Adsorption of nitrous oxide on metallic copper catalysts

With the help of UPS spectroscopy, it has been shown that N₂O decomposes into N₂ and surface Cu₂O over copper catalysts in the temperature range –150, –100°C. The surface oxide oxygen dissolved into the bulk above 100°C to some extent.

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, N₂O –150° –100°C, N₂ Cu₂O. 100°C.

     

The catalytic activity of metallic and deposited oxide catalysts in the decomposition of nitrous oxide

The activity of massive metallic and deposited oxide catalysts in the decomposition of N₂O, which can possibly be used as a propellant, was studied. The data obtained were used to identify the active components such as carriers and transition metal ions and the methods for the preparation of catalysts that can be used as a basis for developing an effective catalyst of the decomposition of N₂O.     

The reaction between nitrous oxide and carbon monoxide over magnesium oxide

The title reaction was carried out with the help of the transient response method over MgO. It was concluded that no catalyst reduction occurred over this catalyst and the reaction proceeded through the reaction between adsorbed nitrous oxide and adsorbed carbon monoxide without participation of MgO oxygen.

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MgO. , - MgO.

     

Cluster ruthenium hydrogenation catalysts

Tetraruthenium dodecacarbonyl tetrahydride and some of its phosphine-substituted derivatives have been tested as homogeneous hydrogenation catalysts. The hydrogenation of cyclohexanone in the presence of H₄Ru₄(CO)₁₂ is first order with respect to the catalyst concentration, the substrate concentration and the partial pressure of hydrogen. The ruthenium cluster is recovered unchanged at the end of the reaction.     

Interaction between catalysts for ammonia synthesis and oxygen

Reversible poisoning of the catalysts for ammonia synthesis by oxygen has been used to eliminate the pyrophoric nature of the reduced catalysts via their treatment by the mixtures of nitrogen, hydrogen or helium with oxygen at catalysis temperatures. Kinetic studies of oxygen sorption, catalyst structure, activity and stability to the secondary oxidation of the samples partially oxidized at various temperatures have revealed that the optimum temperatures to eliminate the pyrophoric effect are 673–773 K.

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, . , , , 673–773 K.

     

Selective oxidation of benzene to phenol over FeAlPO catalysts using nitrous oxide as oxidant

A tetrahedrally coordinated iron in framework substituted microporous AlPO-5 catalysts are shown to be active and selective for the hydroxylation of benzene to phenol, using nitrous oxide as the oxidant.     

Interaction of nitrogen monoxide with alumina-iron oxide catalysts in chemisorption-regeneration regime

IR spectroscopy and thermodesorption have been used to study the surface reactions taking place in chemisorption of NO and NO +02 mixtures on alumina-iron oxide catalysts and palladized alumina-iron oxide catalysts, as well as the reactions that take place upon subsequent heating of these catalysts in helium or in the presence of hydrogen. The role of catalyst promotion by palladium in these reactions is examined critically.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 6, pp. 362–366, November-December, 1996.     

Decomposition of ruthenium olefin metathesis catalysts

The decomposition of a series of ruthenium metathesis catalysts has been examined using methylidene species as model complexes. All of the phosphine-containing methylidene complexes decomposed to generate methylphosphonium salts, and their decomposition routes followed first-order kinetics. The formation of these salts in high conversion, coupled with the observed kinetic behavior for this reaction, suggests that the major decomposition pathway involves nucleophilic attack of a dissociated phosphine on the methylidene carbon. This mechanism also is consistent with decomposition observed in the presence of ethylene as a model olefin substrate. The decomposition of phosphine-free catalyst (H2IMes)(Cl)2Ru=CH(2-C6H4-O-i-Pr) (H2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) with ethylene was found to generate unidentified ruthenium hydride species. The novel ruthenium complex (H2IMes)(pyridine)3(Cl)2Ru, which was generated during the synthetic attempts to prepare the highly unstable pyridine-based methylidene complex (H2IMes)(pyridine)2(Cl)2Ru=CH2, is also reported.     

