Physicochemical and catalytic properties of Pd/C catalysts before and after the deactivation as a result of a dimethylbenzylamine debenzylation–acylation reaction are compared. A comprehensive analysis conducted by a number of methods (chemisorption, X-ray photoelectron spectroscopy, electron microscopy, X-ray diffraction) showed that a tenfold loss of the catalyst activity in the reaction conducted in soft conditions (atmospheric H2 pressure, 25 °C) is related to the formation of a nanoscale graphite phase. While this phenomenon is common for high temperature reactions, it is first discovered at low temperatures.

Rhodium catalysts supported on bayerite and pseudoboehmite alumina, calcined at 800 C, were synthesized and tested in the partial oxidation of methane. Rhodium (III) chloride was used as an active component precursor. The supports and catalysts were investigated by a wide range of physicochemical methods: XRD, SEM and HR TEM, XPS and UV-vis DRS. In both cases, large rhodium particles with a coherent scattering region size of 15-19 nm are formed, and small ones with dimensions less than 1 nm. On the whole, smaller rhodium particles are formed on the bayerite oxide. The catalyst with pseudoboehmite-type support shows better results in the reaction.

Нанесенные катализаторы Ru/MgO, Ru—Cs+/MgO, Ru/γ-Al2O3 и Ru—Cs+/γ-Al2O3, приготовленные методом пропитки с использованием RuOHCl3 и Cs2CO3 в качестве соединений-предшественников, восстановленные в водороде при 450 °C, охарактеризованы методами РФА, PDF и EXAFS. Установлен фазовый состав и локальная структура активного компонента. Показано, что в случае носителя MgO структура цезиевого промотора соответствует оксидам цезия, а для катализаторов на носителе γ-Al2O3 в процессе синтеза происходит взаимодействие ионов рутения и цезия с образованием алюминатов и твердых растворов в структуре носителя.

A comparative study was carried out of the structure of samples of zirconium oxides modified by yttrium and magnesium, synthesized by coprecipitation and calcined during 10 days at a temperature of 1250 °C. Refinement of the structure of the samples according to diffraction data within the framework of the fluorite type, gives high uncertainty factors, regardless of composition, and variation of structural parameters does not reduce their value. EXAFS analysis of the local structure of the samples revealed separate clusters consisting only of yttrium and oxygen ions in the structure of both samples. It has been suggested that the presence of these clusters prevents refinement of structures using the model of statistical solid solution with a fluorite structure.

The features of diffraction on silver nanoparticles located in channels of mesoporous silicate SBA-15 are analyzed. A computer simulation of diffraction patterns is performed for crystallites with different sizes, the cubic structure, and stacking faults. The experimental diffraction patterns are compared with simulated ones. Together with the stacking fault concentration, the average crystallite sizes are determined in the direction normal to the close packed layers and along the layers in the crystal structure.

С использованием комплекса рентгенографических методов изучены особенности структурной организации высокодисперсных медноцериевых CuO—CeO2 катализаторов, полученных методом Пекини. Современный структурный метод исследования наноматериалов — метод анализа распределения атомных пар (межатомных расстояний) — был использован для уточнения фазового состава материалов с выявлением высокодисперсных соединений, определения размеров областей атомарного упорядочения и возможных дефектов. Показано, что материалы, синтезированные из полимерных предшественников, представляют собой смешанные оксиды CuO—CeO2 с высокой концентрацией структурных дефектов. Высокодисперсные индивидуальные соединения меди не зафиксированы. Полученные результаты подтверждают ранее сделанные предположения о возможности встраивания катионов меди в структуру диоксида церия в составе медноцериевых катализаторов.

Problems of X-ray diffraction studies of ultradisperse systems with sizes less then 5-10 nm are discussed in this article. Fine metal and oxide particles supported by various oxides are an important class of catalytic systems. Radial distribution of electronic density or atomic pair distribution function (PDF-method) is effective for studying the local structure (short range atomic arrangement) of nanoparticles. Using this technique, one can directly define interatomic distances and coordination numbers of atomic arrangement, to determine features of the local structure of support and supported nanoparticles. In this message we report some examples of the PDF analysis application: 1) to determine the structure of highly dispersed supports (gamma,eta-alumina) and the active component in supported catalysts containing particles of platinum and gold; 2) to determine the structural aspect of stabilization of the dispersed state of the active component. It was shown epitaxial interaction between the support and the active component.

By means of a complex of powder X-ray diffraction techniques the features of the structural organization of highly dispersed copper-cerium CuO-CeO2 catalysts prepared by the Pechini method are studied. The current structural technique for studying nanomaterials, namely the atomic pair (interatomic distances) distribution function analysis, is used to refine the phase composition of materials with revealing highly dispersed compounds, sizes of atomic ordering regions, and possible defects. It is shown that materials synthesized from polymeric precursors represent mixed CuO-CeO2 oxides with a high concentration of structural defects. Highly dispersed individual copper compounds are not detected. The results obtained support the previous assumptions that copper cations can incorporate into the structure of cerium dioxide in the composition of copper-cerium catalysts.

