Ligand exchange between bis-acetylacetonato cobalt (II) and organotin compounds SnR2Cl2 (R=Ph, Et), I. NMR identification of exchange products in the Co(AA)2?SnPh2Cl2 system

NMR studies of the interaction between bis-acetylacetonato Co(II) and organotin compound SnPh₂Cl₂ (Ph=C₆H₅ ^–) in chloroform solutions with pyridine additive have revealed ligand exchange between the initial components to form Co(II) and Sn(IV) complexes with different numbers of ligands.

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Co(II) SnPh₂Cl₂ (Ph=C₆H₅ ^–). , Co(II) Sn(IV) .

     

Studies on the V2O5?TiO2 system, V. Equilibrium pressures

The oxygen equilibrium pressures from pure V₂O₅ and co-precipitated V₂O₅–TiO₂ system were measured in the range of 200–450 °C. The behavior of the equilibrium pressure with changes of temperature of the samples with and without TiO₂ is attributed to Ti⁴⁺ interaction with the V₂O₅ lattice.

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V₂O₅ - V₂O₅–TiO₂ 200–450°C. TiO₂ Ti⁺⁴ V₂O₅.

     

Studies of the reactions of Br(2P3/2) and Br(2P1/2) with SiH4

Photobromination of SiH₄ under uv-irradiation at various wavelengths has been studied. Rate constants for the elementary reactions Br(²P_3/2)+SiH₄HBr+SiH₃ (k=3.2×10^–11 exp(–21.8±2.5)/RT, cm³/s) and Br^* (²P_1/2)+SiH₄HBr+SiH₃ (k^*=(3±1)×10^–13 cm³/s) have been determined in the temperature range from 300 to 415 K.

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- . Br(²P_3/2)+SiH₄HBr+SiH₃, k=3,2×10^–11 exp (–21,8±2,5)/RT ³/ Br^*(²P_1/2)+SiH₄HBr+SiH₃, k^*=(3±1)×10^{–13 3}/ 300–415 K.

     

51V NMR studies of systems V2O5-KHSO4 and V2O5?K2SO4

Systems V₂O₅–KHSO₄ and V₂O₅–K₂SO₄ have been studied by the⁵¹V NMR method. The first system demonstrates the same states of vanadium as the previously studied V₂O₅–K₂S₂O₇, in this system a compound with an equimolar ratio of components has been found. In V₂O₅–K₂SO₄ the state of vanadium differs from the above systems and the formation of a compound with V/K=4 is observed.

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⁵¹V KHSO₄–V₂O₅ K₂SO₄–V₂O₅. , K₂S₂O₇–V₂O₅, . K₂SO₄–V₂O₅ V/K4.

     

Nature of ethylene complexes on the surface of Ag/SiO2 as evidenced by13C NMR data

The formation of -complexes of C₂H₄ with Ag⁺ on oxidized Ag/SiO₂ catalysts is shown by¹³C NMR. These complexes are similar in nature to those of olefins with silver in solution.

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¹³C , Ag/SiO₂ - C₂H₄ Ag⁺, - .

     

Active site for hydrogenation on reduced V2O5/Al2O3 catalyst

Active sites for C₂H₄ hydrogenation produced by reduction of V₂O₅/Al₂O₃ catalyst pretreated at 450°C were found to be composed of both strong Lewis acid sites associated with V⁴⁺ and basic sites of Al₂O₃. C₂H₄ polymerization concurrent with hydrogenation was assumed to occur on Lewis acid sites with higher acid strengths than those of the hydrogenation sites.

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C₂H₄, V₂O₅/Al₂O₃, 450°C, , Al₂O₃. , , , C₂H₄.

     

Structure of surface species in Mo/Al2O3 catalysts prepared through Mo(V) oxalate

EXAFS and RED structural studies of surface species of Mo/Al₂O₃ catalysts prepared through the anchoring of [Mo₂O₄(C₂O₄)₂(H₂O)]^2– anion to -Al₂O₃ have shown that these surface metal complexes preserve a binuclear structure of the Mo(V) oxalate framework fragment.

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EXAFS Mo/Al₂O₃, [Mo₂O₄(C₂O₄)₂(H₂O)₂]^2– -Al₂O₃. , (V).

     

Inhomogeneity of strong Lewis acid centers on Al2O3 surface

Specificity of the bands at 1630–1620 cm^–1 in IR spectra of coordinatively bonded pyridine has been studied. Three strong Lewis-type acid centers have been revealed on Al₂O₃ surface.

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- 1630–1620 ^–1.

     

Reactivity of coordinated O2? towards. One-electron oxidants

Ion-radical complexes Ti(IV) (O ₂ ^– ) are unreactive towards most oxidants except Ce(IV) and Cr₂O ₇ ^2– . The one-electron redox potential for the O_{2 coord.}/O _{2 coord.} ^– couple lies between 1 and 1.6 V.