Structures and properties of zirconia-supported ruthenium oxide catalysts for the selective oxidation of methanol to methyl formate

The effects of RuO(x) structure on the selective oxidation of methanol to methyl formate (MF) at low temperatures were examined on ZrO(2)-supported RuO(x) catalysts with a range of Ru surface densities (0.2-3.8 Ru/nm(2)). Their structure was characterized using complementary methods (X-ray diffraction, Raman and X-ray photoelectron spectra, and reduction dynamics). The structure and reactivity of RuO(x) species change markedly with Ru surface density. RuO(x) existed preferentially as RuO(4)(2-) species below 0.4 Ru/nm(2), probably as isolated Zr(RuO(4))(2) interacting with ZrO(2) surfaces. At higher surface densities, highly dispersed RuO(2) domains coexisted with RuO(4)(2-) and ultimately formed small clusters and became the prevalent form of RuO(x) above 1.9 Ru/nm(2). CH(3)OH oxidation rates per Ru atom and per exposed Ru atom (turnover rates) decreased with increasing Ru surface density. This behavior reflects a decrease in intrinsic reactivity as RuO(x) evolved from RuO(4)(2-) to RuO(2), a conclusion confirmed by transient anaerobic reactions of CH(3)OH and by an excellent correlation between reaction rates and the number of RuO(4)(2-) species in RuO(x)/ZrO(2) catalysts. The high intrinsic reactivity of RuO(4)(2-) structures reflects their higher reducibility, which favors the reduction process required for the kinetically relevant C-H bond activation step in redox cycles using lattice oxygen atoms involved in CH(3)OH oxidation catalysis. These more reactive RuO(4)(2-) species and the more exposed ZrO(2) surfaces on samples with low Ru surface density led to high MF selectivities (e.g. approximately 96% at 0.2 Ru/nm(2)). These findings provide guidance for the design of more effective catalysts for the oxidation of alkanes, alkenes, and alcohols by the synthesis of denser Zr(RuO(4))(2) monolayers on ZrO(2) and other high surface area supports.     

Correlation between phase composition and activity of complex oxide catalysts

Correlation between the catalytic activity in oxidation of carbonaceous materials and a change in the phase composition of the La_1?x Cs _x VO_4±y and Ce_1?x Pr _x O_2?d catalysts was studied. The activity values obtained by iso- and polythermal methods are close.     

Chemisorption and hydrogen spillover on framework ruthenium catalysts

Conclusions Thermal-desorption and isotope methods were used to investigate the state of hydrogen found on the surface of ruthenium framework catalysts. The possibility of the migration of chemisorbed hydrogen from the ruthenium was demonstrated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1712–1715, August, 1988.     

Interaction of methanol with ruthenium

The interaction of methanol with a clean (110) ruthenium surface has been studied using temperatures programmed desorption methods. Methanol dissociates upon adsorption at 300 K and yields H₂(g) and chemisorbed CO as the dominant products. Randomization of evolved hydrogen was shown to occur during methanol adsorption and also upon subsequent thermal desorption using isotopically labeled methanol, CH₃OD. In addition to hydrogen and CO, small amounts of H₂CO, CH₃OH, CO₂, and H₂O, are also observed upon thermal desorption. In contrast with a previous study of formaldehyde on Ru(110), no detectable CH₄ product is found upon methanol desorption.     

Interaction between fluorenyl alkaline earth salts and ethylene oxide

The ineraction of fluorenyl alkaline earth salts with ethylene oxide in THF was studied. Based on spectral data, a mechanism of the reaction between difluorenylbarium and ethylene oxide was proposed. The kinetics were followed. It was found that the solvent-separated ion pairs were more reactive than the contact ion pairs in the epoxy ring opening. Only low molecular products were obtained in the ethylene oxide polymerization with the fluorenyl salts used.     

Interaction between biimidazole complexes of ruthenium and acetate: hydrogen bonding and proton transfer

