Mechanism of oxygen effect on hyrogenation rate of CO over palladium catalysts

Acceleration of CO hydrogenation by oxygen over palladium catalysts can be accounted for by competing reactions taking place in the CO-H₂O₂ system.

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, CO O₂ , CO–H₂–O₂.

     

Pulse studies of cyclohexane oxidative ammonolysis to adiponitrile over Ti?Sb?O catalysts

The catalytic activities in ammoxidation of cyclohexane to adiponitrile (ADN) was compared with the phase compositions of Ti–Sb–O catalysts. It was shown that the reaction is limited by the step of ADN desorption from the catalyst.

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Ti–Sb–O (). , .

     

Active state of molybdenum in molybdenum-alumina catalysts for propylene oxidation

Catalytic properties of molybdenum-alumina catalysts for propylene oxidation are shown to be determined by water-soluble molybdenum compounds, being apparently aluminomolybdenum heteropoly acids bonded to the catalyst surface.

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, , , , , .

     

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 , .

     

The relationship between the structures of Cu(II) complexes and their chemical transformations: VII

The thermal decompositions of Cu(en)₂(NCS)X. where X^–=Cl^–, Br^–, NO ₃ ^– , BF ₄ ^– and ClO ₄ ^– , have been studied in comparison with the courses of Cu(en)₂(SCN)₂ and Cu(en)₂X₂ decomposition. It is shown that the presence of the thiocyanate group in the complexes Cu(en)₂(NCS)X is the most important factor in the decomposition course, in agreement with the fact that the anions X^– are not coordinated. or are only semicoordinated. Significant differences were found in the courses of thermal decomposition of two forms of Cu(en)₂(NCS)(BF₄) differing in the structure of their coordination polyhedra.

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Zusammenfassung Die thermische Zersetzung von Cu(en)₂(NCS)X (X=Cl Br, NO₃, BF₄ und ClO₄) wurde untersucht und mit der von Cu(en₂(SCN)₂ und Cu(en)₂X₂ verglichem. Der den Verlauf der Zersetzung entscheidend bestimmende Faktor isi die Anw esenheit der Thiocyanat-Gruppe in den Cu(en)₂(NCS)X-Komplexen, was in Übereinstimmung damit steht,. daß die Anionen X nicht oder nur teilweise koordiniert sind. Es wurden signifikante Unterschiedeim Verlauf der thermischen Zersetzung von zwei sich in der Struktur ihrer Kordinationspolyeder unter-, heidenden Formen von Cu(en)₂(NCS)(BF₄) gefunden.

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Cu(en)₂(NCS)X (X^–=Cl^–, Br^–, NO ₄ ^– , NO ₃ ^– , BF₄ ClO₄, Cu(en)₂(SCN)₂ Cu(en)₂(X)₂. , Cu(en)₂(NCS)X X Cu(en) (NCS)BF₄ i .

     

On the relationship between thermal stability and catalytic properties of supported molyboo-vanado-phosphoric heteropoly acids

Catalytic properties of four heteropoly acids of the molybdophosphoric type were studied in the selective oxidation of isobutene to methacrolein. Results show that the highest selectivities for methacrolein were achieved with samples in which the original structure of the heteropoly anion is least affected by thermal destruction.

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. , .

     

Coordination polymers. IX

Poly-(butanediol-1,4-adipate) and poly-(diethyleneglycol-succinate) polyesters and their ionized derivatives, containing Mg²⁺ and Zn²⁺ ions with different stoichiometric ratios to the chain-end COOH groups of the polyesters have been investigated by derivatograph.The thermal decompositions of the metal-containing polyesters differ significantly from those of the unionized polyesters. These differences are connected with the chemical repeating unit of the polyesters and the chemical nature of the metal ions, and proportional to the amount of the latter.An explanation is given of the catalytic effect of metal ions on the process of decomposition of the polyesters.

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Zusammenfassung Poly-(butandiol-1,4-adipat) und Poly-(diethylenglycolsuccinat) polyester und ihre «ionisierten» Derivate — mit Mg²⁺ — und Zn²⁺-Ionengehalt in verschiedenen stöchiometrischen Verhältnissen zu den endständigen COOH-Gruppen der Polyester — wurden im Derivatographen untersucht.Die thermische Zersetzung der metallhaltigen Polyester unterscheidet sich wesentlich von nicht-ionisierten Polyestern. Diese Unterschiede sind mit den sich wiederholenden chemischen Einheiten der Polyester und der chemischen Beschaffenheit der Metallionen verbunden, und proportional dem Anteil derselben.Es wird eine Erklärung des katalytischen Effekts der Metallionen auf den Zersetzungsvorgang der Polyester gegeben.

