A. Andreev

Low-temperature water-gas shift reaction on Auα-Fe2O3 catalyst

The water-gas shift reaction (WGSR) has been studied on Auα-Fe2O3 catalyst. The structure of the samples has been investigated by chemical and physical methods—TEM, X-ray, DTA, FTIR. A high dispersion degree of the gold particles and an increased concentration of the hydroxyl groups on Auα-Fe2O3 has been established in comparison to the pure α-Fe2O3. The results obtained can be explained on the basis of the associative mechanism of the WGSR. The essential aspects are the dissociative adsorption of water on ultrafine gold particles, followed by spillover of active hydroxyl groups onto adjacent sites of the ferric oxide. The formation and decomposition of intermediate species is accompanied by redox transfer Fe3+ Fe2+ in Fe3O4.

TPR and TPD investigation of Auα-Fe2O3

Abstract Temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) studies of Au α- Fe 2 O 3 and α-Fe 2 O 3 samples have been carried out. It was found that the peak maximum due to the Fe 2 O 3 → Fe 3 O 4 reduction of the gold-containing sample was shifted by ∼140 K to lower temperatures in comparison with α-Fe 2 O 3 . A scheme of low-temperature reduction with the participation of reactive surface hydroxyl groups is proposed. By means of TPD, it was established that the hydroxyl coverage on Au α- Fe 2 O 3 was about two times higher than that on α-Fe 2 O 3 . A scheme is suggested which explains the continuous desorption of water to 1083 K from the surface of the gold-containing sample. The results obtained are in agreement with earlier proposed water-gas shift (WGS) reaction mechanism over Au α- Fe 2 O 3 catalysts.

Influence of substituents and ligands of various cobalt (II) porphyrin derivatives coordinately bonded to silica on the oxidation of mercaptan

Cobalt (II) phthalocyanines with either electron-withdrawing or -donating substituents as well as cobalt(II) naphthalocyanine and cobalt(II) tetraphenylphorphyrin are coordinatively bonded to different types of modified silica. The catalytic activities in the oxidation of 2-mercaptoethanol of the different supported porphyrins are compared. The influence (i) of the substituents, correlating with their Hammett constants σp, and (ii) of the ligand types, correlating with their HOMO-LUMO energy gap, are discussed on the basis of the metal LUMO orbital energy. A mechanism is proposed, considering that only one coordination site is offered by the catalyst for the mediation of the electron transfer between the reactants in the redox process. The fine structure of the UV-Vis spectra is referred to as Mie scattering.

Structure and mercaptan oxidation activity of cobalt(II) phthalocyanines covalently bonded to silica of low surface area

Abstract Cobalt(II) 2,9,16,23-tetracarboxyphthalocyanine and cobalt(II) 2,9,16,23-tetraamino-phthalocyanine were covalently bonded to two different species of modified silica with low surface area. The immobilized phthalocyanines exhibit high catalytic activity in the oxidation of 2-mercaptoethanol, being comparable to that of the dissolved low molecular weight tetracarboxy- or tetrasulfo-phthalocyanine cobalt complexes. The diffuse reflectance spectra of the complexes bonded to nonporous silica exhibit a vibrational fine structure which clearly appears in the Soret band region, indicating a coupling between the electronic 1A1g → 1Eu transition and a vibrational transition of the aromatic ring system around 1600 cm−1.

Effect of copper oxide on the catalytic activity of iron-chromia catalyst for water gas shift reaction

It has been established that copper oxide promotes the catalytic activity of iron-chromia catalyst in the water gas shift reaction due to the formation of catalytically active aggregates. However, due to their gradual recrystallization and sintering into larger copper particles, the promoting effect sharply decreases.AbstractУстановлено, что окись меди промотирует каталитическую активность железохромного катализато ра окиси углерода, за счет образования катаитически активных агрегатов. Промотирующее действие меди быстро убывает, что связано с постепенной рекристаллиз ацией и спеканием каталитически активных агрегатв в более крупные кристаллы меди.

Formation and structure of the Re2O7γ-Al2O3 system under precatalysis conditions

The formation of the Re2O7Al2O3 catalyst surface in conditions of precatalysis has been investigated by means of various physical and chemical methods. It is suggested that under oxidative conditions a surface aluminum mesoperrhenate, “AlReVIIO5” is obtained. The same structure is formed finally, irrespective of the amount of rhenium deposited, as well as its valence state, combination (oxides, salts), the alumina carrier structure (γ, θ, nonporous) and phase (solid mixture or solution) of the starting materials. The structure is thermal and moisture stable, and is characterized by diffuse reflectance spectra with bands at 235 and 340 nm and a shoulder at 395 nm. It is not readily transformed into metallic rhenium. After reduction the structure can be completely restored under oxidative conditions only. On heating dried samples in an inert gas atmosphere or in vacuo, low-valence Re(VI) and Re(IV) coexist with Re(VII) on the surface. This is also observed under vacuum treatment of the calcined samples. The formation of a surface mesoperrhenate structure is detected on other carriers as well.

Complete catalytic oxidation of benzene over supported vanadium oxides modified by silver

Abstract A supported metal-metal oxide system, Ag-V 2 O 5 /γ-Al 2 O 3 , was found and studied. It exhibited high catalytic activity in the complete oxidation of one of the most difficult to oxidize hydrocarbons, benzene, with oxygen from the air. This system is able to operate at high liquid hourly space velocity values. At appropriate values of the vanadium: silver ratio, it is possible to develop catalytically active samples of optimum ratio between the V 5+ and V 4+ ions. This optimum ratio is kept by establishing a dynamic equilibrium between these ions in the redox process owing to the promotional effect of finely-divided metallic silver which activates the oxygen. The high catalytic activity is associated with clustered V 4+ ions in the matrix of vanadium pentoxide.

Active forms for water-gas shift reaction on NiMo-sulfide catalysts

The effect of the reaction medium on non-promoted and potassium-promoted NiMo-sulfide catalysts for the water-gas shift (WGS) reaction has been investigated. Water vapor induces hydrolysis of the sulfide phase to oxysulfides which also exhibit catalytic activity. Nickel hydroxide, formed as a result of hydrolysis, manifests a high catalytic activity in the water-gas shift.

Raney type copper-zinc-aluminium catalyst for water-gas shift reaction

Abstract The structure and the catalytic activity in the water-gas shift (WGS ) reaction of a Raney type copper-zinc-alummium catalyst has been studied. It has been established that after leaching of the alloy with alkali solution copper particles are formed, covered by a hydroxycarbonate film containing mainly a hydrotalcite like phase. Most probably this system is the precursor of the active sites, similar to the WGS catalysts obtained by coprecipitation. The Raney type catalysts manifested catalytic activity by an order of magnitude higher than that of the conventional coprecipitated catalysts. This could be explained by the formation of a complex catalytic system, containing a “polyelectrode” of a redox galvanic couple of copper ions, closed via the metal phase.

Study of the Structure and the Redox Reactivity of Nax Encapsulated Co(Ii)-Phthalocyanine

Abstract The preparation of NaX-encaged cobalt phthalocyanine by thermally activated tetramerization of 1,2-dicyanobenzene in cobalt ion-exchanged zeolite results in average loadings