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- O ₂ ^– Ti(IV) , Ce(IV) Cr₂ O ₇ ^2– . - O_{2 .}/O ₂ ^– . 1 1,6 .

     

Evidence by electrical conductivity for an excess of bismuth as Bi+ interstitials at the surface of gamma phase Bi2MoO6. Consequence for selectivity in propene catalytic oxidation

Bismuth molybdate in the alpha phase Bi₂Mo₃O₁₂ behaves as an intrinsic semiconductor, whereas the gamma phase (Bi₂MoO₆) appears as an n-type semiconductor, whose conduction electrons originate from the formation of Bi⁺ interstitials in the excess Bi₂O₃ layer, present at the surface. The elimination of the excess of Bi₂O₃ could account for the synergic effect observed in the mild catalytic oxidation of propene.

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- Bi₂Mo₃O₁₂ , -, Bi₂MoO₆ n-, Bi⁺ Bi₂O₃ , . Bi₂O₃ , .

     

Infrared spectroscopic evidence for the formation of carbonite CO22? ions in CO interaction with basic oxide surfaces

Infrared studies of¹²C¹⁶O,¹³C¹⁶O and¹²C¹⁸O adsorption at 60–300 K on thermally activated CaO and MgO indicate that the CO interaction with O^2– ions yields CO ₂ ^2– ions. These ions are the intermediates of more complex surface compounds and are responsible for the CO isotope exchange with surface oxygen.

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¹²C¹⁶O,¹³C¹⁶O ¹²C¹⁸O 60–300 K CaO MgO - , CO O^2– CO ₂ ^2– , CO .

     

Hysteresis of thermogravimetric curves of nickel catalysts for methane conversion in CH4+CO2 mixture

Characteristic peculiarities of the supercarbonization peak, i. e. the effect of carbon accumulation on the catalyst surface and its subsequent removal under heating in the CH₄+CO₂ mixture have been studied. Hysteresis of thermogravimetric curves in the heating/cooling cycle has been established.

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— . -.

     

Oxidation with MnO2 supported on Y,FAU zeolite

MnO₂ supported on Na-Y,FAU prepared as described in a previous paper has been tested for selective oxidation of benzyl alcohol to benzaldehyde. Experimental results have shown that oxidation is selective and stoichiometric under the conditions used, but the adsorption of the substrate and/or the product on the zeolite support decreases the yield of benzaldehyde.

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MnO₂, Na–Y,FAU, , . . , , , / .

     

Comparison of the sulfurization of CoMoK/Al2O3 catalyst with H2S and CS2

Only H₂S consumption and H₂O formation was found in the sulfurization of CoMoK/Al₂O₃ water gas shift catalyst with H₂S/H₂, but CO₂ was formed first, then CH₄, H₂O and H₂S appeared in the later part of TPS with CS₂/H₂. Carbon deposition on the catalyst during the sulfurization with CS₂/H₂ caused a lower activity than the catalyst sulfurized with H₂S but could be removed in the run of WGS reaction.

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, CoMoK/Al₂O₃, H₂S/H₂ H₂S H₂O, CS₂/H₂ CO₂ CH₄, H₂O H₂S. CS₂/H₂ H₂S, , .

     

Thermochemical studies on the systems ACl/CeCl3 (A=Na-Cs)

The pseudobinary systems ACl/CeCl₃ (A=Na-Cs) were reinvestigated by means of DTA. The following compounds were found and identified through their X-ray patterns (primarily detected compounds in italics):NaCe _1.67 Cl ₆; K₃CeCl₆, K₂CeCl₅,KCe _1.67 Cl ₆;Rb ₃ CeCl ₆, Rb₂CeCl₅,RbCe ₂ Cl ₇; Cs₃CeCl₆, Cs₂CeCl₅,CsCe ₂ Cl ₇. The compounds A₂CeCl₅ crystallize with the K₂PrCl₅ structure. The high-temperature modifications of the compounds A₃CeCl₆ have the cubic elpasolite structure. The hexagonal unit cell of KCe_1.67Cl₆ is related to the CeCl₃ structure: 0.33 Ce³⁺ are substituted by one K^s+. The structure of CsCe₂Cl₇ can be described with a hexagonal subcellZ=4,a=9.72 andc=14.94 Å; however, small superstructure reflexions reduce the symmetry.The thermodynamic functions for the reactionsnACl+CeCl₃=A _n CeCl _n+3(A=K, Rb) were determined by means of e.m.f. measurements.Measurements of the e.m.f.E vs. T yielded the Gibbs enthalpiesG ^r . The temperature-dependence was found to be linear.The most important result is the formation of the elpasolites (A₃CeCl₆) and ACe₂Cl₇.