The hydrogen bonding and deprotonation processes between four ruthenium biimidazole complexes, namely [Ru(bpy)(2)(BiimH(2))](PF(6))(2) (1, bpy is bipyridine, BiimH(2) is 2,2'-biimidazole), [Ru(bpy)(2)-(BbimH(2))](PF(6))(2) (2, BbimH(2) is 2,2'-bibenzimidazole), and [Ru(bpy)(2)(DMBbimH(2))](PF(6))(2) (3, DMBbimH(2) is 7,7'-dimethyl-2,2'-bibenzimidazole) and [Ru(bpy)(2)(TMBbimH(2))](2+) (4, TMBbimH(2) is 5,6,5',6'-tetramethyl-2,2'-bibenzimidazole), and acetate are investigated. Their hydrogen bonded adducts are indeed trapped and observed by absorption spectra and electrochemical experiments in acetonitrile solution in the presence of an excess of acetic acid for the first time. The binding constants log K(B) for these adducts are 6.74 for 1·OAc, 7.11 for 2·OAc, 7.26 for 3·OAc, and 6.99 for 4·OAc. A new approach to calculate the deprotonation constant is also developed by establishing a set of circular equilibria. The equilibrium constants for the first deprotonation step of the complexes log K(A) are 2.74 for 1, 5.19 for 2, 4.54 for 3, and 3.78 for 4. The pK(a1) values of the complexes in acetonitrile solution are calculated by subtracting log K(A) from pK(a) (HOAc in acetonitrile), giving 19.6 for 1, 17.1 for 2, 17.8 for 3, and 18.5 for 4. The degree of proton transfer (D(PT)) can be quantified by the calculation of absorption spectral and redox data, which is 0.41 for 1·OAc, 0.53 for 2·OAc, 0.57 for 3·OAc, and 0.47 for 4·OAc. Interestingly, the binding constant log K(B) (7.26) and D(PT) value (0.57) both reach their maxima at a critical point, where pK(a1) for the complex is 17.8 and ΔpK(a) for the adduct is 4.5 (ΔpK(a) = pK(a)(HOAc) - pK(a1), in acetonitrile solution). Moreover, the binding constant log K(B) shows linear correlation with the degree of proton transfer D(PT).     

Gas-phase thermochemistry of ruthenium carbene metathesis catalysts

Quantitative energy-resolved collision-induced dissociation cross-sections by tandem ESI-MS provide absolute thermochemical data for phosphine binding energies in first- and second-generation ruthenium metathesis catalysts of 33.4 and 36.9 kcal/mol, respectively. Furthermore a study of the ring-closing metathesis in the second-generation system to liberate norbornene by forming the 14-electron reactive intermediate from the intramolecular pi-complex gives an estimate of the olefin binding energy to the 14-electron complex of around 18 kcal/mol, assuming a loose transition state. The results reported here are in remarkably good agreement with the latest DFT calculations using the M06-L functional.     

Highly selective ruthenium metathesis catalysts for ethenolysis

N-Aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium metathesis catalysts are highly selective toward the ethenolysis of methyl oleate, giving selectivity as high as 95% for the kinetic ethenolysis products over the thermodynamic self-metathesis products. The examples described herein represent some of the most selective NHC-based ruthenium catalysts for ethenolysis reactions to date. Furthermore, many of these catalysts show unusual preference and stability toward propagation as a methylidene species and provide good yields and turnover numbers at relatively low catalyst loading (<500 ppm). A catalyst comparison showed that ruthenium complexes bearing sterically hindered NHC substituents afforded greater selectivity and stability and exhibited longer catalyst lifetime during reactions. Comparative analysis of the catalyst preference for kinetic versus thermodynamic product formation was achieved via evaluation of their steady-state conversion in the cross-metathesis reaction of terminal olefins. These results coincided with the observed ethenolysis selectivities, in which the more selective catalysts reach a steady state characterized by lower conversion to cross-metathesis products compared to less selective catalysts, which show higher conversion to cross-metathesis products.     

Chelated ruthenium catalysts for Z-selective olefin metathesis

We report the development of ruthenium-based metathesis catalysts with chelating N-heterocyclic carbene (NHC) ligands that catalyze highly Z-selective olefin metathesis. A very simple and convenient procedure for the synthesis of such catalysts has been developed. Intramolecular C-H bond activation of the NHC ligand, promoted by anion ligand substitution, forms the appropriate chelate for stereocontrolled olefin metathesis.     

Cis-selective ring-opening metathesis polymerization with ruthenium catalysts

Cis-selective ring-opening metathesis polymerization of several monocyclic alkenes as well as norbornene and oxanorbornene-type monomers using a C-H activated, ruthenium-based metathesis catalyst is reported. The cis content of the isolated polymers depended heavily on the monomer structure and temperature. A cis content as high as 96% could be obtained by lowering the temperature of the polymerization.