Yu. A. Chesalov

In situ FTIR Study of the Adsorption of Formaldehyde, Formic Acid, and Methyl Formiate at the Surface of TiO2 (Anatase)

The catalytic properties of TiO2 (anatase) in the reactions of formaldehyde oxidation and formic acid decomposition are examined. At 100–150°C, formaldehyde is converted into methyl formate with high selectivity regardless of the presence of oxygen in the reaction mixture. Formic acid is decomposed to CO and water. Surface compounds formed in the reactions of formaldehyde, formic acid, and methyl formate with TiO2 (anatase) are identified by in situ FTIR spectroscopy. In a flow of a formaldehyde-containing mixture at 100°C, H-bonded HCHO, dioxymethylene species, bidentate formate, and coordinatively bonded HCHO are observed on the TiO2 surface. In the adsorption of formic acid, H-bonded HCOOH and two types of formates (bidentate and unsymmetrical formates) are formed. In the adsorption of methyl formate, H-bonded HCOOCH3, HCOOCH3 coordinatively bonded via the carbonyl oxygen, and bidentate formate are identified.

Determination of surface intermediates during the selective oxidation of formaldehyde over V–Ti–O catalyst by in situ FTIR spectroscopy

Abstract Formaldehyde oxidation to formic acid on V–Ti–O catalyst was studied in a flow-circuit setup with a differential reactor and in the IR cell. Surface intermediates leading to formic acid formation were identified. Catalyst calcination temperature was varied to study its effect on catalyst performance and surface species structure.

The superior activity of the CoMo hydrotreating catalysts, prepared using citric acid: what's the reason?

Abstract It was demonstrated, that the main positive role of citric acid during the hydrotreating catalysts preparation is consist in the formation of bimetallic complex Co 2 [Mo 4 (C 6 H 5 O 7 ) 2 O 11 ]•nH 2 O, that is a good precursor for selective formation of catalyst active phase, so called Co-Mo-S phase type II. The preparation method for this bimetallic complex using different precursor is described. The catalysts prepared by the complex deposition onto alumina support were studied during the different stages of the catalyst genesis. Applicability of these catalysts for ultra low sulfur diesel production was shown.

Mechanistic features of reduction of copper chromite and state of absorbed hydrogen in the structure of reduced copper chromite

The review discusses the experimental data on the unusual mechanism of the reduction of copper cations from the copper chromite, CuCr2O4, structure. Treatment of copper chromite in hydrogen at 180–370°C is not accompanied by water formation but leads to absorption of hydrogen by the oxide structure with simultaneous formation of metallic copper as small flat particles which are epitaxially bound to the oxide. This process is due to the redox reaction Cu2+ + H2 → Cu0 + 2H+; the protons are stabilized in the oxide phase, which is confirmed by neutron diffraction studies. The reduced copper chromite which contains absorbed hydrogen in its oxidized state and the metallic copper particles epitaxially bound to the oxide phase structure exhibit catalytic activity in hydrogenation reactions.

Preparation, active component and catalytic properties of supported vanadium catalysts in the reaction of formaldehyde oxidation to formic acid

Abstract The influence of the support nature was investigated with supported vanadium catalysts prepared by a wet impregnation method. SiO 2 , γ-Al 2 O 3 , ZrO 2 and TiO 2 (anatase) were used as supports. Two series of catalysts were prepared, the first one consisting of catalysts of composition ca. 20% wt. V 2 O 5 /80% wt. support (series 1) and the second one prepared by washing the series 1 samples with nitric acid (series 2). In the catalysts of series 1 (except 20% V 2 O 5 /80% SiO 2 ), vanadium is represented by both monolayer species (monomeric and polymeric VO x ) and crystalline V 2 O 5 phase. When vanadium is supported on SiO 2 , only the crystalline V 2 O 5 is formed. Washing the samples of series 1 with nitric acid removes crystalline V 2 O 5 phase. Monomeric and polymeric vanadia species are more active in the reaction of formaldehyde oxidation to formic acid as compared to V 2 O 5 .