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Zusammenfassung Die pseudobinären Systeme ACl/CeCl₃ (A=Na-Cs) wurden mittels Differenzthermoanalyse (DTA) neu untersucht. Folgende Verbindungen wurden gefunden und durch ihre Röntgenbeugungsmuster charakterisiert (erstmalig nachgewiesene Verbindungen sind kursiv):NaCe _1.67 Cl ₆; K₃CeCl₆, K₂CeCl₅,KCe _1.67 Cl ₆;Rb ₃ CeCl ₆, Rb₂CeCl₅,RbCe ₂ Cl ₇; Cs₃CeCl₆, Cs₂CeCl₅,CsCe ₂ Cl ₇. Die Verbindungen A₂CeCl₅ kristallisieren im K₂PrCl₅-Typ. Die Hochtemperaturmodifikationen der Verbindungen A₃CeCl₆ liegen in der kubischen Elpasolith-Struktur vor. Die hexagonale Elementarzelle des KCe_1.67Cl₆ ist mit der CeCl₃-Struktur verwandt: 0,33 Ce³⁺ sind durch ein K⁺ ersetzt. Die Struktur des CsCe₂Cl₇ kann mit einer hexagonalen Pseudozelle beschrieben werden:a=9,72;c=14,94Å;Z=4; schwache Überstrukturreflexe reduzieren jedoch die Symmetrie. Die thermodynamischen Funktionen für die Reaktionen:n ACl + CeCl₃=A _n CeCl _n+3 (A=K, Rb) wurden durch EMK-Messungen bestimmt. Messungen der Abhängigkeit von e. m. f.E gegenT ergaben die Gibbs-EnthalpienG ^r . Es wurde eine lineare Temperaturabhängigkeit gefunden. Als wichtigstes Resultat ist die Bildung von Elpasoliten (A₃CeCl₆) und von Verbindungen (ACe₂Cl₇) anzusehen.

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ACl/CeCl₃, A . - ( ):NaCe _1.67 Cl ₆; K₃CeCl₆, K₂CeCl₅,KCe _1.67 Cl ₆;Rb ₃ CeCl ₆, Rb₂CeCl₅,RbCe ₂ Cl ₇; Cs₃CeCl₆, Cs₂CeCl₅ CsCe ₂Cl₇. A₂CeCl₅ K₂PrCl₅. A₃CeCl₆ . KCe_1.67Cl₆ CeCl₃, 0,33 Ce³⁺ . CsCe₂Cl₇ a=9,72 Å,c=14,94 Å Z=4. , . n ACl + CeCl₃=A _n CeCl _n+3(A=K, Rb) . . . . . .E , G ^r . ACe₂Cl₇.

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Presented as a poster at the 8th ICTA, Bratislava, 1985.

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This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.     

Chlorination of V2O5 by CCl4. The proposed reaction mechanism

Initial stage of the reaction of CCl₄ with V₂O₅ has been studied by MS and XPS techniques. According to the proposed mechanism dissociatively chemisorbed CCl₄ transforms to CO₂ via adsorbed COCl₂, while surface vanadium atoms involved are gaining step by step two chlorine atoms before the formation of the volatile end-product VOCl₃.

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CCl₄ V₂O₅ . - CCl₄ CO₂ COCl₂, VOCl₃.

     

Structure of vanadium phosphate anion in solutions from17O,51V and31P NMR data

¹⁷O,⁵¹V and³¹P NMR studies indicate that the anion structure of sodium vanadophosphate in an aqueous solution is close to that in crystals of the (CN₃H₆)₈HPV₁₄O₄₂ 7H₂O salt.

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¹⁷O,⁵¹V,³¹P , (CN₃H₆)₈HPV₁₄O₄₂ 7H₂O.

     

Kinetics and mechanism of OsO4 catalyzed oxidation of maleic, fumaric, cinnamic and acrylic acids by acid bromate

The title reactions are zero order in bromate, first order in both substrate and catalyst. The order of reactivity is cinnamic acid>acrylic acid>fumaric acid>maleic acid. A plausible mechanism is discussed.

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, . : > > > . .

     

Dispersity and reducibility of the molybdenum oxide phase in SiO2, SiO2?Al2O3 and γ-Al2O3 supported molybdena catalysts

XRD, isothermal and temperature-programmed reduction (TPR) experiments were carried out with SiO₂, SiO₂–Al₂O₃ and -Al₂O₃ supported catalysts. Molybdena is in a more disperse state on supports containing more alumina and it is more reducible on SiO₂–Al₂O₃ than on SiO₂ or -Al₂O₃. TPR curves were shown to reflect connections between reduction kinetics and dispersity.

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-, , SiO₂, SiO₂–Al₂O₃ -Al₂O₃. , , SiO₂–Al₂O₃ SiO₂ -Al₂O₃. .

     

FTIR investigation of the structure of vanadium oxides on ZrO2 and oxidation of toluene on it

The oxidation of toluene has been studied on V₂O₅/ZrO₂ by both FTIR spectroscopy and pulse method. The results suggest that Lewis-acidic sites play a significant role in the formation of benzaldehyde from toluene.

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V₂O₅/ZrO₂ - , . .