystallization occurs in the range 380–411°C. The so-obtained low-temperature modification β-Gd₂(SO₄)₃, undergoes a monotropic phase transition at about 750°C to the high-temperature form α-Gd₂(SO₄)₃. The powder pattern of this modification was indexed based on monoclinic symmetry with space group C2/c and lattice constants a = 9.097(3), b = 14.345(5), c = 6.234(2) Å, β = 97.75(8)°. The hightemperature modification of gadolinium-sulfate shows decomposition to Gd₂O₂SO₄ at 900°C and, subsequently, decomposition at 1 200°C yields the formation of C-Gd₂O₃.     

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.     

Untersuchungen an oxidischen Katalysatoren. XXIX. Spektroskopische und katalytische Untersuchungen an Ni2+-, Co2+-, Cr3+- und Cu2+-ausgetauschten Mordeniten

Studies on Oxide Catalysts. XXIX. Spectroscopic and Catalytic Investigations on Ni²⁺-, Co²⁺-, Cr³⁺-, and Cu²⁺-exchanged Mordenites NiNaM, CoNaM, CrNaM und CuNaM (M = Mordenite) have been characterized by UV-VIS, EPR and i.r. spectroscopy and the results were compared with the catalytic activity and the activity-time-dependence in the cracking of n-octane and with the shape selectivity in the cracking of a n-octane and isooctane mixture. Water molecules acting as ligands of the exchanged cations are able to dissociate yielding Brönsted acidity. Brönsted sites may be regarded as catalytic active centers in the cracking reaction. Unreduced transition metal cations facilitate the “coking” of the mordenite. The unreduced chromium and cobalt cations for which a position within the main channel is expected, affect the diffusion of the branched paraffin molecule thus increasing shape selectivity.     

Spektroskopische und röntgenographische Untersuchungen an methylenverbrückten Organoantimonverbindungen

Spectroscopic and X-Ray Structure Investigations on Methylene Bridged Organoantimony Compounds The vibrational spectra of (Me₂Sb)₂CH₂ and of the halogen derivatives (Me₂Cl₂Sb)₂CH₂ and (Me₂Br₂Sb)₂CH₂ (Me = CH₃) have been measured and discussed. The i.r. and Raman data for liquid bis(dimethylstibino)methane are consistent with a mixture of two rotamers of C_s and C_2v symmetry, respectively. For the halogen compounds only one form is spectroscopically proved. The X-ray structure determination of (Me₂Cl₂Sb)₂CH₂ · CH₂Cl₂ shows the monoclinic space group P2₁/n with a = 968.2; b = 1746.8; c = 982.2 pm and β = 91.95°. The structure was refined to an R-value of 0.038.