Hybrid material polyvinyl alcohol-copper oxide and its electrical properties

The hybrid material polyvinyl alcohol-copper oxide was produced by the thermal decomposition of polyvinyl alcohol-copper hydroxide complex compound. It was analyzed by means of XRD, UV-VIS, IR, and Raman spectroscopy. It was concluded that the most part of copper oxide has an amorphous structure and consists of -(Cu-O)n- chains. The electrical properties of this material were investigated at direct and alternating current in 80–375 K temperature range.

Transport and thermal characteristics of Cs1 − xRbxH2PO4

The transport and thermal properties of Cs1 − xRbxH2PO4 in a wide range of compositions were studied. The binary salts Cs1 − xRbxH2PO4 (x = 0–0.9) contain solid solutions with a structure of CsH2PO4. The binary salts were synthesized by mechanically mixing the starting components and growing crystals by isothermal evaporation from aqueous solutions. The properties of Cs1 − xRbxH2PO4 salts obtained by different procedures were found to differ considerably. At higher rubidium contents in compounds obtained by mechanical mixing, the superionic transition temperature rose insignificantly, the high-temperature phase conductivity decreased twofold, the low-temperature conductivity increased within the limits of the order of magnitude, and the system of hydrogen bonds was slightly weakened. In Cs1 − xRbxH2PO4 crystals grown from solutions, the temperature of the superionic transition decreased along with its slowing down, and the low-temperature conductivity increased by more than three orders of magnitude because of the higher contents of residual acid aqueous centers in the structure of the salt. These systems are characterized by increased thermal stability.

Effect of the basic surface sites of carbons on the degree of dispersion of platinum catalysts prepared by H2PtCl6 adsorption

In the synthesis of Pt/C catalysts via H2PtCl6 adsorption onto a carbon support, NH4Cl can be formed catalytically during the reduction of the precursor with H2 at 250°C. This compound favors the sintering of metal particles. This effect is likely due to the weakening of metal-support bonding because of NH4Cl adsorption on the Pt surface. The sources of nitrogen and chlorine atoms are basic surface sites of the support, which contain nitrogen atoms in their structure and adsorb Cl− ions from the precursor solution. This effect is typical of active carbons, whose surface contains chemically bound nitrogen as amino groups, and weakens as the Pt/N atomic ratio in the supported catalyst precursors is increased.

Low-temperature decomposition of ammonia borane in the presence of titania

In the presence of anatase, the thermal decomposition of ammonia borane (AB) begins at a lower temperature, which enables AB dehydrogenation at a temperature as low as 80°C. The reduction in the AB decomposition temperature depends on the AB content of the mixture. In situ IR spectroscopy data demonstrate that, in the presence of TiO2, the structural destabilization of AB occurs during heating and is accompanied by the formation of an oxygen-containing boron phase and partial reduction of the titania, which is supported by diffuse reflectance spectroscopy data.

Effect of preparation conditions on the phase composition of the MoVTe(Nb) oxide catalyst for the oxidative conversions of propane

The replacement of expensive propylene by propane, which requires the development of catalysts for the direct oxidation of propane into acrylonitrile, is an important and insufficiently studied problem. Multicomponent MomVnTekNbx oxide systems are promising in one-stage ammoxidation of propane to acrylonitrile. Despite considerable attention of various authors to the preparation methods for these catalysts, the reproducibility of their physicochemical and catalytic properties is low. To optimize the technology of catalyst synthesis, we studied the effect of drying method (evaporation or spray drying) for the aqueous suspension of the initial compounds on the formation of the Mo1V0.3Te0.23(Nb0.12) oxide catalyst. It is shown that the method of drying determines the chemical and phase composition of solid catalyst precursors and the phase composition of the final catalyst in high-temperature treatment. The use of spray drying provides the required physicochemical characteristics of the catalyst (the specific surface area and the phase composition) that determine the high activity and selectivity in the selective conversion of propane. These catalysts contain two crystalline phases: orthorhombic M1 and hexagonal M2 in an optimal ratio of 3: 1.