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-1,4 «» , Mg²⁺ Zn²⁺ . , «» . . .

     

Mechanism of the liquid-phase oxidation of diethyl sulfide catalyzed by heteropoly acids

It has been established that in the oxidation of diethyl sulfide by¹⁸O₂ in CH₃C¹⁶O₂H–H₂ ¹⁶O solution at 369 K catalyzed by heteropoly acids, sulfoxide and sulfone with 44–54%¹⁸O enrichment are formed. The process is accompanied by isotope exchange of molecular oxygen.

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, ¹⁸O₂ CH₃C¹⁶O₂H–H₂ ¹⁶O 369 ¹⁸O 44–54%, .

     

Esterification and acetalization of steroids in the presence of the heteropoly acid H3PW12O40

H₃PW₁₂O₄₀ and H₃PW₁₂O₄₀/SiO₂ are efficient catalysts for esterification and acetalization of steroids (testosterone, 17 -hydroxyprogesterone, 11, 21-diacetoxy-16-hydroxyprednisolone) at 40–82 °C.

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H₃PW₁₂O₄₀ H₃PW₁₂O₄₀/SiO₂ (, 17-, 11,21--16-) 40–82°C.

     

Thermal ignition studies on metallized fuel-oxidizer systems

The thermal ignition behaviour of various mixtures of organic fuels, magnesium and ammonium nitrate (AN) has been examined by differential thermal analysis technique. It has been observed that the thermal decomposition/ignition of organic fuel-AN mixtures is modified significantly in the presence of magnesium metal. The decomposition characteristics of the binary mixtures of AN with various metals indicate the specific action of magnesium and zinc in lowering the decomposition temperature. A possible explanation for the low temperature decomposition is given in terms of the solid state reaction causing the fusion of AN which further reacts with the metal resulting in a highly exothermic reaction.

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Zusammenfassung Mittels DTA wurde das thermische Initiierungsverhalten verschiedener Gemische aus organischen Brennstoffen, Magnesium und Ammoniumnitrat (AN) untersucht. Es wurde festgestellt, daß die thermische Zersetzung/Initiierung von Gemischen aus organischen Brennstoffen und AN durch die Gegenwart von metallischem Magnesium bedeutsam beeinflußt wird. Die Zersetzungscharakteristiken binären Gemische aus AN und verschiedener Metalle zeigen eine spezielle Wirkung von Magnesium und Zink bei der Herabsetzung der Zersetzungstemperatur. Eine mögliche Erklärung für die Zersetzung bei niedrigerer Temperatur kann in Bezug auf die Festkörperreaktion gesehen werden, die das Schmelzen von AN verursacht, welches dann mit dem Metall stark exotherm reagiert.

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, (). , / — . . , , .

     

Studies of transnitrilation mechanism in the presence of trifluoroacetic acid

A non-cyclic imide, an intermediate of transnitrilation, is shown to be formed through the step of unstable isoimide isomerization. The addition of a carboxy group of the acid to the cyano group has been studied. Interaction of acetonitrile with aliphatic carboxylic acids is suggested to follow a concerted but not a synchronous mechanism with prior formation of the N–H bond.

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, — — . . , , N–H.

     

Influence of the dispersity of rhodium catalysts on the Rh?H-bond energy

Hydrogen adsorption on Rh-black and Rh/C catalysts with varying metal content has been investigated. The amount of adsorbed hydrogen per 1 g Rh decreases in the following series of catalysts: 20% Rh/C>10% Rh/C>5% Rh/C>2% Rh/C>Rh-black. The heat of hydrogen adsorption abruptly falls upon going from Rh-black to supported catalysts.

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Rh- Rh/C- . , , 1/Rh, : 20% Rh/C>10% Rh/C>5% Rh/C>Rh-. Rh- .

     

Alkylation of toluene with ethylene on HZSM-5

Alkylation of toluene with ethylene on unmodified large-crystal HZSM-5 has been studied in a flow system at 673 K, atmospheric pressure. The yield of ethyltoluenes increased and that of benzene and xylenes decreased with time on stream. This change in yields was accelerated by increasing the ethylene content of feed and by pretreating the catalyst with ethylene. Selectivity for toluene ethylation increase with increasing space velocity.