Проведен анализ особенностей дифракции от наночастиц серебра, размещенных в каналах мезопористого силиката SBA-15. Выполнено компьютерное моделирование дифракционных картин для кристаллитов разных размеров с кубической структурой и планарными дефектами упаковки. Проведено сравнение экспериментальных дифракционных картин с модельными. Определена концентрация дефектов упаковки и средние размеры кристаллитов в кристаллической структуре в направлении плотнейшей упаковки и вдоль слоев.

Early the atomic pair distribution function (PDF) analysis approach has been used to study the local structure of liquids, glasses and disordered crystalline materials. In this paper, we demonstrate the use of the PDF method to investigate nanomaterials in particular catalysts. Examples of studies to definite the phase composition, structure, defects, microstructure supports and catalysts are shown. The influence of structural defects on the functional characteristics of the catalysts is demonstrated. We give examples of the study of massive highly disperse metals and nanoparticles deposited on matrices.

The possibilities of using powder X-ray diffraction methods in the study of carbon materials are discussed. To determine the phase composition of the crystalline materials the X-ray phase analysis is employed; the real structure is established by the harmonic analysis of diffraction profiles; the structural features and phase composition of the nanomaterials are found by the radial electron density distribution function.

An X-ray study of titaniaand alumina-supported rhodium catalysts for the hydrogenation of hydrocarbons is performed. Rhodium is shown to be present in the form of highly dispersed oxide, independent of the type of support. The atomic structure of alumina changes, while no change in the real structure of titanium oxide is observed.

Samples of a woven mesh of metal wire (fechral) with supported aluminum hydroxide compounds are studied. Aluminum hydroxide is formed in its bayerite modification. Aluminum oxides are produced during calcination: η-Al2O3 at 600°C, and θ-Al2O3 at 900°C. Subsequent modification with silicon, cerium, lanthanum, tungsten, and calcination at the same temperature results in the formation of their oxides. Interaction between alumina and tungsten at 600°C, and alumina and lanthanum at 900°C, are observed.

Modification of nano- and adsorption textures of alumina and silica as well as study of their chemical surface properties have been made. The use of specific templates as structure directing agents allowed varying their textural characteristics and obtaining macroporous and mesoporous functional materials with preferred influence of the substructures on the chromatographic properties of the materials. As packings of chromatographic columns structured materials gave an opportunity to carry out gas chromatographic analysis of mixtures faster than their unstructured analogs. In some cases, the efficiency of columns packed by such materials was just over than those packed by nontemplated counterparts. Modification of silica and alumina by carbonization allowed varying the chemical nature of initial surface and expanding the number of functional materials based on them. It was shown that adsorption potential of dispersion (non-specific) interaction of n-paraffins with carbonized silica and alumina was much higher compared to that of the noncarbonized materials. Some examples of successful application of the studied materials in practical gas chromatography are presented. (C) 2014 Elsevier Inc. All rights reserved.

Platinum nanoparticles supported on carbon nanotubes display higher activity in the water gas shift reaction with close to 100% conversion of CO at 400–450 °C than for platinum supported on SKT activated carbon. A TEM study showed that this effect may be attributed to stabilization of the platinum nanoparticles on the surface of the carbon nanotubes, which prevents their agglomeration during the reaction.

The Pd/Al2O3 catalysts were prepared by the impregnation of aluminum hydroxide, which was synthesized by precipitation in the presence of polyvinyl alcohol, with a solution of palladium nitrate and were heat-treated at different temperatures. The resulting samples were characterized by X-ray diffraction, electron microscopy, diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy and were tested in CO oxidation in two modes: in a temperature-programmed reaction and under isothermal conditions at 20°C in the absence and in the presence of water vapor. The activity of the catalysts in the former mode was almost independent of support preparation conditions, but it was different in the latter mode. The catalyst whose support was obtained in the presence of polyvinyl alcohol and treated at 300°C in an atmosphere of nitrogen exhibited the highest activity in CO oxidation at 20°C. In the absence of water vapor from the reaction mixture, the initial conversion of CO reached 40% and then decreased. In the presence of water vapor, a continuous increase in the conversion of CO to 88% was observed, and the activity was stabilized at this level. The smallest size of palladium metal nanoparticles, the nearly monolayer carbon surface coverage, and the presence of OH groups, which are formed upon the dissociation of water present in the reaction mixture, facilitate an increase in activity.

A size effect was found in the low-temperature steam reforming of bioethanol (15 vol. % ethanol in water) on copper catalysts supported on yttrium-stabilized zirconia: the specific rate of the conversion of ethanol into the key reforming product, acetaldehyde, is virtually independent on the mean diameter of the copper particles in the range 6-10 nm but drops significantly for particles with diameter 1-2 nm. Hypotheses for this observed effect are presented.