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HZSM-5 673 . - , . - - -. .

     

Oxidation of trimethoxybenzenes to benzoquinones with hydrogen peroxide in the presence of heteropolyacid

Trimethoxybenzenes were oxidized to dimethoxy-p-benzoquinones in fairly good yields (50–60%) with hydrogen peroxide in the presence of heteropolyacid in the solvent of acetic or formic acid.

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-- (50–60%) , , .

     

Decomposition of alkanethiols to dialkyl sulfides and hydrogen sulfide

Disproportionation of thiol to sulfide and H₂S takes place on catalysts of various composition, the most active being those with paired acid-base centers. On these catalysts at 200–400°C methanethiol is quantitatively converted to dimethyl sulfide. Disproportionation of ethanethiol and particularly of 2-propanethiol is accompanied by the decomposition of sulfides formed and initial thiols to produce olefins and H₂S.

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H₂S , - . 200–400°C . 2- H₂S.

     

Kinetics of reduction of tungstovanadophosphoric heteropoly anions with VO2+ ions

The rate constants of interactions of PW_12-nV_nO₄₀ ^(3+n)– (n=1–4) heteropoly anions (HPAs) and various PW₁₀V₂O₄₀ ^–5 isomers with VO²⁺ were measured. The reactions occurred via formation of intermediate active complexes with V(IV) ions incorporated into the coordination sphere of HPA.

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VO²⁺ PW_12-nV_nO₄₀ ^–(3+n) (n=1–4) PW₁₀V₂O₄₀ ^–5. , V(IV) .

     

Acetonation of L-sorbose catalyzed by heteropoly acids

Acetonation of L-sorbose—a step of ascorbic acid synthesis—takes place in acetone to yield 85% of diacetone-L-sorbose in the presence of heteropoly acids H₃PW₁₂O₄₀ and H₄SiW₁₂O₄₀ (0.1–0.35%) as catalysts.

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L-— L- — -L- 85% 0.1–0.35% H₃PW₁₂O₄₀ H₄SiW₁₂O₄₀ .

     

Influence of adsorbed anions on the dehydroxylation of synthetic goethite

The influence of surface structure on the dehydroxylation of synthetic goethite has been studied using heat-flux differential scanning calorimetry. Adsorption of various anions by goethite causes a progressive change in both the amount and environment of surface hydroxyls and this is reflected by changes in the DSC curves. These alterations indicate the importance of surface features in determining the course of dehydroxylation and further suggest that, in studies of this type of reaction, the use of synthetic products known to be free of surface contaminants could prove to be of great value in understanding dehydroxylation mechanisms.

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Zusammenfassung Der Einfluß von Oberflächenstrukturen auf die Dehydroxylierung synthetischer Goethite wurde unter Anwendung der Wärmestrom-Differential-Abtastkalorimetrie untersucht. Die Adsorption verschiedener Anione durch Goethit verursacht eine progressive Änderung sowohl der Menge als auch der Umgebung der Oberflächenhydroxyle und dies wird durch die Änderungen der DSC-Kurven wiedergespiegelt. Diese Änderungen zeigen die Bedeutung der Oberflächenbeschaffenheiten bei der Bestimmung des Verlaufs der Dehydroxylierung und weisen ferner darauf hin, daß bei Studien dieses Reaktionstyps der Einsatz synthetischer Produkte, die bekanntlich frei von Oberflächenverunreinigungen sind, sich hinsichtlich der Klärung der Dehydroxylierungsmechanismen als sehr wertvoll erweisen könnte.

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Résumé On a étudié par analyse calorimétrique différentielle (DSC) l'influence de la structure de surface sur la déshydroxylation de goethites synthétiques. L'adsorption d'anions divers par la goethite entraîne une variation progressive à la fois de la quantité et de l'environnement des hydroxyles de surface, ce qui se reflète dans les variation des courbes DSC. Ces altérations indiquent l'importance des propriétés de surface quand il s'agit de déterminer le cours de la déshydroxylation et suggèrent en outre que l'emploi de produits synthétiques connus comme étant exempts de contaminants de surface, pourrait être de grande valeur dans des études de ce type de réactions, pour comprendre les mécanismes de déshydroxylation.

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- . , . , , , , .